Stern J E, Armstrong W E
Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee, Memphis 38163, USA.
J Neurosci. 1996 Aug 15;16(16):4861-71. doi: 10.1523/JNEUROSCI.16-16-04861.1996.
Magnocellular oxytocin (OT) and vasopressin (VP) neurons adopt different firing patterns in response to relevant physiological stimuli. OT neurons selectively display short (2-4 sec), high-frequency bursts of action potentials that are highly synchronized and correlated with OT release during lactation. The present experiments were done to determine whether the electrophysiological properties of OT neurons differ from those of VP neurons, and whether these properties are modulated during lactation to support short bursting activity. Intracellular recordings in vitro were obtained from immunochemically identified supraoptic neurons of diestrous or lactating female rats. Resting membrane potential, input resistance, membrane time constant, and the depolarizing afterpotential did not differ among groups. However, near spike threshold, OT, but not VP, neurons expressed a sustained outward rectification that was removed by small hyperpolarizing pulses and a rebound depolarization that occurred at the offset of these hyperpolarizing pulses. The rebound depolarization was short ( < 2 sec), supported brief bursts of action potentials, and was significantly larger during lactation. Neurons expressing the outward rectification also exhibited strong spike frequency adaptation during prolonged (1-4 sec) depolarization. Spike width, the Ca(2+)- dependent afterhyperpolarization, and the degree of spike broadening of OT, but not VP, neurons were also larger during lactation, suggesting an increase in Ca2+ influx per spike. The results indicate that OT neurons possess properties favoring the expression of short spike trains, and that some of these properties are enhanced during lactation. In addition, spikes in OT neurons may promote more Ca2+ influx in this state.
大细胞性催产素（OT）和血管加压素（VP）神经元在对相关生理刺激的反应中采用不同的放电模式。OT神经元选择性地表现出短暂（2 - 4秒）、高频的动作电位爆发，这些爆发高度同步，且与哺乳期OT的释放相关。本实验旨在确定OT神经元的电生理特性是否与VP神经元不同，以及这些特性在哺乳期是否被调节以支持短暂的爆发活动。体外细胞内记录取自经免疫化学鉴定的动情间期或哺乳期雌性大鼠的视上核神经元。静息膜电位、输入电阻、膜时间常数和去极化后电位在各组之间没有差异。然而，在接近动作电位阈值时，OT神经元而非VP神经元表现出一种持续外向整流，这种整流可被小的超极化脉冲消除，并且在这些超极化脉冲结束时会出现一个反弹去极化。反弹去极化短暂（< 2秒），支持短暂的动作电位爆发，并且在哺乳期显著更大。表现出外向整流的神经元在长时间（1 - 4秒）去极化期间也表现出强烈的动作电位频率适应性。OT神经元而非VP神经元的动作电位宽度、钙依赖性超极化后电位以及动作电位展宽程度在哺乳期也更大，这表明每个动作电位的钙内流增加。结果表明，OT神经元具有有利于表达短动作电位序列的特性，并且其中一些特性在哺乳期会增强。此外，在这种状态下，OT神经元中的动作电位可能会促进更多的钙内流。
