Topography of the ACTH-immunoreactive neurons in the basal hypothalamus of the rat brain.

Cell bodies of the opiocortin neurons were stained immunocytochemically with ACTH antiserum and their location in the basal hypothalamus of the rat brain was mapped. They are present throughout the entire extent of the hypothalamus, from retrochiasmatic area to mammillary body. In the retrochiasmatic area they are a single, midline group horizontally oriented and lying close to the ventral surface. Throughout the extent of the median eminence, ACTH-ir perikarya are located in the arcuate nucleus, adjacent periventricular stratrum and internuclear space between arcuate and ventromedial nuclei; as a group, they are oriented in a dorso-lateral plane. In the mammillary region, the nucleus assumes a more horizontal orientation again, lying close to the ventral surface. No regional differences were noted in cell density except in the retrochiasmatic area and terminal portion of the mammillary region where they were approximately 30% fewer in number.