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1 School of Biomedical Sciences, University of Newcastle, Callaghan, N.S.W., Australia
* To whom correspondence should be addressed. E-mail: alan.brichta{at}newcastle.edu.au.
Fast inhibitory synaptic transmission in the medial vestibular nucleus (MVN) is mediated by GABAA receptors (GABAARs) and glycine receptors (GlyRs). To assess their relative contribution to inhibition in the MVN, we recorded miniature inhibitory postsynaptic currents (mIPSCs) in physiologically characterized type A and type B MVN neurons. Transverse brainstem slices were prepared from mice (3-8 weeks old) and whole-cell patch-clamp recordings were obtained from visualized MVN neurons (CsCl internal; Vm = -70 mV; 23°C). In 81 MVN neurons, 69% received exclusively GABAAergic inputs, 6% exclusively glycinergic inputs, and 25% received both types of mIPSCs. The mean amplitude of GABAAR-mediated mIPSCs was smaller than those mediated by GlyRs (22.6 ± 1.8 vs. 35.3 ± 5.3 pA). The rise time and decay time constants of GABAAR- vs. GlyR-mediated mIPSCs were slower (1.3 ± 0.1 vs. 0.9 ± 0.1 ms and 10.5 ± 0.3 vs. 4.7 ± 0.3 ms respectively). Comparison of type A (n = 20) and type B (n = 32) neurons showed that type A neurons received almost exclusively GABAAergic inhibitory inputs, whereas type B neurons received GABAAergic inputs, glycinergic inputs or both. Intracellular labelling in a subset of MVN neurons showed that morphology was not related to a MVN neuron's inhibitory profile (n = 15), or whether it was classified as type A or B (n = 29). Together, these findings indicate that: 1) both GABA and glycine contribute to inhibitory synaptic processing in MVN neurons, although GABA dominates; and 2) there is a difference in the distribution of GABAA and Gly receptors between Type A and Type B MVN neurons.
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