Estrogen concentration by substance p-immunoreactive neurons in the medial basal hypothalamus of the female rat

We used the combined techinque of steroid autoradiography an dimmunohistochemistry to simultaneoulsy visulaize estrogen‐concentrating and substance P‐immunoreactive (sP‐IR) cells. A substantial proportion (26.1%) of sP‐IR celss that bound estrogen was found in the anterior two thirds of the arcuate nucleus with a rapidly diminishing number of cases (8.7%) in the posterior extent of this nucleus. Highest proportions (42.9%) of sP‐Ir cells retaining estrogen were found in the ventrolateral part of the ventromedial hypothalamic nucleus. The ventral premammillary nuleus was observed to have both populations but coexistence was comparatively infrequent (2.4%). Occasional cases of coesistence were also found in the leteral hypothalamic area. These results provide anatomicat evidence that a subset of SP‐IR neurons are directly reulated by estrogen and support the hypothesis that sP‐containing cells participate in the transduction of hormonal information into a CNS cirucitry taht regulates gonadotropin secretion and sexual bhaviour.