Adenosine selectively blocks parallel-fiber-mediated synaptic potentials in rat cerebellar cortex.

Electrophysiological techniques were used to study the efficacy of adenosine in modulating synaptic transmission mediated from convergent parallel- and climbing-fiber inputs to Purkinje cells. Our results indicate that adenosine application leads to selective blocking of parallel fiber-mediated synaptic activity but not of climbing fiber activity. Adenosine does not alter the action-potential excitability properties of the parallel fibers. However, application of gamma-aminobutyric acid (GABA), which directly affects Purkinje cell dendritic membranes [Malenka, R. C. & Kocsis, J. D. (1982) J. Neurophysiol. 48, 608-621], leads to reduction of both parallel- and climbing-fiber synaptic activity. These results support the proposals that adenosine receptors in the cerebellar cortex are selectively localized on the nonmyelinated parallel fibers and that the blocking action of adenosine is the result of a mechanism other than direct alteration of axon excitability.