The widespread distribution of neuropeptide (NPY) in the central nervous system (CNS) indicates that it may be involved in various regulatory functions. Therefore, the specific receptor binding sites for NPY, which might be involved in mediation of these functions, was investigated and the regulation of these binding sites by α2-adrenoceptors was studied. Because neuropeptides carry out a number of cellular actions by mobilizing intracellular Ca2+, the effects of Ca2+ and of various agents that work through Ca2+ on NPY receptor binding sites are studied in the chapter. [125I]NPY or [3H]NPY binds with high affinity to a single site in the homogenates of rat cerebral cortex and hypothalamus. The specific binding of NPY requires extracellular Ca2+, and various Ca2+ antagonists inhibit the specific binding. It is suggested that the NPY receptor might be linked to a Ca2+-dependent protein kinase and phosphorylation may play a role in the regulation of the receptor activity state. Chronic treatment with the α2-adrenoceptor agonist clonidine slightly increases the maximal binding sites of NPY to cerebral cortical membranes. The depletion of central epinephrine by chronic treatment with a PNMT inhibitor increases the maximal binding sites of NPY to the hypothalamic membrane sites.
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