Neuropeptide YY5 receptor protein in the cortical/limbic system and brainstem of the rat: Expression on gamma-aminobutyric acid and corticotropin-releasing hormone neurons

Neuropeptide Y displays diverse modes of action in the CNS including the mo dulation of cortical/limbic function. Some of these physiological actions h ave been at least partially attributed to actions of neuropeptide Y on the Y5 receptor subtype. We utilized an antibody raised against the Y5 receptor to characterize the distribution of this receptor subtype in the rat corti cal/ limbic system and brainstem. Y5-like immunoreactivity was located prim arily in neuronal cell bodies and proximal dendritic processes throughout t he brain. In the cortex, Y5 immunoreactivity was limited to a subpopulation of small gamma -aminobutyric-acid interneurons (approximately 15 mum diame ter) scattered throughout all cortical levels. Double label immunofluoresce nce was also used to demonstrate that all of the Y5 immunoreactive neurons in the cortex displayed intense corticotropin releasing hormone immunoreact ivity. The most intense Y5 immunoreactive staining in the hippocampus was l ocated in the pyramidal cell layer of the small CA2 subregion and the fasci ola cinerea, with lower levels of staining in the hilar region of the denta te gyrus and CA3 subregion of the pyramidal cell layer. Nearly all of the Y 5 immunoreactive neurons in the hilar region of the hippocampus displayed g amma -aminobutyric-acid immunoreactivity. In the brainstem, Y5 immunoreacti vity was most intense in the Edinger-Westphal nucleus, locus coeruleus and the mesencephalic trigeminal nucleus. The present study provides neuroanatomical evidence for the possible sites of action of the neuropeptide Y/Y5 receptor system in the control of cortic al/limbic function. The presence of Y5 immunoreactivity on cell bodies and proximal dendritic processes in specific regions of the hippocampus suggest s that this receptor functions to modulate postsynaptic activity. These dat a also suggest that the neuropeptide Y/Y5 system may play a role in the mod ulation of a specific population of GABAergic neurons in the cortex, namely those that contain corticotropin-releasing hormone. The location of the Y5 receptor immunoreactivity fits with the known physiological actions of neu ropeptide Y and this receptor. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights reserved.