Decreased cerebellar 3',5'-cyclic guanosine monophosphate levels and insensitivity to harmaline in the genetically dystonic rat (dt).

The dystonic rat (dt) is an autosomal recessive mutant displaying a complex motor syndrome that includes sustained axial twisting movements. The syndrome is correlated with increased glutamic acid decarboxylase activity in the deep cerebellar nuclei and increased cerebellar norepinephrine levels in comparison with phenotypically normal littermates. Biochemical, behavioral, and anatomical techniques were used to investigate the possibility that the abnormalities noted in the cerebellum of the dt rat were indicative of altered function of the major projection neurons of the cerebellar cortex, the Purkinje cells. Phenotypically normal rats showed tremor in response to harmaline, a drug that acts on the inferior olive to produce bursting in the climbing fiber pathway. Dystonic rats were insensitive to the effects of harmaline but did respond to oxotremorine. Levels of the cyclic nucleotide 3',5'-cyclic guanosine monophosphate, a biochemical marker for Purkinje cells, increased in response to harmaline in normal rats but were significantly lower in dystonic rats under both basal and harmaline-stimulated conditions. Purkinje cell soma size was reduced in the dystonic rats but no other morphological correlates of the behavioral or biochemical deficits were noted. Taken together with other observations on this mutant, the results suggest an impairment in the cerebellum or in its connections with lower brainstem and spinal cord sites.