Localization of dynorphin B-like and alpha-neoendorphin-like immunoreactivities in the guinea pig organ of Corti.

Antiserum to dynorphin B and antiserum to alpha-neoendorphin were used in an immunocytochemical examination of the guinea pig organ of Corti. Immunoreactive staining for these two proenkephalin B (prodynorphin)-derived peptides was seen in the lateral system of olivocochlear efferents in the organ of Corti: the inner spiral bundle, the tunnel spiral bundle and by the bases of inner hair cells. Immunoreactive staining with both antisera was also seen in efferent terminals on outer hair cells at or above the level of the nucleus, which may represent terminals of either the lateral or the medial system. No immunoreactive staining was seen in tunnel crossing fibers and at bases of outer hair cells corresponding to the medial system of efferents. The staining seen with antiserum to dynorphin B and to alpha-neoendorphin has similar distribution to that seen with antisera to methionine enkephalin; there may be co-localization of these neuropeptides in the lateral system of efferents. Choline acetyltransferase-like immunoreactivity (co-localized with enkephalin-like immunoreactivity in the lateral system in the brainstem) and glutamic acid decarboxylase (GAD)-like immunoreactivity have also been found in olivocochlear efferents. Further studies will be necessary to determine if the dynorphins are co-localized with other neurotransmitter candidates and what their interactions may be.