AFFERENT SYNAPTIC CHANGES IN AUDITORY HAIR-CELLS DURING NOISE-INDUCEDTEMPORARY THRESHOLD SHIFT

This study presents evidence in support of the hypothesis that one of the sites of failure during noise-induced temporary threshold shift (T TS) is the afferent synapse between auditory hair cells and auditory n erve fibers. Our results show clear evidence indicating changes in the quantity of afferent synapses and the morphology of presynaptic struc tures in the alligator lizard auditory hair cells during TTS. In TTS h air cells there are statistically significant decreases in: 1) the num ber of afferent synapses, 2) the number of synaptic vesicles at the af ferent synapses, 3) the size of synaptic bodies, and 4) the packing de nsity of synaptic vesicles around the synaptic body. These results sug gest that the presynaptic components of the afferent synapse reflect t he functional state of the synapse, and that the reduction of these sy napses, both in number and component size, contributes to TTS.