【作者】 刘双喜；

【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】 声音的时相特征在声音的识别和分类中起关键作用,其中时程、脉冲重复率等是重要的参数。在各级听觉中枢的研究都表明,听觉相关的高级神经活动以及听觉神经元的反应特性与声刺激负载有重要相关性。声刺激的呈现率(stimulus presentation rate,PR)能表征单位时间内动物所接受声刺激的能量和信息量。本研究在自由声场条件下,以所记录神经元的特征频率(characterizing frequency,CF)作为声刺激的频率,强度为最小阈值(minimal threshold,MT)以上5、15、25、35、45dB SPL,时程为10、40及100ms的纯音短声作为刺激,并改变刺激PR(0.5,1,2,3.3,5,6.7,10,20次/秒),记录了戊巴比妥钠(pentobarbital)麻醉昆明小鼠(Mus musculus.Km)的下丘(inferior colliculus,IC)神经元的反应,以初步探明PR对小鼠IC神经元反应的影响以及IC神经元的反应跟随声刺激呈现的能力受声刺激强度及时程的影响。 研究共用11只健康且听力正常的成年小鼠,雌雄不拘,记录到IC神经元176个,结果发现:在短声强度为MT以上5dB SPL、时程为40ms时,随PR的增高,1)绝大多数神经元(87.3%,103/118)的脉冲发放数单调下降,少数(12.7%,15/118)神经元的脉冲发放数呈非单调变化,脉冲发放数与PR之间有显著相关性;2)部分神经元(17.8%,21/118)的发放模式发生改变,主要是由紧张型或相位爆发型向相位型转变;3)将脉冲发放数减小到在实验所用PR范围内具最大发放数一半时的PR定义为临界呈现率(critical presentation rate,CPR),将神经元所能发生反应的最大PR定义为最大呈现率(maximal presentation rate,MRP),其CPR及MRP低于3.3Hz的神经元分别超过70%(75.4%,89/118)和40%(44.9%,53/118);4)在各种短声刺激PR和强度下,反应的脉冲发放数随短声时程的延长有递增、递减、非单调变化等不同趋势;5)随短声时程的延长,具低CPR和低MPR(0.5～3.3Hz)的神经元比例增高,具高CPR和高MPR(>6.7Hz)的神经元的比例降低;6)在各种短声刺激PR和时程下,多数神经元的脉冲发放随短声强度的增高而增强;7)随短声强度的增高,具低CPR和低MRP的神经元的比例降低,具高CPR和高MRP的神经元的比例增高,但在各强度下具低CPR的神经元都占相当比例(38.5%～90%)。 该结果表明,即使在低PR范围内,小鼠IC神经元反应特性与PR密切相关,更多还原

【Abstract】 Presentation rate of sound stimulations (PR) is the parameter representing the energy and information received by animals in limited time. In our experiment, to study the effect of PR on the sound response properties of mouse inferior collicular (IC) neurons and the relationship between the neurons’ ability to follow sound presentations and the duration as well as intensity of the sounds, the tones with different durations (10、 40 and 100 ms)、 intensities(5, 15, 25, 35, and 45 dB SPL above minimal threshold) at characteristic frequency(CF) of recorded neurons were presented to pentobarbital anesthetized mice (Mus musculus, Km) at different PR (0.5,1, 2, 3.3, 5, 7,10, and 20 Hz) under free field stimulation conditions.11 healthy adult mice (male or female) with natural hearing were used for this study and a total of 176 IC neurons were recorded. The PR at which the response changed to 50% in PR- normalized response function was defined as critical presentation rate(CPR), and the PR at which the neurons stopped firing was defined as maximal presentation rate(MPR). The results were as follows: 1) When the intensity of the stimulations was 5 dB SPL above MT and the duration was 40 ms, with the PR increasing, the sound response properties of most recorded neurons were dramatically influenced by changing the PR even within low PR range (< 3.3 Hz). The firing rate of the majority of neurons (87.3%, 103/118) monotonically decreased with the PR increasing, whereas in a smaller fraction of neurons (12.7%, 15/118)it non-monotonically varied. There was significant correlation between the firing rate and the PR (P < 0.01). 2) The discharge patterns in part of neurons (17.8%, 21/118) were transformed with the PR alteration. Many tonic responder (T) and phasic-burst responder (PB) were changed into the phasic responder (P). 3) The total number of neurons with CPR and MPR lower than 3.3 Hz were more than 70% (75.4%, 89/118) and 40% (44.9%, 53/118), respectively. 4) With the duration prolonging, the firing rates of the neurons changed in different patterns(increasing, decreasing, and non-monotonic). The proportion of neurons with low CPR and MPR (ranged from 0.5 to 3.3 Hz) increased, and the proportion of neurons with high CPR and MPR (higher than 6.7 Hz) decreased. 5) With the stimulus intensity increasing, thefiring rate of the majority of the neurons increased. 6) With the stimulus intensity increasing, the proportion of neurons with low CPR and low MPR decreased, while the proportion of neurons with high CPR and high MPR increased. The neurons with low CPR took a important part (38.5 %~ 90%) at these intensity.The results suggests that the sound response properties of IC neurons are closely correlated to the PR of sound stimulation even in relatively low PR range. The effect of the PR on sound response properties of auditory neurons could not be overlooked in hearing studies. Increasing intensity of sound stimulations could enhance the ability to follow the sound presentations of the most IC neurons. The effect of sound duration on the ability was various. Shortening the duration usually could enhance the ability. Properly shortening the duration and increasing the intensity of the sound generally favored the IC neurons to pool more information for neural processing and to represent sound information. The PR’s effect on response of the IC neurons may be mainly ascribed to the neurons’ excitability and the relationship between inhibitory input and excitatory input onto the IC neurons. The difference of the effect of PR on different neurons maybe reflected the neurons’ diverse coding mechanisms and function. How PR, intensity, and duration of sound stimulations jointly affect the response of auditory neurons should be further studied.更多还原