PROJECTIONS FROM VENTROLATERAL HYPOTHALAMIC NEURONS CONTAINING PROGESTIN RECEPTOR-IMMUNOREACTIVITY AND SUBSTANCE P-IMMUNOREACTIVITY TO SPECIFIC FOREBRAIN AND MIDBRAIN AREAS IN FEMALE GUINEA-PIGS

Many neurons within the ventrolateral hypothalamus in guinea pigs cont ain estrogen-induced progestin receptors as well as substance P. Retro grade tracing combined with immunocytochemistry was used to determine the specific projections of this subset of steroid-sensitive cells. Un ilateral Fluoro-Gold injections into the dorsal midbrain, including th e central gray, labeled a large proportion of the ventrolateral hypoth alamic neurons immunoreactive for both progestin receptors and substan ce P (approximately 30%); substantially fewer of these neurons were la beled by unilateral Fluoro-Gold injections into the preoptic area (app roximately 6%), medial amygdala (approximately 10%), or the bed nucleu s of the stria terminalis (approximately 11%). The projections of prog estin receptor-immunoreactive neurons in the ventrolateral hypothalamu s were similar to those of progestin receptor/substance P double-label ed neurons, while a slightly lower percentage of the ventrolateral hyp othalamic, substance P-immunoreactive neurons tended to project to eac h of these areas. These pathways may prove to be components of the neu ral circuitry underlying a variety of functions influenced by gonadal steroid hormones and substance P, such as female sexual behavior, salt intake, nociception and aggression.