Characterization of Adenosine Receptors in the Hippocampus and Other Regions of Rat Brain

Although the potent effects of adenosine and its derivatives on cyclic AMP metabolism and nerve cell activity in the mammalian central nervous system have been known for some time,it is only recently that much attention has been paid to the extracellular receptors which are the primary sites of nucleoside action. Two important developments account for the present flurry of activity in the field of adenosine receptors. First, studies on the interactions of nucleosides with adenylate cyclase revealed both inhibitory and stimulatory effects of a variety of nucleoside analogues on that enzyme. The observation that the pharmacological profiles of these opposite effects differ in several important respects led to the classification of adenosine receptors into two classes, designated A1 (or Ri) and A2 (or Ra), according to the criteria shown in Table 1 (Van Calker et al., 1979; Lodos et al., 1980). This classification scheme has provided an important framework within which to approach the identification and characterization of physiologically active adenosine receptors.