Immobilization Stress Can Mask the c-Fos Expression Induced by Acupuncture in Rats

摘要

Although the clinical practice of acupuncture shows obvious results, the scientific research in acupuncture produce sometimes, subtle or ambiguous effects. Many factors can be associated with these inconsistent results. Acupuncture in laboratory animals must be performed on anesthetized or, if unanesthetized, restrained subjects. This can change several physiological parameters, such as the activation of brain areas and analgesia. It is well established that both anesthesia and immobilization up-regulate c-fos expression in several areas of the CNS, thus limiting the assessment of c-fos expression induced by electroacupuncture (EA). Therefore, in the present study, we have used behavioral (two protocols of repeated immobilization: 6 days, 1 h/day or13 days, 2h/day) and pharmacological means (dexamethasone, 1 mg/kg; diazepam, 5 mg/kg and imipramine, 15mg/kg) in order to reduce the influence of immobilization stress on the background expression of c-Fos thus allowing the subsequent study of EA-associated c-Fos expression and analgesia. We found that repeated immobilization reduces the background neuronal activation in most of the studied brain areas. In animals not submitted to repeated immobilization, no differences were detected between animals submitted to immobilization alone (IMMO), EA at a non- point region (EANP) or EA at the Zusanli point (EA36S). However, in animals subjected to repeated immobilization, EA36S lead to higher levels of analgesia (as measured by the tail-flick test) and of c-Fos expression in the dorsal raphe nucleus and PAGv1 than the EANP. In other structures such as the central medial nucleus of thalamus, posterior hypothalamus, locus coeruleus and the ventrolateral column of the periaqueductal gray matter, the EA36S also induced higher levels of c-Fos expression than EANP, but this difference was not dependent of the immobilization protocols. The drugs did not induce any specific change (could this imply a blockade of EA effects?) in the pattern of c-Fos expression ofanimals IMMO, EANP and EA36S. These results suggest that high background levels of c-Fos expression can preclude the detection of differences between EA36S- and EANP-induced c-Fos expressions. Repeated immobilization is a good strategy for reducing the otherwise high background c-Fos expression induced by immobilization alone, thus allowing a better discrimination of the brain structures specifically activated by EA in the Zusanli point.