Rigas Pavlos, Castro-Alamancos Manuel A
Department of Neurobiology, Drexel University College of Medicine, 2900 Queen Ln., Philadelphia, PA 19129, USA.
J Neurophysiol. 2009 Jul;102(1):119-31. doi: 10.1152/jn.00126.2009. Epub 2009 Apr 29.
The neocortex generates short epochs of persistent activity called up states, which are associated with changes in cellular and network excitability. Using somatosensory thalamocortical slices, we studied the impact of persistent cortical activity during spontaneous up states on intrinsic cellular excitability (input resistance) and on excitatory synaptic inputs of cortical cells. At the intrinsic excitability level, we found that the expected decrease in input resistance (high conductance) resulting from synaptic barrages during up states is counteracted by an increase in input resistance due to depolarization per se. The result is a variable but on average relatively small reduction in input resistance during up states. At the synaptic level, up states enhanced a late synaptic component of short-latency thalamocortical field potential responses but suppressed intracortical field potential responses. The thalamocortical enhancement did not reflect an increase in synaptic strength, as determined by measuring the evoked postsynaptic current, but instead an increase in evoked action potential (spike) probability due to depolarization during up states. In contrast, the intracortical suppression was associated with a reduction in synaptic strength, apparently driven by increased presynaptic intracortical activity during up states. In addition, intracortical suppression also reflected a reduction in evoked spike latency caused by depolarization and the abolishment of longer-latency spikes caused by stronger inhibitory drive during up states. In conclusion, depolarization during up states increases the success of excitatory synaptic inputs to reach firing. However, activity-dependent synaptic depression caused by increased presynaptic firing during up states and the enhancement of evoked inhibitory drive caused by depolarization suppress excitatory intracortical synaptic inputs.
新皮层会产生被称为“上行状态”的短暂持续性活动时期，这与细胞和网络兴奋性的变化有关。我们使用体感丘脑皮质切片，研究了自发上行状态期间持续性皮质活动对皮质细胞内在细胞兴奋性（输入电阻）和兴奋性突触输入的影响。在内在兴奋性水平上，我们发现上行状态期间突触活动引起的预期输入电阻降低（高电导）被去极化本身导致的输入电阻增加所抵消。结果是上行状态期间输入电阻有可变但平均相对较小的降低。在突触水平上，上行状态增强了短潜伏期丘脑皮质场电位反应的晚期突触成分，但抑制了皮质内场电位反应。丘脑皮质增强并不反映突触强度的增加，这是通过测量诱发的突触后电流确定的，而是反映了上行状态期间去极化导致的诱发动作电位（尖峰）概率增加。相比之下，皮质内抑制与突触强度降低有关，这显然是由上行状态期间突触前皮质内活动增加驱动的。此外，皮质内抑制还反映了去极化导致的诱发尖峰潜伏期缩短以及上行状态期间更强抑制驱动导致的长潜伏期尖峰消失。总之，上行状态期间的去极化增加了兴奋性突触输入达到放电的成功率。然而，上行状态期间突触前放电增加导致的活动依赖性突触抑制以及去极化导致的诱发抑制驱动增强抑制了皮质内兴奋性突触输入。
