Recently it has been reported that an increase of striatal dopamine (DA) receptor stimulation leads to an enhancement of striatal cyclic adenosine 3′,5′-monophosphate (cAMP). Moreover the stimulation of muscarinic receptors in the central nervous system (C.N.S.) has been correlated with the increase of cyclic guanosine 3′,5′-monophosphate (cGMP). Since DA in striatum functions as inhibitory transmitter on cholinergic neurons we investigated the effect of an increased stimulation of DA receptors produced by (+) amphetamine and apomorphine on the cGMP content in striatum. On the other hand we studied the cAMP and cGMP levels after chemical degeneration of substantia nigra, when the function of DA receptors is impaired. The increase of striatal cAMP and cGMP levels after (+) amphetamine and apomorphine and the increase of cGMP contents after the lesion of the nigro-striatal patways have been discussed.
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