THE EFFECTS OF GABA ON TEMPORAL DISCHARGE PATTERNS OF IC NEURONS TO ACOUSTIC PULSR TRAIN IN THE BIG BROWN BAT, Eptesicus fuscus
GABA能抑制调制大棕蝠下丘听神经元时间编码模式

In the big brown bat, Eptesicus fuscus, which can use echolocation for hunting and navi-gation, the inferior collicular (IC) neurons responded to every pulse of pulsatile amplitude-modulated (PAM) sound signal train in 10 pps (pulse per second) and 30 pps. But the temporal discharge patterns of IC neurons vary in response to the pulses of 90 pps sound train . The responses of 45(78%) IC neu-rons tested were changed during the application of bicuculline, a competitive antagonist for -aminobu-tyric acid-A (GABA A ) receptors. These neurons responded to every pulse of 10 pps and 30 pps sound train before and during bicuculline application. But when the pulse repetition rate of sound train was 90 pps, the responses of the neurons changed a lot. During bicuculline application, the discharges in-creased and the neurons still responded to every pulse of 90 pps sound train in 17(29%) IC neurons. The responses of 9(15%) neurons increased only at the beginning of 100 ms and decreased greatly in the next 200 ms. In 15(26%) of IC neurons, when the pulses repetition rate was 90 pps, the responses in-creased only in the first several 10 ms and then reduced. There are 4(7%) neurons responding strongly only to the first pulse of 90 pps sound train. The present study suggests that the mechanism of IC pro-cessing temporal information of the sound repetition rate may be more complicated than that of the low-er central auditory system.