Feature extraction of auditory information

声音频率在耳蜗中沿着音调谱沿着编码，并且每个ANF具有特征频率。声音强度和时间信息被编码为动作电位序列。在鸟类耳蜗核中，提取时间信息的通路始于Ncl。大细胞（NM）和角神经（NA）的强度信息。我们比较了这两个核团的突触传递和突触后膜兴奋性的性质，发现了靶点特异性分化。NM的膜兴奋性表现为同时存在低阈值电压激活的K+电导（LT）和高阈值电压激活的K+电导（HT）。NM神经元在突触输入突发的开始或电流注入开始时产生单个动作电位。NA中的神经元的特征在于响应于电流注入或突触输入的突发而产生规则的尖峰。这些神经元没有LT.K+电流， ...更多信息 HT K+电流和Ca ~（2+）激活的K+电流均不明显。钙激活钾电流的活动降低了爆发放电的频率。当一系列突触输入时，NM神经元EPSC的大小显著降低，NA神经元EPSC的大小则中度降低。在不同的时间间隔内施加一对刺激，可使NM EPSC出现两个时相的抑制。第一个相是CTZ敏感的，因此是由于突触后AMPA受体的脱敏，而第二个较慢的相是CTZ抵抗的。在正常的2 mM Ca ~（2+）浓度下，CTZ对NA的EPSC无影响，而在5 mM Ca ~（2+）浓度下，CTZ使EPSC增大，衰减动力学延长，这可能表明突触前终末释放到NM的递质比NA的多，这是由于NM的Ca ~（2+）内流比NA的大。而在NA中，形成了大量的小的钮扣型端子。因此，突触前终末和突触后神经元在形态和功能上可能是特异性分化的靶点。少

Sound frequency is coded along the tonotopy in the cochlea, and each ANF has the characteristic frequency. Sound intensity and timing information are coded as a sequence of action potentials. In the avian cochlear nucleus the pathway to extract temporal information starts at Ncl. Magnocellularis (NM) and intensity information at Ncl.Angularis (NA). We have compared the nature of synaptic transmission and postsynaptic membrane excitability in these two nuclei and found target specific differentiation. The membrane excitability of NM is characterized by the presence of both the low threshold voltage activated K+ conductance (LT) and high threshold voltage activated K+ conductance (HT). NM neuron generates a single action potential at the onset of a burst of synaptic inputs or at the beginning of current injection. The neuron in NA is characterized by a regular spike generation in response to current injection or to the burst of synaptic inputs. These neurons do not have LT.K+ currents bu … More t have large quantity of HT K+ currents and Ca2+ activated K+ currents . The frequency of burst firing was reduced by the activity of Ca2+ activated K+ currents. When a train of synaptic inputs were made, the EPSC size depressed drastic in NM neuron while the depression was moderate in NA neuron. By applying a pair of stimulus at various intervals, the NM EPSC depressed in two phases. The first phase is CTZ sensitive, therefore due to desensitization of postsynaptic AMPA receptors, and the 2nd slower phase was CTZ resistive. In NA, EPSC was not affected by CTZ at normal 2mM Ca2+ concentration, however at 5 mM Ca2+ CTZ increased the EPSC size and prolonged decay kinetics as in NM.This might indicate larger quantity of transmitter released from the presynaptic terminals to NM due to larger Ca2+ influx there than to NA.In NM only a few presynaptic terminals are made and they are known as end bulbs of Held, while in NA a large number of small bouton type terminals are formed. Therefore, presynapitc terminals and postsynaptic neurons are likely differentiated target specifically both in morphology and in function. Less