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The Journal of Neuroscience, November 23, 2005, 25(47):10952-10959; doi:10.1523/JNEUROSCI.2451-05.2005

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Cellular/Molecular
Age-Related Changes in the Inhibitory Response Properties of Dorsal Cochlear Nucleus Output Neurons: Role of Inhibitory Inputs

Donald M. Caspary,^1,2 Tracy A. Schatteman,¹ and Larry F. Hughes²

Departments of ¹Pharmacology and ²Surgery, Southern Illinois University School of Medicine, Springfield, Illinois 62794-9629

Age-related hearing loss frequently results in a loss in the ability to discriminate speech signals, especially in noise. This is attributable, in part, to a loss in temporal resolving power and ability to adjust dynamic range. Circuits in the adult dorsal cochlear nucleus (DCN) have been shown to preserve signal in background noise. Fusiform cells, major DCN output neurons, receive focused glycinergic inputs from tonotopically aligned vertical cells that also project to the ventral cochlear nucleus. Glycine-mediated inhibition onto fusiform cells results in decreased tone-evoked activity as intensity is increased at frequencies adjacent to characteristic frequency (CF). DCN output is thus shaped by glycinergic inhibition, which can be readily assessed in recordings from fusiform cells. Previous DCN studies suggest an age-related loss of markers for glycinergic neurotransmission. The present study postulated that response properties of aged fusiform cells would show a loss of inhibition, resembling conditions observed with glycine receptor blockade. The functional impact of aging was examined by comparing response properties from units meeting fusiform-cell criteria in young and aged rats. Fusiform cells in aged animals displayed significantly higher maximum discharge rates to CF tones than those recorded from young-adult animals. Fusiform cells of aged rats displayed significantly fewer nonmonotonic CF rate-level functions and an age-related change in temporal response properties. These findings are consistent with an age-related loss of glycinergic input, likely from vertical cells, and with findings from other sensory aging studies suggesting a selective age-related decrement in inhibitory amino acid neurotransmitter function.

Key words: dorsal cochlear nucleus; glycine; aging; fusiform cell; auditory; inhibition

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Received June 15, 2005; revised October 17, 2005; accepted October 18, 2005.

This article has been cited by other articles:

				D. M. Caspary, L. Ling, J. G. Turner, and L. F. Hughes Inhibitory neurotransmission, plasticity and aging in the mammalian central auditory system J. Exp. Biol., June 1, 2008; 211(11): 1781 - 1791. [Abstract] [Full Text] [PDF]

				V. C. Kotak, A. E. Takesian, and D. H. Sanes Hearing Loss Prevents the Maturation of GABAergic Transmission in the Auditory Cortex Cereb Cortex, January 24, 2008; (2008) bhm233v1. [Abstract] [Full Text] [PDF]

				C. Alain and K. L. McDonald Age-Related Differences in Neuromagnetic Brain Activity Underlying Concurrent Sound Perception J. Neurosci., February 7, 2007; 27(6): 1308 - 1314. [Abstract] [Full Text] [PDF]

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