Button Duane C, Gardiner Kalan, Marqueste Tanguy, Gardiner Phillip F
Spinal Cord Research Center, Department of Physiology, University of Manitoba, 730 William Avenue, 436 BMSB, Winnipeg, Manitoba, Canada R3E 3J7.
J Physiol. 2006 Jun 15;573(Pt 3):663-77. doi: 10.1113/jphysiol.2006.107292. Epub 2006 Apr 13.
The purpose of this study was to describe the frequency-current (f-I) relationships of hindlimb alpha-motoneurones (MNs) in both anaesthetized and decerebrate rats in situ. Sprague-Dawley rats (250-350 g) were anaesthetized with ketamine and xylazine (KX) or subjected to a precollicular decerebration prior to recording electrophysiological properties from sciatic nerve MNs. Motoneurones from KX-anaesthetized rats had a significantly (P < 0.01) hyperpolarized resting membrane potential and voltage threshold (Vth), increased rheobase current, and a trend (P = 0.06) for a smaller after-hyperpolarization (AHP) amplitude compared to MNs from decerebrate rats. In response to 5 s ramp current injections, MNs could be categorized into four f-I relationship types: (1) linear; (2) adapting; (3) linear + sustained; and (4) late acceleration. Types 3 and 4 demonstrated self-sustained firing owing to activation of persistent inward current (PIC). We estimated the PIC amplitude by subtracting the current at spike derecruitment from the current at spike recruitment. Neither estimated PIC nor f-I slopes differed between fast and slow MNs (slow MNs exhibited AHP half-decay times > 20 ms) or between MNs from KX-anaesthetized and decerebrate rats. Motoneurones from KX-anaesthetized rats had significantly (P < 0.02) hyperpolarized ramp Vth values and smaller and shorter AHP amplitudes and decay times compared to MNs from decerebrate rats. Pentobarbitone decreased the estimated PIC amplitude and almost converted the f-I relationship from type 3 to type 1. In summary, MNs of animals subjected to KX anaesthesia required more current for spike initiation and rhythmic discharge but retained large PICs and self-sustained firing. The KX-anaesthestized preparation enables direct recording of PICs in MNs from intact animals.
本研究的目的是描述麻醉和去大脑大鼠原位后肢α运动神经元（MNs）的频率-电流（f-I）关系。将体重250 - 350 g的Sprague-Dawley大鼠用氯胺酮和赛拉嗪（KX）麻醉，或在记录坐骨神经MNs的电生理特性之前进行前丘去大脑处理。与去大脑大鼠的MNs相比，KX麻醉大鼠的运动神经元具有显著（P < 0.01）超极化的静息膜电位和电压阈值（Vth），升高的基强度电流，以及较小的后超极化（AHP）幅度的趋势（P = 0.06）。响应5 s的斜坡电流注入，MNs可分为四种f-I关系类型：（1）线性；（2）适应性；（3）线性 + 持续性；（4）晚期加速。类型3和4由于持续性内向电流（PIC）的激活而表现出自发性放电。我们通过从峰电位募集时的电流中减去峰电位去募集时的电流来估计PIC幅度。快速和慢速MNs（慢速MNs表现出AHP半衰期> 20 ms）之间或KX麻醉和去大脑大鼠的MNs之间，估计的PIC和f-I斜率均无差异。与去大脑大鼠的MNs相比，KX麻醉大鼠的运动神经元具有显著（P < 0.02）超极化的斜坡Vth值以及更小、更短的AHP幅度和衰减时间。戊巴比妥降低了估计的PIC幅度，并几乎将f-I关系从类型3转变为类型1。总之，接受KX麻醉的动物的MNs在峰电位起始和节律性放电时需要更多电流，但保留了较大的PIC和自发性放电。KX麻醉的制备方法能够直接记录完整动物MNs中的PIC。
