Effect of chronic treatment with neuroleptics on the content of 3',5'-cyclic guanosine monophosphate in cerebellar cortex of rats.

Chronic treatment with haloperidol is associated with complete tolerance to the decreasing effect of the neuroleptic on cerebellar cGMP content, vice versa chronic haloperidol causes hypersensitivity to the enhancing effect of apomorphine on cerebellar cGMP. Thus, the administration of 0.5 mg/Kg of haloperidol decreases cerebellar cGMP by 80% in control rats but fails to alter this nucleotide in rats chronically treated with haloperidol (0.5 mg/Kg twice daily for 20 days). A dose of 0.5 mg/Kg of apomorphine enhances cGMP by approximately 25 and 60 percent in control rats and in rats chronically treated with haloperidol, respectively. The results suggest that: a) There is a functional link between striatum and cerebellum; b) Cerebellar cGMP is a sensitive index of the state of activation of striatal dopamine receptors.