Zhou Q, Godwin D W, O'Malley D M, Adams P R
Department of Neurobiology and Behavior, State University of New York at Stony Brook, 11794-5230, USA.
J Neurophysiol. 1997 May;77(5):2816-25. doi: 10.1152/jn.1997.77.5.2816.
Thalamic neurons have two firing modes: "tonic" and "burst." During burst mode, both low-threshold (LT) and high-threshold (HT) calcium channels are activated, while in tonic mode, only the HT-type of calcium channel is activated. The calcium signals associated with each firing mode were investigated in rat thalamic slices using whole cell patch clamping and confocal calcium imaging. Action potentials were induced by direct current injection into thalamic relay cells loaded with a fluorescent calcium indicator. In both tonic and burst firing modes, large calcium signals were recorded throughout the soma and proximal dendrites. To map the distribution of the channels mediating these calcium fluxes, LT and HT currents were independently activated using specific voltage-clamp protocols. We focused on the proximal region of the cell (up to 50 microm from the soma) because it appeared to be well clamped. For a voltage pulse of a given size, the largest calcium signals were observed in the proximal dendrites with smaller signals occurring in the soma and nucleus. This was true for both LT and HT signals. Rapid imaging, using one-dimensional linescans, was used to more precisely localize the calcium influx. For both LT and HT channels, calcium influx occurred simultaneously throughout all imaged regions including the soma and proximal dendrites. The presence of sizable calcium signals in the dendrites, soma, and nucleus during both firing modes, and the presence of LT calcium channels in the proximal dendrite where sensory afferents synapse, have implications for both the electrical functioning of relay cells and the transmission of sensory information to cortex.
“紧张性”和“爆发性”。在爆发性模式下，低阈值（LT）和高阈值（HT）钙通道均被激活，而在紧张性模式下，仅HT型钙通道被激活。利用全细胞膜片钳技术和共聚焦钙成像技术，在大鼠丘脑切片中研究了与每种放电模式相关的钙信号。通过向加载了荧光钙指示剂的丘脑中继细胞注入直流电来诱发动作电位。在紧张性和爆发性放电模式下，在整个胞体和近端树突中均记录到了大的钙信号。为了绘制介导这些钙通量的通道分布，使用特定的电压钳制方案分别激活LT和HT电流。我们聚焦于细胞的近端区域（距胞体50微米以内），因为该区域似乎被良好钳制。对于给定大小的电压脉冲，在近端树突中观察到最大的钙信号，而在胞体和细胞核中观察到较小的信号。LT和HT信号均如此。使用一维线扫描进行快速成像，以更精确地定位钙内流。对于LT和HT通道，钙内流在包括胞体和近端树突在内的所有成像区域同时发生。在两种放电模式下，树突、胞体和细胞核中均存在相当大的钙信号，以及感觉传入神经突触所在的近端树突中存在LT钙通道，这对中继细胞的电功能以及感觉信息向皮层的传递均有影响。
