Electroacupuncture alleviates affective pain in an inflammatory pain rat model.
Pain has both sensory-discriminative and emotional-affective dimensions. Previous studies demonstrate that electroacupuncture (EA) alleviates the sensory dimension but do not address the affective. An inflammatory pain rat model, produced by a complete Freund adjuvant (CFA) injection into the hind paw, was combined with a conditioned place avoidance (CPA) test to determine whether EA inhibits spontaneous pain-induced affective response and, if so, to study the possibility that rostral anterior cingulate cortex (rACC) opioids underlie this effect. Male Sprague-Dawley rats (250-275 g, Harlan) were used. The rats showed place aversion (i.e. affective pain) by spending less time in a pain-paired compartment after conditioning than during a preconditioning test. Systemic non-analgesic morphine (0.5 and 1.0 mg/kg, i.p.) inhibited the affective reaction, suggesting that the affective dimension is underpinned by mechanisms different from those of the sensory dimension of pain. Morphine at 0.5 and at 1 mg/kg did not induce reward. Rats given EA treatment before pain-paired conditioning at GB 30 showed no aversion to the pain-paired compartment, indicating that EA inhibited the affective dimension. EA treatment did not produce reward or aversive effect. Intra-rACC administration of D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide (CTOP), a selective mu opioid receptor antagonist, but not norbinaltorphimine (nor-BNI), a selective kappa opioid receptor antagonist, blocked EA inhibition of the affective dimension. These data demonstrate that EA activates opioid receptors in the rACC to inhibit pain-induced affective responses and that EA may be an effective therapy for both the sensory-discriminative and the affective dimensions of pain.
Center for Integrative Medicine, School of Medicine, University of Maryland, 520 W. Lombard Street, Baltimore, MD 21201, USA.
Y
Y
Zhang
X
X
Meng
A
A
Li
J
J
Xin
B M
BM
Berman
L
L
Lao
M
M
Tan
K
K
Ren
R-X
RX
Zhang
D015667:Acupuncture Analgesia / Q000379:methods*; D000818:Animals; D004195:Disease Models, Animal; D015671:Electroacupuncture / Q000379:methods*; D007249:Inflammation / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D019964:Mood Disorders / Q000209:etiology / Q000628:therapy*; D010146:Pain / Q000209:etiology / Q000473:pathology* / Q000523:psychology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013315:Stress, Psychological / Q000209:etiology / Q000628:therapy*