Cochlear neuroactive substances.

We have reviewed the experiments done in our laboratory concerning various cochlear neuroactive substances. Data using chemical neuroanatomy and neurochemical techniques are described. They allow the identification and localization of neuroactive substances which could act as neurotransmitters and/or neuromodulators at the different types of synapses in the organ of Corti. Three hypotheses are presented: (1) the inner hair cells use glutamate as a neurotransmitter, but in addition to its excitatory properties, glutamate may also be involved in pathophysiological events affecting afferent auditory dendrites: (2) subpopulations of both the lateral and medial olivocochlear efferent systems can be differentiated by the neuroactive substances they may use: (3) the base and the apex of the cochlea can be distinguished on the basis of neurochemical data.