Sexual experience affects reproductive behavior and preoptic androgen receptors in male mice

Relationship between sexual satiety and motivation, brain androgen receptors and testosterone in male mandarin voles

Androgen receptors participate in the neuroendocrine regulation of male sexual behavior, primarily in brain areas located in the limbic system. Males of many species present a long-term inhibition of sexual behavior after several ejaculations, known as sexual satiety. It has been shown in rats that androgen receptor expression is reduced 24h after a single ejaculation, or mating to satiety, in the medial preoptic area, nucleus accumbens and ventromedial hypothalamus. The aim of this study was to analyze these processes in another animal, the mandarin vole (Microtus mandarinus). We compared differences in androgen receptor (AR) and testosterone (T) expression in various brain areas between male mandarin voles sexually satiated and those exposed to receptive females but not allowed to mate. Sexual satiety was associated with decreased AR and T expression in the lateral septal nucleus (LS), medial amygdala (MeA), medial preoptic area (mPOA) and ventromedial hypothalamic nucleus (VMH). Males exposed to receptive females showed an increase in AR and T expression in the bed nucleus of the stria terminalis (BNST), LS, MeA and VMH. Serum testosterone levels remained unchanged after 24h in males exposed to receptive females or males mated to satiety. These data suggest a relationship between sexual activity and a decrease in AR and T expression in specific brain areas, and a relationship between sexual motivation and increased AR and T expression in other brain areas, independently of testosterone levels.

Modular genetic control of innate behaviors

Many complex behaviors are genetically hardwired. Based on previous findings on genetic control of mating and other behaviors in invertebrate and mammalian systems, I suggest that genetic control of complex behaviors is modular: first, dedicated genes specify different behavioral patterns; secondly, separable genetic networks govern distinct behavioral components. I speculate that modular genetic encoding of complex behaviors may in part reflect modularity in brain development and function. Editor's suggested further reading in BioEssays From songs to synapses: Molecular mechanisms of birdsong memory Abstract.

Oxytocin modulates social interaction but is not essential for sexual behavior in male mice

Recently, several studies have shown different conclusions regarding the effect of oxytocin (OT) on the social behaviors of male mice. Most of these studies used exogenous OT, but currently, investigations of the neural bases of social behavior are increasingly employing gene inactivation. This study aimed to analyze the role of OT in the modulation of social behaviors (i.e., sexual and social interaction behaviors) in male mice with selective deletions of the OT gene (OTKO) and the influence of this deletion in basal vasopressin (AVP) plasma concentrations. Our results showed that in the social interaction test, OTKO mice exhibited lower levels of social behaviors and higher levels of non-social behaviors compared to the wild type (WT) group. Additionally, the OTKO group showed a decrease in the number of agonistic behaviors delivered, and consequently, their dominance score was lower than that of the WT group. In the ethological analysis, the OTKO group had a lower aggressive performance and increased social investigation than the WT group. No significant differences were observed in the sexual behavior between groups. Finally, we found lower AVP plasma concentrations in the OTKO compared with the WT group. In conclusion, our data suggest that OT modulates social investigation behavior and the aggressiveness of male mice. The decrease in AVP concentrations in the OTKO group allows us to infer that AVP is physiologically relevant to these behavioral modulations. However, sexual behaviors do not seem to be affected by the lack of OT or by a decrease in the AVP concentration.