FUNCTIONAL ADENOSINE-A1-RECEPTORS IN GOLDFISH BRAIN - REGIONAL DISTRIBUTION AND INHIBITION OF K-EVOKED GLUTAMATE RELEASE FROM CEREBELLAR SLICES()

In goldfish brain, [H-3]cyclohexyladenosine binding sites are ubiquito usly distributed with a maximum in the hypothalamus and a minimum in t he spinal cord. The binding parameters measured in cerebellar membrane s (K-d = 0.88 +/- 0.08 nM; B-max = 59.65 +/- 2,62 fmol/mg protein) are not significantly different from those of the whole brain. In perfuse d goldfish cerebellar slices, stimulation of cyclic AMP accumulation b y 10(-5) M forskolin was markedly reduced (58.7%) by treatment with 10 (-4) M cyclohexyladenosine, an adenosine Al receptor agonist, and the reduction was reversed in the presence of 10(-4) M 8-cyclopentyltheoph ylline, a selective Al receptor antagonist. In the same brain preparat ion, 30 mM K+ stimulated the release of glutamate, glutamine, glycine and GABA in a Ca2+-dependent manner, whereas the aspartate and taurine release was Ca2+-independent. Cyclohexyladenosine inhibited the 30 mM K+-evoked release of glutamate in a dose-related manner; This effect was reversed by 8-cyclopentyltheophylline. These results support the h ypothesis that adenosine Al receptors present in goldfish cerebellum a re involved in the modulation of glutamate transmitter release.