Central nervous system changes associated with noise-induced hearing loss: an electron microscopic and freeze-fracture study of the chick nucleus magnocellularis.
This investigation assessed the effects of noise-induced hearing loss on the avian nucleus magnocellularis, the homologue of the mammalian cochlear nucleus. Fifteen-day-old chicks were exposed to high-intensity broad-band noise (132 dBA) for 24 to 72 hours. Hearing loss was documented with auditory brain-stem response recordings and scanning electron microscopy of the basilar papilla. Nucleus magnocellularis was assessed with thin-section electron microscopy and freeze-fracture techniques. Freeze-fracture preparations of noise-exposed animals showed a decrease in synaptic vesicle fusion sites at the synaptic active zone, a decrease in re-uptake of presynaptic membrane by coated vesicles, and a shift of the preferential fracture plane at the synapse from the presynaptic membrane to the post-synaptic membrane. These findings support the hypothesis that the effects of noise are not limited to the auditory periphery, but that transneuronal changes extend into the auditory central nervous system.
Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins Hospital, Baltimore, Md. 21205.
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D000818:Animals; D001933:Brain Stem / Q000648:ultrastructure*; D002645:Chickens; D003056:Cochlear Nerve / Q000648:ultrastructure*; D016057:Evoked Potentials, Auditory, Brain Stem; D005614:Freeze Fracturing; D006317:Hearing Loss, Noise-Induced / Q000473:pathology*; D008855:Microscopy, Electron, Scanning; D009925:Organ of Corti / Q000648:ultrastructure; D013572:Synaptic Vesicles / Q000648:ultrastructure