Immunocytochemical localization of aspartate and glutamate in the peripheral vestibular system

Controversy exists concerning the identity of the neurotransmitter in the mammalian peripheral vestibular system. Several candidates have been proposed, including the excitatory amino acids glutamate and aspartate and the inhibitory amino acid gamma-aminobutyric acid (GABA). Previous studies have demonstrated vestibuloneural electrophysiological activity associated with glutamate and aspartate. Paraffin sections of rat vestibular ganglia and end-organs were examined for the presence of glutamate-like and aspartate-like immunoreactivity. Our results demonstrate the presence of both aspartate-like and glutamate-like immunoreactivity in vestibular hair cells, peripheral vestibular nerve fibers, and vestibular ganglion cells. Minimal immunoreactivity was noted in the tissues surrounding these cells. These data add support to the hypothesis that the excitatory amino acids glutamate and aspartate are involved in vestibular neurotransmission.