Evaluation of the noradrenergic pathway and alpha-2 and beta-receptors in the modulation of the analgesia induced by transcutaneous electric nerve stimulation of high and low frequencies

Transcutaneous electric nerve stimulation is a noninvasive method used in clinical Physiotherapy to control acute or chronic pain. Different theories have been proposed to explain the mechanism of the analgesic action of transcutaneous electric nerve stimulation, as the participation of central and peripheral neurotransmitters. The aim of this study was to evaluate the involvement of noradrenergic pathway and of the receptors alfa-2 and beta in the modulation of analgesia produced by transcutaneous electric nerve stimulation of high and low frequency in Wistar rats after chronic treatment with propranolol or yohimbine intraperitoneally. Animals weighing 200 to 300 g were divided into 9 groups (n=8), which were obtained nociceptive thresholds through the Tail Flick before and after application of TENS for comparing the change of pain. The administration of yohimbine or propranolol at a dose of 3 mg/kg was effective in antagonizing the analgesia induced by high (150 Hz) and low (10 Hz) frequency transcutaneous electric nerve stimulation according to ANOVA test followed by Duncan post hoc test (p<0.05). Thus, it is suggested the involvement of alpha-2 and beta noradrenergic receptors in the modulation of transcutaneous electric nerve stimulation-induced analgesia.

经皮神经电刺激（Transcutaneous electric nerve stimulation，TENS）是临床物理治疗中用于控制急性或慢性疼痛的无创手段。目前已提出多种理论用以阐释经皮神经电刺激的镇痛作用机制，其中包括中枢与外周神经递质的参与。本研究旨在评估：在对Wistar大鼠腹腔注射普萘洛尔（propranolol）或育亨宾（yohimbine）进行慢性处理后，去甲肾上腺素能通路以及α2和β受体在高低频经皮神经电刺激所诱导的镇痛调节中的参与情况。体重200至300g的实验动物被分为9组（每组n=8），通过甩尾实验（Tail Flick）检测经皮神经电刺激前后的痛阈，以对比疼痛阈值的变化。经单因素方差分析（ANOVA）结合Duncan事后检验可知，3mg/kg剂量的育亨宾或普萘洛尔可有效拮抗150Hz高频与10Hz低频经皮神经电刺激诱导的镇痛作用（p<0.05）。据此，本研究提示α2与β去甲肾上腺素能受体参与了经皮神经电刺激诱导的镇痛作用的调节。