延髓头端腹内侧区甩尾相关细胞在肌梭传入镇痛中的作用

The function of rostral ventromedial medulla neurons related to tail flick in analgesia produced by muscle spindle afferents

目的 探讨延髓头端腹内侧区 (rostralventromedialmedulla ,RVM)甩尾相关细胞在肌梭传入镇痛中的作用。方法 采用辐射热照射大鼠尾部引起甩尾反射 ,同步记录RVM细胞放电和甩尾反射的方法 ,观察琥珀胆碱 (succinyl choline,SCh)诱发的肌梭传入活动对甩尾相关细胞放电和甩尾反射的影响。结果 ①RVM内的细胞依据其放电活动与甩尾反射的关系可区分为三类 ,即 :在甩尾动作发生前 4 0 0ms左右放电骤停的off cell,在甩尾动作发生前 2 0 0～6 0 0ms放电骤增的on cell,以及与甩尾反射没有关系的N cell。②股动脉注射SCh引起的肌梭传入活动可使绝大多数的off cell发生兴奋 ,表现为放电频率增加 ,“撤”反应延迟出现或不出现 ;可使绝大多数on cell发生抑制 ,表现为放电频率减小 ,“给”反应延迟出现 ;同时使甩尾的潜伏期明显延长。③肌肉注射布比卡因破坏肌梭后 ,股动脉注射相同剂量的SCh ,对off cell的兴奋作用较未注射组明显降低 (P <0 .0 1)。结论 SCh诱发的肌梭传入可使RVM内off cell兴奋 ,on cell抑制 。

Objective To study the function of rostral ventromedial medulla (RVM) neuron in analgesia produced by muscle spindle afferents. Methods We made synchronicrecording of the discharge of RVM neurons and the tail flick reflex (TFR) caused by radiant heat on the tail of rat to observe the effects of muscle spindle afferents induced by succinylcholine (SCh)on discharge of RVM neurons and TFR. Results ①Neurons in RVM could be divided into three different classes according to their discharge related to TFR:“off-cells”that were characterized by an abrupt pause in discharge approximately 400ms prior to the occurrence of tail flick,“on-cells” that showed a sudden increase in discharge 200～600 ms prior to the occurrence of tail flick, and“N-cells ” that displayed no change in discharge related to the TFR. ②After the femoral artery was injected with SCh, most of off-cells were excited and most of on-cells were inhibited. In off-cells discharge frequency increased and the response of abrupt pause in discharge was delayed or disappeared. In on-cells discharge frequency decreased and the response of sudden increase in discharge was delayed. At the same time, the tail flick latency (TFL) was obviously prolonged. ③After most of the muscle spindles in a hind leg were destroyed by intramuscularly injected bupivacaine, the effects of the femoral artery injected with SCh on tail flick- related neurons and TFL were weaker than those in non-injection of bupivacaine. Conclusion RVM plays an important role in analgesia produced by muscle spindle afferents. That off-cells are excited and on-cells are inhibited is one of the mechanisms in the anti-nociceptive action of muscle spindle afferents.