Fos-immunoreactivity within the extended amygdala is correlated with the onset of sexual satiety.

We hypothesized that c-fos expression in the medial amygdala (Me), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA) of the male Syrian hamster brain correlated with sexual satiety. To address this hypothesis, males were mated for 4 consecutive days. Experiment 1 determined whether the number of Fos-immunoreactive (Fos-ir) nuclei was equivalent in two groups of males mated to sexual satiety, one group of rested males (9.67 +/- 0.80 ejaculations) and a second group mated for 4 consecutive days (3.50 +/- 0.56 ejaculations). Fos-ir was increased within the caudal posterodorsal Me (cMePD), the anterodorsal and posteroventral subdivisions of the posteromedial BNST [BNSTpm(ad) and BNSTpm(pv)], the dorsolateral MPOA, and the medial preoptic nucleus of all males mated to sexual satiety compared to nonmated controls. In addition, Fos-ir "clusters" within the cMePD and BNSTpm(ad) were present in males mated to satiety regardless of the number of ejaculations. However, all males achieved multiple ejaculations. Therefore, Experiment 2 examined whether two groups of males stopped at one ejaculation exhibit different patterns of Fos-ir depending on proximity to sexual satiety. Brains of consecutively mated males, closer to satiety than rested males, showed greater BNSTpm(pv) Fos-ir and 5/6 males, but no rested male, exhibited cMePD Fos-ir clusters. These results support the hypothesis that cMePD and BNSTpm(pv) neuronal activation is associated with satiety and may constitute a discrete circuit to terminate mating.