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The Journal of Neuroscience, August 17, 2005, 25(33):7558-7566; doi:10.1523/JNEUROSCI.1735-05.2005

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Development/Plasticity/Repair
Complex Regulation of Spiral Ganglion Neuron Firing Patterns by Neurotrophin-3

Zhiping Zhou, Qing Liu, and Robin L. Davis

Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, New Jersey 08854

Auditory information is conveyed into the CNS via the spiral ganglion neurons, cells that possess distinctive electrophysiological properties that vary according to their cochlear innervation. Neurons from the base of the cochlea fire action potentials with shorter latencies and durations with more rapid accommodation than apical neurons (Adamson et al., 2002b). Interestingly, these features are altered by exposure to brain-derived neurotrophic factor and neurotrophin-3 (NT-3), suggesting that the electrophysiological diversity is not preprogrammed into the neurons but instead results from extrinsic regulation. In support of this, gradients of neurotrophins exist in the cochlea that could account for the apex- base differences in firing. To understand the determinants of spiral ganglion function, we characterized the NT-3 concentration dependence and mode of action on spiral ganglion neurons. Whole-cell current-clamp recordings were made from mouse basal spiral ganglion neurons (postnatal day 5) exposed to different concentrations of NT-3 for 3 d in vitro. Measurements of accommodation, latency, onset time course, and action potential latency revealed a nonmonotonic dependence on NT-3 concentration, with a peak effect occurring at 10 ng/ml. Addition of NT-3 at different time points showed that neurotrophin exposure altered the firing features of existing neurons rather than supporting differential survival. These experiments establish that the electrophysiological phenotype of spiral ganglion neurons depends critically on the precise concentration of NT-3 and that the functional organization of this component of the peripheral auditory system results from a complex interplay between multiple kinds of neurotrophins and their cognate receptors.

Key words: NT-3; trkB; spiral ganglion; neurotrophin; hearing; cochlea

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Received May 1, 2005; revised June 12, 2005; accepted July 7, 2005.

This article has been cited by other articles:

				J. Flores-Otero, H. Z. Xue, and R. L. Davis Reciprocal Regulation of Presynaptic and Postsynaptic Proteins in Bipolar Spiral Ganglion Neurons by Neurotrophins J. Neurosci., December 19, 2007; 27(51): 14023 - 14034. [Abstract] [Full Text] [PDF]

				Q. Liu and R. L. Davis Regional Specification of Threshold Sensitivity and Response Time in CBA/CaJ Mouse Spiral Ganglion Neurons J Neurophysiol, October 1, 2007; 98(4): 2215 - 2222. [Abstract] [Full Text] [PDF]

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