Afferent and efferent nerve endings of the outer hair cells in the rabbit.

The afferent and efferent nerve endings of the outer hair cells of the rabbit were investigated electron-microscopically. The afferent nerve ending was 1.4 X 2.0 microns in size and contained small vesicles, spherical mitochondria, and occasionally multivesicular bodies. The partially thick and dense membranes on either side of the synaptic cleft were observed and this region of the synaptic cleft was high in electron density. This area was considered to be an active zone of the afferent nerve ending. The efferent nerve ending was 4.0 X 6.0 microns in size and contained many synaptic vesicles, many oblong mitochondria, and multivesicular bodies. Synaptic vesicles were concentrated at some sites opposite the synaptic cleft. This area was thought to be an active zone where vesicles discharge their contents into the synaptic cleft. Furthermore, in some places of the synaptic cleft there were gaps (0.16 X 0.68 microns) which contained small vesicles. The gaps in the synaptic cleft have been briefly discussed.