A SPECIFIC HARMALINE-EVOKED INCREASE IN CEREBELLAR 5'-NUCLEOTIDASE ACTIVITY

Harmaline-induced changes in 5''-nucleotidase (5''-ND) activity were examined in cerebellar fractions from rats with an intact inferior olive (IO) or prior destruction of the IO by 3-acetylpyridine (3-AP) intoxication. Harmaline markedly increased 5''-ND activity in the crude homogenate (P < 0.05) and P2 fraction (P < 0.001) of cerebella from rats with an intact IO. This increased was absent in the P1, P3 and S3 fractions and it was abolished by 3-AP olivectomy. It was also absent in basal ganglia P2 fractions. Since harmaline produces rhythmic complex spike discharges of Purkinje cells by activating IO neurons climbing fiber activation per se increases 5''-ND activity in the P2 fraction. A climbing fiber-induced local increase in 5''-ND activity at parallel fiber-Purkinje cell synapses may result in a local increases in adenosine concentration. This may account for climbing fiber-evoked suppression of simple spike activity.