Blackwell Kim T, Czubayko Uwe, Plenz Dietmar
Krasnow Institute of Advanced Studies and School of Computational Sciences, George Mason University, Fairfax, Virginia 22030, USA.
J Neurosci. 2003 Oct 8;23(27):9123-32. doi: 10.1523/JNEUROSCI.23-27-09123.2003.
Up states are prolonged membrane potential depolarizations critical for synaptic integration and action potential generation in cortical and striatal neurons. They commonly result from numerous concurrent synaptic inputs, whereas neurons reside in a down state when synaptic inputs are few. By quantifying the composition, frequency, and amplitude of synaptic inputs for both states, we provide important constraints for state transitions in striatal network dynamics. Up and down states occur naturally in cortex-striatum-substantia nigra cocultures, which were used as an in vitro model in the present study. Spontaneous synaptic inputs during down states were extracted automatically in spiny projection neurons and fast spiking interneurons of the striatum using a newly developed computer algorithm. Consistent with a heterogeneous population of synaptic inputs, PSPs and PSCs showed no correlation in amplitude and rise time and occurred at relatively low frequencies of 10-40 Hz during the down state. The number of synaptic inputs during up states, estimated from the up-state charge and the unitary charge of down-state PSCs, was 217 +/- 44. Given the average up-state duration of 284 +/- 34 msec, synaptic input frequency was approximately 800 Hz during up-states for both neuronal types. Many down-state events reversed at the chloride reversal potential and were blocked by GABA(A) antagonists. The high correlation between up- and down-state reversal potential suggests that despite these drastic changes in synaptic input frequency, the ratio of inhibitory to excitatory currents is similar during both states.
去极化状态是膜电位的延长去极化，对皮质和纹状体神经元的突触整合和动作电位产生至关重要。它们通常由大量同时发生的突触输入引起，而当突触输入很少时神经元处于超极化状态。通过量化两种状态下突触输入的组成、频率和幅度，我们为纹状体网络动力学中的状态转换提供了重要的限制条件。去极化和超极化状态在皮质-纹状体-黑质共培养物中自然发生，在本研究中被用作体外模型。使用新开发的计算机算法，在纹状体的棘状投射神经元和快速发放中间神经元中自动提取超极化状态下的自发突触输入。与异质性的突触输入群体一致，在超极化状态下，兴奋性突触后电位（PSP）和兴奋性突触后电流（PSC）在幅度和上升时间上没有相关性，并且以相对较低的10 - 40 Hz频率发生。根据超极化状态下的电荷和超极化状态下PSC的单位电荷估计，去极化状态下的突触输入数量为217±44。考虑到去极化状态的平均持续时间为284±34毫秒，两种神经元类型在去极化状态下的突触输入频率约为800 Hz。许多超极化状态下的事件在氯离子反转电位处反转，并被GABA(A)拮抗剂阻断。去极化和超极化状态反转电位之间的高度相关性表明，尽管突触输入频率发生了这些剧烈变化，但两种状态下抑制性电流与兴奋性电流的比率相似。
