Properties of binding sites for [3H]cyclohexyladenosine in the hippocampus and other regions of rat brain: a quantitative autoradiographic study.

The properties of binding sites for the adenosine receptor ligand, [3H]cyclohexyladenosine ([3H]CHA), were investigated in rat brain using quantitative autoradiography. Scatchard analysis of the binding data showed that there were no significant differences between Kd values for [3H]CHA in any of the regions investigated. The highest concentrations of [3H]CHA binding sites were found in the cerebellum (molecular layer) and the stratum oriens and stratum radiatum of the hippocampus (CAI region). Displacement curves obtained using N-ethylcarboxamidoadenosine (NECA) and the R- and S-diastereoisomers of phenylisopropyl adenosine (PIA) showed the [3H]CHA binding sites to have the pharmacological properties of A1-adenosine receptors, i.e. the order of potency for these derivatives was R-PIA greater than NECA greater than S-PIA, in all regions tested. Further, [3H]CHA binding was in all cases attenuated by the guanosine triphosphate derivative, beta, gamma-imidoguanosine triphosphate. These results indicate that [3H]CHA binding sites throughout the central nervous system have the properties of A1-adenosine receptors and that these are in all regions associated with guanine nucleotide regulatory proteins.