CLIMBING FIBER ACTIVATION AND 3',5'-CYCLIC GUANOSINE MONOPHOSPHATE (CGMP) CONTENT IN CORTEX AND DEEP NUCLEI OF CEREBELLUM

Harmaline (28 .mu.mol/kg i.v.), cold exposure (4.degree. C) or isoniazid (2.2 mmol/kg s.c.) increased the cGMP content in rat cerebellar cortex several-fold. Isoniazid but not harmaline or cold exposure increased cGMP in the deep cerebellar nuclei (nuclei interpositus, vestibularis and fastigius) and striatum. In rats treated with the nicotinamide antagonist 3-acetylpyridine (3-AP) (0.66 .mu.mol/kg i.p. 4 days before) the tremorogenic effect of harmaline and the increase of cerebellar cortex cGMP produced by this alkaloid was abated. The increase of cGMP following exposure to cold was reduced. Isoniazid and glutamate (10 .mu.mol intraventricularly) increased cGMP to the same extent in control and 3-AP treated rats. Since 3-AP produces in rat a massive degeneration of the inferior olivary nucleus and of the climbing fibers but leaves intact all the other cerebellar elements, an increase of cGMP content in postsynaptic cerebellar elements (presumably Purkinje cells) may be an expression of an increased release of an excitatory transmitter from either the climbing fibers or the parallel fibers.