Sex, Stress, and Neurogenesis

Sci couldn’t help but notice all the tweets going around the other day talking about how sex stressed you out but was ultimately good for you. She contemplated saving it for a Friday Weird Science, but it’s not THAT weird (though it is interesting), and anyway Sci has something brewing for teh weird skienz.

So this is going to be a post for today. Let’s talk about sex. And let’s talk about stress. And then let’s talk about how increases in glucocorticoids are not the be all end all of psychiatric pathology. Leuner et al. “Sexual Experience Promotes Adult Neurogenesis in the Hippocampus Despite an Initial Elevation in Stress Hormones” PLoS ONE, 2010.

Sadly, this was in rats. Even with the blood draws (and the brain slicing at the end), I bet humans would line up for this study. “You must have sex. LOTS of sex. Also, you will be paid.” Gee…

So as you may have heard from other posts Sci has done on the topic, the issue of neurogenesis is a pretty big deal. Basically, we used to think that you were born with all the neurons you would ever have. But that is in fact not true, and certain areas of your brain will continue to produce neurons all the way through your life. One of those areas is what’s called the subgranular zone of the hippocampus. This area produces neurons that then migrate to other areas of the hippocampus.

Why is this important? Recently scientists have found that antidepressant drugs (like Prozac and Zoloft) increase the birth of new neurons in the hippocampus, and that these increases in neurogenesis are associated with behaviors that we have come to associate with antidepressant properties. Basically if an antidepressant is working in a rat, you will see neurogenesis and you will also see increases in sucrose consumption, increases in tasty food consumption, and increases in struggle in tests like the forced swim test or tail suspension test.

Interestingly, scientists have found that while antidepressants increase neurogenesis, stress DECREASES neurogenesis. This seems like a bit of a no brainer, as we know that people under chronic or severe acute stress are more likely to suffer depression, but of course this is a key toward a possible mechanism.

And so a lot of studies have since focused on the effects of stress on neurogenesis, and how to counteract that stress. To do this, scientists tend to use either stress itself (which creates for long hours) or giving stress chemicals called glucocorticoids, like cortisol (which is a lot less stress on your grad student). This has created a lot of really good studies, but this study highlights some of the problems with this:

NOT ALL STRESS lead to decreases in neurogenesis.

This study investigated the effects of sex, but other studies have come before it. In particular, there have been some studies on exercise. We all know exercise is stressful, right? I mean, for many people it’s psychologically relaxing, but exercise puts stress on your body and releases stress hormones. Despite this, exercise INCREASES neurogenesis in the hippocampus, reduces anxiety, and is generally good for rats (and probably also humans, as Sci thinks back virtuously on her run yesterday). So it appears that not all stresses are created equal, and some may be better for you than others.

So we know about exercise, but what about SEX?! Sex is a physically trying act (well, ok, I guess it depends on how you do it), but it’s also known to decrease anxiety and generally make for some happy critters. So what about neurogenesis?

To look at this, the authors took a bunch of rats. Some of them had sex once. The luckier ones got to have sex for 14 days straight. Then they looked at the cortisol levels, and THEN they looked at neurogenesis. To look at how the neurogenesis might have effects on behavior, they also looked at anxiety-like behaviors.

And here’s figure 1:

As you can see above, it appears that all male rats like to have sex. I was SHOCKED, SHOCKED I TELL YOU!

Really I just wanted to use that table.

Moving on.

Here you can see the results when rats were exposed to acute sex (Sci loves the phrase “acute sex”), wherein they had sex only once. You can see that their corticosterone levels (a stress hormone) went up, and SO DID their hippocampal neurogenesis. So it looks like here that the neurogenesis increases in response to sex despite an increase in stress hormones.

But the chronic sex exposure is actually what had Sci interested:

On the left you can see the corticosterone levels after male rats were exposed to sex for 14 days (it’d be really interesting to see this in female, but I think that the difference between female rats and female humans in this regard may be a lot more pronounced than a difference between male rats and male humans). You can see that when the rats were gettin’ some on the daily, their corticosterone levels go back down (compared to the acute sex), so that they look normal, but the neurogenesis in the hippocampus only goes UP, showing that chronic sexual experience is pretty good for your neurogenesis.

Here you can see the effects of chronic sexual experience on measures of anxiety. As you might imagine, rats who were gettin’ some were a good bit more relaxed than rats who weren’t. They ate more tasty food in a novel environment (normally rats exposed to a novel environment get nervous and can’t eat a lot). They also asked the rats if they could spend less time in the open arms of a plus maze, but it really looks like that didn’t pan out. Sci thinks they may have had more luck with other tests, like forced swim.

So the basic conclusions are that sex is great. It increases neurogenesis in the hippocampus and makes rats less anxious.

Sci thinks it’s a little odd that so many people focused on the acute sexual experience as being the big deal here. It’s not completely unusual that an event would be associated with both increases in stress hormones AND increases in neurogenesis (see exercise). What Sci found interesting is that sex quickly ceased to be stressful, and that neurogenesis quickly increased. It’d be interesting to see how much this neurogenesis effect correlates with “antidepressant-like” effects. For example, can chronic sex combat the decrease in neurogenesis seen with unpleasant types of stress? Can chronic sex produce effects that we would normally associate with antidepressants? Could sex be the best antidepressant of all?

And to get more meta about it, Sci’s very interested in this finding because of the rewarding aspects. Sex is well known to be highly motivational, and thus is rewarding. I’d be interested to see how the neurogenesis in the hippocampus in response to sex or exercise correlates to the rewarding properties of stuff. Are the effects generally positive? In what way? I’m not sure how you’d test it, but it’d be really interesting to find out.

Leuner B, Glasper ER, & Gould E (2010). Sexual experience promotes adult neurogenesis in the hippocampus despite an initial elevation in stress hormones. PloS one, 5 (7) PMID: 20644737

12 Responses

  1. I’m always skeptical of presumed neurological parallels between rodents and humans, considering they’ve been evolving independently for 90 MYears or so. But I’m especially skeptical when it comes to sex, which is an activity with enormous social consequences and has probably been evolving independent social roles, especially in the higher primates.

    OTOH, this fits in well with the differences between bonobos and chimpanzees: bonobos have (much) more sex and a much less stressful status competition, while chimpanzees (especially dominant males) have a _much_ more stressful status competition with a different, and much more hostile, role for sex.

  2. “acute” versus “chronic” sex is hilarious.

    I’m always skeptical of presumed neurological parallels between rodents and humans, considering they’ve been evolving independently for 90 MYears or so.

    Of course that is a scientifically underinformed view. The question is rather about which systems are we talking about and what degree of inference (given what we know about species differences) can be made. Also, whether there is predictive validity irregardless of face or construct validity.

    Now in terms of this paper, sci, the real question here is the usual when it comes to hippocampal neurogenesis. Specificity. Just about everything that is a difference from the normal lab life increases hippocampal neurogenesis. An enrichment effect if you like. So you have to ask what controls to run.

  3. Just about everything that is a difference from the normal lab life increases hippocampal neurogenesis. An enrichment effect if you like. So you have to ask what controls to run.

    Yes, this. I think Sex is really just another form of enrichment. :) Perhaps compare the neurogenesis to rats given just toys? I’d LOVE to see a comparison to masturbation but I don’t think we can do that in rats.

    I also think it’s important as to what the neurogenesis is DOING. Where are these going, where are they incorporated, and what information are they conveying once they get there.

  4. re: what the neurogenesis is doing… I have wondered the same thing. Why does exercise, sex and even pregnancy (i.e. pregnancy-stimulated neurogenesis) cause neurogenesis? Perhaps preparing the brain for problem solving required in parenting? or protecting and feeding off-spring? perhaps it occurs with sex because it means the organism was successful and brain needs to problem solve in order to get more.. perhaps to defend mates? perhaps with excercise because sudden acute exercise may signal that that the environment is changing (and potentially there is an emergency or a need to move) and therefore the brain needs to get into gear for a novel environment? or being on the go means foraging for food which would require high cognitive ability…

    I have no idea…

    Interesting stuff… I would also be interested to see if masturbation does the same… it may not which is a major jip… I also wonder if thinking about exercise causes neurogenesis? I wish someone would get on studying that… while I stretch out on the couch and think about push ups…

  5. I blogged about this paper last week as well, but my knowledge is more slanted towards the endocrine side and less on the neurological side. I’m glad to read about it from your perspective.

  6. [...] Scicurious posts about the sex and neurogenesis paper that I blogged about last week. from → Uncategorized ← Geeking out [...]

  7. This is simply a “girls just want to have fun” sort of study although in this case the “girls” were guy rats.

    I.E. having fun on a regular basis is good for our mental health. It probably doesn’t make much difference if the fun is from having great sex, participating in sports we enjoy, shopping for a great pair of high heels if that is our thing, going dancing or whatever.

    In “Dancing in the Streets: A History of Collective Joy” by Barbara Ehrenreich the author points out that prior to our religious/rich taskmasters crushing the human spirit it was the norm in societies to have extended celebrations of joy twice per week.

    This was stopped in order to give more power to religious leaders and more profit to the rich. After all happy people don’t need to get regular religious fixes nor do they feel the need to work themselves to death to profit the rich.

  8. Taking into account drugmonkey’s point, I’m interested in at least three conditions:
    *rats with new toys (is it the novelty?)
    *rats with new exercise wheels (is it the energy expenditure? Table 1 implies that the sex is fairly vigorous)
    *rats with sex

    Also, I’m curious if the acute vs. chronic pattern (i.e. high corticosterone/high neurogenesis vs. low corticosterone/high neurogenesis) is identical to that seen with exercise. Also, you mentioned blood draws. Is plasma corticosterone identical to brain corticosterone?

  9. In spite of the inconclusiveness of this study, a friend of mine pointed out an awesome pick-up line that this study makes possible that I thought worth sharing:

    “Hey baby, let’s grow some new neurons tonight so I have something to remember you by!”

  10. TYBO FTW!!!!

  11. [...] In male rats, sex promotes neurogenesis and reduces anxiety. More discussion here. [...]

  12. [...] In male rats, sex promotes neurogenesis and reduces anxiety. More discussion here. [...]

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