Department of Molecular and Integrative Physiology and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Neuroscience. 2012 Apr 19;208:49-57. doi: 10.1016/j.neuroscience.2012.01.043. Epub 2012 Jan 31.
Studies in the vertebrates have shown that the time-locking ability of central auditory neurons decreases progressively along the ascending auditory pathway. This decrease is presumably attributed to a progressive reduction in the fidelity of synaptic transmission and an increase in the influence of synaptic inhibition along the cascade. The extent to which neurons' intrinsic biophysical properties contribute to the change in time-locking ability is unclear. We carried out whole-cell patch clamp recordings from the auditory thalamus of leopard frogs and compared their biophysical properties and time-locking abilities (determined by cell's responses to depolarizing pulse trains applied intracellularly) with those of lower auditory brainstem neurons. We found that frog thalamic neurons were homogeneous, exhibiting uniformly sustained, regular firing patterns, but not having low-threshold transient Ca2+ current which mammal thalamic neurons generally possess. Furthermore, intrinsic biophysical properties of the thalamic neurons are such that the time-locking ability of these neurons was very poor. The homogeneity of thalamic auditory neurons is in contrast to the heterogeneity of lower auditory brainstem neurons, with different phenotypes exhibiting different time-locking abilities and with sustained-regular phenotype consistently showing the worst time-locking ability among all biophysical phenotypes. Auditory nuclei along the ascending auditory pathway showed a progressive increase in the population of sustained-regular phenotype-this corresponded to a systematic decrease in the overall time-locking ability, with neurons in the dorsal medullary nucleus showing the best, and thalamic neurons exhibiting the poorest time-locking ability, whereas neurons in the torus semicircularis displayed intermediate time-locking ability. These results suggest that the biophysical characteristics of single neurons also likely play a role in the change in temporal coding ability along the ascending auditory pathway.
研究脊椎动物表明，中枢听觉神经元的时间锁定能力沿着听觉通路逐渐下降。这种下降可能归因于突触传递保真度的逐渐降低和沿着级联的突触抑制的影响增加。神经元内在生物物理特性对时间锁定能力变化的贡献程度尚不清楚。我们从豹蛙的听觉丘脑进行全细胞贴片钳记录，并将其生物物理特性和时间锁定能力（通过细胞对施加的去极化脉冲串的反应来确定）与较低的听觉脑干神经元进行比较。我们发现，青蛙丘脑神经元是同质的，表现出均匀持续的规则放电模式，但没有哺乳动物丘脑神经元通常具有的低阈值瞬态 Ca2+电流。此外，丘脑神经元的内在生物物理特性使得这些神经元的时间锁定能力非常差。丘脑听觉神经元的同质性与较低听觉脑干神经元的异质性形成对比，不同表型表现出不同的时间锁定能力，并且持续-规则表型始终表现出所有生物物理表型中最差的时间锁定能力。沿着听觉通路的听觉核显示出持续-规则表型的群体逐渐增加-这与整体时间锁定能力的系统下降相对应，其中背髓核中的神经元表现出最佳的时间锁定能力，而丘脑神经元表现出最差的时间锁定能力，而环丘的神经元表现出中间的时间锁定能力。这些结果表明，单个神经元的生物物理特性也可能在沿听觉通路的时间编码能力变化中起作用。
