Increase in glutamate-aspartate transporter (GLAST) mRNA during kanamycin-induced cochlear insult in rats

Kanamycin (KM)-induced changes in expression of the gene for glutamate-aspa rtate transporter (GLAST) in the rat cochlea were analyzed by Northern blot ting. With the administration of KM (600 mg/kg/day) once daily for 20 days, the expression of GLAST mRNA gradually increased and reached a peak on day 20. Although the expression of GLAST mRNA remained at a high level until 1 2 days after the completion of the KM treatment, it then fell to the normal level within 2 months. Such KM treatment resulted in loss of both inner an d outer hair cells and a concomitant profound permanent threshold shift. Th e present findings suggest that during KM administration, high concentratio ns of extracellular glutamate released by collapsing hair cells induced GLA ST mRNA expression. Increased GLAST mRNA might play an important role in th e prevention of the secondary death of spiral ganglion neurons from glutama te neurotoxicity. (C) 1999 Elsevier Science B.V. All rights reserved.