Distribution of alpha-neoendorphin immunoreactivity in the diencephalon and the brainstem of the dog

Alpha-neoendorphin (alpha -NE) is an opiate decapeptide derived from the pr odynorphin protein. Its anatomical distribution in the brain of mammals oth er than the rat. particularly in carnivores. is less well known than for ot her opiate peptides. In the present work, we have charted the distribution of a-NE immunoreactive fibers and perikarya in the diencephalon and the bra instem of the dog. The highest densities of labeled fibers were found in th e substantia nigra and in patches within the nucleus of the solitary tract. Moderate densities appeared in the arcuate nucleus (Ar), median eminence, entopeduncular nucleus, ventral tegmental area, retrorubral area, periaqued uctal central gray, interpeduncular nucleus and lateral parabrachial nucleu s. Groups of numerous labeled perikarya were localized in the magnocellular hypothalamic nuclei, Ar and in the central superior and incertus nuclei in the metencephalon. Moreover. less densely packed fibers and cells appeared widely distributed throughout many nuclei in the region studied. These res ults are discussed with regard to the pattern described in other species. I n addition. the present results were compared with the distribution of met- enkephalin immunoreactivity in the diencephalon and the brainstem of the do g that we have recently described. Although the distributions of these two peptides overlap in many areas, the existence of numerous differences sugge st that they form separate opiate systems in the dog. (C) 2001 Elsevier Sci ence B.V. All rights reserved.