Cellular and pharmacological characterization of NPY Y1 receptor expression in cultured rat hippocampal neurons and astrocytes

Neuropeptide Y (NPY) and NPY receptors are concentrated in the hippocampal formation where they modulate cognitive functions and seizures. The cellular mechanisms underlying the physiological roles of NPY in the hippocampus are still rather elusive. Cultured hippocampal cells offer a simple model to study the expression of hippocampal NPY receptor subtypes and their respective cellular distribution.; The present thesis examines the presence of NPY receptors in primary dissociated hippocampal cells in culture using a combination of molecular, pharmacological and immunocytochemical approaches. Receptor binding experiments revealed the preferential expression of Y1-like receptors over the Y2, Y4 and Y5 subtypes in rat hippocampal cultures. Cultured hippocampal cells expressed high level of Y1 receptors and very low amounts (below detection) of the Y2, Y 4 and Y5 receptor binding sites. The genuine nature of the Y1-like receptor expressed in these cells was confirmed using amplification (RT-PCR) of Y1 receptor mRNAs. The cellular phenotype expressing Y1 receptor was investigated using double labeling methods. Specific autoradiographic and immunolabeling signals of Y1-like receptors were observed on neurons (70% of the total population of neurons) and astrocytes (20% of the total population of glia cells) as revealed respectively by neuron specific enolase (NSE) and glial fibrillary acidic protein (GFAP) immunostaining. The Y1 receptor labeling is distributed uniformly over neuronal cell bodies and processes compared to a non-uniform and clustered distribution on type I astrocytes. Neurons labeled by the various Y1 receptor markers were mostly glutamate-positive as revealed by double labeling. Interestingly, a small proportion (2--5%) of NPY-positive hippocampal neurons (NPY-positive cells represent around 10% of the total population of neurons) were also enriched with Y1 receptor labeling. These results suggest the possible autoregulatory role for the Y1 receptor on NPY release.; Taken together, these anatomical and pharmacological results suggest that Y1 receptor may play an important role in the hippocampus via the regulation of astrocytic and/or neuronal functions and the modulation of the release of glutamate and/or NPY.