下丘神经元声信号处理过程中的相互作用与整合

In auditory neurophysiology, processing of auditory information carried by sound has traditionally been explained by neural interactions of divergent and convergent projections. As a common target of ascending and descending pathways of auditory system, the central nucleus of inferior colliculus (ICc) receives complex excitatory and inhibitory inputs from several lower brain stem nuclei, contralateral IC, and high auditory as well as nonauditory structures. There are also numerous intrinsic terminates as either focused or diffused projection onto IC neurons. A growing body of literature indicates that ICc is one of the most important integrative centers of the auditory region. However, up to date how to integrate sound information between ICc neurons remains litter known. In order to elucidate the characteristic of neural integration between neurons within auditory functional circuits even more, it is necessary to probe directly the process and mechanism of interaction between both central neurons at cellular lever. .By taking advantage of ICc neuron's tonotopic organization arranged in best frequency (BF) and using a pair of 3 M KCL glass electrodes to simultaneously record with a particular two-tone stimulation paradigm under free field conditions, interaction and integration between ICc neurons during sound signal processing were studied. Our experiments were conducted on 16 big brown bats (Eptesicus fuscus) tranquilized and anesthetized with Innoval-Vet (Fentanyl 0.08 mg / kg b. w., Droperidol 4 mg / kg b. w.) and Nembutal (50 mg / kg b. w.). Results of the first part are as follows: 1) 81.8% (36/44) paired neurons yielded mutually inhibitory spectral integration while others (18.2%, 8/44) were mutually facilitated; 2) The most best frequencies (BFs) of correlated neurons (86.4%, 36/44) with integration were within the range of 20 -30 kHz. Although there were nearly one half of paired neurons (45.5%, 20/44) whose BFs differences were less than 2 kHz, the spectral integration between those neurons (13.6% 6/44) whose BFs differences were more than 10 kHz also can be observed; 3) The sound responses selectivity of IC neurons to frequency and intensity were dynamically modulated by frequency spectral integration. For better understanding the mechanism underling integration, the role of GABAergic inhibition in neural interactions between paired IC neurons were investigated in our further experiments. Rate-level functions (RLFs) and rate-frequency tuning curves (FTCs) of 33 paired neurons were obtained. The results showed: 1) Bicuculline (Bic) application expanded FTCs (n=29) and increased RLFs (n=32) to varying degrees; 2) Increasing discharges of ICc neurons during Bic application typically enhanced inhibition or facilitation to paired neurons (FTCs: 75.9%, 22/29; RLFs: 84.4%, 27/32). However, no clear changes of FTCs (24.1%, 7/29) and RLFs (15.6%, 5/32) of a few neurons were observed; 3) Spectral integration of neurons were affected after Bic application in two ways: partial neurons (32%, 8/25) continued to be inhibited or facilitated while the other (68%,17/25) were influenced very little when two-tone stimulating；4)The efficiency of integration was correlated with recording depths, discharge patterns, and BF differences between paired ICc. In addition, the effects of a neural modulator, Galanin on inferior collicular neurons respond to sound were investigated. Preliminary data of 56 neurons indicate that Galanin could modulate responds of IC neurons in frequency domain and intensity domain..We first directly examined inhibition and facilitation of auditory responses of two simultaneously recorded neurons which were correlative with sound signal processing and acquired the new knowledge of neural integration characteristics of auditory neurons within IC circuits. The data provided immediate functional evidence that there are mutual interactions of ICc neurons within iso-frequency lamina or between iso-frequency lamminae. Results of this project would be significant for expounding the mechanism underlying processing of

动物中脑下丘是重要的听觉中枢，其声调组构按最佳频率排列成同频层。已有的单电极或单点电生理研究方法，有碍对声信号处理过程中神经元间相互关系和整合的了解，越来越强烈地受到人们的关注。本研究以蝙蝠下丘为模式结构，用双电极同时检测两个神经元，研究在处理同一感觉事件时的相互关系，窥探声信号处理过程中整合的奥秘。..