Cerebellar Binding of Avian Pancreatic Polypeptide*

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Abstract
The regional CNS and species specificity of the previously observed [125I]iodoavian pancreatic polypeptide ([125I]iodo-APP) specific binding to chick brain membranes were determined. The avian species examined were chicken, pigeon, duck, quail, chukar and pheasant [Gallus domesticus, Columba livia, Anser domesticus, Colinus virginianus, Alectorius graeca, Phasianus colchicus, respectively]. In all species, the vast majority (> 90%) of APP binding was localized to the area of the cerebellum; other brain regions specifically bound small amounts of APP. Cerebellar hemisphere (folia) regions may have greater specific binding capacities than deep cerebellar nuclei, although all avian cerebellar preparations exhibited affinities for APP on the order of 10-10 M and binding capacities from approximately 0.2-1.5 pmol/mg protein for the high affinity sites. The measured affinity for binding of APP to these cerebellar binding sites is consistent with normal plasma concentrations (3-6 ng/ml) of APP in all Aves examined. Mammalian (rat and beef) brain membranes, regardless of topographical region, showed low specific binding of [125I]iodo-APP and [125I]iodobovine PP. APP is apparently neither contained in nor released from avian CNS synaptosomal elements.