Receptor synapses without synaptic ribbons in the cochlea of the cat.

Abstract

Recepto-neural junctions thought to be chemical synapses without synaptic ribbons or vesicle aggregates are described. Such synapses occurred in the cat between the outer hair cells of the cochlea and auditory nerve fibers. These synapses were formed by flat or indented junctions having symmetric membrane complexes associated with smooth endoplasmic reticulum and coated vesicles in the outer hair cell cytoplasm. Inner hair cells had recepto-neural junctions with asymmetric membrane complexes; synaptic ribbons and vesicles gathered at 1 type of junction, while the other type associates with endoplasmic reticulum. Gap junctions were not seen at cochlear synapses but did link supporting cells. Inner and outer hair cell synapses may have different properties. The role of synaptic vesicles and endoplasmic reticulum in the storage and release of transmitters is discussed.