title: Carbon disulfide potentiates the effects of impulse noise on the organ of Corti.
abstract: Occupational noise can damage workers' hearing, and the phenomenon is even more dangerous when noise is associated with an ototoxic solvent. Aromatic solvents are known to provoke chemical-induced hearing loss, but little is known about the effects on hearing of carbon disulfide (CS2) when combined with noise. Co-exposure to CS2and noise may have a harmful effect on hearing, but the mechanisms involved are not well understood. For instance, CS2is not thought to have a cochleotoxic effect, but rather it is thought to cause retrocochlear hearing impairment. In other words, CS2could have a distal neuropathic effect on the auditory pathway. However, a possible pharmacological effect of CS2on the central nervous system (CNS) has never been mentioned in the literature. The aim of this study was to assess, in rats, the effects of a noise (continuous vs. impulse), associated with a low concentration of CS2[(short-term threshold limit value) x 10 as a safety factor] on the peripheral auditory receptor. The noise, whatever its nature, was an octave band noise centered at 8kHz, and the 250-ppm CS2exposure lasted 15min per hour, 6h per day, for 5 consecutive days. The impact of the different experimental conditions on hearing loss was assessed using distortion product oto-acoustic emissions and histological analyses. Although the LEX,8h (8-h time-weighted average exposure) for the impulse noise was lower (84dB SPL) than that for the continuous noise (89dB SPL), it appeared more damaging to the organ of Corti, in particular to the outer hair cells. CS2exposure alone did not have any effect on the organ of Corti, but co-exposure to continuous noise with CS2was less damaging than exposure to continuous noise alone. In contrast, the cochleo-traumatic effects of impulse noise were significantly enhanced by co-exposure to CS2. Therefore, CS2can clearly modulate the middle-ear reflex function. In fact, CS2may have two distinct effects: firstly, it has a pharmacological effect on the CNS, modifying the trigger of the acoustic reflex; and secondly, it can make the organ of Corti more susceptible to impulse noise. The pharmacological effects on the CNS and the effects of CS2on the organ of Corti are discussed to try to explain the overall effect of the solvent on hearing. Once again, the results reported in this article show that the temporal structure (continuous vs. impulse) of noise should be taken into consideration as a key parameter when establishing hearing conservation regulations.
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France; Departament de Ciències Fisiològiques and Institute of Neurosciences, Universitat de Barcelona, 08907 L'Hospitalet de Llobregat, Catalonia, Spain.
authors.forename: Maria
authors.initials: M
authors.lastname: Carreres Pons
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France.
authors.forename: Monique
authors.initials: M
authors.lastname: Chalansonnet
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Venet
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Thomas
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Nunge
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France.
authors.forename: Lise
authors.initials: L
authors.lastname: Merlen
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Cosnier
authors.affiliation: Departament de Ciències Fisiològiques and Institute of Neurosciences, Universitat de Barcelona, 08907 L'Hospitalet de Llobregat, Catalonia, Spain; Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), 08907 L'Hospitalet de Llobregat, Catalonia, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Llorens
authors.affiliation: Institut National de Recherche et de Sécurité, Rue du Morvan, CS 60027, F-54519 Vandœuvre Cedex, France; DevAH EA 3450-Développement, Adaptation et Handicap, Régulations cardio-respiratoires et de la motricité-Université de Lorraine, F-54500 Vandœuvre. France. Electronic address: pierre.campo@inrs.fr.
authors.forename: Pierre
authors.initials: P
authors.lastname: Campo
mesh_terms: D000161:Acoustic Stimulation; D000704:Analysis of Variance; D000818:Animals; D001309:Auditory Threshold / Q000187:drug effects; D002246:Carbon Disulfide / Q000494:pharmacology*; D004195:Disease Models, Animal; D005260:Female; D034381:Hearing Loss / Q000209:etiology*; D008855:Microscopy, Electron, Scanning; D009622:Noise / Q000009:adverse effects*; D009925:Organ of Corti / Q000187:drug effects* / Q000473:pathology / Q000648:ultrastructure; D017084:Otoacoustic Emissions, Spontaneous / Q000187:drug effects / Q000502:physiology; D011571:Psychoacoustics; D051381:Rats; D020318:Rats, Long-Evans; D012997:Solvents / Q000009:adverse effects*; D013997:Time Factors
chemical_list: D012997:Solvents; D002246:Carbon Disulfide
keywords: Carbon disulfide; Combined exposure; Impulse noise; Middle-ear reflex; Rats; Risk assessment