Demonstration of ejaculation-induced neural activity in the male rat brain using 5-HT1A agonist 8-OH-DPAT.

Previous studies from our laboratory indicated that existence of ejaculation-related neural activation within the circuitry underlying mating behavior in the male rat. Clusters of Fos-immunoreactive neurons were present only following ejaculations and not after intromissions. However, it was not clear if this pattern of neural was specific to ejaculation or a result of summation of sexual activity preceding ejaculation. In the present study, the facilitative effect of the 5-HT1A receptor agonist 8-OH-DPAT on ejaculatory behavior was used to analyze the pattern of Fos immunoreactivity ejaculation preceded by minimal sexual activity. Male rats treated with 8-OH-DPAT (0.4 mg/kg) achieved ejaculation after a shortened latency and low numbers of mounts and intromissions. Ejaculation-induced Fos immunoreactivity was present in clusters of neurons in the lateral part of the posterodorsal medial amygdala, in two subregions of the posteromedial bed nucleus of the stria terminalis, in the posterodorsal preoptic nucleus, and in the parvicellular part of the subparafascicular thalamic nucleus. Males that ejaculated with the first intromission and were treated with a higher dose of 8-OH-DPAT (0.8 mg/kg) exhibited similar clusters of Fos-positive neurons in all areas except the posterodorsal preoptic nucleus. The results demonstrate the existence of a specific ejaculation-related subcircuit within a larger neural circuitry involved in male sexual behavior.