Spinocerebellar ataxia type 1 (
SCA1) is a
neurodegenerative disease caused by an abnormal expansion of
glutamine (Q) encoding CAG repeats in the ATAXIN1 (ATXN1) gene and characterized by progressive
cerebellar ataxia,
dysarthria, and eventual deterioration of bulbar functions.
SCA1 shows severe degeneration of cerebellar Purkinje cells (PCs) and activation of Bergmann glia (BG), a type of cerebellar astroglia closely associated with PCs. Combining electrophysiological recordings,
calcium imaging techniques, and chemogenetic approaches, we have investigated the electrical intrinsic and synaptic properties of PCs and the physiological properties of BG in
SCA1 mouse model expressing mutant ATXN1 only in PCs. PCs of
SCA1 mice displayed lower spontaneous firing rate and larger slow afterhyperpolarization currents (sIAHP) than wildtype mice, whereas the properties of the synaptic inputs were unaffected. BG of
SCA1 mice showed higher
calcium hyperactivity and gliotransmission, manifested by higher frequency of NMDAR-mediated slow inward currents (SICs) in PC. Preventing the BG
calcium hyperexcitability of
SCA1 mice by loading BG with the
calcium chelator BAPTA restored sIAHP and spontaneous firing rate of PCs to similar levels of wildtype mice. Moreover, mimicking the BG hyperactivity by activating BG expressing Gq-DREADDs in wildtype mice reproduced the
SCA1 pathological phenotype of PCs, i.e., enhancement of sIAHP and decrease of spontaneous firing rate. These results indicate that the intrinsic electrical properties of PCs, but not their synaptic properties, were altered in
SCA1 mice and that these alterations were associated with the hyperexcitability of BG. Moreover, preventing BG hyperexcitability in
SCA1 mice and promoting BG hyperexcitability in wildtype mice prevented and mimicked, respectively, the pathological electrophysiological phenotype of PCs. Therefore, BG plays a relevant role in the dysfunction of the electrical intrinsic properties of PCs in
SCA1 mice, suggesting that they may serve as potential targets for therapeutic approaches to treat the
spinocerebellar ataxia type 1.