豚鼠下丘神经元声音时程调谐特性及γ氨基丁酸能抑制的作用

目的观察豚鼠下丘神经元的时程调谐特性并探讨γ氨基丁酸（gamma—aminobutyricacid，GABA）能抑制对时程调谐的作用。方法23只健康豚鼠，雌雄不拘。在麻醉状态下采用复合式多管微电极记录下丘中央核神经元响应：通过对等强度不同频率短纯音的响应确定神经元的最佳反应频率；通过对等强度不同时程信号的响应确定神经元的时程调谐特性。经微电泳仪将GABA—A受体阻断剂（荷包牡丹碱）注射到所记录的神经元周围，通过比较注射前后神经元响应模式的变化确定GABA能抑制对神经元时程调谐的作用或影响。结果豚鼠下丘神经元，特别是持续响应神经元的时程调谐特性往往表现在对声信号的瞬态给声响应（给声反应）中。在记录到的207个神经元中，共有93个神经元细胞表现出明显的时程选择特性。在其中67个神经元成功观察了注射荷包牡丹碱后的响应变化，发现44个细胞时程选择特性消失或者是转变为时程调谐弱的模式。结论与以往在蝙蝠的报道不同，豚鼠下丘神经元的时程调谐特性往往表现在其瞬时给声响应之中。GABA能抑制是时程选择性形成的重要因素之一。

Duration-tuning of the neurons in the inferior colliculus of guinea pigs and the role of γ-aminobutyric acid mediated inhibition

OBJECTIVE: To evaluate duration tuning in the inferior colliculus (IC) of guinea pigs and the role of GABA-mediated inhibition on this tuning. METHODS: Totally 23 healthy albino guinea pigs of either sex were employed in this study. After anesthesia, spikes of neurons in inferior colliculus were recorded using five-barrel glass-pipettes. The characteristic frequency was determined by recording iso-intensity response curves at moderate intensity level (40-70 dB SPL) and duration tuning was measured with signals of fixed intensity and varied durations. GABA-A receptor antagonist, bicuculline, was applied to neurons by means of in vivo micro-iontophoresis through one channel in the five-barrel glass-pipettes. RESULTS: IC neurons of guinea pigs, especially for those who showed sustained temporal response pattern, showed stronger duration tuning in their transient response peak to signal onset. Among 207 neurons recorded, totally 93 neurons were found to show clear duration selectivity. The duration selectivity was eliminated or turned to be weaker in most of the neurons in which the effect of bicuculline was observed successfully. CONCLUSIONS: Unlike what was reported in bats, duration selectivity may be a trainsient process for most of IC neurons in guinea pigs. Duration selectively of IC neurons in the guinea pig was also largely dependent on the GABAergic inhibition.