ALTERED EXCITATORY AMINO-ACID FUNCTION AND MORPHOLOGY OF THE CEREBELLUM OF THE SPASTIC HAN-WISTAR RAT

A mutant strain of Han-Wistar rat carries an autosomal recessive gene producing spastic paresis which is characterized by ataxia, tremor and hind limb rigidity. Brains of affected rats and unaffected littermate controls were transected at the mesencephalon into rostral and caudal portions (the caudal portion contained the cerebellum and brainstem). Poly(A)+ mRNA was isolated from pooled rostral or caudal portions and injected into Xenopus oocytes. The oocytes were voltage-clamped and exposed to 1 mM L-glutamate, 500-mu-M kainate, 500-mu-M quisqualate, 200-mu-M N-methyl-D-aspartate (NMDA) or 1 mM gamma-aminobutyric acid (GABA). Oocytes injected with mRNA isolated from the caudal portions of the affected rat brains exhibited statistically significant increases in glutamate and kainate peak current responses compared to oocytes injected with mRNA from other brain samples. No differences were noted in the responses of the groups when exposed to quisqualate, NMDA or GABA. Cerebellar and brain stem mRNA were also isolated separately in different groups of mutants and unaffected littermates. Only oocytes injected with cerebellar mRNA from mutants displayed statistically significant increases in responses to glutamate and kainate. In parallel morphological studies changes in the cerebellum of mutants were also observed. These consisted of a loss of Purkinje cells and an asymmetrical disarrangement of the granule cell layer of cerebellar cortex. Taken together, the physiological and morphological results suggest that alterations in glutamate/kainate receptors in the cerebellum are phenotypic manifestations of the Han-Wistar mutation. The results are consistent with the hypothesis that this mutant rat might serve as a model of glutamate/kainate excitotoxicity in the brain.