Fung S J, Barnes C D
Arch Ital Biol. 1987 Jul;125(3):171-86.
The present study was aimed at determining if inputs from the locus coeruleus (LC) have any effect on repetitive firing of ventral horn motoneurons in cats. In hindlimb flexor and extensor motoneurons stimulated intrasomatically with current below the threshold for repetitive discharges, added LC-evoked excitatory post-synaptic potentials (EPSPs) were consistently found to produce repetitive firing, suggesting a lowering in the repetitive firing threshold attributable to excitatory LC inputs. With those extensor motoneurons showing episodic, self-sustained firing, LC-EPSPs introduced during the quiescent period were capable of starting a continuous discharge with rhythmic frequencies higher than the spontaneous activity. In some of these cells, intracellularly applied hyperpolarizing current was able to stop the spontaneous discharges. Subsequently, LC stimuli were found to reinitiate repetitive discharges, thus counteracting the ongoing suppression of the motoneurons. Quantitative analysis of the single-spike afterhyperpolarization (AHP) indicated a consistent reduction in its amplitude and time course (duration, time-to-peak, half-decay time) for flexor and extensor motoneurons in response to LC conditioning stimuli. Present results suggest an excitatory LC action on the repetitive discharges of cat motoneurons accompanied by a concurrent decrease in the amplitude and time course of the single-spike AHPs.
本研究旨在确定蓝斑（LC）的输入是否对猫脊髓腹角运动神经元的重复放电有任何影响。在对后肢屈肌和伸肌运动神经元进行低于重复放电阈值的电流体腔内刺激时，持续发现添加的LC诱发的兴奋性突触后电位（EPSP）会产生重复放电，这表明由于LC的兴奋性输入，重复放电阈值降低。对于那些表现出阵发性、自发放电的伸肌运动神经元，在静息期引入的LC-EPSP能够以高于自发活动的节律频率开始持续放电。在其中一些细胞中，细胞内施加的超极化电流能够停止自发放电。随后，发现LC刺激能重新引发重复放电，从而抵消对运动神经元持续的抑制作用。对单峰后超极化（AHP）的定量分析表明，屈肌和伸肌运动神经元对LC条件刺激的反应中，其幅度和时间进程（持续时间、峰值时间、半衰期）持续降低。目前的结果表明，LC对猫运动神经元的重复放电有兴奋性作用，同时单峰AHP的幅度和时间进程会同时降低。
