Castro-Moure F, Goshgarian H G
Department of Anatomy and Cell Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201, USA.
Exp Neurol. 1996 Sep;141(1):102-12. doi: 10.1006/exnr.1996.0143.
Differentiation between traumatic and activity dependent plasticity in the CNS has been a challenge to neuroscientists in the past. We describe a cooling device that allows reversible block of the inspiratory drive to phrenic motoneurons without injury to the spinal cord at the C2 level. Thus, this experimental approach can be used to differentiate between the plasticity induced by blockade of synaptic activity in the phrenic nucleus from the trauma-induced plasticity caused by a C2 spinal cord hemisection which would also interrupt descending inspiratory drive. Complete block of axon transmission of the respiratory pathways running unilaterally in the ventral as well as in the lateral funiculus was achieved by approximation of a cold probe to the ventral surface of the spinal cord. The spinal cord surface temperature was lowered to 7 degrees C. The temperature was maintained by a cold recirculated alcohol system. The efficacy of the reversible block was assessed by bilateral continuous EMG activity recording from the hemidiaphragms ipsilateral and contralateral to the cold application. Quantitative analysis of the EMG hemidiaphragmatic signals was performed in two sham-operated control (no cold application) and an experimental (cold application) group of Sprague-Dawley rats. The control groups were employed to confirm that the surgical exposure of the cord and/or the chronic placement of the probe and the administration of IV dopamine given to maintain stable blood pressure did not affect respiration. No significant change occurred in EMG hemidiaphragmatic activity in control animals. The descending pathway from the rVRG to the phrenic nucleus was completely and continuously blocked for 4 h in all four experimental animals as demonstrated by abolition of the EMG hemidiaphragmatic signal ipsilateral to cold block. In all experimental animals hemidiaphragmatic activity returned when the cold block was removed. The recovered EMG activity was significantly higher than pre-block values. Interestingly, EMG activity contralateral to the block did not change significantly from control values after the block was removed, but was significantly enhanced during cold block. The present results suggest that cold block provides a means of studying activity-dependent plasticity in the respiratory pathways of the spinal cord.
过去，区分中枢神经系统中创伤性可塑性和活动依赖性可塑性一直是神经科学家面临的一项挑战。我们描述了一种冷却装置，它能够可逆地阻断膈运动神经元的吸气驱动，而不会对C2水平的脊髓造成损伤。因此，这种实验方法可用于区分由膈核突触活动阻断诱导的可塑性与由C2脊髓半横断引起的创伤性可塑性，后者也会中断下行吸气驱动。通过将冷探头靠近脊髓腹侧表面，实现了在腹侧和外侧索中单侧运行的呼吸通路轴突传递的完全阻断。脊髓表面温度降至7摄氏度。温度由冷循环酒精系统维持。通过对冷刺激同侧和对侧半膈肌进行双侧连续肌电图活动记录，评估可逆阻断的效果。对两组假手术对照（未进行冷刺激）和一组实验（进行冷刺激）的Sprague-Dawley大鼠的半膈肌肌电图信号进行了定量分析。对照组用于确认脊髓的手术暴露和/或探头的长期放置以及为维持稳定血压而静脉注射多巴胺不会影响呼吸。对照动物的半膈肌肌电图活动没有显著变化。如冷阻断同侧半膈肌肌电图信号消失所示，在所有四只实验动物中，从延髓腹外侧呼吸组到膈核的下行通路在4小时内被完全且持续阻断。在所有实验动物中，去除冷阻断后，半膈肌活动恢复。恢复后的肌电图活动显著高于阻断前的值。有趣的是，阻断去除后，阻断对侧的肌电图活动与对照值相比没有显著变化，但在冷阻断期间显著增强。目前的结果表明，冷阻断提供了一种研究脊髓呼吸通路中活动依赖性可塑性的方法。
