Abstract
Noise-induced hearing loss (NIHL) and resulting comorbidities like subjective tinnitus are common diseases in modern societies. A substance shown to be effective against NIHL in an animal model is the Ginkgo biloba extract EGb 761. Further effects of the extract on the cellular and systemic levels of the nervous system make it a promising candidate not only for protection against NIHL but also for its secondary comorbidities like tinnitus. Following an earlier study we here tested the potential effectiveness of prophylactic EGb 761 treatment against NIHL and tinnitus development in the Mongolian gerbil. We monitored the effects of EGb 761 and noise trauma-induced changes on signal processing within the auditory system by means of behavioral and electrophysiological approaches. We found significantly reduced NIHL and tinnitus development upon EGb 761 application, compared to vehicle treated animals. These protective effects of EGb 761 were correlated with changes in auditory processing, both at peripheral and central levels. We propose a model with two main effects of EGb 761 on auditory processing, first, an increase of auditory brainstem activity leading to an increased thalamic input to the primary auditory cortex (AI) and second, an asymmetric effect on lateral inhibition in AI.
Highlights
A universal characteristic of modern societies, both in developing and developed countries, is the steadily increasing level of noise exposure within our working environments and during leisure time activities
We propose a model with two main effects of EGb 761 on auditory processing, first, an increase of auditory brainstem activity leading to an increased thalamic input to the primary auditory cortex (AI) and second, an asymmetric effect on lateral inhibition in AI
We describe the effects of the EGb 761 extract on the behavioral level (acoustic startle response (ASR) audiometry), the auditory brainstem level (electrophysiological recordings of auditory brainstem responses (ABR)), and the central level (electrophysiological recording of local field potentials (LFP) and single and multiunit responses in auditory cortex (AC))
Summary
A universal characteristic of modern societies, both in developing and developed countries, is the steadily increasing level of noise exposure within our working environments and during leisure time activities (for review see [1]). Statistical data show that in 2000 about 9% of the general population in the USA display hearing impairments [2]. Several studies from North America and Europe report up to 15% of this age group to readily display significant hearing deficits [4], which reflects an increase of hearing loss among children and adolescents of around 10% [2, 3]. As hearing loss may be etiologically responsible for the development of a number of secondary diseases, like hyperacusis (for review see [5]), tinnitus [6, 7], or depression due to social isolation [8], the problem of NIHL should be of immensely growing importance. Between 5% and 15% of the general population report to be affected and around 1% state that their quality of life is considerably impaired by their persistent perception of a phantom sound [9]
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