Li Jianli, Bickford Martha E, Guido William
Department of Anatomical Sciences and Neurobiology, University of Louisville, Louisville, Kentucky 40292, USA.
J Neurophysiol. 2003 Jul;90(1):291-9. doi: 10.1152/jn.01163.2002. Epub 2003 Mar 12.
It has been proposed that the thalamus is composed of at least two types of nuclei. First-order relay nuclei transmit signals from the periphery to the cortex while higher order nuclei may route information from one cortical area to another. Although much is known about the functional properties of relay neurons in first-order nuclei, little is known about relay neurons belonging to higher-order nuclei. We investigated the electrophysiological properties of relay cells in a higher-order thalamic nucleus using in vitro intracellular recordings from thalamic slices of the rat's lateral posterior nucleus (LPN). We found neurons of the LPN possess many of the same membrane properties as first-order relay neurons. These included low-threshold calcium spikes (IT) and burst firing, a mixed cation conductance (IH) that prevented membrane hyperpolarization, and a transient K+ conductance that delayed spike firing (IA). The repetitive firing characteristics of LPN neurons were more distinct. One group of cells, located in the more caudal regions of the LPN responded to depolarizing current pulses with a train of action potentials or in a regular spiking (RS) mode. This form of firing showed a steep but highly linear increase in firing frequency with increasing levels of membrane depolarization. Another group of cells, located in the more rostral regions of the LPN, responded to depolarizing current pulses with clusters of high-frequency bursts or in a clustered spiking (CS) mode. The overall firing frequency rose nonlinearly with membrane depolarization, but the frequency of a given burst remained relatively constant. The caudal LPN receives input from the superior colliculus, whereas the rostral LPN receives input from layers V and VI of the visual cortex. Thus the RS and CS cells may be driven by subcortical and cortical inputs respectively, and the distinct temporal properties of their response modes may be a necessary component of the LPN circuitry.
有人提出，丘脑至少由两种类型的核组成。一级中继核将信号从外周传递到皮层，而高级核可能将信息从一个皮层区域传递到另一个皮层区域。虽然我们对一级核中中继神经元的功能特性了解很多，但对属于高级核的中继神经元却知之甚少。我们使用大鼠外侧后核（LPN）丘脑切片的体外细胞内记录，研究了高级丘脑核中中继细胞的电生理特性。我们发现LPN的神经元具有许多与一级中继神经元相同的膜特性。这些特性包括低阈值钙尖峰（IT）和爆发式放电、防止膜超极化的混合阳离子电导（IH）以及延迟尖峰放电的瞬时钾电导（IA）。LPN神经元的重复放电特性更为明显。一组位于LPN更靠尾侧区域的细胞，对去极化电流脉冲以一串动作电位或规则发放（RS）模式做出反应。这种放电形式显示，随着膜去极化水平的增加，放电频率呈陡峭但高度线性的增加。另一组位于LPN更靠头侧区域的细胞，对去极化电流脉冲以高频爆发簇或簇状发放（CS）模式做出反应。总体放电频率随着膜去极化呈非线性上升，但给定爆发的频率保持相对恒定。尾侧LPN接收来自上丘的输入，而头侧LPN接收来自视觉皮层V层和VI层的输入。因此，RS细胞和CS细胞可能分别由皮层下和皮层输入驱动，它们不同的时间反应特性可能是LPN神经回路的一个必要组成部分。
