Department of Neurobiology and Behavior, Stony Brook University, Stony Brook, New York 11794-5230, USA.
J Neurophysiol. 2012 Nov;108(9):2554-67. doi: 10.1152/jn.00927.2011. Epub 2012 Jul 25.
In the rat, external urethral sphincter (EUS) activation during micturition consists of three sequential phases: 1) an increase in tonic EUS activity during passive filling and active contraction of the bladder (guarding reflex), 2) synchronized phasic activity (EUS bursting) associated with voiding, and 3) sustained tonic EUS activity that persists after bladder contraction. These phases are perturbed following spinal cord injury. The purpose of the present study was to characterize individual EUS motor unit (MU) patterns during micturition in the spinally intact and transected adult rat. EUS MU activity was recorded from either the L5 or L6 ventral root (intact) or EUS muscle (transected) during continuous flow cystometry in urethane-anesthetized adult female Sprague-Dawley rats. With the use of bladder pressure threshold and timing of activation, four distinct patterns of EUS MU activity were identified in the intact rat: low threshold sustained, medium/high threshold sustained, medium/high threshold not sustained, and burst only. In general, these MUs displayed little frequency modulation during active contraction, generated high-frequency bursts of action potentials during EUS bursting, and varied in terms of the duration of sustained tonic activity. In contrast, three general patterns of EUS MU activity were identified in the transected rat: low threshold, medium threshold, and high threshold. These MUs exhibited considerable frequency modulation during active contraction of the bladder, no bursting behavior and little to no sustained firing. The prominent frequency modulation of EUS MUs is likely due to the enhanced guarding reflex seen in EUS whole muscle electromyogram recordings in transected rats (D'Amico SC, Schuster IP, Collins WF 3rd. Exp Neurol 228: 59-68, 2011). In addition, EUS MU recruitment in transected rats more closely followed predictions by the size principle than in intact rats. This may reflect the influence of local synaptic circuits or intrinsic properties of EUS motoneurons that are active in intact rats but attenuated or absent in transected rats.
在大鼠中，排尿时的尿道外括约肌（EUS）激活包括三个连续的阶段：1）在膀胱被动充盈和主动收缩期间，EUS 张力增加（保护反射），2）与排尿相关的同步相活动（EUS 爆发），3）在膀胱收缩后持续的 EUS 张力。这些阶段在脊髓损伤后受到干扰。本研究的目的是描述脊髓完整和横切成年大鼠排尿时单个 EUS 运动单位（MU）的模式。在乌拉坦麻醉的成年雌性 Sprague-Dawley 大鼠的连续流动膀胱测压期间，从 L5 或 L6 腹根（完整）或 EUS 肌肉（横切）记录 EUS MU 活动。使用膀胱压力阈值和激活时间，在完整大鼠中鉴定出四种不同的 EUS MU 活动模式：低阈值持续、中/高阈值持续、中/高阈值不持续和仅爆发。一般来说，这些 MU 在主动收缩期间很少有频率调制，在 EUS 爆发期间产生高频动作电位爆发，并且在持续紧张活动的持续时间方面有所不同。相比之下，在横切大鼠中鉴定出三种一般的 EUS MU 活动模式：低阈值、中阈值和高阈值。这些 MU 在膀胱主动收缩期间表现出相当大的频率调制，没有爆发行为，几乎没有持续放电。EUS MU 的突出频率调制可能是由于在横切大鼠的 EUS 整块肌肉肌电图记录中观察到增强的保护反射（D'Amico SC、Schuster IP、Collins WF 3rd。Exp Neurol 228：59-68，2011）。此外，横切大鼠中的 EUS MU 募集更接近地遵循大小原则的预测，而不是完整大鼠。这可能反映了局部突触回路或 EUS 运动神经元固有特性的影响，这些特性在完整大鼠中活跃，但在横切大鼠中减弱或不存在。
