Research paper The role of GABAergic inhibition in shaping duration selectivity of bat inferior collicular neurons determined with temporally patterned sound trains Chung-Hsin Wu 1 , Philip H.-S. Jen * Division of Biological Sciences and Interdisciplinary Neuroscience Program, University of Missouri-Columbia, 208 Lefevre Hall, MO 65211, United States Received 9 August 2005; received in revised form 3 March 2006; accepted 7 March 2006 Available online 27 April 2006 Abstract A previous study has shown that duration selectivity of neurons in the inferior colliculus (IC) of the big brown bat, Eptesicus fuscus becomes sharper with increasing pulse repetition rate (PRR). The present study examines the role of GABAergic inhibition in improving duration selectivity of bat IC neurons with PRR by means of iontophoretic application of GABA as well as its antagonist, bicuculline. Duration selectivity of IC neurons is studied by plotting the duration tuning curves with the number of impulses per pulse against the pulse duration. Duration tuning curves of IC neurons are described as band-, short-, long- and all-pass in terms of filtering properties to sound duration. Bicuculline application produces more pronounced broadening of duration tuning curves at high than at low PRR. Con- versely, GABA application produces more pronounced narrowing of duration tuning curves at low than at high PRR. In either case, sharpening of duration selectivity of IC neurons with increasing PRR is abolished during drug application. The duration tuning curves of IC neurons progressively broadens with recording depth. Broadening of duration tuning curves during bicuculline application is more pronounced for neurons at upper than at deep IC. This progressive decrease in duration selectivity with recording depth is discussed in relation to spatial distribution gradient of GABA A receptors in the IC. Possible biological significance of these findings relevant to bat echolocation is discussed. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Bat; Bicuculline; Duration selectivity; GABA; Pulse repetition rate; Pulse trains 1. Introduction Sound duration is an important feature that contributes to the distinct spectral and temporal attributes of individ- ual biological sounds. Previous studies of selectivity of auditory neurons to sound duration has been conducted in many animals including frogs (Feng et al., 1990; Gooler and Feng, 1992; Narins and Capranica, 1980), bats (Casse- day et al., 1994, 2000; Ehrlich et al., 1997; Fuzessery and Hall, 1999; Galazyuk and Feng, 1997; Jen and Feng, 1999; Jen and Schlegel, 1982; Jen and Zhou, 1999;Pinheiro et al., 1991; Zhou and Jen, 2001), cats (He et al., 1997), chinchillas (Chen, 1998), mice (Brand et al., 2000) and rats (Perez-Gonzalez et al., 2006). These studies show that most auditory neurons behave as band-, short- or long-pass fil- ters to pulse duration such that they respond maximally to a specific duration or a range of durations. In the mammalian auditory pathway, the central nucleus of the inferior colliculus (IC) receives and integrates excit- atory and inhibitory inputs from many lower auditory nuclei (Adams, 1979; Casseday and Covey, 1995; Oliver et al., 1994; Shneiderman and Oliver, 1989). Neurotrans- mitters that mediate the inhibitory inputs are c-aminobu- tyric acid (GABA) or glycine (Fubara et al., 1996; Oliver 0378-5955/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.heares.2006.03.001 Abbreviations: BD, best duration; BF, best frequency; DW, duration width; nDW, normalized duration width; PRR, pulse repetition rate; GABA, c-aminobutyric acid; IC, inferior colliculus; MT, minimum thre- hold; PST, peri-stimulus-time histogram * Corresponding author. Tel.: +1 573 882 7479; fax: +1 573 884 5020. E-mail address: jenp@missouri.edu (P.H.-S. Jen). 1 Present address: Department of Life Science, National Taiwan Normal University, Taipei, Republic of China. www.elsevier.com/locate/heares Hearing Research 215 (2006) 56–66 Hearing Research