小鼠中脑下丘神经元对单、双耳听觉信息突触反应的多样性研究

Diversity of Synaptic Responses of Inferior Colliculus Neurons to Monaural and Binaural Auditory Stimulations in Mice

目的研究小鼠中脑下丘单个神经元对单耳对侧、同侧声刺激的突触反应及双侧同时刺激的整合反应,探索其潜在的神经生理学基础与神经环路。方法52只正常C57小鼠,采用声刺激系统记录下丘单个神经元对单耳对侧、单耳同侧声刺激的频率-幅度反应域(frequency-amplitude response areas,FARA),获得神经元的特征频率(characteristic frequency,CF)和最低阈值(minimum threshold,MT)。采用活体全细胞膜片钳技术,在最适声刺激条件下(即声音参数为CF与MT),记录下丘同一个神经元分别对单耳对侧、单耳同侧声刺激的突触反应,以及双侧声音同时刺激时的突触整合反应,对记录到的突触反应及整合反应进行分类分析。结果共记录到146个下丘神经元,CF-对侧与CF-同侧分别为14.9±4.8、14.7±5.0 kHz,两者成直线相关且相关系数为1.0258;MT-对侧为19.3±19.3 dB,显著低于MT-同侧(45.1±18.6 dB),差异有统计学意义(P<0.001)。根据神经元对单耳刺激的反应是兴奋(excitation,E)、无反应(no response,O)还是抑制(inhibition,I),可将这146个神经元分成7种不同类型,即EE、EO、EI、II、IO、IE和CM(complex-mode,CM)双耳神经元,分别占66.4%(97/146)、15.8%(23/146)、4.1%(6/146)、6.8%(10/146)、1.4%(2/146)、1.4%(2/146)和4.1%(6/146)。根据双耳整合特性,EE神经元可分成抑制EE/I、易化EE/F和无整合EE/N三种类型,分别占38.1%(37/97)、20.6%(20/97)和41.2%(40/97)。EO和II神经元对双耳信息的整合反应可出现抑制和无整合两种,EI神经元仅表现出抑制的整合反应,而IO和IE神经元则呈双耳无整合效应。结论EE、EO、EI、II、IO、IE和CM这7种不同类型的下丘双耳神经元各自具有不同的双侧突触结构和神经环路。

Objective To study the synaptic responses of single neurons in the mice midbrain inferior colliculus(IC)to unilaterally contralateral and ipsilateral acoustic stimulations and their binaural integration to bilateral stimulations,and to explore the potential neurophysiological basis and neural circuits.Methods Using the acoustic stimulation system,the frequency-amplitude response areas(FARA)of a single IC neuron were recorded under the contralateral and ipsilateral acoustic stimulations respectively in a total of 52 normal C57 mice.The characteristic frequency(CF)and minimum threshold(MT)of IC neurons were obtained.The postsynaptic potentials(PSPs)of a same IC neuron in response to contralateral,ipsilateral and bilateral optimal acoustic stimulations(ie,CF and MT)were recorded using in-vivo whole cell patch clamp.The synaptic reactions and binaural integrations were classified and analyzed.Results A total of 146 IC neurons were recorded.Their CF-contralateral and CF-ipsilateral were 14.9±4.8 kHz and 14.7±5.0 kHz on average respectively.The correlation between them was linear and the correlation coefficient was 1.0258.The MT-contralateral was 19.3±19.3 dB,significantly lower than MT-ipsilateral 45.1±18.6 dB,showing a significant difference(P<0.001).According to the single-ear input characteristics,the 146 neurons were divided into 7 different types,namely,EE,EO,EI,II,IO,IE and CM binaural neurons,which were accounted for 66.4%(97/146),15.8%(23/146),4.1%(6/146),6.9%(10/146),1.4%(2/146),1.4%(2/146)and 4.1%(6/146),respectively.Furthermore,based on the binaural integrations,EE neurons were divided into three types inhibition(EE/I),facilitation(EE/F)and no integration(EE/N),accounting for 38.1%(37/97),20.6%(20/97)and 41.2%(40/97),respectively.EO and II neurons showed two kinds of integration response,inhibition or no integration,to binaural information.EI neurons only had integration response of inhibition,while IO and IE neurons showed no integration effect to bilateral stimulations.Conclusion This study suggests that these 7 different types of binaural neurons in the inferior colliculus have different bilateral synaptic structures and neural circuits.