ULTRASTRUCTURAL-LOCALIZATION OF GLUTAMATE AND ASPARTATE IMMUNOREACTIVITIES IN GERBIL INNER HAIR-CELLS

The endogenous neurotransmitter released at the base of cochlear inner hair cells (IHCs) is still not clear. L-Glutamate is the most likely candidate at present. Although it has been demonstrated that IHCs cont ain high levels of glutamate, the association of glutamate with synapt ic release has not yet been established. In this study, presynaptic lo cation of glutamate and aspartate immunoreactivities was examined by u sing the postembedding immunogold technique. The results show that nei ther glutamate nor aspartate exhibit immunoreactivities around the syn aptic vesicles of IHCs. Although the results do not support the hypoth esis that glutamate or aspartate is the endogenous neurotransmitter, t he possibility that the real transmitter is a substance with a structu re very similar to glutamate or aspartate cannot be excluded.