Enkephalin-like immunoreactivity in the guinea pig organ of Corti: ultrastructural and lesion studies.

Enkephalin-like immunoreactivity (ELI) was examined in a light and electron microscopic study of the normal guinea pig cochlea and of cochlea de-efferented through evulsion of the vestibular nerve. Antiserum to methionine enkephalin, 164, which gives immunoreactive labeling of only the lateral system of efferents, and antiserum 163, which gives immunoreactive labeling of lateral and medial efferents, were used. In de-efferented cochleae no immunoreactive labeling was seen with either antiserum, confirming that in the organ of Corti ELI is confined to efferents. At the ultrastructural level antiserum 163 but not 164 showed ELI in efferent terminals at the base of outer hair cells. ELI with 164 was seen in efferents ending on outer hair cells at the level of the nucleus. Medially, ELI was seen with both antisera in the inner and tunnel spiral bundles. Efferent terminals containing ELI were seen apposing afferent dendrites, other efferents and the inner hair cell. However, only rarely could synaptic contacts be unambiguously identified and then only with afferent dendrites.