Astrocytes in the medial preoptic area modulate ejaculation latency in an experience-dependent fashion.

Abstract

While sexually experienced males copulate at a higher frequency than sexually inexperienced males, there is still a great deal of variability in their behavior. Within the medial preoptic area (mPOA) of the hypothalamus, glutamate modulates some of this variability. Glutamate levels, for example, increase during sexual activity, peaking with ejaculation and falling precipitously during the post-ejaculation interval. Whereas lower glutamate levels after ejaculation translates to longer post-ejaculatory intervals, administration of glutamate uptake inhibitors into the mPOA increases the number of ejaculations a male rat achieves over a mating bout, and reduces the latency to ejaculate once mating begins. Because astrocytes modulate the availability of neuronal glutamate, we hypothesized that differences in the number of GFAP-positive astrocytes in the mPOA may account for variability in sexual behavior. To this end, we examined whether the number of astrocytes in the mPOA related to ejaculation latency as well as to the duration of the post-ejaculatory interval (PEI) in sexually experienced and sexually inexperienced males. Results indicate that the number of astrocytes negatively correlated with latency to reach ejaculations in sexually inexperienced but not sexually experienced rats while the number of astrocytes and PEI were not related. Astrocyte numbers did not vary between inexperienced and experienced subjects indicating that astrocyte processes may differentially project to sex-relevant glutamatergic synapses or that glutamatergic innervation of the mPOA changes as a function of sexual experience.