“…The adenosine A, receptor is expressed at high levels in the cerebral cortex, hippocampus, and cerebellum (Mahan et al,199 1). Identical or closely related receptors are present postsynaptically, where they lower cyclic AMP, activate K+ channels, and/or inhibit Ca2+ channels (for review, see Stone,I99 l), and presynaptically, where they inhibit, via a pertussis toxin-sensitive guanine nucleotide binding protein (G protein) (Dolphin and Prestwich, 1985;Spuler and Grafe, 1989;Stone, 1991), the evoked release of a number of transmitters, including glutamate (Dolphin and Archer, 1983;Dolphin and Prestwich, 1985;Prestwich et al, 1987;Burke and Nadler, 1988;Dunwiddie et al, 1990;Poli et al, 1991), but notably excluding y-aminobutyric acid (GABA) (Yoon and Rothman,199 1).…”