Preoptic area estradiol-concentrating neurons project to the hypothalamus in female rats

Estradiol (E₂)-concentrating neurons afferent to the ventromedial nucleus of the hypothalamus (VMH) were identified by combining fluorescent retrograde tracing with steroid hormone autoradiography. The majority of E₂-concentrating neurons that projected to the VMH were located in the medial preoptic area. In the entire medial preoptic area, 10.0% of the E₂-sensitive neurons sent axons that terminated in the VMH. Twenty percent of the E₂-concentrating neurons located in the periventricular preoptic area projected to the VMH. Of the E₂-concentrating neurons found in the medial preoptic nucleus, 8.0% sent axons directly to the VMH. The bed nucleus of the stria terminalis, septum, and medial amygdala contained very few E₂-receptive neurons that projected to the VMH. Preoptic area E₂-concentrating neurons that project to the VMH may be part of a neural circuit that influences reproduction.