Domestic application of infrared patch clamp techniques on brain slices is limited.The key of the technique is to prepare high-quality brain slices.The present paper describes the preparation procedure of brainstem slices and the spontaneous firing properties of rat medial vestibular nucleus (MVN) neurons.By infrared differential interference contrast technique,neurons of rat MVN were visualized directly at the depth of 50-100 μm undeeath the surface of slices.Firing activities of MVN neurons were recorded by the whole-cell patch clamp technique in artificial cerebrospinal fluid (ACSF) and low Ca2+ -high Mg2+ fluid.The firing mode was more irregular and depressive in low Ca2+ - high Mg2+ fluid than in ACSF.According to the averaged waveform of action potentials,cells were classified as the neurons with monophasic after-hyperpolarization potential (AHP),and the neurons with biphasic AHP.The resting membrane potential (RMP),input resistance (Rin) and membrane capacitance (Cm) of neurons were recorded and compared between groups.With infrared videomicroscopy,patch clamp recordings could be made under direct observation in freshly prepared brainstem slices.The discharge activities of MVN neurons were spontaneous and the firing mode was modulated by extracellular calcium concentration.The basic membrane properties of two types of neurons were not significantly different,while the differences in waveform might play a role in the segregation between tonic and kinetic cells.