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The Journal of Neuroscience, December 10, 2003, 23(36):11296-11304

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Cellular/Molecular
Comparative Distribution of Glutamate Transporters and Receptors in Relation to Afferent Innervation Density in the Mammalian Cochlea

David N. Furness and D. Maxwell Lawton

MacKay Institute of Communication and Neuroscience, School of Life Sciences, Keele University, Keele, Staffordshire, ST5 5BG, United Kingdom

The local expression of proteins involved in handling glutamate may be regulated by the number and activity of synapses in regions of glutamatergic innervation. The systematically varying innervation of inner hair cells (IHCs) of the cochlea provides a model to test this suggestion. IHCs are glutamatergic and form a single row along the cochlear spiral. Along this row the number of afferent fibers terminating on IHCs increases toward the base, reaching a peak and thereafter declining. The afferents are segregated so that higher spontaneous rate fibers terminate on the pillar-cell side of the IHC and lower rate fibers terminate on the modiolar side. Using immunofluorescence and postembedding immunogold labeling, we investigated the distributions of the glutamate-aspartate transporter (GLAST or excitatory amino acid transporter 1), vesicular glutamate transporter (VGLUT1), and the AMPA receptor glutamate receptor 4 (GluR4) along the spiral. Immunofluorescent labeling for GLAST in IHC supporting cells increased in intensity to a peak in the region of 6-9 mm from the apex. Immunogold labeling for GLAST was greater overall in these cells in the 10 mm region than in the 1 mm region and also on the pillar-cell side of the IHC compared with the modiolar side. Immunogold labeling for GluR4 was confined to synaptic sites, represented by puncta in immunofluorescence. The relative numbers of puncta changed with a gradient similar to that of GLAST labeling. VGLUT1 labeling occurred in IHCs but showed no clear cochleotopic gradient. These data suggest that both the density of innervation and the activity levels of glutamatergic synapses may be involved in modulating regional expression of GLAST.

Key words: glutamate; cochlea; inner hair cells; GLAST; GluR4; VGLUT1; EAAT1

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Received July 14, 2003; revised October 3, 2003; accepted October 3, 2003.

This article has been cited by other articles:

				N. Obholzer, S. Wolfson, J. G. Trapani, W. Mo, A. Nechiporuk, E. Busch-Nentwich, C. Seiler, S. Sidi, C. Sollner, R. N. Duncan, et al. Vesicular Glutamate Transporter 3 Is Required for Synaptic Transmission in Zebrafish Hair Cells J. Neurosci., February 27, 2008; 28(9): 2110 - 2118. [Abstract] [Full Text] [PDF]

				E. Glowatzki, N. Cheng, H. Hiel, E. Yi, K. Tanaka, G. C. R. Ellis-Davies, J. D. Rothstein, and D. E. Bergles The glutamate-aspartate transporter GLAST mediates glutamate uptake at inner hair cell afferent synapses in the mammalian cochlea. J. Neurosci., July 19, 2006; 26(29): 7659 - 7664. [Abstract] [Full Text] [PDF]

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