HETEROGENEITY IN THE NEUROPEPTIDE Y-CONTAINING NEURONS OF THE RAT ARCUATE NUCLEUS - GABAERGIC AND NON-GABAERGIC SUBPOPULATIONS

Neuropeptide Y, produced in the arcuate nucleus of the hypothalamus, p lays a key role in the central regulation of anterior pituitary and ap petitive functions. The pleiotropic nature of neuropeptide Y in these mechanisms indicates the existence of heterogeneity in the hypothalami c neuronal population producing neuropeptide Y. In this study, we repo rt the coexistence of neuropeptide Y and the amino acid transmitter, g amma-aminobutyric acid (GABA), in neuronal perikarya of the arcuate nu cleus. Fluorescent double immunolabeling for neuropeptide Y and glutam ic acid decarboxylase was carried out on vibratome sections collected through the hypothalamic arcuate nuclei of animals that were pretreate d with colchicine. It was found that about one third of the neuropepti de Y-producing arcuate nucleus perikarya co-expressed glutamic acid de carboxylase. This population of neuropeptide Y-containing GABAergic ne urons were distributed longitudinally within the arcuate nucleus locat ed predominantly in its dorsomedial aspects. These results show that t here are at least two distinct populations of neuropeptide Y-producing neurons in the arcuate nucleus: a subset of neuropeptide Y and GABA-c o-producing neurons located in the dorsomedial arcuate nucleus and a s ubset of non-GABAergic neuropeptide Y cells located in the ventral arc uate nucleus. This heterogeneity in the neuropeptide Y-producing perik arya of the hypothalamus may help explain adverse neuroendocrine and b ehavioral effects of arcuate nucleus neuropeptide Y.