A minimal stress model for the assessment of electroacupuncture analgesia in rats under halothane

Abstract

The 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 120min. Under 0.5% halothane, TFL were then measured in groups receiving EA at intensity of 3, 10 or 20 volt (V), 1 or 2mg/kg morphine, 20V EA plus naloxone, or control. Subsequently, the effect of EA on formalin-induced 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. TFL remained constant at 0.5% halothane, and needle insertion and electrical stimulation were well tolerated. Under 0.5% halothane, EA increased TFL and suppressed formalin-induced hyperalgesia in an intensity-dependent and naloxone-reversible manner. EA of 20V 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 analgesia while maintaining physiological and biochemical response in the experiment.

Effects of Electroacupuncture at BL60 on Formalin-Induced Pain in Rats

“…However, in the present study, electroacupuncture treatment at BL60 acupoint reduced the number of c-Fos positive neurons in not only superficial layer laminae I-II but also in deep layer laminae III–VI of the spinal cord at the L4-5 level, compared to a formalin injection only group. This result is consistent with other studies which observed a reduction of c-Fos expression in both superficial and deep layers of the spinal cord dorsal horn in the electroacupuncture-treated groups of a carrageenan-induced pain rat model [16, 36] and a formalin model [17]. Furthermore, it is considered that the mechanism of pain suppression by electroacupuncture at BL-60 acupoint is due to its action at the spinal cord level, but not at the supra-spinal level.…”

“…There have been numerous studies that observed the pain-relieving effects of acupuncture [13, 16, 17, 23–25]. To our knowledge, however, there are no reports except for Kim et al [26] and Zou et al [27] to study the pain-relieving effects of acupuncture at the BL60 acupoint.…”

“…A dilution of formalin in saline was used for the experiments herein: 50  μ L of 5% formalin was used for injection, which is widely used to induce maximum pain response [16, 17], while avoiding adverse phenomena, such as ceiling effect, backward walking, and freezing [16, 17]. …”

Amitriptyline converts non-responders into responders to low-frequency electroacupuncture-induced analgesia in rats

“…In addition, the withdrawal thresholds to MS in the incised and nonincised paws of sham EA rats treated with saline or amitriptyline also did not change throughout the post-incision period of observation. We can conclude that isoflurane anesthesia is unlikely to interfere with the EA-induced increase in TFL or reduction in incision hyperalgesia, as proposed elsewhere (Wen et al, 2007).…”

“…Procedures were conducted in rats anesthetized with isoflurane (in oxygen flow; 2% for induction, and 0.5% for maintenance) to minimize the stress induced by the animal restraint that is necessary for needle insertion and stimulation (Wen et al, 2007). Stainless steel acupuncture needles (0.18 mm× 8 mm) were inserted at a depth of 5 mm into each hind leg at the acupoints Zusanli and Sanyinjiao.…”