Cerebellar granule‐cell‐specific GABAA receptors attenuate benzodiazepine‐induced ataxia: evidence from α6‐subunit‐deficient mice

Abstract

Benzodiazepine- and alcohol-induced ataxias in rodents have been proposed to be affected by the γ-aminobutyric acid type A (GABA_A) receptor α6 subunit, which contributes to receptors specifically expressed in cerebellar granule cells. We have studied an α6 –/– mouse line for motor performance and drug sensitivity. These mice, as a result of a specific genetic lesion, carry a precise impairment at their Golgi-granule cell synapses. On motor performance tests (rotarod, horizontal wire, pole descending, staircase and swimming tests) there were no robust baseline differences in motor function or motor learning between α6 –/– and α6 +/+ mice. On the rotarod test, however, the mutant mice were significantly more impaired by diazepam (5–20 mg/kg, i.p.), when compared with α6 +/+ control and background C57BL/6J and 129/SvJ mouse lines. Ethanol (2.0–2.5 g/kg, i.p.) produced similar impairment in the α6 –/– and α6 +/+ mice. Diazepam-induced ataxia in α6 –/– mice could be reversed by the benzodiazepine site antagonist flumazenil, indicating the involvement of the remaining α1β2/3γ2 GABA_A receptors of the granule cells. The level of activity in this synapse is crucial in regulating the execution of motor tasks. We conclude that GABA_A receptor α6 subunit-dependent actions in the cerebellar cortex can be compensated by other receptor subtypes; but if not for the α6 subunit, patients on benzodiazepine medication would suffer considerably from ataxic side-effects.