Melanin-concentrating hormone-producing neurons in birds

The peptidergic melanin-concentrating hormone (MCH) system was investigated by immunocytochemistry in several birds. MCH perikarya were found in the p eriventricular hypothalamic nucleus near the paraventricular organ and in t he lateral hypothalamic areas. Immunoreactive fibers were very abundant in the ventral pallidum, in the nucleus of the stria terminalis, and in the se ptum/diagonal band complex, where immunoreactive pericellular nets were pro minent. Many fibers innervated the whole preoptic area, the lateral hypotha lamic area, and the infundibular region. Some fibers also reached the dorsa l thalamus and the epithalamus. The median eminence contained only sparse p rojections, and the posterior pituitary was not labeled. Thus, in birds, a neurohormonal role for MCH is not likely. Immunoreactive fibers were observ ed in other regions, such as the intercollicular nucleus, stratum griseum p eriventriculare (mesencephalic tectum), central gray, nigral complex (espec ially the ventral tegmental area), reticular areas, and raphe nuclei. Altho ugh no physiological investigation concerning the role of MCH has been perf ormed in birds, the distribution patterns of the immunoreactive perikarya a nd fibers observed suggest that MCH may be involved in functions similar to those described in rats. In particular, the projections to parts of the li mbic system (ventropallidal ganglia, septal complex, hypothalamus, dorsal t halamus, and epithalamus) and to structures concerned with visceral and oth er sensory information integration suggest that MCH acts as a neuromodulato r involved in a wide variety of physiological and behavioral adaptations (a rousal) with regard to feeding, drinking, and reproduction. (C) 1999 Wiley- Liss, Inc.