【作者】 李安安；

【导师】 陈其才； 吴飞健；

【作者基本信息】 华中师范大学 ， 动物学， 2006， 硕士

【摘要】 下丘在中枢听觉系统中占据着关键位置,大量证据表明它是低位听觉通路、听皮层和运动系统之间的中介。下丘接受来自不同通路大量低位脑干听觉核团的上行输入以及来自对侧下丘的交叉输入和听皮层的下行输入。长期以来,人们对下丘在频率、强度和时间编码,声定位或声源方向编码,双耳反应特性,重复声脉冲信号处理或脉冲重复率处理,以及离皮层调控等方面做了大量研究,尤其是对听觉信息的处理过程和机制、以及调控方面的研究特别引人注目。 为探讨回声定位蝙蝠和昆明小鼠下丘神经元的声反应情况及下丘神经元在不同类型噪声前掩蔽条件下的声反应模式,本实验共由三个部分构成。在第一部分,通过在自由声场条件下,采用单单位胞外微电极记录方法,研究了普通伏翼蝠下丘神经元基本声反应特性。结果发现,在所得的65个下丘神经元中:特征频率在18.9～76.7kHz(42.94±11.29)之间,最小阈值在29～80dB SPL(58.65±12.62)之间,潜伏期在3.1～10.4ms(6.10±1.47)之间;特征频率随记录深度的增加而增大,与最小阈值之间没有显著相关性;发放类型包括相位型(73.9%)、梳齿型(15.4%)和紧张型(10.7%)3种基本类型;频率调谐曲线均为开峰型,多数神经元(72.3%)调谐曲线较宽阔,少数(27.7%)较狭窄,并且多数神经元的频率调谐曲线高频边比低频边陡。 尽管昆明小鼠下丘神经元对纯音的反应已有深入研究,但其对调频声的反应如何却未见报道。在第二部分的研究中,在自由声场条件下,采用单单位细胞外记录方法,观察了昆明小鼠下丘神经元对调频声尤其是快调频声刺激的反应情况。根据神经元对调频声及纯音反应的阈值差异,所记录的99个下丘神经元可分为三种类型:对调频声刺激反应的阈值低于纯音的为Ⅰ型(57/99,57.6%),二者阈值相当的为Ⅱ型(12/99,12.1%),而纯音阈值低于调频声的为Ⅲ型(30/99,30.3%)。通过分析下丘神经元对上、下扫时发放数的差异,发现有36个(36/99,36.4%)神经元表现出方向选择性,其中22个(22/99,22.2%)为上扫敏感,其余14个(14/99,14.2%)为下扫敏感,并且上扫敏感性神经元比下扫敏感性神经元在Ⅰ、Ⅱ和Ⅲ型神经元中有更广的分布范围。通过比较发现,Ⅰ型神经元和方向选择性神经元的特征频率都非常集中分布在10～20kHz范围内(77.2%和83.3%)。此外,对其中24个神经元采取了不同调制速度的调频声刺激,大多数(15/24,62.5%)神经元对快调频声反应最为敏感,并且随着调制速度的升高,方向选择性神经元的比例有下降趋更多还原

【Abstract】 The inferior colliculus (IC) occupies a strategic position in the central auditory system. Evidence from lots of studies indicates that it is an interface between lower brainstem auditory pathways, the auditory cortex and motor systems. The IC receives ascending input from a number of auditory nuclei in the lower brainstem. Moreover, it receives crossed input from the opposite IC and descending input from auditory cortex. For a long time, many experiments were performed on IC to study the encoding of sound frequency, intensity and duration. Many other aspects such as sound location, binaural properties, processing of pulse repetition rate, and corticofugal modulation also have studied extensively.In order to explore the response properties of the IC neurons in echolocating bats and mice, and the different forward masking patterns of sustained noise burst and segmental noise bursts in the IC, the present study was consist of three sections. In the first section, to study the acoustic response properties of the IC in the pipistrellus abramus, single unit extracellular recording with microelectrode was used in free field conditions. In the 65 recorded neurons, the results showed: Characteristic frequency (CF) , minimum threshold (MT) and response latency was between 18.9 and 76.7 kHz (42.94 ± 11.29), 29 and 80dB SPL (58.65 ± 12.62), 3.1 and 13.4 ms (6.10 ± 1.47), respectively; CFs increased with the recording depth, but CF and MT were not correlated; There were three different types of discharge patterns in the IC, including phasic pattern (73.9%), chopper (15.4%) and tonic (10.7%); The types of frequency tuning curves (FTC) were all V-shaped, most of which were wide type and few were narrow type. In addition, the high-frequency slope was often steeper than the low-frequency slope.Very few study was performed on the IC using frequency modulated (FM) stimuli though much of the response properties were studied using pure tone in the mouse (Mus musculus, Km). For this purpose, in the second section, we observed the response of IC neurons to FM especially rapid FM stimuli in the free-field conditions. According to the MT difference between the pure tone and FM stimuli, the 99 IC neurons recorded were classified into three types. Type Ⅰ neurons (57/59, 57.6%) were characterized by the lower FM stimuli MT then pure tone stimuli while type Ⅲneurons (30/99, 30.3%) with lower MT when presented with pure tone stimuli. In type Ⅱ neurons (12/99, 12.1%), the MT was equal when the kind of tone were presented. Through analyzing the different firing rate between up-sweep and down-sweep, we found that 36 IC neurons (36/99, 36.4%) were direction selective and among them 22 (22/99, 22.2%) were up-selective and 14 (14/99, 14.2%) were down-selective. Up-selective neurons had a wider distribution range than down-selective neurons in type ⅠⅡⅢneurons. We also found that CFs of both type Ⅰ and direction selective neurons had very densest distribution inthe range of 10~20 kHz (77.2% and 83.3% respectively). In addition, we observed the responses of 24 IC neurons to FMs stimuli of three different modulation rate and we found that most of the neurons (15/24, 62.5%) were much sensitive to rapid FMs stimuli. Further more, the proportion of the direction selective neurons had decrease decline when the modulation rate was increasing (45.8% vs 41.7% vs 33.3%). The results suggested that the IC of mouse could process FMs stimuli effectively and FMs with directions made significant roles in sound communication in the mouse.Although there has been a growing body of literature showing the neural correlation of forward masking caused by a pure tone masker in the auditory neurons, relative few studies have addressed the description of how the forward masking caused by a noise burst, especially a sequence of noise bursts, is transformed into neuronal representation in the central auditory system. In the third section, using a noise forward masking paradigm under free field stimuli conditions, the current in vivo study was devoted to exploring it on the inferior collicular (IC) neurons in the mouse. A total of 96 IC neurons were recorded. Rate-intensity functions (RIFs) with and without the presentation of masker, sustained noise burst (SNB) or segmental noise burst (SGNB), were measured in 51 neurons. We found that the relative masker intensities were distributed over a wide range between 21 dB below the minimum threshold (MT) and 19 dB above the MT of the corresponding probe tone. The masking effect of the SGNB on firing rate in nearly half a number of neurons (type I, 45.1%,) was stronger than that of the SNB (P < 0.001), whereas in a smaller fraction of neurons (type III, 17.7%,) it was weaker than the SNB (P < 0.001). There was no significant difference of masking effect between the SNB and SGNB in type II neurons (37.2%, P > 0.05). Irrespective of type I or type III neurons, ihe inhibitory effects of both kinds of maskers were all greater at lower probe intensities but decreased significantly with the increase of probe intensity (P < 0.001). Interestingly, as the probe intensity increased, the difference of masking effect between the SNB and SGNB was disappeared (P > 0.05). In addition, we observed that temporal masking pattern could be transformed when the masker was changed from the SNB to SGNB. The main type of this transformation was from early-inhibition to equivalent-inhibition pattern (53.9%, 7/13). Our data provide the evidence that the inhibitory effect of these two maskers has differential weights over time and intensity domains of the IC neurons responding to a pure tone. This suggests that the forward masking of noise is by no means the source of simply suppression in neuronal firing rate. There might be a few of active neural modulating ways in which the coding of temporal acoustical information can be operated.更多还原