cGMP is thought to play a role in cerebellar signalling yet its production within Purkinje cells has never been detected. In the present study, the hydrolysis of a fluorescent substrate analogue, 2′-O-anthranyloyl cyclic GMP, by type 5 phosphodiesterase was monitored within Purkinje cells in slices and in culture. Nitric oxide, either endogenous released from adjacent neurons or pharmacologically applied, accelerated the rate of hydrolysis in a manner that was dependent on soluble guanylyl cyclase, demonstrating that nitric oxide triggers cyclic GMP production in Purkinje cells, which in turn activates type 5 phosphodiesterase. We conclude that NO acts as an intercellular messenger in the cerebellar cortex and that parallel fibre terminals are a probable source of nitric oxide.
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