Feature extraction of auditory information

声频沿耳蜗拓扑编码，每个ANF都有其特征频率。声强和时间信息被编码为一系列动作电位。在鸟类耳蜗核中，提取时间信息的途径从Ncl开始。大细胞炎（NM）和Ncl的强度信息。活动(NA)。我们比较了这两个核的突触传递性质和突触后膜兴奋性，发现了目标特异性分化。NM的膜兴奋性表现为低阈值电压激活K+电导（LT）和高阈值电压激活K+电导（HT）的同时存在。NM神经元在突触输入脉冲开始或电流注入开始时产生单个动作电位。NA神经元的特征是对电流注入或突触输入的爆发有规律地产生尖峰。这些神经元没有ltk +电流，但有大量的HT K+电流和Ca2+激活的K+电流。Ca2+激活的K+电流的活性降低了突发放电的频率。在一系列突触输入后，NM神经元EPSC的大小明显下降，NA神经元EPSC的大小则有中度下降。在不同时间间隔施加一对刺激，可使中脑EPSC分两个阶段下降。由于突触后AMPA受体的脱敏，第一阶段是CTZ敏感的，第二阶段是CTZ抗性的。在NA中，正常2mM Ca2+浓度下的CTZ对EPSC没有影响，但在5 mM Ca2+ CTZ下，EPSC的大小增加，衰变动力学延长。这可能表明更多的递质从突触前末端释放到NM由于更多的Ca2+内流比NA。NM只形成少量的突触前末端，称为Held的端球，而NA则形成大量的小钮扣型末端。因此，突触前终末和突触后神经元在形态和功能上都可能是特异性分化的目标。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