Cerebellar binding of avian pancreatic polypeptide

Studies were carried out to determine the regional central nervous system and species specificity of the previously observed [¹²⁵I]iodoavian pancreatic polypeptide ([¹²⁵I] iodo-APP) specific binding to chick brain membranes. The avian species examined were chicken, pigeon, duck, quail, chukar, and pheasant. 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^-10M 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. Preliminary experiments indicate that APP is neither contained in nor released from avian central nervous system synaptosomal elements.