Projections of the sexually dimorphic anteroventral periventricular nucleus in the female rat.

The anteroventral periventricular nucleus of the hypothalamus (AVPV) is a sexually dimorphic nucleus in the preoptic region that appears to be a nodal point in forebrain circuits, mediating hormonal feedback on gonadotropin secretion. The results of anterograde transport experiments indicate that the AVPV sends ascending projections to the ventral part of the lateral septal nucleus, the parastrial nucleus, and the region adjacent to the vascular organ of the lamina terminalis (OVLT) that contains a subpopulation of gonadotropin releasing hormone (GnRH)-containing neurons. The majority of projections from the AVPV pass caudally through the periventricular zone of the hypothalamus and form dense terminal fields in the periventricular nuclei, parvicellular parts of the paraventricular nucleus, and in the arcuate nucleus. Inputs to medial zone nuclei are more limited, with substantial projections to only the medial preoptic and dorsomedial nuclei. The AVPV sends few projections to the caudal brainstem, but terminals were observed reliably in the periaqueductal gray and medial part of the nucleus of the solitary tract. Anterograde double-labeling experiments demonstrate terminals derived from neurons in the AVPV in close apposition to GnRH-containing neurons in the preoptic region, and to dopaminergic neurons in the arcuate nucleus. Thus, the organization of projections from the AVPV in female rats suggests that neurons in this nucleus may influence the secretion of luteinizing hormone and prolactin through direct projections to GnRH neurons and tuberoinfundibular dopaminergic neurons.