A Minimal Stress Model for the Assessment of Electroacupuncture Analgesia in Rats under Halothane

use of anesthetics in acupuncture analgesia is controversial . We evaluate a steady-state light anesthesia model to test whether minimal stress manipulation and reliable measurement of analgesia could be simultaneously achieved during electroacupuncture (EA) in animals. A series of experiments were performed. Firstly, EA compliance and tail- flick latencies (TFL) were compared in rats under 0.1%, 0.3%. 0.5% . 0.7%, or 1. 1% halothane for 120 min. Under 0.5% halothane , TEL were then measured in groups receiving EA at intensity of 3, 10 or 20 volt (V), I or 2 mg/kg morphine, 20 V EA plus naloxone, or control. Subsequently, the effect of EA on formalininduced hyperalgesia was tested and c-fos expression in the spinal dorsal horn was analyzed. Rats exhibited profound irritable behaviors and highly variable TFL under 0.1% or 0.3% halothane, as well as a time- dependent increase of TFL under 0.7% or 1.1% halothane . TEL remained constant at 0.5% halothane, and needle insertion and electrical stimulation were well tolerated. Under 0.5% halothane, EA increased TFI and suppressed formalin-induced hyperalgesia in an intensity -dependent and naloxone- reversible manner. EA of 20 V prolonged TFL by 74 %, suppressed formalin-induced hyperalgesia by 32.6% and decreased c-fos expression by 29.7% at the superficial and deep dorsal horn with statistically significant difference. In conclusion, 0.5% halothane provides a steady-state anesthetic level which enables the humane application of EA stimulus with the least interference on analgesic assessment . This condition serves as a minimal stress EA model in animals devoid of stress-induced analszesia while maintaining physiological and biochemical response in the experiment. (c) 2006 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved