EFFERENT PROJECTIONS FROM THE OVARIAN-STEROID RECEPTOR-CONTAINING AREA OF THE VENTROLATERAL HYPOTHALAMUS IN FEMALE GUINEA-PIGS

The ventrolateral hypothalamus (VLH) in female guinea pigs includes a subset of neurons which contain estrogen and progestin receptors, and which are implicated in the regulation of female sexual behavior by st eroid hormones. However, little is known about where these neurons pro ject, and consequently which other brain areas are involved in sexual behavior in female guinea pigs. The anterograde tracer Phaseolus vulga ris-leucoagglutinin was used to label efferents from the ovarian stero id receptor-containing part of the VLH. To identify the correct placem ent of the tracer specifically within the group of neurons containing estrogen receptors, medial hypothalamic sections were also immunostain ed for estrogen receptors. Forebrain areas receiving dense projections from the ventrolateral hypothalamus included the bed nucleus of the s tria terminalis, medial preoptic area, anterior hypothalamic area, ant erior ventromedial hypothalamus, and caudal ventrolateral hypothalamus . The midbrain central gray was also heavily labeled, Moderate innerva tion was observed in the forebrain in the basolateral amygdala, medial preoptic nucleus, lateroanterior hypothalamic nucleus, dorsal hypotha lamic areas, posterior hypothalamus, zona incerta, and in the midbrain interspersed among the central and lateral tegmental tracts. The majo r efferent pathways from the VLH appeared to travel rostrally through the mediobasal hypothalamus and preoptic area, and caudally via the me dial thalamic nuclei and periventricular fiber system, These findings are similar to those of previous studies tracing the efferents from th e ventromedial nucleus in rats and from the lateral hypothalamus in gu inea pigs. Many of these areas that receive input from the steroid rec eptor rich area within the VLH are likely to be involved in the regula tion of female sexual behavior.