The effects of anesthetics on spinal dorsal horn neuronal activity

麻醉药抑制脊髓背角宽动态范围(WDR)神经元对伤害性刺激的时相活动。然而，麻醉剂对由紧张性疼痛状态引起的WDR神经元活动的影响，如福尔马林试验，尚不清楚。因此，我们观察了静脉麻醉药氯胺酮和硫胺酮(3、10和30 mg·kg~(-1))、吸入麻醉药异氟烷和氟烷(0.5%和1.5%)对福尔马林试验诱发的WDR神经元活动的影响。此外，硫柳汞和氯胺酮的剂量-反应曲线在预先给药和后来给药之间进行了比较。方法和结果：在去大脑，脊髓横断猫(L1-2)，皮下(S.C.)将福尔马林(0.05ml；5.0%)注入大鼠后爪脊髓WDR神经元的感受区。这种注射在持续…的神经元中引起立即和持续的放电或爆发活动更多，至少60分钟。注射福尔马林前5分钟静脉注射硫戊醛和氯胺酮以剂量依赖的方式抑制这种神经元放电。而在福尔马林注射后5min给予硫辛醛和氯胺酮，对神经元放电的抑制作用明显减弱。1超前吸入麻醉药、异氟醚、氟烷与治疗后给药无明显差异。一个S.C.在同一感受野注射生理盐水(0.05ml)只能引起短暂的神经元兴奋，活动在L-2分钟内恢复到注射前的水平。结论：福尔马林注射可靠地产生猫脊髓背角神经元活动的持续爆发，并且预先静脉注射硫柳汞和氯胺酮可显著降低这种活动。硫代戊醛和氯胺酮，而不是吸入麻醉剂，抑制这种神经反应的能力被发现与福尔马林注射的时间有关。较少

The phasic activity of wide dynamic range (WDR) neurons in the spinal dorsal horn in response to noxious stimulation is suppressed by anesthetics. However, the effects of anesthetics on the activity of WDR neurons that is evoked by a tonic pain state, as in the formalin test, are not well understood. Therefore, we examined the effects of intravenous anesthetics, ketamine and thiamyla1 (3, l0 and 30 mg.kg^<-1> inhalational anesthetics, isoflurane and halothane (0.5% and l.5%) on the activity of WDR neurons that is evoked by the formalin test. In addition, dose-response curves for thiamylal and ketamine were compared between preemptive administration and later administration.Methods and Results : In decerebrate, spinal cord-transected cats (L1-2), a subcutaneous (s.c.) injection of formalin (0.05 ml ; 5.0%) was placed in the receptive fields of spinal WDR neurons in the hind paw. This injection elicited an immediate and continuous discharge or burst of activity in the neurons that lasted … More for at least 60 minutes. Intravenous thiamylal and ketamine, administered 5 min prior to the injection of formalin inhibited this neuronal discharge in a dose-dependent manner. However, when thiamylal and ketamine was administered 5 min after the injection of formalin, the inhibitory effect on the neuronal discharge was significantly smaller. 1n contrast, preemptive administerted inhalatinal anesthetics, isoflurane and halothane did not different from the posttreatment administration. An s.c. injection of saline (0.05 ml) in the same receptive field elicited only transient neuronal excitation and the activity returned to the pre-injection level within l-2 min.Conclusions : The results suggest that an injection of formalin reliably produces a continuous burst of neuronal activity in the spinal dorsal horn of cats and, moreover, that this activity can be markedly reduced by the preemptive intravenous administration of thiamylal and ketamine. The ability of thiamylal and ketamine, but not inhalational anesthetics, to inhibit this neuronalresponse was found to be related to the timing of the formalin injection. Less