Inhibitory and Excitatory Postsynaptic Currents of Medial Vestibular Nucleus Neurons of Rats

The medial vestibular nucleus (MVN) neurons are controlled by excitatory synaptic transmission from the vestibular afferent and commissural projections, and by inhibitory transmission from interneurons. Spontaneous synaptic currents of MVN neurons were studied using whole cell patch clamp recording in slices prepared from 13- to 17-day-old rats. The spontaneous inhibitory postsynaptic currents (sIPSCs) were significantly reduced by the $GABA_A$ antagonist bicuculline ($20{\mu}M$), but were not affected by the glycine antagonist strychnine ($1{\mu}M$). The frequency, amplitude, and decay time constant of sIPSCs were $4.3{\pm}0.9$ Hz, $18.1{\pm}2.0$ pA, and $8.9{\pm}0.4$ ms, respectively. Spontaneous excitatory postsynaptic currents (sEPSCs) were mediated by non-NMDA and NMDA receptors. The specific AMPA receptor antagonist GYKI-52466 ($50{\mu}M$) completely blocked the non-NMDA mediated sEPSCs, indicating that they are mediated by an AMPA-preferring receptor. The AMPA mediated sEPSCs were characterized by low frequency ($1.5{\pm}0.4$ Hz), small amplitude ($13.9{\pm}1.9$ pA), and rapid decay kinetics ($2.8{\pm}0.2$ ms). The majority (15/21) displayed linear I-V relationships, suggesting the presence of GluR2-containing AMPA receptors. Only 35% of recorded MVN neurons showed NMDA mediated currents, which were characterized by small amplitude and low frequency. These results suggest that the MVN neurons receive excitatory inputs mediated by AMPA, but not kainate, and NMDA receptors, and inhibitory transmission mediated by $GABA_A$ receptors in neonatal rats.