昆明小鼠下丘神经元对调频声的反应

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情况却未见报道。本研究在自由声场条件下,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%)。与Ⅲ型神经元相比,Ⅰ型神经元具有较低的CF和Q20dB(P<0.05和P<0.001)和较高的RB20dB(P<0.05)。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,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地分布在10kHz-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势(45.8%vs41.7%vs33.3%)。上述结果提示,昆明小鼠下丘神经元能有效处理调频声刺激,且具有方向选择性的调频声在昆明小鼠的声通讯中占有重要地位。

Responses of inferior collicular neurons to frequency-modulated sweeps in the Kunming mouse

Very few studies have been performed on the inferior colliculus (IC) by using frequency modulated (FM) stimulus though its acoustical response properties have been investigated by using pure tone in the Kunming mouse (Mus musculus, Km). In the present paper, the responses of IC neurons to FM stimulus in the free-field conditions were examined. The main results were as follow: 1) according to the difference in the MT for pure tone and FM stimuli, the 99 IC neurons recorded were classified into three types; type Ⅰ neurons (57/99, 57.58%) were characterized by the lower MTs for the FM stimuli than for pure tone stimuli, while type Ⅲ neurons (30/99, 30.30%) were characterized by the lower MTs for the pure tone stimuli; a small fraction of neurons (type Ⅱ,12/99, 12.12%) exhibited no change of the MT when both types of stimuli were presented; 2) comparison of type A with type C neurons, we found that the former had lower characteristics frequencies (CFs) and Q20dB (P＜0.05 and P＜0.001, respectively) but higher frequency response bandwidth at 20 dB above the MT (RB20dB, P＜0.05); 3) 36 IC neurons (36/99, 36.36%) were direction selective and among them 61.11% (22/36) were up-selective and 38.89% (14/36) were down-selective neurons; up-selective neurons had a wider distribution across type Ⅰ, Ⅱ, and Ⅲ neurons than down-selective neurons; 4)the CFs of type Ⅰ and direction selective neurons had densest distribution over the range of 10 kHz-20 kHz (77.19% and 83.33%, respectively); 5) among the 24 recorded neurons responding to 3 different modulation rates, most of them (15/24, 62.50%) were more sensitive to rapid FM stimuli; the proportion of the direction selective neurons decreased with the increasing modulation rates (45.83% vs 41.77% vs 33.33%). Our data suggest that IC neurons of Km mouse could process FM stimuli effectively. FM sounds may play a significant role in acoustic communication in the Km mouse.