SYNAPTIC SPECIALIZATIONS ASSOCIATED WITH THE OUTER HAIR-CELLS OF THE JAPANESE MACAQUE

Across species the innervation of outer hair cells (OHCs) shows a rema rkable similarity. There are, however, notable differences in fine str ucture. The present work describes the normal synaptic morphology of O HCs in the Japanese macaque (Macaca fuscata), as determined by examina tion of serial sections with transmission electron microscopy. The ner ve endings at the base of OHCs were divided primarily into two groups: vesiculated (efferent) and non-vesiculated (afferent). In addition, w e found supranuclear efferent nerve endings and reciprocal synapses in all three cochlear turns. We also found presynaptic bodies in OHCs at the afferent synapse, the branching of afferent nerve fibers and axod endritic synapses between afferent and efferent fibers in the outer sp iral bundle and just beneath OHCs. In terms of synaptic structure, the data indicate that the Japanese macaque is more similar to that of th e human than other species examined to date.