Haedo Rodolfo J, Golowasch Jorge
Department of Biological Sciences, Rutgers University, New Jersey, USA.
J Neurophysiol. 2006 Oct;96(4):1860-76. doi: 10.1152/jn.00385.2006. Epub 2006 Jun 28.
Neurons exhibit long-term excitability changes necessary for maintaining proper cell and network activity in response to various inputs and perturbations. For instance, the adult crustacean pyloric network can spontaneously recover rhythmic activity after complete shutdown resulting from permanent removal of neuromodulatory inputs. Dissociated lobster stomatogastric ganglion (STG) neurons have been shown to spontaneously develop oscillatory activity via excitability changes. Rhythmic electrical stimulation can eliminate these oscillatory patterns in some cells. The ionic mechanisms underlying these changes are only partially understood. We used dissociated crab STG neurons to study the ionic mechanisms underlying spontaneous recovery of rhythmic activity and stimulation-induced activity changes. Similar to lobster neurons, rhythmic activity spontaneously develops in crab STG neurons. Rhythmic hyperpolarizing stimulation can eliminate, but more commonly accelerate, the emergence of stable oscillatory activity depending on Ca(2+) influx at hyperpolarized voltages. Our main finding is that upregulation of a Ca(2+) current and downregulation of a high-threshold K(+) current underlies the spontaneous homeostatic development of oscillatory activity. However, because of a nonlinear dependence on stimulus frequency, hyperpolarization-induced oscillations appear to be inconsistent with a homeostatic regulation of activity. We find no difference in the activity patterns or the underlying ionic currents involved between neurons of the fast pyloric and the slow gastric mill networks during the first 10 days in isolation. Dynamic-clamp experiments confirm that these conductance modifications can explain the observed activity changes. We conclude that spontaneous and stimulation-induced excitability changes in STG neurons can both result in intrinsic oscillatory activity via regulation of the same two conductances.
神经元表现出长期的兴奋性变化,这对于响应各种输入和扰动来维持适当的细胞和网络活动是必要的。例如,成年甲壳类动物的幽门网络在因永久性去除神经调节输入而完全关闭后,能够自发恢复节律性活动。已证明离体的龙虾口胃神经节(STG)神经元可通过兴奋性变化自发产生振荡活动。节律性电刺激可消除某些细胞中的这些振荡模式。这些变化背后的离子机制仅得到部分理解。我们使用离体的蟹STG神经元来研究节律性活动自发恢复和刺激诱导的活动变化背后的离子机制。与龙虾神经元类似,蟹STG神经元中也会自发产生节律性活动。节律性超极化刺激可以消除,但更常见的是加速稳定振荡活动的出现,这取决于超极化电压下的Ca(2+)内流。我们的主要发现是,Ca(2+)电流的上调和高阈值K(+)电流的下调是振荡活动自发稳态发展的基础。然而,由于对刺激频率的非线性依赖性,超极化诱导的振荡似乎与活动的稳态调节不一致。我们发现在隔离培养的前10天内,快速幽门网络和慢速胃磨网络的神经元在活动模式或所涉及的潜在离子电流方面没有差异。动态钳实验证实,这些电导修饰可以解释观察到的活动变化。我们得出结论,STG神经元中自发和刺激诱导的兴奋性变化都可以通过调节相同的两种电导导致内在振荡活动。