Golding N L, Robertson D, Oertel D
Department of Neurophysiology, University of Wisconsin, Madison 53706, USA.
J Neurosci. 1995 Apr;15(4):3138-53. doi: 10.1523/JNEUROSCI.15-04-03138.1995.
Acoustic information in auditory nerve discharges is integrated in the cochlear nuclei, and ascends through several parallel pathways to higher centers. Octopus cells of the posteroventral cochlear nucleus form a pathway known to carry information in the timing of action potentials. Octopus cells have dendrites oriented to receive converging input from many auditory nerve fibers. In all 34 intracellular recordings from anatomically identified octopus cells in slices, shocks to the auditory nerve evoked brief, consistent, graded EPSPs. EPSPs were about 1 msec in duration. At all but the lowest shock strengths, the delays between shocks and the peaks of resultant EPSPs had SDs of 0.02 msec. Polysynaptic excitation, perhaps arising from the axon collaterals of octopus cells, was observed. No detectable glycinergic or GABAergic inhibition was evoked with shocks. The input resistances were low, around 10 M omega, voltage changes were rapid, with time constants of about 1 msec, and action potentials were small. The low input resistance resulted in part from a Cs(+)-sensitive conductance. In the presence of 10 or 15 mM extracellular Cs+ the time constants increased 20-fold in the hyperpolarizing voltage range. As several subthreshold inputs were required to produce suprathreshold responses, octopus cells detect the coincident firing of auditory nerve fibers. Under physiological conditions the low input resistance and resulting short time constant limit the time over which temporal summation of excitation from auditory nerve fibers can occur and thus provide temporal precision to electrical signaling.
听神经放电中的声学信息在耳蜗核中整合，并通过几条平行通路向上传递至更高的中枢。后腹侧耳蜗核的章鱼细胞形成了一条已知的在动作电位时间上携带信息的通路。章鱼细胞的树突定向排列，以接收来自许多听神经纤维的汇聚输入。在切片中对34个经解剖学鉴定的章鱼细胞进行的细胞内记录中，对听神经的电刺激诱发了短暂、一致、分级的兴奋性突触后电位（EPSP）。EPSP的持续时间约为1毫秒。除了最低的刺激强度外，刺激与由此产生的EPSP峰值之间的延迟标准差为0.02毫秒。观察到多突触兴奋，可能源于章鱼细胞的轴突侧支。电刺激未诱发可检测到的甘氨酸能或γ-氨基丁酸能抑制。输入电阻较低，约为10兆欧，电压变化迅速，时间常数约为1毫秒，动作电位较小。低输入电阻部分是由对铯（Cs⁺）敏感的电导导致的。在细胞外存在10或15毫摩尔铯离子的情况下，在超极化电压范围内时间常数增加了20倍。由于需要几个阈下输入才能产生阈上反应，章鱼细胞能够检测听神经纤维的同步放电。在生理条件下，低输入电阻和由此产生的短时间常数限制了听神经纤维兴奋的时间总和能够发生的时间，从而为电信号传导提供了时间精度。
