Differential localization of adenosine A1 receptors in the rat hippocampus: quantitative autoradiographic study

[3H]Cyclohexyladenosine ([offCHA) was used to label adenosine A1 receptors in the rat hippocampus by quantitative autoradiography, and selective lesions in the neurons intrinsic to CA1 and CA3 subfields were chemically produced to determine the cellular localization of A1 receptors. Lesioning the CA3 subfield by intracerebroventricular kainic acid injection caused a 50% reduction in the maximal binding capacity of [3H]CHA in the CA3 subfield with no alteration in binding affinity. Five days after unilateral CA3 lesioning, a reduction of [3H]CHA binding by 10-30% of ipsi- and contralateral was observed in the dendritic fields in the CA1 region, though a significant reduction was restricted to the ipsilateral stratum radiatum. Thirty-five days after CA3 lesioning, [3H]CHA binding in the stratum radiatum in the CA1 subfield ipsilateral to the CA3 lesion revealed a small reduction in Bmax values but no alteration in Bmax in other sublayers of the CA1. The Kd values in all regions of the hippocampus were not different from the control values. Selective CA1 pyramidal cell lesioning by transient ischemia caused a 70% reduction of [3H]CHA binding sites in the CA1 subfield. Neither CA1 nor CA3 lesions altered [3H]CHA binding in the stratum moleculare of the dentate gyrus. These results suggest that only a small population of adenosine A1 receptors are associated with the terminals of the CA3 pyramidal cells (Schaffer collaterals and commissural fibers) in the CA1 subfield. A1 receptors in the CA1 and CA3 subfields are predominantly located on intrinsic pyramidal cells.