ON THE RELATIONSHIP OF NEUROPEPTIDE-Y Y1 RECEPTOR-IMMUNOREACTIVE NEURONAL STRUCTURES TO THE NEUROPEPTIDE Y-IMMUNOREACTIVE NERVE-TERMINAL NETWORKS - A DOUBLE IMMUNOLABELING ANALYSIS IN THE RAT-BRAIN

Neuropeptide Y is the most abundant peptide in the mammalian central n ervous system and exhibits a variety of potent neurobiological functio ns. In the present study, double immunolabelling histochemistry was pe rformed, using previously characterized antibodies against neuropeptid e Y and the neuropeptide Y Y1 receptor subtype, to clarify the cellula r distribution of Y1 receptors in the rat brain in relation to the neu ropeptide Y-immunoreactive systems. Based on fluoresence and confocal laser microscopy analysis, morphological evidence is presented that th e perikaryal and dendritic Y1 receptorlike immunoreactivity demonstrat ed in discrete regions of the tel-, diencephalon and of the lower brai n stem, shown to be cytoplasmic and membrane associated, in many brain regions is not co-distributed with the neuropeptide Y-immunoreactive terminal network. These findings may partly be explained by the existe nce of volume transmission in Y1 receptor-mediated neuropeptide Y tran smission involving short to long distance diffusion and/or convection of neuropeptide Y from its site of release to the neuronal target cell s, containing the high-affinity Y1 receptors. Furthermore, neuropeptid e Y and Y1 receptor-like immunoreactivities were in no case co-localiz ed in the same nerve cell, suggesting that, in the rat brain, the Y1 r eceptor subtype may not be a neuropeptide Y autoreceptor. (C) 1998 IBR O. Published by Elsevier Science Ltd.