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GABAergic inhibition modulates intensity sensitivity of temporally patterned pulse trains in the inferior collicular neurons in big brown bats

Luan Ruihong, Wu Feijian, Philip H.-S.Jen, Sun Xinde

School of Life Sciences, East China Normal University.Shanghai 200062；China；Division of Biological Sciences, University of Missouri-Columbia, MO 65211

Abstract

The echolocating big brown bats （Eptesicusfuscus） emit trains of frequency-modulated （FM） biosonar signals with duration, amplitude, repetition rate, and sweep structure changing systematically during interception of their prey. In the present study, the sound stimuli of temporally patterned pulse trains at three different pulse repetition rates （PRRs） were used to mimic the sounds received during search, approach, and terminal stages of echolocation. Electrophysiological method was adopted in recordings from the inferior colliculus （IC） of midbrain. By means of iontophoretic application of bicuculline, the effect of GABAergic inhibition on the intensity sensitivity of IC neurons responding to three different PRRs of 10, 30 and 90 pulses per second （pps） was examined. The rate-intensity functions （RIFs） were acquired. The dynamic range （DR） of RIFs was considered as a criterion of intensity sensitivity. Comparing the average DR of RIFs at different PRRs, we found that the intensity sensitivity of some neurons improved, but that of other neurons decayed when repetition rate of stimulus trains increased from 10 to 30 and 90 pps. During application of bicuculline, the number of impulses responding to the different pulse trains increased under all stimulating conditions, while the DR differences of RIFs at different PRRs were abolished. The results indicate that GABAergic inhibition was involved in modulating the intensity sensitivity of IC neurons responding to pulse trains at different PRRs. Before and during bicuculline application, the percentage of changes in responses was maximal in lower stimulus intensity near to the minimum threshold （MT）, and decreased gradually with the increment of stimulus intensity. This observation suggests that GABAergic inhibition contributes more effectively to the intensity sensitivity of the IC neurons responding to pulse trains at lower sound level.

Key words: bat;intensity sensitivity;inferior colliculus;pulse repetition rate;echolocation

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Citing This Article：

Luan Ruihong, Wu Feijian, Philip H.-S.Jen, Sun Xinde. GABAergic inhibition modulates intensity sensitivity of temporally patterned pulse trains in the inferior collicular neurons in big brown bats. Acta Physiol Sin 2007; 59 (6): 805-813 (in Chinese with English abstract).