Weekend links

Here are some links of things I found interesting this week:

From ScienceNews.org, Sadness response strengthens with age.

In a recent study, people in their sixties felt sadder than people in their twenties did after viewing an emotionally distressing scene from a movie. This heightened emotional response to sorrow may reflect a greater compassion for other people and may strengthen social bonds, researchers propose.

Janet at Adventures in Ethics and Science posts on Research methods and primary literature.

I think there's value for students in digging up, and digging through, the primary literature of the discipline in which they are learning to do research. Sure, you don't want the primary literature to seem more authoritative as a source of knowledge than the actual experimental system a student is studying. But neither, I think, does it make sense to just throw an experimental system at a student and say "Here, come up with a good research question and figure out how to answer it."

Christina at Oscillator posts about the mechanism and evolution of motion sickness:

What is going on in our guts and brains when we're in a moving vehicle that makes us throw up? Why can't we just deal with motion better? As it negatively affects so many, this nauseating (did you know: the word nausea itself comes from the Greek word for boat!) inconvenience associated with technologically-assisted travel by sea, land, air, or IMAX screens has been the focus of intense and sometimes wacky research for more than 100 years. Although a great deal of mechanistic evidence for how motion sickness happens has been described, the theories of why it happens are still controversial and fascinating.

From LabSpaces.net, Aging and longevity tied to a specific brain region in mice.

Researchers watched two groups of mice, both nearing the end of a two-day fast. One group was quietly huddled together, but the other group was active and alert. The difference? The second set of mice had been engineered so their brains produced more SIRT1, a protein known to play a role in aging and longevity. "This result surprised us," says the study's senior author Shin-ichiro Imai [...]. "It demonstrates that SIRT1 in the brain is tied into a mechanism that allows animals to survive when food is scarce. And this might be involved with the lifespan-increasing effect of low-calorie diets."

From EurekAlert, Unique means of animal locomotion reported for first time.

[T]he gut of the crawling tobacco hawkmoth caterpillar (Manduca sexta) moves forward independently of and in advance of the surrounding body wall and legs, rather than moving along with them. [...]"Understanding this novel motion system may help efforts to design soft-bodied robots," said the article's senior author, Barry Trimmer [...]. "It may also prompt re-examination of the potential role soft tissues play in biomechanical performance of humans and other animals."

Isis blogs about how physiology was cooler 40 years ago:

John Severinghaus is a big deal in physiology. If you have ever been in the hospital and had to have the O2 and CO2 in your blood measured to determine if your heart and lungs were working properly, you can thank John Severinghaus for the ability to have that test done. Dr. Severinghaus built the first blood gas machine and is credited for the first functioning CO2 and O2 electrodes.

Ethan at An Inordinate Fondness for Beetles blogs about recreational sex as a survival strategy:

There are plenty of studies out there on human sexuality that seem to assume that evolution hasn't quite caught up with all our modern sexual tinkering, seeing as how they start off assuming all sex, and all our sex drives, stem only from a fundamentally a reproductive urge [...]. There are points where this makes sense–genetically-driven instinct won't catch on to the advent of The Pill for a few millenia to come. But other purposes for sex, and forms of non-reproductively oriented sex, have been around for more than enough time.

Razib at Gene Expression blogs about The Anglo Revolutions:

The idea that whites, or at least "non-ethnic" whites, "have no culture," gets at the root of it. What is assumed, what is background, what is default, is not deemed worthy of history. When it comes to Anglo history and culture the commanding heights remain of interest, William Shakespeare, the King James Bible, the Magna Carta, etc. But much of the more mundane detail is of little general interest compared to the more salient identities of race, religion, and such. I believe this causes real pragmatic problems.

Saturday Sciuridae

I realize I've been quiet lately, but that's just because there are big things going on off-screen right now. I hope to be back to my usual posting volume (and get back to talking about science as opposed to blathering about my life and animals) on Monday. In the meantime, let's look at a brief lesson in gray squirrel life history, in pictures:











Source: 1 2 3 4 5

Also check out the adorable squirrel puppets here. If you're a significant other of mine, you may want to take note that these would make a good present somewhere down the line.

The year to come

I have blogged before on the transition into grad school and my progress in the past year, but this month's Scientiae is about looking in the future to the year to come.

This coming year is going to be pretty wicked. By this time next year I will hopefully have become a published scientist, defended my thesis, gotten a job in government or industry (please oh please oh please), and moved into a much better apartment or townhouse.

The published scientist bit will hopefully be happening sooner rather than later. Next week I'll be sending the first draft of a manuscript to my advisor and collaborator, and if everything goes as planned, we'll be submitting it before the summer is over. I plan to aim high; Advisor thinks it might be PNAS-worthy, and I'm inclined to agree. They published a semi-related paper by my collaborator two years ago, so I'm hoping that lightning will strike twice. I'll start there and then work my way down, probably to the comparative zoology and physiology journals, if it isn't accepted.

I am pretty confident on the thesis front. As I mentioned before, my thesis is basically written. There's a small side project that my advisor wants me to do that I'll probably tack on to the thesis, but otherwise there isn't much left to do to it other than revise and refine. I don't think many master's degree students are this far along at the end of their first year (certainly not in my department, where it is pretty normal for an M.S. to take about 3 years), so I'm thankful for that. Defending the thesis, however, will be a whole different beast. I hate public speaking. I hate standing in front of a room of people and talking, especially when I have to memorize what I'm saying instead of just winging it. You'd think winging it would be more nerve wracking, but no. My 'teaching' requirement involves me hanging out in a room while students come in and ask me questions about the lecture material, so I've gotten good at explaining things on a whim, but I suck at prepared speeches. I even took a public speaking class! I guess for some people it just never gets easy.

I think I am most nervous about finding a job. I intend to graduate in the spring of next year, at which point I have to decide if I want to get a PhD or a job. Right now I am leaning towards job, and there are several big science companies in my area, but I don't really have any contacts. My high school friend's sister works at one, but as a chemist, not a biologist, so I don't know if she could help me. My grandpa knows the governor, but I doubt that would help me much in getting a government job. Honestly, I have no idea what to do at this point. I have a few more months to brainstorm before I need to get started searching, so I hope something comes to me.

I have been feeling like I've outgrown my current apartment, which I've been living in for four years, for a while now. I think moving into a new place will help me move past the college/grad school mentality and shift into adult mode. I also really, really want a dishwasher and clothes washer/dryer. I don't know how I've lived without them for so long. K and I have already agreed that if we're still together this time next year when our leases are up, we'll get a nice big apartment together. On top of wanting to be around him as much as possible, it's also financially sensible.

So, yes. Those are my goals for the coming year: publish, thesis, job, and apartment. In that order.

Birthday cat and lab stuff.

Sorry for the radio silence yesterday. I had a big day full of thesising, teaching Undergrad T how to filter his samples, cleaning grime off of the evaporimeter (Labmate J swears by toothpaste for this job, but I didn't have any handy), desperately searching for autosampler vial caps in all the little hiding places in the lab, and then going to pre-birthday dinner with K and my dad (today's my actual birthday though-- happy birthday to me!).



Today I'm meeting K at the adoption agency during his lunch break to pick up my new cat. I'm excited but I have a lot to do to prepare. I need to completely sanitize the litterbox so that it isn't overwhelmed with Kitty's (that's my current cat's name, Kitty) scent and I also need to vacuum the house for the same reason. I need to designate a safe space for her if she and Kitty don't hit it off immediately (which I doubt they will, Kitty hasn't been exposed to another cat since he was a kitten). Fortunately they're both fixed, so that isn't an issue.

I also plan on finishing my thesis proposal today. My advisor said that with a few minor changes to the last draft, it was ready to be approved by my committee. I have one last paper to read and cite and then it should be ready to go. I feel a little silly that I'm just now finishing my thesis proposal, especially considering the fact that the lab work and data analysis are completely finished, and the manuscript coming from my thesis work is already written (not revised or publishable yet, but written). Also, I'm a little afraid to admit this, but I have no idea how to send my proposal to Drs. Bat and Bug. I mean, I know I'm just supposed to email it to them, but I feel like there's some kind of unwritten rule about HOW I'm supposed to approach them about it, and I have no idea what the rule(s) may be. Maybe I'll talk to Labmate Li tomorrow about it if she's around. I would just ask Advisor, but apparently he's on a 1.5 month vacation that nobody told me about. I've been emailing him back and forth about my proposal all last week, and I had no idea he wasn't just sitting around in his office. Oops?

I need to bang out some ideas with Labmate A about Undergrad T's work and the paper that will be coming from it. See, Labmate A and I are co-advising Undergrad T, because he's working with Labmate A's samples (also some samples from a former labmate of ours who is also a collaborator on my work), but I'm the only one in the lab who knows the protocol for the specific measurements he wants to take, so I trained him in how to do the extractions and Labmate A taught him how to do -ography. I have no idea if I'm going to be an author on the resultant paper or not. All I've done so far is train the kid how to do the extractions, but it'd be a shame not to have my input on the paper since I'm the resident expert on 'protein channels' in our lab. Unfortunately I also don't know how to approach someone about wanting to co-author on a paper they're in charge of. Again, I feel like there are unwritten rules on this that I just plain don't know.

New and exciting things

It has already been an exciting day at casa mia, and as of this typing it isn't even noon yet. We'll gloss over the bit where at 7am I felt like I was gonna hurl and then had a minor panic attack about it and get on to the better stuff:

Jason at The Thoughtful Animal chose my post Methods Fail: Testing the pre-menopausal cougar hypothesis for his Editor's Selections this week at ResearchBlogging.org. Thanks, Jason!

Brian has invited me to blog at LabSpaces! I was very flattered that he asked and my first instinct was to say yes, but I want to sit on it for a few days to consider. I really like the idea of joining a new blog network that looks promising and helping to build up their little island in the science blog archipelago that Bora loves to speak about. I also like the mix of bloggers they currently have, so those are both big plusses. However, I do like the amount of control I have over the layout of my blog as an independent (I'm a bit of a control freak if you hadn't figured that out already), and I also feel like I'm just starting to establish myself out here (I've only been blogging at this location for about a month) and I wouldn't want to alienate any readers I've managed to get by packing up and moving elsewhere so soon. I don't know, we'll see. Either way I am quite flattered and even if I choose not to join, LabSpaces is a place I will be watching closely because I think they have a good project going on.

My 26th birthday is this Thursday, and K is getting me a new cat. We went to an adoption center over the weekend and I fell in love with this small grey shorthair female. She's already spayed and old enough to eat adult cat food, but her disposition is much more kitten-like than my current cat, which is exactly what he needs. One of the selling points on getting a second cat is that I need someone to whip Kitty (yes, my cat's name is Kitty) into shape. He's gotten a bit fat in the last year. I don't want to be one of THOSE PEOPLE who post pictures of their cats on their blog all the time, but you'll have to forgive me when we go pick her up later this week. I probably won't be able to control myself.

Advisor is pushing me to finish my manuscript ASAP because he has a research project he wants me to work on while I'm on paid vacation. Doesn't seem very much like a vacation if I have to work through the whole thing, but I guess that's academic life. That's also why I don't want to be an academic, but I digress. Speaking of, I should probably get off my ass and work on that this afternoon.

Edit: I also started a discussion on the definition of sexual intercourse when you allow for gay/lesbian sex over in the comments of an unrelated post on Gene Expression. Sorry, Razib.

Caloric restriction as a treatment for malignant brain tumors

Caloric restriction (CR), which is significantly limiting the intake of food, has been known to increase lifespan and have a reducing effect on non-invasive tumors. CR limits blood glucose levels and forces the body to dip into its fat reserves for energy. These fat deposits are broken down into ketones, which provide an alternate source of fuel for the electron transport chain in the mitochondria. Ketones can be used by body cells without much of a disturbance, but when nerve cells are forced to use ketones, it can have a negative impact on nerve function and coordination. Often the body will switch to ketones while there are still glucose reserves available, because it wants to save that glucose for the brain. Have you ever watched a marathon and seen a runner hit the wall? Suddenly their movements become jerky and uncoordinated, and they look as though they're going to fall all over themselves? That's because they've pushed themselves so hard that they've used up all their available glucose, and they aren't able to make new glucose quickly enough, so their brain has been forced to switch over to ketone use. Point being, ketones can be used for energy by the brain, but it isn't a state you'd want to be in on purpose unless it was extremely advantageous for you to do so.

As I said, CR-induced ketosis has been known to reduce non-invasive brain tumors. It appears that cancer cells are highly dependent on glycolysis for energy and for some reason (unknown to me, although I'm sure there's literature out there on it) seem incapable of mitochondrial respiration. As such, they cannot use ketones for energy like healthy cells can. Up until now, this hasn't been tested in more invasive cancers, where the tradeoff in neurological impairment might be worth it to stop or delay the spread of the cancer. This was the basis of a recent paper by Shelton et al., Calorie restriction as an anti-invasive therapy for malignant brain cancer in the VM mouse, in ASN Neuro. The authors developed a mouse model to test the effect of CR on the spread of glioblastoma multiforme, "the most malignant and invasive form of adult primary brain cancer," according to the authors.

(Most of this is self-explanatory, but figure D is measuring ketone levels. Click to enlarge.)

The mice were induced with the brain cancer, and then supplied food either ad libitum (as much as they cared to eat) or at 40% of their normal intake once per day. The mice were measured for body weight, blood glucose levels, and ketone levels, as well as several different tests for the location and abundance of tumor cells. The calorie restricted (CR) mice had lower body weights, lower plasma glucose levels, and higher ketone levels than the ad libitum (AL) mice, as expected.



As you can see above, the cancer cells (dark purple) are spreading further and more diffuse into the cortex in the AL mice than the CR mice. And as you can see below, the number of cancer cells in a given histological section of the brain were higher in AL than CR mice.



Finally, one very interesting finding is that the CR mice also experienced decreased angiogenesis (generation of blood vessels) in tumor areas than AL mice. Both density and diameter of blood vessels was reduced in CR mice.



As it seems, caloric restriction decreases tumor spread and angiogenesis in a malignant brain cancer mouse model. This is strong evidence that cancer cells have difficulty proliferating under metabolic stress, even when healthy cells are functioning normally. Metabolic control, where appropriate, can be a non-invasive treatment for benign and malignant brain tumors, although like all cancer treatments it isn't without significant risk. It is also worth mentioning that CR did not completely stop the spread of the malignant cancer, although it did slow it down significantly, so it is likely that CR would have to be used in tandem with other treatments.

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Shelton, L., Huysentruyt, L., Mukherjee, P., & Seyfried, T. (2010). Calorie restriction as an anti-invasive therapy for malignant brain cancer in the VM mouse ASN NEURO, 2 (3), 171-177 DOI: 10.1042/AN20100002

Photo: giant rats!

ScienceDaily reports on an archeological excavation of  eight rat species weighing over a kilogram. One of the rat species weighed over SIX kilograms.

Above is one partially intact skull compared to the skull of a normal black rat. This isn't even the biggest skull they found. Dude.

Stress endocrine pathway may have preceded vertebrate evolution.

Steroid endocrines are all derivatives of cholesterol, and are responsible for metabolism, homeostasis, growth, and reproduction. Some steroid endocrines include the sex endocrines that are responsible for reproduction and the development of secondary sex characteristics, and aldosterone which is important in ion homeostasis. Corticosteroids are also steroid hormones. I've blogged about the importance of corticosteroids before, and the corticosteroid endocrine pathway is highly conserved in vertebrates.

(I lost the source for this image, if you know it please email me.)

As with most endocrine pathways, corticosteroids are the result of an endocrine cascade starting with the hypothalamus. The hypothalamus produces corticotrophin releasing hormone (first endocrine). CRH causes the anterior pituitary gland to release adrenocorticotropic hormone (second endocrine), which tells the adrenal cortex to produce and release corticosteroids (third endocrine) such as cortisol. The third endocrine has a negative impact on the first two endocrines, which is to say that it down-regulates its own production. Corticosteroids are produced in response to environmental stress to maximize survival by regulating metabolism and immune response.

This corticosteroid pathway is conserved in both tetrapods and bony fishes (there is a slight difference in that bony fishes do not appear to use aldosterone to the extent that tetrapods do). Only recently have scientists found evidence for corticosteroid pathways in an invertebrate species, the sea lamprey. Lampreys are the closest living relative to the earliest vertebrates, so this provides some evidence that the corticosteroid pathway preceded vertebrate evolution.

In an open-access paper in PNAS, Close et al. identified a specific corticosteroid, 11-deoxycortisol, in sea lampreys. Similarly to vertebrates, this corticosteroid was regulated by the same hypothalamus-pituitary pathway and its apparent function was to mediate the stress response. 11-deoxycortisol is a direct precursor to corticosterone and cortisol, which are the major biologically active corticosteroids in higher vertebrates. This implies that while the endocrine pathway may have preceded vertebrate evolution, the specific enzyme responsible for converting 11-deoxycortisol to corticosterone and cortisol may not have been present.

Derivation of steroid endocrines.

The authors found that the CRH genome in lampreys is 88% similar to that in humans! 11-deoxycortisol suppressed the action of sex endocrines, similar to glucocorticoids in humans and other vertebrates. Lampreys, however, have very low levels of endocrines like aldosterone, which is in agreement with the fact that bony fishes use glucocorticoids in both ion homeostasis and metabolism, whereas tetrapods developed two different pathways for regulating these functions using aldosterone and cortisol. The authors hypothesize that the corticosteroid model in the sea lamprey represents the primitive condition of vertebrates.

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Close, D., Yun, S., McCormick, S., Wildbill, A., & Li, W. (2010). 11-Deoxycortisol is a corticosteroid hormone in the lamprey Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0914026107

Cancer

Finding out that a friend has cancer affects a person in two simultaneous ways: they are concerned for their friend's well being but also reminded of their own mortality. It is confusing and sad and uncomfortable, and there's nothing you can really offer your friend by way of comfort except to listen to whatever they have to say about it. It is particularly confusing when, for example, said friend is a 24 year old girl with breast cancer. I'm not gonna lie, I'm a little freaked out about the whole thing, but nowhere near as freaked out as my friend is (and boy, does this put certain things in perspective). She found out the day after her birthday, how unfair is that? My own birthday is in a few days, and now I just have kind of an ooky feeling about it. K seems pretty optimistic that all of her symptoms point to a benign tumor, but last night she was talking about chemo and buying wigs and wondering whether or not this would affect her fertility (she's getting married next year, and she's one of those girls who will want to start a family asap).

"It's funny... When I was a kid, I thought grown-ups never worried about anything. I trusted my parents to take care of everything, and it never occurred to me that they might not know how. I figured that once you grew up, you automatically knew what to do in any given scenario. I don't think I'd have been in such a hurry to reach adulthood if I'd known the whole thing was going to be ad-libbed." - Calvin's dad, Calvin and Hobbes

Hairless rodent saturday

This is the part where I scare away the few readers I've managed to get so far. I have an unnatural affinity for hairless rodents. Yes, I like 'em fuzzy, but I also like 'em naked. I have this poster on my office wall next to my desk:

Hairless mice are ADORABLE as shit. You can't deny it.

Just look at their little faces!

Hairless rats aren't bad either. Look at this guy! He's begging for a cracker. But, why stop there...

I know it is Rodent Saturday, but we can't let rodents have all the fun. These kittens look so confused about their very existence.

By the time you read this, I am probably already on my way to that wedding. Cross your fingers I don't lose my shit (in the bad way) today.

Blogging with Substance

Grazie to Bora for tagging me in a Blogging with Substance meme.

1. Sum up your blogging motivation, philosophy and experience in exactly 10 words.


"My research is boring; need an outlet for cooler stuff." Wow, that was hard. 10 words isn't enough space, but I guess that's the point.

2. Pass it on to 10 other blogs with substance.


Oh dear. I don't know that 10 other blog writers even read my blog at this point, so I will say that if any of you I'm linking to in the sidebar to the right happen to come across this, consider yourself tagged.

On a personal note, I'm having a pretty rough day. I have to go to a friend's wedding upstate tomorrow, and as I've mentioned before on this blog, I am highly agoraphobic. There is nothing that sounds enjoyable to me about sitting in a car for two hours, sitting in a wedding for 1-2 hours, going to a crowded reception, and then sitting in the car for another two hours to get home. All of that is panic attack central for me, and I'm starting to get pretty nervous about it. I keep trying to distract myself, because I know that panic is a positive feedback loop. The more I think about it, the more nervous I'll get, and the worse time I'll have tomorrow.

It helps to know that if I survive the trip tomorrow, I have nothing else planned between now and late September. I'll probably wind up taking an Ativan or two, hopefully that'll get me through it.

Methods Fail: Testing the pre-menopausal cougar hypothesis.

ScienceDaily has an article from earlier this month, Ticking Biological Clock Increases Women's Libido, New Research Shows, that claims that women who are approaching menopause become "more willing to engage in a variety of sexual activities to capitalize on their remaining childbearing years" and that they are more prone to one night stands and "adventurous bedroom behavior" than their younger counterparts. According to the article:

Compared with the other groups, women with low fertility were more likely to experience:
- Frequent sexual fantasies
- Thoughts about sexual activities
- More intense sexual fantasies than their younger counterparts
- A more active sex life and willingness to have a one-night stand
- A willingness to have casual sex

Bear in mind that this 'low fertility group', as they have chosen to define it, stretches all the way from 27-45 year old women. I am only one year away from this group, and already my sex drive is much lower than it was in my teens and early twenties, so this does not jibe at all with my own experiences, but, hey, whatever. Everyone's different, and it is hard to deny the cougar phenomenon, as much as I hate that word. However I find it hard to believe that women age 27-35 or so could possibly be considered to have 'low fertility'. To get to the bottom of this rationale, and also to determine how the authors defined such things as "casual sex" and "more intense sexual fantasies" I looked up the source paper: Reproduction expediting: Sexual motivations, fantasies, and the ticking biological clock by Easton et al.

After reading the article it seems that women experience a drop in fertility from their late 20s to mid 30s, which rapidly drops off after 35. Okay, so they're lower fertility, perhaps, but I still think it is a stretch to say that they have low fertility. Whatever. Now on to the terminology of "intense sexual fantasies":

The intensity of a sexual fantasy also influences motivation to engage in sexual activity such that more intense sexual fantasies are correlated with higher rates of sexual intercourse (e.g., Rösler & Witztum, 1998). RE women should therefore experience more intense sexual fantasies than women who are not expediting reproduction (Prediction 1.3). Previous research on differences in sexual fantasies as a function of age indicated women between the ages of 26 and 35 reported more sexual fantasies than younger and older women (e.g., Purifoy et al., 1992), lending partial support to the present predictions.

Do you see in there, anywhere, a way of measuring the relative 'intensity' of a sexual fantasy? Yeah, me either. On to the methods (where I found out that the participants were self-selected from Craigslist, which I'll get to in a minute):

Participants answered several questions regarding their sexual thoughts, fantasies, and behaviors. Using 1–7 Likert scales, participants answered how often they think about sexual activities (never to over 10 times a day), how frequently they fantasize about sex (never to daily) and how intense their fantasies are (very mild to very intense). Lower scores indicated less time, frequency, or lower intensities.

Still no definition of 'intensity' for sexual fantasies. If the women are asked to determine for themselves what constitutes a mild vs. intense sexual fantasy, there is going to be extreme variation between individuals based on their sexual experiences, what is considered 'normal' sex based on their exposure and values, and all types of demographic factors (age, sexuality, location, etc). This is a very amorphous interpretation of the idea at best. Also... let's be real. Craigslist attracts a certain kind of people. I'm not making a judgment on the people who use Craigslist, I'm just saying it's a niche market with a very large personals section. These are confounding factors that I think bias the study in ways the authors didn't discuss.

Another thing about Craigslist (and this is just my very subjective opinion based on my own experiences): it is widely used by younger people (in the 20s demographic) because it is generally younger people who are looking for jobs, apartments, and using the personal ads to find romantic partners (this is backed up by the sample sizes of their volunteers, as about 600 were between the ages of 18-26 and only about 200 were between the ages of 27-45). People who are a bit older are generally more settled in their lives, they already have homes and jobs and are more likely to have long term partners. I would say that people who are in their mid-30s who are using Craigslist have probably recently experienced an upset in the flow of their life: the loss of a job or a partner, or recent relocation due to the loss of a job or partner. These things might cause a person to be more sexually adventurous because they either need to find a new partner OR they need something to keep them sane while they try to get their life back on track (whether they're having that extra sex with their partner or with others). What this boils down to is that I would say that the 20s demographic of Craigslist users probably are a relatively decent representation of 20s in the population, whereas Craigslist users in their 30s and 40s probably represent a much smaller subset of the population, likely either a disrupted and/or 'hornier' population. Again, these are just my opinions based on my experience with Craigslist and the people who use it.

As an interesting aside, in the results section, the authors note that people who reported anything other than a heterosexual orientation were excluded from the analysis. Why? What is the rationale for this? That's a question I would dearly like to see answered.

I am glad that the authors acknowledge that their results may not be based on fertility at all:

The present findings may reflect mere sexual experience increasing comfort with sexuality, and not by a reproduction expediting adaptation designed to capitalize on remaining fertility. Differences in sexual experience would explain why younger women were consistently different from older women. Previous research indicates sexual fantasy behavior changes as a function of sexual experience. Women with more sexual experience report having more sexual fantasies than those with less sexual experience (e.g., Pelletier & Herold, 1988).

I don't think that the rationale for this paper is inherently flawed, but I do think that the methods used to test their hypothesis could have been way, way better. My main issue is their choice to use self-selected volunteers from Craigslist as their sample population. I also take issue with their lack of hard definitions for the intensity of sexual fantasies, which vary wildly across populations and between individuals.

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Easton, J., Confer, J., Goetz, C., & Buss, D. (2010). Reproduction expediting: Sexual motivations, fantasies, and the ticking biological clock Personality and Individual Differences, 49 (5), 516-520 DOI: 10.1016/j.paid.2010.05.018

Surprise bunny encounter.

I had another grumpy day today (man, this has been a bad week), but my spirits were lifted by this little guy that K and I found munching in a clover patch outside my apartment. He wasn't scared of us at all, I was able to get within just a few feet of him to snap these photos.







Do you see the darling little white patch on his head? You can't tell from the photos, but he's incredibly tiny, probably still just a juvenile, but I didn't see any adult bunnies anywhere.

Menopause as an evolutionary strategy.

Okay, this blog is going to get to the core of a topic I find insanely interesting, which is the fact that humans generally live a long, loooong time past their reproductive years. I mean yeah, men can keep churning out the sperm in their old age, but women can sometimes live twice as long (or more!) as their fertile years! Is it just me, or is that cool as shit? Today I am going to talk about Evolution of the menopause: life histories and mechanisms by Rashidi and Shanley.

Life stages of various primates.

My apologies for the crappy graph quality, as I only have access to a crappy pdf scan for this paper. As you can see, human females often live 20+ years after menopause, whereas most other primates only live a few years past the end of their reproductive stage. (You'll also notice that weaning has shifted to the middle of infancy in humans instead of occurring at the border of infancy and childhood.)

One hypothesis for why female humans live so long past their reproductive stage is that perhaps we're just out-living our viable eggs? Historically, humans didn't live much longer than what we now consider 'middle' age, but as I mentioned earlier this week, we've seen a sharp decline in middle-age mortality in the past 200 years. As longevity continues to increase, we are just living that much longer past our reproductive age. The authors state that "Life-expectancy, however, is dominated by early life mortality and obscures the fact that a human female who attains maturity can expect to live well beyond her menopause." I would have liked to see some references to back this up, especially since third world countries are booming with young people of reproductive age, many of which will not live to see menopause.

Rejecting this hypothesis that humans simply outlive their gametes, they explore the idea that menopause might actually be an adaptive trait in humans. Their first hypothesis is based on the fact that as we age, reproduction becomes more and more dangerous for the mother. After a certain age, it makes sense for a woman to cease trying to have new children because of the increased risk of mortality for her and the increased risk of birth defects for her children. Instead, it makes much more sense for the woman to focus on raising her existing children rather than trying to have new children. Remember how I mentioned above that humans are weaned much earlier than other primates? This idea comes into play here, because since infants are relatively quick to be weaned, it is easy for other family members to step in and care for the infant while younger mothers concentrate on having more babies (or going back to work or whatever it is the modern mother does, but for the sake of evolution we'll pretend that her job is now to get pregnant with another child to spread her genes around a bit more). Therefore, similarly to the above, it also makes sense that if a woman doesn't have any children of her own to care for when she reaches menopause, she can step in and help care for her grandchildren. However, this mother/grandmother effect is hard to test empirically.

Grandma takes care of little Sally so that Momma can go get knocked up again. Actually maybe I should have used a photo of the Palin family for this one...? (Source)

Another hypothesis bears on the idea that, historically, women left the home group or tribe and got married to men who lived relatively far away. When they first joined this new community, they would have had no blood relatives. At this point, they would want to focus on only having their own children and not caring for any of the existing children in the community, since she had no genetic stake in their survival. The elder women in the community might help her raise her children because it was their son or grandson that she was having children with, so they would have genetic stake in the survival of her children. The idea is that as the woman gets older and her children and grandchildren were integrated into the society, the benefit of helping out with parenting would continue to rise for that individual, and she would focus less on investing considerable amounts of energy into having her own children and more on investing a bit less energy into caring for her descendants as they begin to fill the new community. There is no evidence that this was the practice in every human culture, though, and it is possible that in other cultures the males were the ones who left the home society, and in others still all of the offspring stayed nearby, so this hypothesis is hard to prove universally.

Now once all these sprog go out and populate the town, Momma can invest some time in helping someone ELSE have kids for a change. (Source)

A third hypothesis rests on the importance of the father. If it is true that a child's father is generally older than its mother (I am skeptical as to the truth of that), and that the mortality rate of males is higher than females, then it stands to reason that children born late in life might lose the father during the course of that child's development. If the above is all true AND the father carries a substantial amount of the burden for caring for the child, then it would be advantageous for females to stop having children past a certain age to diminish the risk of having to raise the child on her own. However, for this theory to uphold, it would have to be proven that fathers are generally significantly older than mothers, and that fathers carry a substantial burden of childcare. As you can see, I don't lend this theory much credence.

Yeah. Right. (Source)

Now that we've talked about life history reasons why menopause might be adaptive, let's talk about physiology for just a moment. What could be the mechanism by which menopause evolved? The authors bring up an interesting relationship seen in rodent models between a cytokine, called LIF, responsible for (among other things) blastocyst implantation and a gene, called p53, responsible for (again, among other things) up-regulating the gene responsible for LIF. p53 function declines as the mice age, but reproduction can be restored in mice with diminished p53 functionality if they are administered LIF. Evolutionarily speaking, p53 is ancient and the gene that codes for LIF is relatively young, and the authors hypothesize that putting LIF downstream of p53 may be responsible for menopause. They think that this might be selectively advantageous because it diminishes the chance of late-life implantation in a model where a late-life pregnancy is less likely to be successful to begin with. If the egg can't implant, the mother doesn't waste any energy on a pregnancy that isn't likely to succeed.

In sum, it becomes less advantageous for women to have children of their own as they get older. The chances of dying during childbirth go up due to aging, and the chances of birth defect go up due to a lifetime of accumulated damage to the mother's oocytes. No matter how you cut it, late life pregnancies are less likely to succeed. After a certain age, it becomes selectively advantageous for women to stop investing energy in getting pregnant and to start focusing on existing children or grandchildren. And because of the young age of weaning in human infants, it is relatively easy for elder women to take over the care for younger women in their family, so that those women can continue to churn out more sprog to populate the planet with.

[As an interesting aside, both searches for 'three generations' and 'father with children' on Google image search bring up pictures of Barack Obama's family on the first page.]

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Rashidi, A., & Shanley, D. (2009). Evolution of the menopause: life histories and mechanisms Menopause International, 15 (1), 26-30 DOI: 10.1258/mi.2009.009005

Mr./Ms. vs Dr.

Today I received the following email:

Hello. I took [class] with Ms. B------ about two - three years ago, and currently I'm in the process of applying to graduate school. The graduate school that I am applying to would like a copy of the syllabus for your course to see if it fulfills their physiology requirement. Can you provide me with the [class] course syllabus?

I tried contacting Ms. B------ directly, but my attempts have been unsuccessful.

S----- J----

My response:

Hi—I've attached DR. B------'s syllabus from this quarter.

Michelle

I wonder if CB were a man, would this student have called her Mr., or would he have defaulted to the correct title of Dr.? Either way, people be pissin' me off today.

Doin' it capybara-style.

I didn't have time to write a post for this morning because I spent all day yesterday sulking around and being grumpy about various things, some pretty important and some rather petty and silly. I'm also a bit grumpy this morning because I have four hours of office hours to look forward to this afternoon because my students' final exam is tomorrow. I am in need of some serious rodent therapy.

They should call it capybara-style. Source.

Some other people have written some very great posts, though, and you should read them this morning once you've gotten your fill of capybara sex.

Dr. Zen at Neurodojo explores the difference between slit and round pupils in snake eyes.

Razib at Gene Expression: Knowledge is not value-free.

Darren at Tetrapod Zoology has two great posts up about American Pronghorns.

UPDATE: Scicurious posts about the sex and neurogenesis paper that I blogged about last week.

Geeking out about machines.

The meeting I went to this afternoon for the -ometry machine was actually pretty interesting. They've come up with this new technology that allows us to more seamlessly transfer our -ography samples (which give us quantitative data) into the -ometry machine (which gives us qualitative data). Basically, making it easier for us to know exactly what it is that we're seeing in our systems. This could be very useful to me. When I decided to stay in this lab for my M.S., I originally planned to do a project based on learning -ometry and applying it to a lot of projects we currently have underway using -ography. Then I realized that it could take me years just to learn how to use the fucking -ometry machine, and I gave up on that idea. For a Ph.D., sure, but not for an M.S. If Advisor decides that this machine is worth our time and money, I might decide that it is worth my time to learn -ometry after all. I have time in my schedule for a side project, and I'm not too happy with the one Advisor currently wants me to do. Maybe I can convince him to buy this machine so I can do something I actually care about..?

Some tunes for the morning.

Here, have some pretty music to brighten your morning.



The hook, loosely translated, means "the night is my blanket". I'm cranky because Advisor is out of town and he's making us go in his stead to some meeting with representatives that are trying to sell us some new -ography machine, but this music is making me feel better.

Determining the phylogeny of Panthera palaeosinensis.

The feline subfamily Pantherinae is comprised of the so-called "big cats" and includes the four extant species of the Panthera genus (tigers, lions, jaguars, and leopards), which are set apart by their unique ability to roar, and also the two species of clouded leopards and the snow leopard. There is some debate as to whether or not snow leopards should belong in Panthera, but that is neither here nor there.

Artist's reconstruction of P. palaeosinensis.

One of the oldest known species of Pantherinae from the fossil record is Panthera palaeosinensis from Plio-Pleistocene China. It has been primarily assumed to be an ancestor of tigers, but others have suggested that it may be the ancestor to leopards, or possibly two or more lineages in Panthera. These estimates are primarily based on the fact that the size of the only known intact skull is somewhere between the size of a large leopard or a tiger, but skull size alone isn't enough to determine phylogenetic relationships. Genetic and life history factors can contribute to the growth of an animal, and many ecological factors can affect skull size, meaning that taxonomists need to look at specific morphologies as well as size when determining phylogeny.

A cast of P. palaeosinensis. Source.

It is with this in mind that Mazák set out to determine P. palaeosinensis's affinity by comparing a cast of the holotype skull to over 600 skulls of extant and extinct Pantherinae specimens. He found that when shape was considered in the absence of size considerations, P. palaeosinensis is closer to lions and leopards rather than tigers. His methods were somewhat validated by the fact that three distinct clusters emerged: clouded leopards, snow leopards, and all of Panthera, which is in agreement with classical descriptions of the clade.

P. palaeosinensis comfortably nestled between lions and leopards.

These results suggest that P. palaeosinensis is most likely the ancestor of at least two extant lineages of Panthera and not a primitive tiger as previously believed. It is also possible that P. palaeosinensis is basal to the entire genus. This has implications for current theories as to the evolution and radiation of the Pantherinae. The current theory based on molecular phylogenies is that Pantherinae radiated out of Asia over 5 million years ago, however the oldest fossil specimens are found in Africa from about 3 million years ago. The morphologies of P. palaeosinensis appear to be more primitive than those of the African fossils, which lends further evidence towards the Asian origin hypothesis for Panthera.

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MAZÁK, J. (2010). What is Panthera palaeosinensis?
Mammal Review, 40 (1), 90-102 DOI: 10.1111/j.1365-2907.2009.00151.x

How important are appearances, really?

Like every other grad student in history (I imagine), I have mixed feelings about my advisor. There are lots of things about him that I respect, and there are many ways in which he's been an immense help to me, but there are an equal number of ways in which his existence makes my life hard. He's a stubborn, blunt guy with a very loud bark, and sometimes that works for you, sometimes it works against you. But one thing I have always admired about my advisor is the fact that he's never told me I had to look or act a certain way to be taken seriously as a scientist.

When I first joined this lab as an undergrad, I had pink hair and two facial piercings. Of that, all that is left today is my lip stud, but it was my own choice to get rid of the pink hair and the eyebrow ring. I think about my lip ring about as often as I think about my earlobe, because by now it is just another part of me. I forget that I have it, even when I'm looking right at it. And every so often someone will behave oddly around me, and it isn't until (much) afterwards when I realize, oh, they were probably reacting to my piercing. It isn't often that it happens, but often enough for me to wonder what the hell is wrong with people. People have enough trouble taking young women seriously as a scientist to begin with, and if you throw non-traditional facial adornment into the mix, who knows what they think.

But, my advisor took me as I was, and when it came time to attend conferences and present research, he never asked me to take out my piercings to change my hair color. He told me that the work can and should stand for itself. It makes me wonder... the idea behind scientific communication is that it shouldn't matter who does the research as long as it makes a sound argument backed up by good data and factual analysis. However, scientists are human beings, and often the knowledge of who does what piece of research can change our opinion of that research. If some old dude passes by me standing in front of my poster at a conference, he's going to make a snap judgment about my work based on the fact that I'm female and my appearance. He may or may not realize that he's doing it, but he does. I always wonder what people's motivations are when they approach me. Are they actually interested in my work, or do they just want to find out if I know what I'm talking about?

The last nail in the coffin of Sb? Perhaps.

I can't say that I was surprised to learn that Bora of A Blog Around The Clock was leaving ScienceBlogs, because I got a pingback a few days ago from his new hangout. I assumed that he'd been considering making a move for a while and wanted a backup plan in case he really did decide to leave, but man, I had no idea he was going to go out with such a big bang. His farewell post is a painful but necessary read for anyone who has ever spent a sizeable chunk of time reading or writing on Sb. I will continue to read his blog wherever he ends up.

The continued increase in human longevity

I have a raging science crush on Tom Kirkwood, the director of the Institute for Ageing and Health at Newcastle University. I was lucky enough to read one of his manuscripts in the review stage several years ago, and ever since then I've been absolutely hooked on his work on human aging. In undergrad I worked part time at a local ice cream shop, and I read the whole 30 page manuscript behind the counter one slow winter night at work. It took me almost the entire shift, but it seriously felt like nothing because the reading was just that compelling. I am particularly fond of his work with Daryl Shanley on menopause, and I have a post planned for the near future on a recent review paper Shanley wrote with a colleague on the subject.

Kirkwood published an excellent article in Nature a few years ago called A systematic look at an old problem. Despite the fact that we keep expecting to eventually hit a wall in terms of how long humans can live, longevity keeps increasing. Life expectancy has been steadily increasing during the past 200 years or so. Prior to the mid-20th century this was due to rapidly advancing technology in sanitation, vaccines, and antibiotics, which in turn lead to decreases in early- to mid-life mortality. Since then, the increase in life expectancy has been due to a decline in late-life mortality, which Kirkwood notes is a relatively new phenomenon.

Past increases in life expectancy and predictions for the future.

Previous explanations for the aging process have involved the shortening of telomeres over a lifetime, the accumulation of oxidative damage, and the eventual 'running-down' of one's mitochondria, however the true reason is probably a combination of all of the above and more. The current consensus is that aging is caused by a lifetime of accumulated molecular damage that eventually results in diseases like cancer, Alzheimer's, and other health issues associated with the elderly.

But if ageing is a matter of things falling apart, can research realistically hope to achieve anything useful? The answer is emphatically yes — there is plenty of evidence that it is possible to intervene in the underlying causative mechanisms. Indeed, the malleability of the ageing process, as revealed by demography, derives precisely from the fact that it seems to be possible to slow the rate at which damage accumulates. Human longevity continues to increase when further gains from reducing mortality earlier in life are negligible because nowadays we reach old age, on average, in better condition than ever before.

I am not going to cover the whole article in this post, but I feel as though this excerpt in particular underlines the reason why all of this is so fascinating. It is the inherent optimism and mystery behind why we age the way we do, and why we continue to live longer and longer.

---

Kirkwood, T. (2008). A systematic look at an old problem Nature, 451 (7179), 644-647 DOI: 10.1038/451644a

Sunday foooooooooooood.

I've been in a kitchen-y mood this weekend, and I wanted to share some of my productivity. These are simple to make and not very expensive, so they're ideal for grad students!

Cim's chocolate cake of DOOM.

I got this recipe quite a few years ago from a friend of mine, but I had never tried to make it until yesterday. This isn't a sweet cake, it is more of a dark chocolate cake, so it needs a sweet icing. The original recipe is doubled because it is supposed to be a double-layer cake, but I didn't want nearly as much. If you like, you can double all the ingredients and then bake in two 8x8 or one 8x16 pan to make the full cake.

1 cup flour
1/2 cup white sugar
1/2 cup brown sugar
3/8 cup unsweetened cocoa*
1 teaspoon baking soda
1/2 teaspoon baking powder
1/4 teaspoon salt
1 egg
1/4 cup vegetable oil
1/2 cup cold brewed coffee or black tea
1/2 cup milk

* (Unfortunately the original recipe called for 3/4 cup and there's no good way to half this. I just eyeballed 1 and a half 1/4 cups.)

Stir together dry ingredients in a large bowl. Beat wet ingredients lightly, then slowly add dry ingredients. Beat on medium speed for 3-4 minutes. Pour into 8x8 inch pan and bake at 350*F for ~30 minutes. Cool completely, then ice with something fruity or coffee-flavored. I used strawberry icing and it came out wonderfully.

Beef pot roast with vegetables.

I got this recipe from my grandma. It is a great recipe for the summer because you make it in a slow cooker instead of an oven, so you don't raise the temperature of the room. It is also great for winter because it is warm and hearty, and it is great for graduate students because all you have to do is toss everything into the crock pot in the morning before you go to the lab, and bam, dinner is ready for you when you get home.

You can add chopped onion to the mix if you like, but I find it flavorful enough without it. I also make a variant of this occasionally with apples and cinnamon instead of zucchini and spinach, if you want something very slightly sweet.

~2 lb beef roast (I prefer bottom round.) [Depending on size and cut, anywhere from $5-$10]
1 zucchini squash [~$1.00]
4-6 red potatoes [~$0.80]
2 big handfuls of baby spinach [$2.40 for 1 bag]
1 14 oz. can beef broth [$0.75]
salt, pepper, and basil

Total cost: $10 to $15 for 4-6 servings.

Line the bottom of your slow cooker with the baby spinach, then chop the zucchini into thick slices and quarter the red potatoes, then add to the pot. Put the roast on top, pour in the broth and then season the meat to taste with the salt, pepper, and basil. Cook on high heat for at least six hours.

More thesising.

K wants to go see Despicable Me today, which I desperately want to see, but I had to say no because I was counting on working on my thesis today. Infinite sadfaces. We were actually supposed to go see it yesterday, but then we wound up spending the whole evening running around town looking for a new man bag for him to take to work. How hard is it to find a canvas messenger bag anymore? Pretty goddamn hard.

I'm making a lot of progress on my thesis, though! It is funny how the amount of work that you need to do feels insurmountable until you actually start doing it, and then you realize it wasn't that much work after all. And on the contrary, when you think something isn't going to take very long, you wind up spending the whole day on it. Funny how that works, eh?

I had a poop-my-pants moment of fear earlier when I was working on some updates to my model that Advisor asked me to do, and I accidentally saved the new file over the template file that I use for all permutations of my model. Um. Oops. I almost flipped my shit (in a bad way), but then I remembered that I keep a redundant system because I have two laptops that I routinely use. I just copied the template file over from my netbook. Crisis averted!

Rodent Saturday!

Today's required rodent reading is this post on squirrels and cedar-mice by Christopher at Catalogue of Organisms. It includes a wonderful photo of an Indian giant squirrel eating what looks suspiciously like a fish biscuit.

Indian Giant Squirrel, Ratufa indica. Source.

Now, for my contribution to Saturday's rodent blog, I will tell you about a new mouse species of the South American Akodon genus that was described earlier this year by Braun and colleagues in New species of Akodon (Rodentia: Cricetidae: Sigmodontinae) from central Argentina.

Species of the genus Akodon are unique to South America and live mostly along the Andes from Venezuela to the southernmost parts of the continent in a very diverse variety of habitats. The species described in this paper, Akodon viridescens, is native to the Cuyo Region in northwestern Argentina, particularly the Córdoba Montane Savanna.

Location of specimen collection. The shaded area is the Córdoba Montane Savanna.

The namesake for this new species comes from an unusual characteristic: the fur of this mouse species actually has an iridescent green hue in natural sunlight! I am imagining something akin to an old soda bottle in the sunlight. Unfortunately I could not find any images of these critters on the interwebs, but here's a photo of another Akodon spp. From Peru:

Look how adorable! What a dear little creature. Source.

The authors were at least kind enough to include a photo of the critter's skull, for those of you who like bones:

Skull and teeth of A. viridescens. Click to enlarge.

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Braun, J., Mares, M., Coyner, B., & Van Den Bussche, R. (2010). New species of Akodon (Rodentia: Cricetidae: Sigmodontinae) from central Argentina Journal of Mammalogy, 91 (2), 387-400 DOI: 10.1644/09-MAMM-A-048.1

I'm a nerd and K is a safari explorer.

My own mother called me a nerd on facebook because I was gushing about nephrophysiology during lecture this morning. THANKS MOM! I love you too.

K is at his first day of Real Job today. He showed me the uniform. They gave him a shirt to wear and instructed him to wear it with khaki pants. Except... the thing is... the t-shirt is khaki too. I took one look at him this morning and thought to myself, "Dear God, he looks like a zoo keeper." He just needs one of those little safari hats. Please don't tell him I said that.

Advisor wants to include my 'protein channels' model in a speech he's giving at a conference next month. Argh! Ack! That means I have to perfect it, um, right now. He's also pushing me to get that manuscript to him very very soon, but I'm all, "I don't waaaaannnnaaaa..." It is Friday, I want to sit around and veg out in front of the TV. I haven't felt too relaxed lately. I think I'm going to take the weekend off. So much for writing.

It is probably in bad taste to use an 'in my pants' phrase when talking about the kidneys.

I think I may have jinxed myself (in a good way) because all of my students seemed to understand the hemoglobin saturation curve today! Talk about serendipity. For some reason it was just clicking with them today, so that's a pretty good sign. Tomorrow we get to start the <3 <3 renal system <3 <3! (I totally cream my pants over stuff like glomerular filtration rate and counter current multiplication.) Then a week from today the class will be over and I have sweet delicious freedom until the middle of September. Well, sweet delicious semi-freedom since Advisor has a project he wants me to work on, but at least I get to set my own schedule and I don't have to wake up at 7am every day if I don't want to. Small victories, right?

I'm feeling better today, but not any more productive than yesterday. Oh well, there's always the weekend. I feel like I write better on the weekend anyway.

Cool stuff from the interwebs:

- Isis teaches us that veins are squishy.
- Mo at Neurophilosophy tells us that by deleting a single gene, researchers can make female mice exhibit masculine behaviors and try to mate with other females. She adds a caveat that this probably has little to nothing to do with human sexuality.
- GrrlScientist alludes to changes that may be afoot regarding ScienceBlogs.

Not exactly breaking news: sex reduces anxiety!

It has long been known that, in addition to all the physical health benefits of exercise, it also promotes good mental health. Regular exercisers experience reduced stress and anxiety despite the fact that the physical exertion of exercise itself actually releases stress endocrines, called corticosteroids. You are probably familiar with some corticosteroids even if you aren't an endocrinologist.

Click here if the embed doesn't work for you. Note: I do NOT recommend or endorse this product.

Advertisements for cortisol blockers as weight-loss treatment are in vogue right now, but the efficacy of such supplements is suspect. For one thing, your body needs a certain level of cortisol for proper function, so it isn't a great idea to go blocking them all willy-nilly. By the same token, you definitely don't want too many corticosteroids floating around in your body. Historically, stress was induced by starvation, so the function of corticosteroids is to prepare the body to go without food for a while. Corticosteroids increase glucose utilization and promote the breakdown of fat, protein, and eventually bone. The energy liberated by this process is stored as fat near the vital organs, hence why the cortisol blocker commercials target people with 'belly fat'. In the present day, stress can be caused by a plethora of things other than starvation, but the body's response to stress remains the same. In addition to breaking down the body's resources to liberate energy, corticosteroids also temporarily block growth and development all over the body, including neurogenesis and proper brain function, which can manifest as elevated anxiety.

But back to exercise. As I said above, despite causing elevated levels of corticosteroids, physical activity results in an increase in mental health and brain function for most people. This phenomenon has recently been linked to the idea that exercise is mentally linked to personal reward. As Leuner and colleagues put it in their paper, Sexual Experience Promotes Adult Neurogenesis in the Hippocampus Despite an Initial Elevation in Stress Hormones, "[A] recent study showed that rewarding intracranial self-stimulation is sufficient to increase adult neurogenesis, suggesting that the hedonic aspect of physical exercise may be responsible for its beneficial effects on structural plasticity," (see article for citation). The authors decided to test this pleasure/reward hypothesis by seeing what effect sexual activity has on corticosteroid levels and anxiety.

"Adult male rats were exposed to a sexually-receptive female once (acute) or once daily for 14 consecutive days (chronic) and levels of circulating glucocorticoids were measured." The rats were also measured for neurogenesis and dendritic complexity in the hippocampus. "Finally, to evaluate whether sexual experience alters hippocampal function, rats were tested on two tests of anxiety-like behavior: novelty suppressed feeding and the elevated plus maze."

Corticosteroid levels and neurogenesis in response to acute sexual activity.

As you can see in the image above, rats that were briefly exposed to sexually receptive females experienced an increase in corticosteroid levels compared to a control, but also experienced increased neurogenesis (that's what that stuff on the right Y-axis means) compared to a control.

Corticosteroid levels and neurogenesis in response to chronic sexual activity.

However, rats that were allowed access to a sexually receptive female for two weeks did not experience an increase in corticosteroid levels, but still experienced increased neurogenesis compared to a control.

One test for anxiety - time to feed in a novel setting.

When tested for anxiety, both sexually active and control rats had similar performances on the maze, but sexually active rats were quicker to feed in an unfamiliar setting than control rats. This was not due to a difference in appetite, since both sets of rats performed similarly when fed in their familiar cages.

It is clear that sex and exercise have similar positive effects on the brain despite increasing corticosteroid levels. Both of these activities have been shown to be rewarding in rodent models (but, really, just consider how you feel after taking a run or having sex), suggesting that the harmful effects of physically stressful behaviors may be overridden if the behavior itself evokes pleasure in the individual.

This possibility raises questions about what factors associated with reward might participate in protecting the brain from the negative influence of stress hormones and further, whether similar or other factors are responsible for the beneficial effects of sexual experience. In this regard, a role for neuromodulators altered with sexual experience and known to influence adult neurogenesis, like opiates or dopamine, seem plausible, as does oxytocin, a neuropeptide that buffers the brain and body against some of the adverse consequences of stress hormones.

Not only did sex result in increased neurogenesis and decreased anxiety, but recurring sexual activity brought sex-induced corticosteroid levels back down to the level of control over time. So, sex gets less stressful the more you have it? Okay, sign me up!

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Leuner, B., Glasper, E., & Gould, E. (2010). Sexual Experience Promotes Adult Neurogenesis in the Hippocampus Despite an Initial Elevation in Stress Hormones PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011597

Random sick day crap. Also gas exchange.

Other people blog about stuff I've blogged about. Imagine that.

- Neuroskeptic tackles the issue of autism and wealth.
- Allison at Dormivigilia blogs about referee bias in soccer.

I also discovered a very useful blog today called Better Posters. It is all about how to make better scientific posters, and surprisingly active considering the subject. How much can there possibly be to say about how to make a poster? Apparently a lot.

I've been way too unproductive today. I took a sick day off work because I had a rough night last night and a rough morning this morning, so I've been sitting around all day eating soup, reading Calvin and Hobbes (mom got me the collector's edition for my birthday, holy crap), and napping. I have a general feeling of malaise but no real symptoms aside from a sore throat and meh stomach (not exactly nauseated, but upset in some way I can't articulate), so hopefully this is just a funk and it'll go away by tomorrow. I'm hoping it is just stress and anxiety (possibly related to the pressure to churn out my manuscript, perhaps?) and not any kind of actual illness.

I missed lecture today on one of my favorite subjects to think about but one of my least favorite subjects to try to explain to students: gas exchange.

Source.

No matter HOW many times I try to explain the oxyhemoglobin dissociation curve, most of my students just don't get it. It's a pretty abstract idea that can be hard to absorb for a lot of students, especially when they only have the minimum prerequisites of 5 credit hours of biology or chemistry in order to take this class. To put it very simply, hemoglobin binds to oxygen when the partial pressure of oxygen is high (such as in the lungs) and kicks off oxygen when the PP of oxygen is low (such as in tissues that are actively doing work). I don't know what makes this so hard to grasp. If I were a better teacher I'd probably be able to communicate it in a more intuitive way. Fortunately I don't aspire to be a teacher after grad school.

Uncinate processes link birds and dinosaurs

I read a lovely paper last night that took to task the findings of an older paper by one of my closest collaborators. I think both papers are very strong papers and I would love to discuss my thoughts on the issue here, but I feel as though the topic might be a little too close to home (and jeopardize my pseudonymity), so today I'll discuss something completely unrelated instead. :)

Comedic aside: the first sentence of the review paper below mentions three lineages of flying vertebrates. I was having trouble coming up with the third, so I asked K, "Name a vertebrate that flies other than birds and bats." His responses were flying squirrels (not true flight), fish ("Swimming is like flying, right?"), and then he asked, "Are there any flying plants?" Oh dear. I swear he isn't as dumb as he looks on paper. You'd think that if he was going to leave the clade of vertebrates altogether, he'd at least come up with insects before jumping to hypothetical flying plants. But I digress. Actually, I still haven't figured out what the third lineage is, although I suspect that what we group together as 'bats' might actually be two distinct lineages. Or maybe the authors were referring to an extinct lineage that I'm not familiar with. I'll have to look that up later.

Birds have evolved incredibly unique and efficient respiratory systems to match the high energetic cost of locomotion by flight. Mammals, which, along with birds, are endotherms and thus have a relatively high metabolic rate compared to reptiles and amphibians, use a tidal respiratory system. Air enters and leaves the lungs from the same opening, and the entire volume of stale air is not expelled in one exhale. Thus, fresh air and stale air mix in the lungs every time you inhale, which causes decreased efficiency. In contrast, birds have a one-way flow of air through the lungs, aided by the use of air sacs. Air enters the lungs via posterior air sacs and leaves the lungs via anterior air sacs, ensuring one way flow (so that fresh and stale air do not mix) and, combined with cross-current exchange between the parabronchi and blood capillaries, more efficient gas exchange.

Source: http://www.peteducation.com/article.cfm?c=15+1829&aid=2721

Above is a rather simplified schematic of this process. Following one air packet: on the first inhale, the air travels to the posterior air sac. On the first exhale, the air passes through the lungs. On second inhale, the air leaves the lungs and enters the anterior air sac, and on the second exhale, the air leaves the body. (For more information on the physiology of avian respiration, this website is an excellent resource.)

Birds lack a diaphragm as seen in humans and other mammals. Instead, both inhalation and inspiration are active muscle processes, and respiratory rhythms must be coordinated with flight rhythms. The movement of the ribs and sternum must be coordinated so that the upward rebound of the sternum during the power stroke of flying is occurring at the same time as exhalation, since the net result is a decrease in thoracic cavity volume.

Source:  http://people.eku.edu/ritchisong/skeleton.html

Recent interest in avian ventilation has focused on the significance of uncinate processes (UP), which are small caudo-dorsal projections from the ribs (see above figure) and are the subject of a recent review paper by Codd entitled Uncinate processes in birds: Morphology, physiology and function. UP are thought to function during inspiration, such that when a muscle attached to the UP contracts, it generates a torque that pulls the ribs forward and increases thoracic volume. Thus, the UP act as little levers for moving the ribs via muscle attachment. "Recent geometric modelling of the avian rib cage confirmed this lever-arm action and also demonstrated that having UP can increase the effective mechanical advantage by a factor or 2–4 for the movement of the ribs[.]" The UP have different morphologies in birds with different locomotor strategies, most likely due to the different breathing strategies necessary to maintain different types of locomotion. In some birds, the UP can also play roles in perching, egg-laying, and vocalization.

When the birds were resting on their sternum, thereby restricting normal movements, ventilation was achieved by an increase in activity of [the muscle attached to the UP] that resulted in a lateral flaring of the rib cage. It appears, therefore, that there is a switch in the mechanics of ventilation in birds associated with different postures. [...] Given our new understanding of the role of the UP in avian ventilation, and the fact that these processes are greatly reduced in species adapted to running or walking, it seems likely that the mechanics of ventilation in cursorial birds may be different from those of flying, diving or swimming species.

UP are also further evidence that birds are descended from therapod dinosaurs, as UP have been found in many Maniraptoran species.

Interestingly the UP in these dinosaurs are cartilaginously attached to the vertebral ribs (as they are in Apteryx and the Spheniciformes) suggesting that the ventilatory mechanics may be similar and also depend on enhanced flexing at the join to the rib. Given the fragmentary nature of the fossil record and the fact that UP are small bones easily lost during fossilisation or fossil excavation, it seems likely these processes are much more widely distributed.

Source: http://people.eku.edu/ritchisong/554notes1.html
(Click to embiggen.)

Above is a comparison of avian uncinate processes (top) and those of Maniraptors (bottom). The presence of these morphologies in dinosaurs would suggest that the avian air sac system of breathing may have actually evolved before flight, instead of the other way around!

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Codd, J. (2010). Uncinate processes in birds: Morphology, physiology and function☆ Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology, 156 (3), 303-308 DOI: 10.1016/j.cbpa.2009.12.005