Distribution of β-lipotropin (β-LPH), adrenocorticotropin (ACTH) and α-melanocyte-stimulating hormone (α-MSH) in the rat brain. I. Origin of the extrahypothalamic fibers

By immunocytochemical techniques, the neuronal cell bodies containing ACTH, β-LPH and α-MSH have only been found in the area of the arcuate nucleus of the hypothalamus, whereas positive nerve fibers have been observed in many hypothalamic and extra-hypothalamic areas. The possible contribution of neurons which could be located in other brain areas has been studied in the rat by experiments involving hypothalamic deafferentation or destruction of the acurate nucleus. Fourteen days after deafferentation, no immunoreactive fibers could be detected in extrahypothalamic areas whereas the concentration of positive cell bodies and fibers remained unchanged within the hypothalamic island. In rats which had been injected in the neonatal period with monosodium glutamate (MSG), which selectively destroys the arcuate nucleus, only a few immunostained cell bodies were observed in hypothalamic region lateral to the arcuate nucleus. As compared to control animals, the concentration of immunostained fibers in both hypothalamic and extrahypothalamic regions was markedly decreased. These results strongly suggest that neuronal cell bodies producing ACTH, β-LPH and α-MSH are located in the region of the arcuate nucleus and send axonal projections into many brain areas.