Autoradiographic localization of specific kainic acid binding sites in pigeon and rat cerebellum

The pigeons cerebellum contains a unique kainic acid binding site characterized by a relatively low binding affinity and cooperative binding properties. Dry-mount autoradiographs of incubated tissue sections demonstrate that this type of binding site is exclusively localized in the molecular and Purkinje cell layers of the cerebellar cortex, suggesting that it is related to the Purkinje cell dendritic tree. The affinity, cooperativity and pharmacological properties of the binding were not modified by prior perfusion of the brain with a low concentration of formaldehyde. Moreover, the maximal binding was higher in tissue sections than in membrane preparations. The selective localization and specific kinetic properties of this binding site suggest that it may play a physiological role. The high affinity type of binding site, which is present in both rat and pigeon cerebellum, is localized in the molecular, and to a lesser extent, the granular layer. This may imply that this second binding site is related to other types of cellular elements, such as the granule cells.