Specific neuropeptide Y binding sites in chicken brain.

In the present study, 125I-labeled neuropeptide Y (NPY) binding to chicken brain regions was evaluated. Cerebellum and cerebral cortex membranes bound significantly more 125I-NPY specifically than did membranes from other brain regions. Scatchard plots of NPY binding to cerebellar membranes were curvilinear; the high-affinity component had an affinity (Kd) of 1.1 nM, with a receptor concentration (Ro) of 182 fmol/mg membrane protein. Scatchard plots of NPY binding to chicken cerebral cortex membranes were linear, with a Kd of 0.63 nM and Ro of 90 fmol/mg. Unlabeled avian pancreatic polypeptide (APP) inhibited 125I-NPY binding to cerebellar membranes with a constant at which 50% inhibition occurs of 0.5 nM but showed essentially no affinity for cerebral cortex NPY binding sites. As previously reported, 125I-APP bound to cerebellar membranes with a Kd of 0.365 nM and an Ro of 323 fmol/mg, and unlabeled NPY showed about one order of magnitude lower affinity than did unlabeled APP for 125I-APP binding sites. Pseudo-Hill coefficients for APP binding to cerebellar APP receptors and NPY binding to cerebellar NPY receptors were 0.9. In contrast, pseudo-Hill plots for APP competition for 125I-NPY binding were curvilinear. It is concluded that the chicken cerebellum contains distinct APP and NPY receptors, whereas cerebral cortex contains only NPY receptors. APP is capable of binding with high affinity to the cerebellar, but not the cortical, NPY receptor.