On the relationship of neuropeptide Y Y1 receptor-immunoreactive neuronal structures to the neuropeptide Y-immunoreactive nerve terminal networks. A double immunolabelling analysis in the rat brain.

Neuropeptide Y is the most abundant peptide in the mammalian central nervous system and exhibits a variety of potent neurobiological functions. In the present study, double immunolabelling histochemistry was performed, using previously characterized antibodies against neuropeptide Y and the neuropeptide Y Y1 receptor subtype, to clarify the cellular distribution of Y1 receptors in the rat brain in relation to the neuropeptide Y-immunoreactive systems. Based on fluorescence and confocal laser microscopy analysis, morphological evidence is presented that the perikaryal and dendritic Y1 receptor-like immunoreactivity demonstrated in discrete regions of the tel-, diencephalon and of the lower brain 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 existence of volume transmission in Y1 receptor-mediated neuropeptide Y transmission involving short to long distance diffusion and/or convection of neuropeptide Y from its site of release to the neuronal target cells, containing the high-affinity Y1 receptors. Furthermore, neuropeptide Y and Y1 receptor-like immunoreactivities were in no case co-localized in the same nerve cell, suggesting that, in the rat brain, the Y1 receptor subtype may not be a neuropeptide Y autoreceptor.