Stoelzel Carl R, Bereshpolova Yulia, Gusev Alexander G, Swadlow Harvey A
Department of Psychology, University of Connecticut, Storrs, Connecticut 06269, USA.
J Neurosci. 2008 May 7;28(19):5018-28. doi: 10.1523/JNEUROSCI.4726-07.2008.
We used spike-triggered current source-density analysis to examine axonal and postsynaptic currents generated in the visual cortex of awake rabbits by spontaneous spikes of individual sustained and transient dorsal lateral geniculate nucleus (LGNd) neurons. Using these data, we asked whether sustained/transient sensory responses are related to short-term synaptic dynamics at the thalamocortical synapse. Most sustained (34 of 40) and transient (24 of 25) neurons generated axonal and monosynaptic responses in layer 4 and/or 6 of the aligned cortical domain, with input from transient neurons arriving approximately 0.3 ms earlier and 100-200 microm deeper. Postsynaptic cortical responses generated by both thalamic cell classes were reduced in amplitude after a preceding impulse and slowly recovered over a period of >750 ms. We interpret this to reflect interval-dependent recovery from chronic depression at the thalamocortical synapse, caused by significant spontaneous firing of LGNd cells (approximately 8 Hz). Surprisingly, postsynaptic cortical responses generated by spontaneous spikes of sustained thalamic neurons were more depressed than those of transient neurons. This difference was seen both in layers 4 and 6. The depression saturated rapidly with multiple preceding impulses, and postsynaptic responses generated by sustained neurons during maintained visual stimulation remained sufficiently robust to allow a sustained flow of information to the cortex. Our results indicate a relationship between the sensory response properties of thalamic neurons and the short-term dynamics of their synapses, and suggest that cortical recipients of sustained and transient thalamic inputs will differ considerably in their response modulation by prior impulse activity.
我们使用锋电位触发的电流源密度分析，来检测清醒兔视觉皮层中由单个持续性和瞬态性背外侧膝状核（LGNd）神经元的自发放电所产生的轴突电流和突触后电流。利用这些数据，我们探究持续性/瞬态性感觉反应是否与丘脑皮质突触处的短期突触动力学有关。大多数持续性神经元（40个中的34个）和瞬态性神经元（25个中的24个）在对齐的皮质区域的第4层和/或第6层中产生轴突和单突触反应，瞬态性神经元的输入比持续性神经元早约0.3毫秒到达，且深入100 - 200微米。两种丘脑细胞类型所产生的突触后皮质反应在之前的冲动后幅度降低，并在超过750毫秒的时间内缓慢恢复。我们认为这反映了丘脑皮质突触处由LGNd细胞显著的自发放电（约8赫兹）导致的慢性抑制的间隔依赖性恢复。令人惊讶的是，持续性丘脑神经元的自发放电所产生的突触后皮质反应比瞬态性神经元的更受抑制。这种差异在第4层和第6层中均可见。这种抑制在多个先前冲动作用下迅速饱和，并且在持续视觉刺激期间持续性神经元所产生的突触后反应仍足够强劲，以允许信息持续流向皮层。我们的结果表明丘脑神经元的感觉反应特性与其突触的短期动力学之间存在关联，并表明持续性和瞬态性丘脑输入的皮质接收者在其对先前冲动活动的反应调制方面将有很大差异。
