Release of Glutamate from the Vestibular Nerve in the Medial Vestibular Nucleus as a Neurotransmitter:In VivoMicrodialysis Study

Histochemical and electrophysiological studies suggest that glutamate is the primary afferent neurotransmitter from the vestibular nerve to vestibular nucleus. To further examine this possibility, a microdialysis study using alpha-chloralose-anesthetised cats was performed to elucidate whether glutamate is released from the vestibular nerve terminal in the medial vestibular nucleus (MVN). A microdialysis probe (CMA/10.2 mm) was inserted into the MVN and perfused with Ringer solution at 2 microliters/min. Samples were collected at 10-min intervals. Endogeneous glutamate was measured using the HPLC-ECD method. When electrical repetitive stimuli (200 microseconds duration, 0.5 mA, and 5 Hz) were given to the vestibular nerve for 10 min, an increase in the release of glutamate was observed in the MVN but not in the spinal trigeminal nucleus. These findings indicate that glutamate is the afferent neurotransmitter from the vestibular nerve to the MVN neurons.