Diazepam reduces synaptic GABA type areceptor availability via multiple trafficking mechanisms

OBJECTIVE Investigate the effects of diazepam(DZP) on γ2 subunit containing GABA type A receptor(GABA A R) trafficking.METHODS Immunofluorescence microscopy measured surface GABA A Rs and gephyrin in rat cortical neurons after 24 h exposure of 1.0 μmol·L^(-1) DZP.Biochemical studies of mice injected with 10 mg·kg^(-1) DZP vs vehicle were assessed for γ2 subunit and total gephyrin cortical levels 12 h post-injection.Ubiquitination of the γ2 subunit was studied by immunoprecipitation after 12 h of 1.0 μmol·L^(-1) DZP exposure.A γ2 subunit encoding an N terminal fluorogen-activating peptide and pH-sensitive green fluorescent protein(γ2 pH FAP) measured lysosomal targeting of γ2 containing GABA A Rs.RFP-gephyrin and γ2 pH FAP synaptic diffusion rates were examined using fluorescence recovery after photobleaching(FRAP).RESULTS Extrasynaptic levels of γ2 GABA A Rs decreased by 12.2%,while synaptic gephyrin S270 phosphorylation increased by 18.3% in DZP-treated neurons after 24 h compared to control(P<0.05).Dendritic levels of gephyrin were also reduced to 74.1% of control,while S270 phosphorylation was elevated by 25.2%(P<0.05;P<0.01).Mice 12 h post-DZP injection demonstrated a 12.7% and 26.1% decrease in total γ2 and gephyrin levels,respectively(P<0.05;P<0.01).12 h DZP treatment enhanced γ2 subunit ubiquitination 1.13-fold relative to control(P<0.05).Internalized γ2 pH FAP GABA A Rs associated with lysosomes was 8.0% higher in neurons treated with 12-16 h DZP compared to control.Pilot FRAP experiments suggest gephyrin and γ2 have increased mobility and turnover at synapses following DZP.CONCLUSION DZP treatment decreases γ2 GABA A R levels and gephyrin scaffolding function after one day of exposure,which may contribute to the formation of DZP tolerance.

Modulation of firing activity by endogenous GABA_A receptors in the globus pallidus of MPTP-treated parkinsonian mice

The globus pallidus in rodents,equivalent to the external segment of the globus pallidus in primates,plays an important role in movement regulation.Previous studies have shown abundant γ-aminobutyric acid（GABA）ergic innervation and GABAA receptors in the globus pallidus.In this study,we investigated the effects of endogenous GABAA receptors on the spontaneous firing activity of pallidal neurons in both normal and MPTP-treated mice using multi-barrel electrodes extracellular recordings in vivo.We found that in normal mice,pressure ejection of 0.1 mmol/L gabazine,a specific GABA A receptor antagonist,increased the spontaneous firing rate of globus pallidus neurons by 27.6 ± 5.6%.Furthermore,in MPTP mice（14 days after MPTP treatment）,0.1 mmol/L gabazine increased the firing rates by 51.0 ± 7.9%,significantly greater than in normal mice.These results suggest that endogenous GABAA receptors modulate the activity of globus pallidus neurons.The present findings may provide a rationale for investigations into the potential role of GABAA receptors in Parkinson’s disease.