Age-related Hearing Loss Ear and Brain Mechanisms

Otolaryngology Department, University of Rochester School of Medicine & Dentistry, Rochester, New York 14642-8629, USA.
Annals of the New York Academy of Sciences (Impact Factor: 4.38). 08/2009; 1170(1):708-17. DOI: 10.1111/j.1749-6632.2009.03931.x
Source: PubMed


Loss of sensory function in the aged has serious consequences for economic productivity, quality of life, and healthcare costs in the billions each year. Understanding the neural and molecular bases will pave the way for biomedical interventions to prevent, slow, or reverse these conditions. This chapter summarizes new information regarding age changes in the auditory system involving both the ear (peripheral) and brain (central). A goal is to provide findings that have implications for understanding some common biological underpinnings that affect sensory systems, providing a basis for eventual interventions to improve overall sensory functioning, including the chemical senses.

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Available from: Robert D Frisina, Jul 16, 2014
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    • "The effects of aging impact all sensory modalities but mostly those that rely on sophisticated peripheral receptors, such as the cochlea of the inner ear. Age-related hearing loss, presbycusis, is one of the most common causes of hearing loss (Frisina, 2009; Jonsson et al., 1998; Ohlemiller, 2004; Schacht and Hawkins, 2005). In the developed world, presbycusis affects approximately 40% of the population at the age of 60, and the hearing loss progresses by approximately 1 dB per year thereafter. "
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    ABSTRACT: We report here beneficial effects of life-long dietary restriction on the progression of age-associated cochlear degeneration in female Sprague-Dawley rats. Thirty-month old rats on a 70% dietary restriction were compared to ad libitum fed age-matched rats, and three-month old adult rats. As expected, aged dietary restricted rats displayed about 20% higher survival rate than age-matched rats fed ad libitum. This difference was reflected also in the auditory system. In the dietary restricted group, 73% of the subjects had preserved auditory reflexes (Preyer), and only modest degeneration of the stria vascularis of the inner ear was observed. In contrast, aged ad libitum fed animals, of which only 15% had detectable Preyer reflexes, showed a marked thinning, cellular degeneration and loss of cell processes in the stria vascularis. The extent of loss of sensory hair cells (~24%) was similar in both the aged groups, and neither group showed a significant reduction in the number of spiral ganglion neurons across adult life-span. The observations thus demonstrate that dietary restriction delays age-related degradation of the auditory system. The results provide further insights into the mechanisms of strial presbycusis.
    Full-text · Article · Jul 2013 · Experimental gerontology
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    • "Auditory function in mammals, including humans, is known to be significantly affected by aging, ultimately resulting in presbycusis with alterations occurring both in the inner ear and in the central auditory system (Syka, 2002; Frisina and Rajan, 2005; Gates and Mills, 2005; Ohlemiller and Frisina, 2008; Frisina, 2009, 2010; Gordon-Salant et al., 2010). The central component of presbycusis is thought to be significantly associated with age-related alterations in the processing of the temporal parameters of complex acoustical stimuli within the central auditory system, especially the IC and auditory cortex (Strouse et al., 1998; Walton et al., 1998, 2002; Frisina and Walton, 2006; Walton et al., 2008; Walton, 2010; Suta et al., 2011). "
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    ABSTRACT: The inferior colliculus (IC) plays a strategic role in the central auditory system in relaying and processing acoustical information, and therefore its age-related changes may significantly influence the quality of the auditory function. A very complex processing of acoustical stimuli occurs in the IC, as supported also by the fact that the rat IC contains more neurons than all other subcortical auditory structures combined. GABAergic neurons, which predominantly co-express parvalbumin (PV), are present in the central nucleus of the IC in large numbers and to a lesser extent in the dorsal and external/lateral cortices of the IC. On the other hand, calbindin (CB) and calretinin (CR) are prevalent in the dorsal and external cortices of the IC, with only a few positive neurons in the central nucleus. The relationship between CB and CR expression in the IC and any neurotransmitter system has not yet been well established, but the distribution and morphology of the immunoreactive neurons suggest that they are at least partially non-GABAergic cells. The expression of glutamate decarboxylase (GAD) (a key enzyme for GABA synthesis) and calcium binding proteins (CBPs) in the IC of rats undergoes pronounced changes with aging that involve mostly a decline in protein expression and a decline in the number of immunoreactive neurons. Similar age-related changes in GAD, CB, and CR expression are present in the IC of two rat strains with differently preserved inner ear function up to late senescence (Long-Evans and Fischer 344), which suggests that these changes do not depend exclusively on peripheral deafferentation but are, at least partially, of central origin. These changes may be associated with the age-related deterioration in the processing of the temporal parameters of acoustical stimuli, which is not correlated with hearing threshold shifts, and therefore may contribute to central presbycusis.
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    Full-text · Article · Aug 2009 · Annals of the New York Academy of Sciences
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