Reduced postsynaptic GABAA receptor number and enhanced gaboxadol induced change in holding currents in Purkinje cells of the dystrophin-deficient mdx mouse

Abstract

Duchenne muscular dystrophy (DMD) is caused by the absence of a functional transcript of the protein dystrophin. DMD is associated with a range of cognitive deficits that are thought to result from a lack of the protein dystrophin in brain structures involved in cognitive functions. The CNS involvement extends to an impairment of cognitive abilities, with many DMD boys having significant reduction in IQ. In the cerebellum, dystrophin is normally localized at the postsynaptic membrane of GABAergic synapses on Purkinje cells. Here, we investigate the effect of an absence of dystrophin on the number of GABAA channels located at the synapse in cerebellar Purkinje cells of the dystrophin-deficient mdx mouse. Whole-cell patch-clamp recordings of spontaneous miniature inhibitory postsynaptic currents (mIPSCs) were performed in cerebellar slices from mdx and littermate control mice. Our results showed that the number of receptors at GABAergic synapses in the cerebellar Purkinje cell was significantly reduced in mdx mice (38.38±2.95) compared to littermate controls (53.03±4.11). Furthermore, when gaboxadol was added to the bath, the change in holding current in mdx mice was significantly enhanced (65.01±5.89pA) compared to littermate controls (37.36±3.82pA). The single channel unitary conductance and the rise and decay time of mIPSCs were not significantly different in these two groups of mice, indicating that those GABAA channels located at the postsynaptic sites in the mdx mice function normally. Conclusion: There is a reduction in the number of functional receptors localized at GABAergic synapses in the cerebellar Purkinje cells of dystrophin-deficient mdx mice and an increase in a gaboxadol induced holding current, which is evidence for an increase in extrasynaptic GABAA receptors in mdx mice. We hypothesize that the absence of dystrophin, from mdx Purkinje cells, reduces the number of post-synaptic GABAA receptors and as a result there is an increase in extrasynaptic receptors. If similar changes occur in the CNS in boys with DMD, it will impact on the function of neural networks and may contribute to some of the motor, behavioral and cognitive impairment apparent in many boys with DMD.