Sakamoto T, Atsuta Y, Mori S
J Neurophysiol. 1986 Mar;55(3):449-68. doi: 10.1152/jn.1986.55.3.449.
Stimulation of the dorsal portion of the caudal tegmental field (DTF) in the pons resulted in hyperpolarization of extensor alpha-motoneurons (alpha-MNs) that persisted for several minutes after cessation of the stimulation. The resulting inhibition of alpha-MN discharge led to a progressive reduction in the number of active motor units. Renshaw cells, persistently active at high levels of extensor muscle tone, were abruptly silenced by DTF stimulation. Active discharge was renewed at the time of cessation of the stimulation but at a frequency reduced in proportion to the persistently lowered level of extensor muscle tone. Ia primary afferents were tonically active during the high extensor tonus of reflex standing. DTF stimulation was accompanied by a brief, slight increase in Ia discharge frequency followed by a reduction in frequency variably correlated to the magnitude of extensor force reduction. Orthodromically elicited Ia EPSPs in the soleus alpha-MNs were reduced in peak voltage, time to peak, and half width during the hyperpolarization accompanying DTF stimulation. All of these parameters recovered beyond their prestimulus values with the cessation of DTF stimulation in spite of the persisting hyperpolarization. Antidromically initiated invasion of the somatodendritic (SD) segment of the motoneuron membrane was delayed and sometimes blocked during DTF stimulation. At the same time, the peak voltage of the SD action potential was reduced. There was an immediate recovery of these changes on termination of DTF stimulation, although the poststimulus hyperpolarization persisted. Intracellular injection of depolarizing current steps during DTF stimulation revealed a depression of membrane excitability that persisted during the hyperpolarization that followed the termination of the DTF stimulation. Depolarizing and hyperpolarizing steps of intracellular current were used to demonstrate a reduction of cellular input resistance during DTF stimulation. The resistance values rapidly returned to prestimulus levels following the cessation of DTF stimulation. It was demonstrated that the degree of resistance change is greater and that the magnitude of DTF-induced hyperpolarization is smaller for low-resistance cells than for high-resistance cells. Iontophoretically induced increase in intracellular Cl- resulted in a reversal of both Ia IPSPs and the hyperpolarization induced by DTF stimulation. The hyperpolarization enduring after DTF stimulation was not affected by the Cl- injection.
刺激脑桥尾侧被盖区（DTF）的背侧部分会导致伸肌α运动神经元（α-MNs）超极化，这种超极化在刺激停止后会持续几分钟。由此对α-MN放电的抑制导致活跃运动单位数量逐渐减少。在伸肌肌张力处于高水平时持续活跃的闰绍细胞，会因DTF刺激而突然沉默。在刺激停止时，活跃放电恢复，但频率与伸肌肌张力持续降低的水平成比例下降。在反射性站立的高伸肌紧张状态下，Ia类初级传入纤维呈紧张性活动。DTF刺激伴随着Ia放电频率短暂、轻微增加，随后频率降低，其降低程度与伸肌力量降低幅度存在不同程度的相关性。在DTF刺激引起的超极化期间，比目鱼肌α-MNs中顺向引发的Ia兴奋性突触后电位（EPSPs）在峰值电压、峰值时间和半宽度上均降低。尽管超极化持续存在，但随着DTF刺激停止，所有这些参数都恢复到刺激前的值以上。在DTF刺激期间，由逆向引发的运动神经元膜体树突（SD）段的侵入延迟，有时会被阻断。同时，SD动作电位的峰值电压降低。尽管刺激后超极化持续存在，但在DTF刺激终止时，这些变化立即恢复。在DTF刺激期间进行细胞内注入去极化电流阶跃，显示膜兴奋性降低，这种降低在DTF刺激终止后的超极化期间持续存在。利用细胞内电流的去极化和超极化阶跃来证明在DTF刺激期间细胞输入电阻降低。刺激停止后，电阻值迅速恢复到刺激前水平。结果表明，低电阻细胞的电阻变化程度更大，而DTF诱导的超极化幅度比高电阻细胞小。离子电渗法诱导细胞内Cl-增加导致Ia抑制性突触后电位（IPSPs）和DTF刺激诱导的超极化均发生逆转。DTF刺激后持续的超极化不受Cl-注入的影响。
