抑制性频谱整合对大棕蝠下丘神经元声强敏感性的影响

摘要

自由声场条件下,采用特定双声刺激方法研究了不同频率通道之间的非线性整合对下丘神经元声强敏感性的调制作用.实验在12只麻醉与镇定的大棕蝠(Eptesicus fuscus)上进行,双电极同步记录2个配对神经元的声反应动作电位.主要结果如下:1)所获110个(55对)配对神经元中,85.5%表现为抑制性频谱整合作用,其余14.5%为易化性频谱整合;2)阈上10 dB(SPL)放电率抑制百分比与神经元最佳频率(BF)及记录深度呈负相关;3)抑制效率随声刺激强度升高而逐步下降;4)当掩蔽声分别位于神经元兴奋性频率调谐曲线(FTC)内(MSin)/外(MSout)时,其抑制效率存在差异.前者的放电率抑制百分比及声反应动力学范围(DR)下降百分比均显著高于后者;5)抑制性频谱整合导致3类DR改变:61.6%为下降、10.9%增加、另有27.5%变化小于10%.本结果进一步支持如下设想:下丘不同频率通道之间的抑制性频谱整合参与了对强度编码的主动神经调制活动[动物学报50(3):380-388,2004].%By means of a particular two-tone paradigm under free field stimuli conditions, the current in vivo study was undertaken to explore whether the nonlinear integration between different frequency channels might modulate the sensitivity of sound intensity in inferior collicular (IC) neurons. We recorded neural spike activities simultaneously from 2 sites in the IC of 12 tranquilized and anesthetized big brown bat Eptescus fuscus with a pair of 3 M KCl glass electrodes. The following major findings were made. 1) Of 110 sampled neurons, the responses of 85.5 % paired neurons (94/110) were inhibited whereas the others (14.5 %, 16/110) were facilitated by addition of paired sound. 2) Percent inhibition in firing rate at 10 dB above MT decreased with increasing either best frequencies (BFs) or recording depth significantly. 3) Inhibition efficiency was large at lower stimulus intensity but decreased significantly with increasing stimulus intensity. 4)Neurons with a masker sound within their frequency tuning curves (FTCs, MSin) received more inhibition and more dynamic range (DR) reduction than those with a masker sound out of their FTCs (MSout). 5) There were three types of DR variation. DR of 61.6 % (45/73) neurons decreased, 10.9 % (8/73) increased, and 27.5 % (20/73) unchanged or changed within 10 %. Our data further support the hypothesis that the inhibitory spectral integration of different frequency channels in the IC might involve an active neural modulation of intensity coding [Acta Zoologica Sinica 50 (3): 380-388, 2004].