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.