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The Journal of Neuroscience, February 21, 2007, 27(8):1954-1963; doi:10.1523/JNEUROSCI.2894-06.2007

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Behavioral/Systems/Cognitive
Contribution of NMDA and AMPA Receptors to Temporal Patterning of Auditory Responses in the Inferior Colliculus

Jason Tait Sanchez,^1,2 Donald Gans,^1,2 and Jeffrey J. Wenstrup¹

¹Department of Neurobiology, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272, and ²School of Speech Pathology and Audiology, Kent State University, Kent, Ohio 44270

Correspondence should be addressed to Jeffrey J. Wenstrup, Department of Neurobiology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, P.O. Box 95, Rootstown, OH 44272. Email: jjw{at}neoucom.edu

Although NMDA receptors (NMDARs) are associated with synaptic plasticity, they form an essential part of responses to sensory stimuli. We compared contributions of glutamatergic NMDARs and AMPA receptors (AMPARs) to auditory responses in the inferior colliculus (IC) of awake, adult mustached bats. We examined the magnitude and temporal pattern of responses to tonal signals in single units before, during, and after local micro-iontophoretic application of selective antagonists to AMPARs [NBQX (1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide)] and NMDARs [CPP ((±)3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid)]. Combined blockade of AMPARs and NMDARs eliminated excitatory responses in nearly all neurons, whereas separate blockade of each receptor was quantitatively similar, causing substantial (>50%) spike reductions in 75% of units. The major result was that effects of receptor blockade were most closely related to the first-spike latency of a unit. Thus, AMPAR blockade substantially reduced spikes in all short-latency units (<12 ms) but never in long-latency units (12 ms). NMDAR blockade had variable effects on short-latency units but reduced spikes substantially for all long-latency units. There were no distinct contributions of AMPARs and NMDARs to early and late elements of responses. Thus, AMPAR blockade reduced early (onset) spikes somewhat more effectively than NMDAR blockade in short-latency units, but NMDAR blockade reduced onset spikes more effectively in long-latency units. AMPAR and NMDAR blockade were equally effective in reducing later elements of sustained responses in short-latency units, whereas NMDAR blockade was much more effective in long-latency units. These results indicate that NMDARs play multiple roles for signal processing in adult IC neurons.

Key words: CPP; NBQX; glutamate; temporal pattern; latency; mustached bat

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Received July 7, 2006; revised Jan. 17, 2007; accepted Jan. 18, 2007.

Correspondence should be addressed to Jeffrey J. Wenstrup, Department of Neurobiology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, P.O. Box 95, Rootstown, OH 44272. Email: jjw{at}neoucom.edu

This article has been cited by other articles:

				J. T. Sanchez, D. Gans, and J. J. Wenstrup Glycinergic "Inhibition" Mediates Selective Excitatory Responses to Combinations of Sounds J. Neurosci., January 2, 2008; 28(1): 80 - 90. [Abstract] [Full Text] [PDF]

				S. Augustinaite and P. Heggelund Changes in firing pattern of lateral geniculate neurons caused by membrane potential dependent modulation of retinal input through NMDA receptors J. Physiol., July 1, 2007; 582(1): 297 - 315. [Abstract] [Full Text] [PDF]

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