COLOCALIZATION OF SOMATOSTATIN, NEUROPEPTIDE-Y, AND NADPH-DIAPHORASE IN THE CAUDATE-PUTAMEN OF THE RAT

Somatostatin, neuropeptide Y, and nicotinamide adenine dinucleotide ph osphate-diaphorase are colocalized within a small population of medium aspiny neurons in the caudate-putamen of the rat. The extent of coloc alization, however, appears to be in dispute. In order to examine the question of colocalization between these three neuroactive substances, a series of double-labelling experiments was performed. This was acco mplished by combining immunocytochemistry for somatostatin or neuropep tide Y or enzyme histochemistry for nicotinamide adenine dinucleotide phosphate-diaphorase with in situ hybridization for somatostatin and/o r neuropeptide Y mRNA. The results of such analysis indicate that nico tinamide adenine dinucleotide phosphate-diaphorase and somatostatin mR NA are 100% colocalized throughout the caudate-putamen, except for the area bordering the globus pallidus. All neurons that contain neuropep tide Y contain somatostatin message. Only 84% of the neurons that cont ain somatostatin mRNA, however, also contain neuropeptide Y. Neurons t hat contain somatostatin 28 but not neuropeptide Y are found throughou t the caudate-putamen. These results indicate that the somatostatin ne uron population in the rat caudate-putamen is not homogeneous. Instead , the medium aspiny neuron population is actually composed of several subpopulations based on the content of neuroactive substances. (C) 199 5 Wiley-Liss, Inc.