GABA-like immunoreactivity in the squirrel monkey organ of Corti

The distribution of gamma-aminobutyric acid (GABA)-like immunoreactivity in the squirrel monkey organ of Corti was determined using an antiserum against GABA conjugated to bovine serum albumin. Immunoreactive labeling was seen in the region of the inner spiral bundle, the synaptic region below inner hair cells, in terminals contacting the basal part of outer hair cells, and in tunnel spiral fibers. Examples of each of these immunoreactive components could be observed in all cochlear turns. In the region of inner hair cells, immunoreactive labeling took the form of numerous small puncta randomly distributed below the base of the cells. In the region of outer hair cells, large globular immunoreactive structures reminiscent of terminal endings at the subnuclear level were observed. Since similar structures were seen at the base of outer hair cells in other cochleas processed for AChE, we conclude that GABA-like immunoreactivity was contained in efferent terminals which synapse on outer hair cells. These results strengthen previous evidence for the presence of GABA in the olivocochlear system of the mammalian cochlea.