BACKGROUND: The medial vestibular nucleus (MVN) is involved in the reflex control of the head and eyes, and the recovery of vestibular function after vestibular lesions. This study was performed to investigate the characteristics of inhibitory postsynaptic currents (IPSC) and the roles of metabotropic glutamate receptors on inhibitory synaptic transmissions. METHODS: Whole cell patch clamp recordings were carried out from MVN neurons in brainstem slice of neonatal rats. RESULTS: The frequency and amplitude of the IPSC were significantly reduced by GABAA a n t a g o n i s t bicuculline (20 microM) but were not affected by the glycine antagonist strychnine (1 microM). The baseline frequency, amplitude and decay time constant of spontaneous IPSC (sIPSC) were 4.9+/-1.8 Hz, 25.9+/-3.1 pA, 8.7+/-0.5 ms, respectively. Glutamate (1 mM) increased the frequency of sIPSC, but decreased that of the miniature IPSC (mIPSC) in MVN neurons. Such dual effects of glutamate were mimicked by group I, II metabotropic glutamate receptor (mGluR) agonist ACPD (20 microM). The specific mGluR 2, 3 agonist DCG-IV (3 microM) reduced mIPSC frequency, but did not increase sIPSC frequency. The mGluR 1, 5 agonist DHPG (100 microM) increased sIPSC and mIPSC frequency. CONCLUSIONS: These data suggest that the IPSC recorded from MVN neurons are mediated mainly by GABAA receptors and glutamate-induced modulations of inhibitory synaptic transmissions can influence the excitability of MVN neurons.