Department of Neuroscience, Johns Hopkins University, Baltimore, MD 21218, United States.
Neurosci Lett. 2011 Jul 12;498(3):179-84. doi: 10.1016/j.neulet.2011.02.051. Epub 2011 Mar 6.
The anterodorsal nucleus of the thalamus contains a high percentage of head-direction cells whose activities are correlated with an animal's directional heading in the horizontal plane. The firing of head-direction cells could involve self-sustaining reverberating activity in a recurrent network, but the thalamus by itself lacks strong excitatory recurrent synaptic connections to sustain tonic reverberating activity. Here we examined whether a single thalamic neuron could sustain its own activity without synaptic input by recording from individual neurons from anterodorsal thalamus in brain slices with synaptic blockers. We found that the rebound firing induced by hyperpolarizing pulses often decayed slowly so that a thalamic neuron could keep on firing for many minutes after stimulation. The hyperpolarization-induced persistent firing rate was graded under repeated current injections, and could be enhanced by serotonin. The effect of depolarizing pulses was much weaker and only slightly accelerated the decay of the hyperpolarization-induced persistent firing. Our finding provides the first direct evidence for single-cell persistent activity in the thalamus, supporting the notion that cellular mechanisms at the slow time scale of minutes might potentially contribute to the operations of the head-direction system.
丘脑的前背核包含了很大比例的头方向细胞，这些细胞的活动与动物在水平面上的方向朝向相关。头方向细胞的放电可能涉及到在一个递归网络中自我维持的回响活动，但丘脑本身缺乏强的兴奋性递归突触连接来维持紧张的回响活动。在这里，我们通过在含有突触阻断剂的脑片上记录单个前背核神经元，来检查单个丘脑神经元是否可以在没有突触输入的情况下维持自身的活动。我们发现，超极化脉冲诱导的反弹放电常常缓慢衰减，因此在刺激后，一个丘脑神经元可以持续放电数分钟。在重复的电流注入下，超极化诱导的持续放电率是分级的，并且可以被 5-羟色胺增强。去极化脉冲的作用要弱得多，只能稍微加速超极化诱导的持续放电的衰减。我们的发现为丘脑的单细胞持续活动提供了第一个直接证据，支持了这样一种观点，即分钟级慢时间尺度上的细胞机制可能有助于头方向系统的运作。
