ACTH-immunoreactive neurons and their projections in the cat forebrain.

The organization of adrenocorticotropin (ACTH)-immunoreactive (IR) cell bodies and fibers in the cat forebrain is described. ACTH-IR cell bodies are found only in and around the arcuate nucleus of the hypothalamus (ARH). They are not detected elsewhere even after pretreatment with colchicine. ACTH-IR fibers are present in discrete areas of the hypothalamus, the septo-limbic areas and in the paraventricular thalamic nucleus. Complete electrolytic lesions of the ARH destroy ACTH-IR cell bodies as well as fibers in all parts of the brain. These results suggest that, in the cat forebrain, the ARH is the only source of ACTH-IR fibers.