Ririe Douglas G, Liu Baogang, Clayton Bridgette, Tong Chuanyao, Eisenach James C
Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1009, USA.
Anesthesiology. 2008 Jul;109(1):111-7. doi: 10.1097/ALN.0b013e31817c1ab9.
Withdrawal thresholds in the paw are lower in younger animals, and incision further reduces these thresholds. The authors hypothesized that these differences result in part from changes in intrinsic electrophysiologic properties of large neurons.
Using isolated whole dorsal root ganglion, current clamping was performed to determine the electrophysiologic properties of large neurons before and after incision in animals aged 1 and 4 weeks. Mechanical withdrawal thresholds were used to follow paw sensitivity.
After paw incision, withdrawal thresholds decreased to a similar degree at both ages, but returned to control threshold at 72 h only in the 1-week-old animals. The resting membrane potential was less negative and the rheobase and the resistance of the membrane were lower at baseline in the 1-week-old animals (P < 0.05). After incision, the membrane potential became more depolarized and the rheobase was less in both ages. These changes remained 72 h after the incision in both ages.
These findings suggest that lower mechanical thresholds in the younger animals may be partially attributed to the intrinsic electrophysiologic properties of the larger-diameter afferent neurons. The lack of resolution of the electrophysiologic changes in the young despite the resolution of the withdrawal response suggests that continued input from large fibers into the central nervous system may occur at this age despite the apparent resolution of behavioral changes. Further studies are needed to determine the etiology of these differences, their impact in the central nervous system, and whether theses changes can be prevented.
年幼动物爪部的撤针阈值较低，而切开手术会进一步降低这些阈值。作者推测，这些差异部分源于大神经元内在电生理特性的变化。
使用分离的完整背根神经节，采用电流钳技术来测定1周龄和4周龄动物切开手术前后大神经元的电生理特性。通过机械撤针阈值来跟踪爪部敏感性。
爪部切开术后，两个年龄段的撤针阈值均下降到相似程度，但仅1周龄动物在72小时时恢复到对照阈值。1周龄动物基线时的静息膜电位负值较小，基强度和膜电阻较低（P < 0.05）。切开术后，两个年龄段的膜电位均变得更去极化，基强度降低。这些变化在切开术后72小时在两个年龄段均持续存在。
这些发现表明，年幼动物较低的机械阈值可能部分归因于较大直径传入神经元的内在电生理特性。尽管撤针反应恢复，但年幼动物电生理变化未得到解决，这表明尽管行为变化明显恢复，但在这个年龄段可能仍有大纤维持续向中枢神经系统输入信号。需要进一步研究来确定这些差异的病因、它们对中枢神经系统的影响以及这些变化是否可以预防。
