Localization and characterization of neuropeptide Y in the brain of Microcebus murinus (Primate, Lemurian)

Abstract

The distribution of neuropeptide Y (NPY) in the brain of the lemur Microcebus murinus was determined by immunocytochemistry with the aid of a highly specific antiserum against synthetic porcine NPY. When compared with previous immunohistochemical data obtained in primates and other mammalian species, the localization of NPY-immunoreactive (IR) structures in the Microcebus murinus brain revealed particular features. (1) Numerous NPY-IR perikarya and a dense network of IR nerve terminals were found in the supraoptic and suprachiasmatic nuclei, respectively. The occurrence of NPY-IR perikarya in the supraoptic nucleus, also reported in the squirrel monkey, seems to be specific to primates. In the squirrel monkey, the suprachiasmatic nucleus exhibits only a moderate innervation, whereas in humans it appears totally devoid of NPY-IR fibers. (2) IR perikarya and axon processes were observed in many upper brainstem areas, in particular in the interpeduncular, raphe pontine, dorsal tegmental, parabrachial, and dorsal raphe nuclei, in the locus coeruleus, the nucleus of the solitary tract, and the reticular formation; in this latter area, the occurrence of two categories of NPY-IR neurons was demonstrated on the basis of their morphology and localization, suggesting that they may play distinct roles. (3) NPY-IR nerve processes could be traced over a long distance. (4) For the first time, numerous NPY-IR terminals were observed close to the lumen of the various cerebral ventricles. The immunoreactive NPY-like peptide was characterized by combining high performance liquid chromatography (HPLC) analysis and radioimmunoassay quantification. The dilution curves obtained with synthetic porcine NPY and serial dilutions of occipital cortex, paraventricular and supraoptic hypothalamus, posterior hypothalamus, medulla oblongata, or preoptic area extracts were parallel. The highest amounts of NPY were measured in the hypothalamus and telencephalon. HPLC analysis resolved a single peak of NPY-like immunoreactivity that exhibited the same retention time as synthetic porcine NPY. The distribution of NPY in the lemurian brain is discussed with respect to phylogeny and putative functions.