【作者】 王欣；

【导师】 陈其才；

【作者基本信息】 华中师范大学 ， 动物学， 2009， 博士

【摘要】 本研究采用自由声场刺激,在动物下丘（inferior colliculus,IC）以细胞外记录等方法,用不同声刺激模式,在哺乳动物昆明小鼠（Mus musculus Km）和回声定位蝙蝠日本伏翼蝠（Pipistrellus abramus）的下丘记录到289个神经元,测定了不同声刺激模式对IC神经元的掩蔽效应、恢复周期（recovery cycle,RC）、频率调谐（frequency tuning）等反应特性的影响,并对这些实验结果进行了分析和讨论。主要研究结果如下:1.所做的小鼠IC神经元的弱噪声前掩蔽研究结果表明,掩蔽声使大部分神经元FTC锐化（p<0.01,n=25）,并有随掩蔽声时程的延长而锐化程度增加的趋势（p<0.05）。通过计算神经元频率调谐曲线（frequency tuning curve,FTC）的反转斜率（inverse-slope,IS）,发现弱噪声前掩蔽对高频边的抑制率明显高于低频边,大部分神经元的高频边反转斜率(IS_high)减小,且有随掩蔽声时程延长而程度增强的趋势（p<0.01）;而低频边反转斜率(IS_low)则未观察到有规律的变化。另外,还观察到掩蔽声可使IC神经元对探测声反应的最小阈值（minimum threshold,MT）升高,且其幅度随掩蔽声时程的延长而增大（p<0.001,n=31）。2.为了探讨弱噪声前掩蔽对神经元频率调谐的作用机制,在记录过程中,向受噪声抑制的神经元电泳导入γ-氨基丁酸（γ-aminobutyric acid,GABA）能受体拮抗剂荷包牡丹碱（bicuculline,BIC）,发现神经元FTC拓宽,再加入弱噪声后锐化的程度下降或弱噪声所致的前掩蔽效应完全被取消,在给40 ms弱噪声前掩蔽声刺激时,Q₁₀%(percent Q₁₀ value,Q₁₀%)由导入BIC前的26.15±18.52%降至13.21±8.85%,Q₃₀%从39.85±24.27%降至17.89±13.78%;给80 ms弱噪声前掩蔽声刺激时,Q₁₀%从导入BIC前33.57±16.24%降至15.62±7.51%,Q₃₀%从52.64±23.61%降至26.98±12.77%。可见去GABA能抑制可部分或完全解除弱噪声引起的前掩蔽效应。3.蝙蝠作为一种主动生物声纳动物,借助听自己发声信号的回声来感知周围环境,其听中枢内的神经元必须具备处理脉冲-回声对（pulse-echo pair,P-E pair）的能力。对蝙蝠IC神经元做不同脉冲-回声对刺激模式下的恢复周期（recovery cycle,RC）测定时,发现在等频率和等强度条件下,神经元的RC随声刺激时程延长而延长（one-way ANOVA,p<0.05）;当模拟发声脉冲强度大于模拟回声强度10 dB（即强度差为10 dB）时,神经元的RC也随声刺激时程延长而延长,且趋势更加明显（one-way ANOVA,p<0.01）;强度差为20 dB时,IC神经元的RC不再随声刺激时程延长而变化（one-way ANOVA,p>0.05）。可见声刺激时程和强度的改变可影响IC神经元的RC,且声刺激强度和时程之间存在相互关联,由此推测,声刺激时程和强度的同时改变可能对听中枢神经元处理P-E信息的有重要影响。4.声刺激时程既是声信号的基本参数,也是听中枢神经元所要提取的声信息之一。为进一步分析声刺激时程与强度对神经元RC的影响,在最佳时程下匹配P-E之间的强度差,发现最佳时程在1-2 ms的时程选择性神经元,在强度差为10 dB时,对1.5 ms声刺激RC最短;最佳时程在4-6 ms的神经元,在强度差分别为10 dB和20 dB时,对4 ms声刺激RC较短;最佳时程在8-20 ms的神经元,在强度差为20dB时,对10 ms声刺激RC最短。这些结果提示,不同IC神经元具有不同最佳反应时程的特性,适应了蝙蝠在不同捕食时相接受不同重复率回声和不同时程回声的需要,并通过时相整合和神经调制来更好地处理回声信息,对靶物进行精确地定位。更多还原

【Abstract】 Using the excellular recording method under free field stimulation condition,we studied the response property of 289 inferior colliculus neurons of mouse（Mus musculus Km）、and bats（Pipistrellus abramus） to different sound stimulus pattern.We measured the forward masking,recovery cycle,frequency tuning of IC neurons.The obtained results are summarized as following:1.The forward masking induced by weak noise（masker） could sharpen frequency tuning curves（FTC） of most IC neurons（P<0.01,n=25） in mouse and this effect increased with masker duration increasing（P<0.05）.By calculating the inverse-slope（IS） of both limbs on FTC,we found the inhibitory rate caused by forward masking to high limb of FTC was notably higher than low limb of FTC.Most IShigh of FTC was decreased with masker duration increasing（P<0.01）,however,there was no a regular change in IS_low of FTC.The masker could also increase the minimum threshold（MT） of response to probe sound in IC neurons（P<0.001,n=31） and this threshold up-shift was elevated with masker duration increasing.2.After BIC application to 33 IC neurons by ionophoresis,the neural inhibition induced by 40-ms masker（weak noise） was decreased or compltely cancelled and the percent change of Q₁₀ and Q₃₀ of FTCs decreased from 26.15±18.52%to 13.21±8.85% and 39.85±24.27%to 17.89±13.78%,respectively.Under the 80-ms masker stimulation condition,BIC application caused the percent change of Q₁₀ and Q₃₀ decreasing from 33.57±16.24%to 15.62±7.51%and 52.64±23.61%to 26.98±12.77%,respectively.These results showed that GABAergic disinhibition by BIC application could partly or compeletly remove the masking caused by masker（weak noise）.3.During hunting,the insectivorous bats can analyze echo of their emitted sound signal and extrac information from echo,which is used to guide their prey.Therefore,the neurons in brain of bats must have an ability to generate the response to the pulse-echo （P-E） pairs.By delivering P-E pairs at three amplitude differences and three durations, we examined the recovery cycle of bat’s IC neurons under each amplitude difference and three duration conditions.Nine recovery cycles were plotted for each neuron.The recovery cycle of these IC neurons prolonged with the duration increasing at the amplitude difference of 0 dB（one-way ANOVA,p<0.05） and 10 dB（one-way ANOVA,p<0.01）,but this phenomenon was not observed at the amplitude difference of 20 dB（one-way ANOVA,p>0.05）.These results demonstrated that the duration of P-E pairs and amplitude difference between P-E pairs could affect the recovery cycle of IC neurons and there was a correlation between the duration and amplitude difference.4.The sound duration was both a basic sound parameter and one kind of the sound information to be extracted by central auditory neurons.In order to further analyze effect of sound duration and amplitude of P-E pairs on the recovery cycle of IC neurons,we examined that IC neurons having the best duration of 1-2 ms had the shortest recovery cycle at amplitude difference of 10 dB under P-E pair stimulation condition with 1.5-ms duration.The IC neurons having the best duration of 4-6 ms had the shortest recovery cycle at the amplitude differences of 10 and 20 dB under P-E pair stimulation condition with 4-ms duration.The IC neurons having the best duration of 8-20 ms had the shortest recovery cycle at the amplitude differences of 20 dB under P-E pair stimulation condition with 10-ms duration.These results suggested that the different IC neurons had the different best duration and the duration selectivity of IC neurons could modulate their recovery cycles,which fitted to accept the echo of different repetition rate and duration and process echo information through temporal integration and neural modulation.更多还原