Pierre Campo

Age-related decline of auditory function in the chinchilla (Chinchilla laniger)

The aim of this study was to examine the functional consequences of aging in the chinchilla, a rodent with a relatively long life span and a range of hearing similar to that of humans. Subjects were 21 chinchillas aged 10-15 years, and 23 young controls. Thresholds were determined from auditory evoked potentials (EVPs), and outer hair cell (OHC) functioning was assessed by measuring 2f1-f2 distortion product otoacoustic emissions (DPOAEs). Six cochleas from 11-12-year-old animals were examined for hair cell loss and gross strial pathology. The results show that the chinchilla exhibits a small but significant decline of auditory sensitivity and OHC functioning between 3 and 15 years of age, with high-frequency losses exceeding and growing more rapidly than low-frequency losses. Compared to rodents with shorter life spans, the chinchilla has a rate of loss that is more similar to that of humans, which could make it a valuable model for understanding the etiology of human presbycusis.

Effects of noise on inferior colliculus evoked potentials and cochlear anatomy in young and aged chinchillas

Like many aging humans, the aging chinchilla tends to lose high-frequency sensitivity at a faster rate than low-frequency sensitivity. This feature, combined with its excellent low-frequency hearing, makes the chinchilla attractive as an animal model for studying the relationship between noise-induced hearing loss (NIHL) and age-related hearing loss (AHL). In the present study, we examined susceptibility to noise in 15 aged (10-15 years old) and 15 young chinchillas. Two levels of noise were used, with the aim of determining whether age-related differences exist in the magnitude and rate of recovery from temporary threshold shifts produced by a moderate-level (95 dB) noise exposure, or in susceptibility to permanent threshold shifts and cochlear damage caused by a high-level (106 dB) noise exposure. Thresholds and response amplitudes at 0.5, 1, 2, 4, 8 and 16 kHz were determined from evoked potentials recorded from the inferior colliculus. Cochlear histology was performed on animals exposed to high-level noise. The results suggest that older animals are equally vulnerable to moderate-level noise, but may be slightly more vulnerable to high-level noise. For moderate-level exposures, there appears to be a simple additive relationship (in dB) between AHL and NIHL. For high-level exposures, the relationship may be more complex.

EchoScan: a new system to objectively assess peripheral hearing disorders

Pure-tone air-conduction audiometry (PTA) is the reference clinical test used in Europe and the United States to measure the extent of hearing loss. It is a subjective, behavioral test, which measures thresholds of hearing sensations and perceptions based on patient responses to frequency-specific pure-tone stimuli. PTA can detect hearing problems due to cochlear or retro-cochlear impairment, without identifying the source of the problem. In contrast, cubic distortion product otoacoustic emissions (DPOAEs) detect inner-ear dysfunctions, particularly those involving the outer hair cells sensitive to noise and ototoxicants. Recently, ototoxicants were shown to have an action on the central nuclei driving the middle-ear acoustic reflex. Therefore, a new device, called EchoScan, was conceived to collect and measure performance both in the middle- and inner-ear. Its originality: the use of a battery of DPOAE measurements associated with contra-lateral acoustic stimulation. Changes in DPOAE amplitude due to ageing and gender were incidentally detected and EchoScan was more sensitive than impedancemetry to detect the stapedial reflex. EchoScan can be used both in clinical investigations and in occupational medicine, especially for the auditory follow-up of people exposed to noise or ototoxic agents. EchoScan could be promising to assess early detection in programs to prevent hearing loss.

Bruit et agents ototoxiques

Resume But de l’etude L’objectif de cette revue bibliographique est d’evaluer la pertinence de la reglementation destinee a limiter les expositions bruyantes d’origine professionnelle pour diminuer les risques de surdite des personnes exposees a des bruits et a des agents ototoxiques chimiques d’origine professionnelle ou extra-professionnelle. Si le bruit reste sans conteste la nuisance la plus nocive pour l’audition des personnes exposees sur ou en dehors de leur lieu de travail, les risques de potentialisation des effets traumatiques du bruit d’origine professionnelle lors d’une co-exposition avec des ototoxiques d’origine chimique sont rarement abordes dans la litterature et ne sont pas pris en consideration par la legislation. Resultats Cette etude repose sur des resultats obtenus avec differents modeles experimentaux : le rat, le cobaye et le chinchilla, mais egalement sur des resultats epidemiologiques et des observations cliniques. D’une facon generale, le risque de surdite a ete evalue d’abord dans des conditions d’exposition aux seuls agents ototoxiques identifies tels que les antibiotiques aminoglycosidiques, les diuretiques, l’aspirine, les anti-tumoraux et les solvants aromatiques, puis lors d’une co-exposition avec le bruit, lorsque les donnees de la litterature le permettaient. Discussion L’analyse souligne l’absence de reglementation specifique pour des personnes exposees a la fois au bruit et a des agents ototoxiques chimiques fragilisant l’oreille interne (vestibule et cochlee). Une cochlee contaminee par un agent ototoxique pourrait se reveler plus vulnerable a une agression sonore qu’une oreille exposee uniquement au bruit. Conclusion Compte tenu de la duree d’exposition a un agent chimique, meme apres cessation de l’exposition, les donnees experimentales recentes presentees dans cette revue devraient etre prises en consideration par les responsables de la reglementation en vue de proteger l’audition des personnes exposees a des nuisances multiples.

1150 Mixie, a tool to improve assessment of chemical risk in case of multiple exposure

Introduction Multiple exposure to chemicals is a common situation in workplaces. However, most methods used to evaluate chemical risk do not consider the potential effects of mixtures. The aim is to present a tool helping to evaluate chemical risk in case of multiple exposure. Methods MiXie is a web tool (http://www.inrs-mixie.fr/http://www.inrs-mixie.fr/) developed in Quebec in 1997 and adapted to the French context by the French National Research and Safety Institute for the prevention of occupational accidents and diseases (INRS). It helps industrial hygienists to assess the potential risk of multi-exposure. Additivity of effects is the basic assumption. Results Whenever measurements of atmospheric concentrations are provided, MiXie calculates the exposure index of the mixture (i.e. the sum of the ratios between each concentration measured and its occupational exposure limit value x 100). If this index exceeds 100%, MiXie signals that there is a potential risk for certain organs, even though each limit value is respected. When measurements of atmospheric concentrations are not provided, MiXie highlights the common effects classes of the substances present and warns about a potential risk of additive effects. If the mixture contains a substance belonging to the ‘cancer’ or ‘sensitizer’ effect class, additivity does not apply and MiXie warns the industrial hygienist regardless of the concentration measured. Conclusion The MiXie database helps to identify potential risk situations related to multi-exposure to chemicals. Such situations may go unnoticed with a monosubstance approach. But MiXie users should be aware of its limits: additivity does not apply to all situations, the number of substances is restricted (130), etc. Experts are working to improve the tool by increasing the number of substances, making it more user-friendly, etc.