Durk Pearson & Sandy Shaw’s®
Life Extension NewsTM
Volume 16 No. 3 • March 2013


HAPPY NEW YEAR!

Sex, Stress Hormones, and Adult Neurogenesis

Starting 2013 With Some GOOD NEWS!

New research suggests that sexual experience is not only pleasurable, but also reduces anxiety and increases adult neurogenesis in adult male rats. We report here on three recent studies.1–3

Why do rats have all the fun by getting to be the subjects in these sexual studies? First, rats are much easier to maintain under constant laboratory conditions and to sample for plasma constituents such as glucocorticoids, which could inhibit sexual activity, induce anxiety, and inhibit neurogenesis. Rats are also easier to get in groups with similar genetic background, thus avoiding some confounding effects. Anyway, the rats in these studies were very enthusiastic subjects but were still “sacrificed” in the end in order to assess brain effects. Well it was fun while it lasted.

In the first paper,1 the researchers studied whether sex, a rewarding stressor that, like other stressors, increases glucocorticoids, would have similar negative effects as non-rewarding stressors.

The adult male rats1 were exposed to a sexually-receptive female rat once (acute) or once daily for 14 consecutive days (chronic) and their levels of circulating glucocorticoids were measured. Their sexual encounters were videotaped and then analyzed for mounts, intromissions, and ejaculations. On the last day, the rats were injected with BrdU (bromodeoxyuridine, a DNA synthesis marker). The scientists explain that “the majority of new cells in the dentate gyrus express the mature neuronal marker NeuN 2 weeks post BrdU labeling.” An additional cohort of naive and sexually-experienced rats were tested for anxiety on the elevated plus maze and on the novelty-suppressed feeding paradigm (where the latency to chew a ~2 g food pellet in the center of a bright area was recorded. The longer latency indicated anxiety).

The results showed that chronic sexual experience enhanced cell proliferation and adult neurogenesis without altering glucocorticoid levels. Sexual experience produced more new neurons (those labeled with BrdU and examined after a 2 week survival). Acute sexual experience (a single encounter with a sexually-receptive female rat) resulted in enhanced cell proliferation in the dentate gyrus despite substantially elevated glucocorticoid levels.

The sexually experienced rats were less anxious than naive controls when tested on the novelty suppressed feeding paradigm.

As the researchers note, despite the increase in glucocorticoids (in the rats receiving a single (acute) sexual experience), neurogenesis still took place, even though stressors that increase glucorticoids generally reduce adult neurogenesis. The authors suggest that whether glucocorticoids increase or not, it is the rewarding (hedonic) aspect of the brain stimulation that overrides the inhibitory effect of glucocorticoids on neurogenesis. As the researchers also note, another example of a rewarding stressor is exercise that, despite increasing glucocorticoids, also reduces anxiety and enhance adult neurogenesis in mice and men.

In the second paper,2 researchers studied the effect of oral feeding of Lycium barbarum< (wolfberry, also called Goji) polysaccharides (LBP) in adult male Sprague-Dawley rats for its effects on copulation, ejaculation, and shortening of ejaculation latency. After 21 days of LBP feeding, there was significant improvement of all these sexual functions. Moreover, the sexual inhibition caused by chronic corticosterone (glucocorticoids) was prevented by LBP. While increased corticosterone suppressed neurogenesis in subventricular zone and hippocampus of adult rats, this was reversed by LBP.

“Significant correlation was found between neurogenesis and sexual performance, suggesting that the newborn neurons are associated with reproductive successfulness. Blocking neurogenesis in male rats abolished the pro-sexual effect of LBP.”2 “Our results showed that the beneficial effect was not only revealed in normal, healthy rats, but also in rats with sexual inhibition induced by corticosterone. The ‘rescuing’ effect of LBP on male sexual behavior suggests that LBP may be useful to treat male sexual dysfunction.”2 As in the study1 discussed above, adult neurogenesis in the SVZ (assessed by the number of BrdU-positive cells in the corticosterone-treated animals was significantly lower than that in animals not given corticosterone.

An in vitro study carried out by the same researchers as part of the study showed that LBP treatment at 1 μg/ml and 10 μg/ml increased cell proliferation in a neural stem cell line. Corticosterone treatment suppressed the cell proliferation of the neural stem cells, while co-administration with LBP at 10 μg/ml could reverse the suppression.2

Unsurprisingly, the third paper3 is very similar to the second paper2 as the researchers were the same; paper #3 was published the year before paper #2. Accordingly, the adult male rats were treated with either corticosterone and/or paroxetine, an SSRI type (similar to Prozac®) antidepressant. The findings included that corticosterone treatment inhibited male sexual performance, while paroxetine enhanced it. The researchers summed it up: “These results suggest that cell proliferation in the SVZ and hippocampus may be involved in the reproduction of the male rodents, and pharmacological treatments may affect sexual functioning through alteration of neurogenesis.” Paroxetine is an SSRI antidepressant drug that, as a class, have been found to generally increase neurogenesis.

References

  1. Leuner et al. Sexual experience promotes adult neurogenesis in the hippocampus despite an initial elevation in stress hormones. PLoS ONE 5(7): e11597, doi:10.1371/journal.pone.0011597.
  2. Lau et al. Polysaccharides from wolfberry prevents corticosterone-induced inhibition of sexual behavior and increases neurogenesis. PLoS ONE 7(4):e33374. doi:10.1371/journal.pone.0033374.
  3. Lau et al. Effect of corticosterone and paroxetine on masculine mating behavior: possible involvement of neurogenesis. J Sex Med. 8:1390-1403 (2011).

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