Afferent synaptic changes in auditory hair cells during noise-induced temporary threshold shift

• Published in: Hearing research 1995-04, Vol.84 (1), p.81-90
• Main Authors: Henry, William R., Mulroy, Michael J.
• Format: Article
• Language: English
• Subjects: Acoustic Stimulation; Alligator lizard; Anguidae; Animals; Auditory Threshold - physiology; Basilar Membrane - physiology; Biological and medical sciences; Cochlea; Cochlea - physiology; Disease Models, Animal; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Fundamental and applied biological sciences. Psychology; Gerrhonotus; Hair cell; Hair Cells, Auditory - cytology; Hair Cells, Auditory - ultrastructure; Hearing Loss, Noise-Induced - etiology; Image Processing, Computer-Assisted; Lizards; Microscopy, Electron; Microscopy, Electron, Scanning; Nerve Fibers - physiology; Neurons, Afferent - cytology; Neurons, Afferent - physiology; Neurons, Afferent - ultrastructure; Noise-induced hearing loss; Presynaptic Terminals - physiology; Synapse; Synapses - physiology; Synapses - ultrastructure; Synaptic body; Synaptic Vesicles - physiology; TTS; Vertebrates: nervous system and sense organs; Vestibulocochlear Nerve - physiology
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/0378-5955(95)00014-U

This study presents evidence in support of the hypothesis that one of the sites of failure during noise-induced temporary threshold shift (TTS) is the afferent synapse between auditory hair cells and auditory nerve fibers. Our results show clear evidence indicating changes in the quantity of afferent synapses and the morphology of presynaptic structures in the alligator lizard auditory hair cells during TTS. In TTS hair cells there are statistically significant decreases in: 1) the number of afferent synapses, 2) the number of synaptic vesicles at the afferent synapses, 3) the size of synaptic bodies, and 4) the packing density of synaptic vesicles around the synaptic body. These results suggest that the presynaptic components of the afferent synapse reflect the functional state of the synapse, and that the reduction of these synapses, both in number and component size, contributes to TTS.