Forward Masking Is Dependent on Inner Hair Cell Activity

Abstract

The goal of this study was to test the hypothesis that the inner hair cell complex (inner hair cell and dendritic contacts) is solely responsible for generating the slope of the forward masking curve. To test this hypothesis two experiments were performed. The first was to measure forward masking from the Bronx waltzing mouse, a mutant possessing an inner hair cell defect. The Bronx waltzing mouse demonstrated an approximately 60-dB auditory brainstem response (ABR) threshold shift compared to CBA/CBA mice at 8 and 12 kHz. The slope of the forward masking curve was significantly reduced compared to the control group, particularly at the early delay times between 0 and 4 ms. The second model employed kainic acid to affect the dendrites beneath the inner hair cell. After the intracochlear infusion of kainic acid, there was an approximately 47-dB ABR threshold shift at 4 and 8 kHz compared to pre-infusion thresholds. The slope of the forward masking curve from the kainic-acid group was significantly reduced compared to the artificial-perilymph group. Primarily the early delay times were affected by kainic acid (0-4 ms). Morphological analysis showed that there was extensive swelling of the afferent nerve radial dendrites under the inner hair cells. The results from the present study, as well as the preceding article, suggest that the analysis of the slope of the forward masking curve may be used for the detection of inner hair cell or radial dendrite damage, independent of outer hair cell damage. The present finding could provide a useful means of employing a clinical test for determining the function of the inner hair cell complex using a non-invasive measure of auditory function.

Tinnitus and Other Auditory Problems – Occupational Noise Exposure below Risk Limits May Cause Inner Ear Dysfunction

“…Experiments on mice, using auditory brainstem responses[17], have suggested that forward masking results indicate the status of the IHCs. After the offset of a noise burst the masking effect on a brief tone decreases rapidly in a good ear, but, according to that article, not in an ear with loss of IHCs.…”

Ventral approach to rat inner ear preserves cochlear function

“…), as described previously [16]. ABR measurements were performed immediately before and after operations.…”

Auditory brainstem responses in 10 inbred strains of mice

“…Therefore, the measurement of ABR has become a useful and practical procedure for the determination of hearing levels in animals and young children (Arnold, 2000;Musiek et al, 1994;Parham et al, 2001). In mice, the ABR threshold has been used successfully to estimate audiometric thresholds in hearing and genetic research (Davis et al, 2002;Duan and Canlon, 1996;Erway et al, 1996;Erway et al, 1993;Hirose and Liberman, 2003;Money et al, 1995;Munemoto et al, 1998;Rosowski et al, 2003;Szymko-Bennett et al, 2003). A PubMed search using key words of mouse, ABR, and threshold has revealed 80 of these studies since 1985.…”