Modulation of synaptic GABA_A receptor function by zolpidem in substantia nigra pars reticulata

Aim: The substantia nigra pars reticulata (SNr) constitutes one of the output centers of the basal ganglia, and its abnormal activity is believed to contribute to some basal ganglia motor disorders. Different lines of evidence revealed a major contribution of GABA_A receptor-mediated synaptic inhibition in controlling the activity of SNr. The benzodiazepine binding site within the GABA_A receptor is a modulation site of significant clinical interest. A high density of benzodiazepine binding sites has been reported in the rat SNr. In the present study, we investigate the effects of activating benzodiazepine binding sites in the SNr. Methods: Whole-cell patch-clamp recordings and motor behavior were applied. Results: Superfusion of zolpidem, a benzodiazepine binding agonist, at 100 nmol/L significantly prolonged the decay time of GABA_A receptor-mediated postsynaptic currents. The prolongation on decay time induced by zolpidem was sensitive to the benzodiazepine antagonist flumazenil, confirming the specificity on the benzodiazepine site. Zolpidem at 1 μmol/L exerted a stronger prolongation on the decay time. A further experiment was performed on behaving rats. A unilateral microinjection of zolpidem into the rat SNr caused a robust contralateral rotation, which was significantly different from that of control animals receiving the vehicle injection. Conclusion: The present in vitro and in vivo findings that zolpidem significantly potentiated GABA currents and thus inhibited the activity of the SNr provide a rationale for further investigations into its potential in the treatment of basal ganglia disorders. © 2008 CPS and SIMM.