Projections of the posterodorsal preoptic nucleus and the lateral part of the posterodorsal medial amygdala in male gerbils, with emphasis on cells activated with ejaculation

The posterodorsal preoptic nucleus (PdPN) and the lateral part of the posterodorsal medial amygdala (MeApd) express Fos with ejaculation in male gerbils. Ejaculation-activated cells participate in the PdPN and MeApd projections to each other and to the sexually dimorphic preoptic area (SDA), but those projections involve less than 20% of the activated PdPN cells and less than 50% of the activated MeApd cells. To identify other potential targets of ejaculation-activated cells, we traced PdPN and lateral MeApd outputs using biotinylated dextran amine. The principal part of the bed nucleus of the stria terminalis (BSTpr) and the anteroventral periventricular nucleus (AVPv) were labeled from both sites and were injected with Fluoro-Gold to determine whether PdPN and lateral MeApd cells that express Fos with ejaculation would be retrogradely labeled. Fluoro-Gold was also applied to the dorsomedial hypothalamus (DMH) and retrorubral field (RRF) because such injections label PdPN cells in rats. The PdPN-DMH projection is minimal in gerbils, involving few, if any, ejaculation-related cells. Ejaculation-activated PdPN cells project to the AVPv (43%), dorsal BSTpr (30%), and RRF (12%). Those in the lateral MeApd project to the dorsal BSTpr (43%) and AVPv (18%). When these percentages are combined with those for ejaculation-activated cells involved in the PdPN and lateral MeApd projections to each other and to the medial SDA, the totals reach 100%. Thus, every PdPN and MeApd cell activated with ejaculation may participate in one of these projections. Similar projections may contribute to the similar behavioral effects of the PdPN and MeApd.