The effect of inhalation anesthetic on wind up phenomenon of spinal dorsal horn neurons

我们研究了氟烷对猫脊髓宽动态范围（WDR）神经元感受野扩张的影响。通过向WDR神经元外周感受野中心（通常为后爪）注射一种炎症剂卡拉胶（CG）诱导其扩张。猫经氨基甲酸乙酯和氯氯蔗糖麻醉，行腰椎椎板切除术。将填充3M KCl的玻璃微电极插入脊髓。通过观察示波器和听后爪周围触觉刺激的声音来识别脊髓背角神经元的活动。然后，我们通过机械的无害和伤害性刺激或热刺激来决定神经元的性质。对所有刺激方式均有反应且对机械刺激的反应随施加的刺激强度成比例逐渐增加的神经元被认为是WDR神经元。接受野是通过用毛刷进行无害的机械刺激来决定的。对照组在注射CG （20mg）后2小时感受野开始扩张，在注射后4小时达到最大，并保持最大水平至注射后6小时。氟烷组于CG注射前20 min至注射后2 h吸入0.5%氟烷。吸入氟烷时感受野略小于基线。氟烷停药后2小时（注射CG后4小时）感受野开始扩张，吸入结束后4小时（注射CG后6小时）感受野达到最大值。扩张水平最终与对照组相近。上述结果表明，氟烷可抑制CG诱导的WDR神经元感受野的扩张，但在吸入过程中这种作用有限。

We have investigated the effect of halothane on the expansion of the receptive field of the wide dynamic range (WDR) neuron in the spinal cord of cats. The expansion was induced by the injection of an inflammatory agent, carrageenan (CG), into the center of peripheral receptive field of WDR neuron, usually hindpaw. Cats were anesthetized by urethane and chloralose, underwent lumbar laminectomy. A glass microelectrode filled with 3M KCl was inserted into the spinal cord. The activity of spinal dorsal horn neurons were identified by observing oscilloscope and hearing the sound responded to peripheral tactile stimulation of a hindpaw. Then we decided the character of the neuron by giving mechanical innocuous and nociceptive stimulation or heat stimulation. Neurons which responded to all stimulus modality and the response of which to mechanical stimulation increased gradually in proportion to the strength of applied stimuli were regarded as WDR neurons. The receptive field was decided by giving innocuous mechanical stimulation using brush. In the control group, the receptive field began to expand 2 hours after the injection of CG (20mg), reached maximum at 4 hours and remained maximum level until 6 hours after injection. In halothane group, 0.5% halothane was inhaled from 20 min before CG injection until 2 hours after CG injection. The receptive field was slightly smaller than baseline during halothane inhalation. The receptive field began to expand 2 hours after halothane discontinuation (4 hours after CG injection) and reached maximum at 4 hours after the end of halothane inhalation (6 hours after CG injection). The level of expansion was similar to that of control group finally. These results suggest that halothane inhibits the expansion of receptive field of WDR neuron induced by the injection of CG,but this effect is limited during its inhalation.