Glutamate-like immunoreactivity during hair cell recovery after gentamicin exposure in the chinchilla vestibular sensory periphery

Objective: Determine the expression of glutamate by immunohistochemistry in normal and recovering vestibular hair cells in the chinchilla crista ampullaris after gentamicin ototoxicity, Study Design: In five groups of three animals each, ototoxicity was produced by placing gentamicin (50 mu g)-impregnated Gelfoam pellets within the perilymphatic space of the superior semicircular canal. Animals were sacrificed at 1, 2, 4, 8, and 16 weeks after treatment. A group of normal (n=3) animals was also processed. Methods: For the detection of glutamate the inner ears of these animals were dissected, and the horizontal cristae ampullaris embedded in plastic. Two-micron-thick tissue sections were obtained and incubated with monoclonal antibodies against glutamate, The immunoreaction was detected using the avidinbiotinylated-complex technique and diaminobenzidine was the chromogen, Results: Normal sensory epithelia demonstrated type I and type II hair cells with moderate glutamate-like immunoreactivity, Supporting cells demonstrated no glutamate-like immunoreactivity, Afferent nerve fibers and calyxes surrounding type I hair cells demonstrated strong glutamate-like inmunoreactivity, At 1 and 2 weeks after treatment the few type II hair cells surviving ototoxic treatment (15%-18%) contained moderate glutamate-like immunoreactivity, supporting cells showed no immunoreactivity, and nerve terminals and fibers displayed strong immunoreactivity, At 4 and 8 weeks after treatment, recovered hair cells (80%) had greater glutamate-like immunoreactivity when compared with normal hair cells, supporting cells displayed no glutamate-like immunoreactivity, and afferent fibers contained strong glutamate-like immunoreactivity, At 16 weeks, glutamate-like immunoreactivity in hair cells returned to normal level. Conclusion: Glutamate may be used as an indicator of hair cell differentiation and as an index of the molecular recovery of hair cells after ototoxicity.