Mapping of alpha-melanocyte-stimulating hormone-like immunoreactivity in the cat diencephalon.

Using an indirect immunoperoxidase technique, we studied the location of alpha-melanocyte-stimulating hormone-like fibers and cell bodies in the cat diencephalon. In the thalamus, almost all the immunoreactive fibers were found in the midline region, whereas in the hypothalamus immunoreactive fibers were observed in the whole structure. The hypothalamus showed a higher density of both immunoreactive fibers and cell bodies; no immunoreactive neurons were found in the thalamus. The densest network of immunoreactive fibers was observed in the epithalamus (nucleus periventricularis anterior) and in the hypothalamic nuclei filiformis, hypothalami ventromedialis, arcuatus, periventricularis hypothalami, area hypothalamica dorsalis, and hypothalamus posterior. A high density of immunoreactive neurons was found in the nucleus arcuatus, in the hypothalamus lateralis, and in the area hypothalamica dorsalis; a low density was found in the nucleus hypothalami ventromedialis and in the hypothalamus dorsomedialis. By comparison with the studies of previous researchers, these data showed a more widespread distribution of alpha-melanocyte-stimulating hormone-like immunoreactive fibers and perikarya in the feline hypothalamus. Moreover, our findings indicate that the peptide is widely distributed in the cat diencephalon, suggesting that alpha-melanocyte-stimulating hormone might be involved in several physiological functions.