Electron microscopic localization of N-terminal proenkephalin (synenkephalin) immunostaining in the guinea pig organ of Corti.

Using a pre-embedding immunoelectron microscopic technique, anti-synenkephalin immunostaining has been demonstrated within efferent varicosities (originating from the brainstem) of the inner spiral bundle and the tunnel spiral bundle of the organ of Corti. Axodendritic synapses were observed between the anti-synenkephalin immunostained varicosities and auditory dendrites connected to inner hair cells. No anti-synenkephalin immunostaining was found in any efferents at the outer hair cell level. We suggest that this immunolocalization of synenkephalin in the organ of Corti allows a better differentiation of the cochlear efferent systems on a neurochemical basis. The whole lateral system, or at least a significant part of it, could be referred to as the 'enkephalin-containing efferent system'.