Zemianek Jill M, Shultz Abraham M, Lee Sangmook, Guaraldi Mary, Yanco Holly A, Shea Thomas B
Center for Cellular Neurobiology & Neurodegeneration Research, Department of Biological Sciences, University of Massachusetts Lowell, 01854, USA.
Int J Dev Neurosci. 2013 Apr;31(2):131-7. doi: 10.1016/j.ijdevneu.2012.11.003. Epub 2012 Dec 3.
A predominance of excitatory activity, with protracted appearance of inhibitory activity, accompanies cortical neuronal development. It is unclear whether or not inhibitory neuronal activity is solicited exclusively by excitatory neurons or whether the transient excitatory activity displayed by developing GABAergic neurons contributes to an excitatory threshold that fosters their conversion to inhibitory activity. We addressed this possibility by culturing murine embryonic neurons on multi-electrode arrays. A wave of individual 0.2-0.4 mV signals ("spikes") appeared between approx. 20-30 days in culture, then declined. A transient wave of high amplitude (>0.5 mV) epileptiform activity coincided with the developmental decline in spikes. Bursts (clusters of ≥3 low-amplitude spikes within 0.7s prior to returning to baseline) persisted following this decline. Addition of the GABAergic antagonist bicuculline initially had no effect on signaling, consistent with delayed development of GABAergic synapses. This was followed by a period in which bicuculline inhibited overall signaling, confirming that GABAergic neurons initially display excitatory activity in ex vivo networks. Following the transient developmental wave of epileptiform signaling, bicuculline induced a resurgence of epileptiform signaling, indicating that GABAergic neurons at this point displayed inhibitory activity. The appearance of transition after the developmental and decline of epileptiform activity, rather than immediately after the developmental decline in lower-amplitude spikes, suggests that the initial excitatory activity of GABAergic neurons contributes to their transition into inhibitory neurons, and that inhibitory GABAergic activity is essential for network development. Prior studies indicate that a minority (25%) of neurons in these cultures were GABAergic, suggesting that inhibitory neurons regulate multiple excitatory neurons. A similar robust increase in signaling following cessation of inhibitory activity in an artificial neural network containing 20% inhibitory neurons supported this conclusion. Even a minor perturbation in GABAergic function may therefore foster initiation and/or amplification of seizure activity, as well as perturbations in long-term potentiation.
在皮质神经元发育过程中，兴奋性活动占主导地位，同时伴有抑制性活动的持续出现。目前尚不清楚抑制性神经元活动是否仅由兴奋性神经元引发，或者发育中的γ-氨基丁酸（GABA）能神经元所表现出的短暂兴奋性活动是否有助于形成一个兴奋性阈值，从而促进它们向抑制性活动的转变。我们通过在多电极阵列上培养小鼠胚胎神经元来探讨这种可能性。在培养约20 - 30天时，出现了一波单个幅度为0.2 - 0.4毫伏的信号（“尖峰”），随后信号强度下降。高幅度（>0.5毫伏）的癫痫样活动的短暂波与尖峰的发育性下降同时出现。在尖峰下降后，爆发（在回到基线之前的0.7秒内≥3个低幅度尖峰的簇）仍然持续存在。添加GABA能拮抗剂荷包牡丹碱最初对信号传导没有影响，这与GABA能突触发育延迟一致。随后有一段时间，荷包牡丹碱抑制了整体信号传导，证实了GABA能神经元在离体网络中最初表现出兴奋性活动。在癫痫样信号的短暂发育波之后，荷包牡丹碱诱导癫痫样信号再次出现，表明此时GABA能神经元表现出抑制性活动。癫痫样活动发育和下降之后出现转变，而不是在低幅度尖峰发育性下降之后立即出现，这表明GABA能神经元的初始兴奋性活动有助于它们向抑制性神经元的转变，并且抑制性GABA能活动对于网络发育至关重要。先前的研究表明，这些培养物中少数（25%）的神经元是GABA能的，这表明抑制性神经元调节多个兴奋性神经元。在一个含有20%抑制性神经元的人工神经网络中，抑制性活动停止后信号传导出现类似的强劲增加，支持了这一结论。因此，即使GABA能功能出现轻微扰动，也可能促进癫痫活动的起始和/或放大，以及对长时程增强的扰动。
