title: Cochlear neuropathy in the rat exposed for a long period to moderate-intensity noises.
abstract: Damaging effects on the cochlea of high-intensity acoustic overexposures have been extensively documented, but only few works have focused on the danger of moderate noise levels. Using scanning and transmission electron microscopy, we explored the noise-induced neuroepithelial changes that occur in the cochlea of rats subjected to moderate intensities, 70 and 85 dB SPL, for an extended period of time (6 hr/day over 3 months). Although the full quota of outer and inner sensory hair cells remained present, we detected discrete abnormalities, likely resulting from metabolic impairment, in both types of hair cell within the basal region of the cochlea. In contrast, important noise-dependent losses of spiral ganglion neurons had occurred. In addition, we found cytoplasmic accumulations of lipofuscin-like aggregates in most of the surviving cochlear neurons. These results strongly suggest that noise levels comparable to those of certain working environments, with sufficient exposure duration, pose a severe risk to the cochlea. Moreover, our data support the notion that long-duration exposure to moderate noise is a causative factor of presbycusis.
authors: Laboratory of Toxicology, Ergonomics and Occupational Environment, Faculty of Medicine of Tunis, Tunis El-Manar University, Tunis, Tunisia; Laboratory of Integrated Physiology, Faculty of Sciences of Bizerte, Carthage University, Tunis, Tunisia.
authors: Noura
authors: N
authors: Gannouni
authors: Marc
authors: M
authors: Lenoir
authors: Khemais
authors: K
authors: Ben Rhouma
authors: Michèle
authors: M
authors: El May
authors: Olfa
authors: O
authors: Tebourbi
authors: Jean Luc
authors: JL
authors: Puel
authors: Abada
authors: A
authors: Mhamdi
mesh_terms: D000818:Animals; D002452:Cell Count; D003051:Cochlea / Q000473:pathology / Q000648:ultrastructure; D004195:Disease Models, Animal; D006198:Hair Cells, Auditory / Q000473:pathology / Q000648:ultrastructure; D008854:Microscopy, Electron; D009622:Noise / Q000009:adverse effects*; D011571:Psychoacoustics; D051381:Rats; D017208:Rats, Wistar; D011984:Sensory Receptor Cells / Q000378:metabolism / Q000648:ultrastructure; D013136:Spiral Ganglion / Q000473:pathology / Q000648:ultrastructure; D013997:Time Factors; D000160:Vestibulocochlear Nerve Diseases / Q000209:etiology* / Q000473:pathology
keywords: efferent innervation; lipofuscin; presbycusis; spiral ganglion neurons