MacDonell C W, Power K E, Chopek J W, Gardiner K R, Gardiner P F
Spinal Cord Research Centre, Department of Physiology & Pathophysiology, University of Manitoba, Winnipeg, Manitoba, Canada.
Health Leisure and Human Performance Research Institute, Faculty of Kinesiology and Recreation Management, University of Manitoba, Winnipeg, Manitoba.
J Physiol. 2015 May 15;593(10):2327-42. doi: 10.1113/JP270239. Epub 2015 Apr 17.
This study examined motoneurone properties during fictive locomotion in the adult rat for the first time. Fictive locomotion was induced via electrical stimulation of the mesencephalic locomotor region in decerebrate adult rats under neuromuscular blockade to compare basic and rhythmic motoneurone properties in antidromically identified extensor motoneurones during: (1) quiescence, before and after fictive locomotion; (2) the 'tonic' period immediately preceding locomotor-like activity, whereby the amplitude of peripheral flexor (peroneal) and extensor (tibial) nerves are increased but alternation has not yet occurred; and (3) locomotor-like episodes. Locomotion was identified by alternating flexor-extensor nerve activity, where the motoneurone either produced membrane oscillations consistent with a locomotor drive potential (LDP) or did not display membrane oscillation during alternating nerve activity. Cells producing LDPs were referred to as such, while those that did not were referred to as 'idle' motoneurones. LDP and idle motoneurones during locomotion had hyperpolarized spike threshold (Vth ; LDP: 3.8 mV; idle: 5.8 mV), decreased rheobase and an increased discharge rate (LDP: 64%; idle: 41%) during triangular ramp current injection even though the frequency-current slope was reduced by 70% and 55%, respectively. Modulation began in the tonic period immediately preceding locomotion, with a hyperpolarized Vth and reduced rheobase. Spike frequency adaptation did not occur in spiking LDPs or firing generated from sinusoidal current injection, but occurred during a sustained current pulse during locomotion. Input conductance showed no change. Results suggest motoneurone modulation occurs across the pool and is not restricted to motoneurones engaged in locomotion.
本研究首次在成年大鼠的虚拟运动过程中对运动神经元特性进行了检测。在神经肌肉阻滞条件下，通过电刺激去大脑成年大鼠的中脑运动区诱导虚拟运动，以比较在以下期间逆向鉴定的伸肌运动神经元的基本和节律性运动神经元特性：(1) 虚拟运动前后的静止期；(2) 紧接类似运动活动之前的“紧张”期，在此期间外周屈肌（腓骨）和伸肌（胫骨）神经的振幅增加但尚未出现交替；以及(3) 类似运动的发作期。通过屈肌 - 伸肌神经活动交替来识别运动，在此期间运动神经元要么产生与运动驱动电位（LDP）一致的膜振荡，要么在神经活动交替期间不显示膜振荡。产生LDP的细胞被如此称呼，而那些不产生的则被称为“闲置”运动神经元。运动期间的LDP和闲置运动神经元具有超极化的动作电位阈值（Vth；LDP：3.8 mV；闲置：5.8 mV），在三角斜坡电流注入期间基强度降低且放电率增加（LDP：64%；闲置：41%），尽管频率 - 电流斜率分别降低了70%和55%。调制在紧接运动之前的紧张期开始，具有超极化的Vth和降低的基强度。在尖峰LDP或正弦电流注入产生的放电中未发生动作电位频率适应，但在运动期间的持续电流脉冲期间发生。输入电导没有变化。结果表明运动神经元调制发生在整个神经元群中，并不局限于参与运动的运动神经元。
