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First published online on August 9, 2007.
Copyright © 2007 by The Physiological Society
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jphysiol.2007.137976v1
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George A. Spirou
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Received June 4, 2007
Revised July 3, 2007
Accepted after revision August 9, 2007

Development of Gerbil Medial Superior Olive: Integration of Temporally Delayed Excitation and Inhibition at Physiological Temperature

Florin V. Chirila1, Kevin C. Rowland1, Jesse M. Thompson1, and George A. Spirou1*

1 West Virginia University

* To whom correspondence should be addressed. E-mail: gspirou{at}hsc.wvu.edu.

The sensitivity of medial superior olive (MSO) neurons to tens of microsecond differences in interaural temporal delay (ITD) derives in part from their membrane electrical characteristics, kinetics and timing of excitatory and inhibitory inputs, and dendrite structure. However, maturation of these physiological and structural characteristics are little studied, especially in relationship to the onset of auditory experience. We showed, using brain slices at physiological temperature, that MSO neurons exhibited sensitivity to simulated temporally delayed (TD) EPSCs (simEPSC), injected through the recording electrode, by the initial phase of hearing onset at P10, and TD sensitivity was reduced by block of low threshold potassium channels. The spike generation mechanism matured between P10-16 to support TD sensitivity to adult-like excitatory stimuli (1-4 ms duration) by P14. IPSP duration was shorter at physiological temperature than reported for lower temperatures, was longer than EPSP duration at young ages, but approached the duration of EPSPs by P16, when hearing thresholds neared maturity. Dendrite branching became less complex over a more restricted time frame between P10-12. Because many physiological and structural properties approximated mature values between P14-16, we studied temporal integration of simEPSCs and IPSPs at P15. Only a narrow range of relative onset times (<1 ms) yielded responses showing sensitivity to TD. We propose that shaping of excitatory circuitry to mediate TD sensitivity can begin before airborne sound is detectable, and that inhibitory inputs having suboptimal neural delays may then be pruned by cellular mechanisms activated by sensitivity to ITD.


Key words: Auditory system • Inhibitory postsynaptic potential (IPSP) • Synaptic integration







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