Brazhnik E S, Fox S E
Institute of Theoretical and Experimental Biophysics, Russian Academy of Science, Puschino.
Exp Brain Res. 1997 May;114(3):442-53. doi: 10.1007/pl00005653.
The electrophysiological properties of neurons of the medial septal nucleus and the nucleus of the diagnonal band of Broca (MS/DB) were studied using intracellular methods in urethane-anesthetized rats. Three types of rhythmically bursting neurons were identified in vivo on the basis of their action potential shapes and durations, afterhyperpolarizations (AHPs), membrane characteristics, firing rates and sensitivities to the action of muscarinic antagonist: (1) Cells with short-duration action potentials and no AHPs (2 of 34 rhythmic cells, 6%) had high firing rates and extremely reliable bursts with 6-16 spikes per theta cycle, which were highly resistant to scopolamine action. (2) Cells with short-duration action potentials and short-duration AHPs (8 of 34 rhythmic cells, 24%) also had high firing rates and reliable bursts with 4-13 spikes per theta cycle, phase-locked to the negative peak of the dentate theta wave. Hyperpolarizing current injection revealed a brief membrane time constant, time-dependent membrane rectification and a burst of firing at the break. Depolarizing current steps produced high-frequency repetitive trains of action potentials without spike frequency adaptation. The action potential and membrane and characteristics of this cell type are consistent with those described for GABAergic septal neurons. Many of these neurons retained their theta-bursting pattern in the presence of muscarinic antagonist. (3) Cells with long-duration action potentials and long-duration AHPs (24 of 34 rhythmic cells, 70%) had low firing rates, and usually only 1-3 spikes per theta cycle, locked mainly to the positive peak of the dentate theta rhythm. Hyperpolarizing current injection revealed a long membrane time constant and a break potential; a depolarizing pulse caused a train of action potentials with pronounced spike frequency adaptation. The action potential and membrane properties of this cell type are consistent with those reported for cholinergic septal neurons. The theta-related rhythmicity of this cell type was abolished by muscarinic antagonists. The phasic inhibition of "cholinergic" MS/DB neurons by "GABAergic" MS/DB neurons, followed by a rebound of their firing, is proposed as a mechanism contributing to recruitment of the whole MS/DB neuronal population into the synchronized rhythmic bursting pattern of activity that underlies the occurrence of the hippocampal theta rhythm.
采用细胞内记录方法，在乌拉坦麻醉的大鼠上研究了内侧隔核和布罗卡斜角带核（MS/DB）神经元的电生理特性。根据动作电位的形状和时程、超极化后电位（AHPs）、膜特性、放电频率以及对毒蕈碱拮抗剂作用的敏感性，在体鉴定出三种节律性爆发神经元：（1）动作电位时程短且无AHPs的细胞（34个节律性细胞中的2个，占6%），放电频率高，每个θ周期有6 - 16个峰电位，爆发极为可靠，对东莨菪碱作用具有高度抗性。（2）动作电位时程短且AHPs时程短的细胞（34个节律性细胞中的8个，占24%），放电频率也高，每个θ周期有4 - 13个峰电位，与齿状θ波的负峰锁相。注入超极化电流显示膜时间常数短暂、时间依赖性膜整流以及在去极化时爆发放电。注入去极化电流阶跃产生高频重复动作电位序列，无峰频率适应。这种细胞类型的动作电位以及膜特性与已描述的GABA能隔区神经元一致。许多这类神经元在毒蕈碱拮抗剂存在时仍保持其θ爆发模式。（3）动作电位时程长且AHPs时程长的细胞（34个节律性细胞中的24个，占70%），放电频率低，每个θ周期通常只有1 - 3个峰电位，主要与齿状θ节律的正峰锁相。注入超极化电流显示膜时间常数长且有去极化电位；去极化脉冲引起一串有明显峰频率适应的动作电位。这种细胞类型的动作电位和膜特性与已报道的胆碱能隔区神经元一致。这种细胞类型的θ相关节律性被毒蕈碱拮抗剂消除。提出“GABA能”MS/DB神经元对“胆碱能”MS/DB神经元的相位抑制，随后其放电反弹，是促使整个MS/DB神经元群体募集到同步节律性爆发活动模式中的一种机制，该活动模式是海马θ节律产生的基础。
