Effects of GABA-mediated inhibition on direction-dependent frequency tuning in the frog inferior colliculus |
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Authors: | H Zhang J Xu A S Feng |
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Institution: | (1) Department of Molecular and Integrative Physiology, and the Beckman Institute, University of Illinois at Urbana Champaign, Urbana, IL 61801, USA e-mail: huiming@spine.npa.uiuc.edu, Tel.: +1-217-333-7071; Fax: +1-217-244-5180 , US |
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Abstract: | Earlier studies from our laboratory have shown that the frequency selectivity of neurons in the frog inferior colliculus
is direction dependent. The goal of this study was to test the hypotheses that gamma-aminobutyric acid or GABA (but not glycine)-mediated
synaptic inhibition was responsible for the direction-dependence in frequency tuning, and that GABA acted through creation
of binaural inhibition. We performed single unit recordings and investigated the unit's free-field frequency tuning, and/or
the unit's response to the interaural level differences (under dichotic stimulation), before and during local applications
of antagonists specific to gamma-aminobutyric acid a and glycine receptors. Our results showed that application of bicuculline produced a broadening of free-field frequency tuning,
and differential changes in free-field frequency tuning depending on sound direction, i.e., more pronounced at azimuths at
which the unit exhibited narrower frequency tuning under the pre-drug condition, thereby typically abolishing direction dependence
in tuning. Application of strychnine produced no change in frequency tuning. The results from dichotic stimulation further
revealed that bicuculline typically elevated and/or flattened the unit's interaural-level-difference response function, indicating
a reduction in the strength of binaural inhibition. Our study provides evidence that gamma-aminobutyric acid-mediated binaural
inhibition is important for direction dependence in frequency tuning.
Accepted: 24 July 1998 |
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Keywords: | Frog Frequency-threshold-curve Rate-level function Interaural-level-difference Binaural inhibition |
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