The anatomy of neuropeptide-Y-containing neurons in rat brain.

The distribution of neuropeptide Y in the central nervous system of adult male rats was investigated using indirect immunofluorescence, the peroxidase-antiperoxidase technique and by radioimmunoassay of microdissected brain regions. The different methods were in good agreement and showed that neuropeptide Y had a widespread distribution and was present in extremely high concentrations. The highest concentrations of neuropeptide Y were found in the paraventricular hypothalamic nucleus and hypothalamic arcuate nucleus, which also contained the highest density of immunoreactive fibers and numbers of perikarya, respectively. The suprachiasmatic nucleus, median eminence, dorsomedial hypothalamic nucleus and paraventricular thalamic nucleus showed high concentrations as well as high densities of fibers. Moderate concentrations were found in the bed nucleus of the stria terminalis, although a high density of fibers was found. Areas with moderate concentrations and densities of fibers were the medial preoptic area, anterior hypothalamic area, periventricular nucleus, posterior hypothalamus and the medial amygdaloid nucleus. The nucleus of the solitary tract contained a low concentration of neuropeptide Y although a high number of immunoreactive perikarya was found in colchicine-treated rats. Low concentrations were also measured in the cerebral cortex, yet relatively high numbers of cell bodies and fibers were found dispersed through the cortex. The extremely high concentrations and widespread distribution of neuropeptide Y in the central nervous system suggests a number of important physiological roles for this neurotransmitter candidate.