Localization of enkephalin-like immunoreactivity in acetylcholinesterase-positive cells in the guinea-pig lateral superior olivary complex that project to the cochlea.

Olivocochlear fibers have been demonstrated to have acetylcholinesterase-positive staining both in brainstem and cochlea. Olivocochlear fibres in the cochlea have also been determined to contain enkephalin-like immunoreactivity. In this study, we first determined the source of olivocochlear fibers in the guinea-pig using horseradish peroxidase and wheat germ agglutinin in retrograde transport studies. These cells were then examined for enkephalin-like immunoreactivity followed by acetylcholinesterase staining on the same sections to determine which cells and fibers showed staining for both. It was found that cells in the guinea-pig lateral superior olive that project to the cochlea have both enkephalin-like immunoreactivity staining and acetylcholinesterase-positive staining. Cells in other areas giving rise to olivocochlear fibers showed only acetylcholinesterase staining. These results suggest that there is co-localization of enkephalin and acetylcholine in a population of olivocochlear cells and fibers.