Glutamate-like immunoreactivity in the peripheral vestibular system of mammals

Using a specific antibody raised against glutamate (Glu) conjugated to bovine serum albumin with glutaraldehyde, the distribution of Glu-like immunoreactivity was studied by postembedding staining in semithin sections of nonosmicated or osmicated tissue through the vestibular sensory epithelia and ganglia of different mammalian species (mouse, rat and cat). Strong immunoreactive staining was found in all ganglion neurons and their peripheral and central nerve processes as well as in the two types of sensory hair cells whereas, in contrast, supporting cells were devoid of immunoreactivity. Glu-like immunoreactivity found in vestibular fibers and ganglion neurons, is in good agreement with the proposition of glutamate as the neurotransmitter involved in vestibular nerve transmission. In sensory hair cells, glutamate, apart from its metabolic function, may play a role in synaptic transmission between the sensory cells and the vestibular afferent fibers.