Investigação do envolvimento do Sistema endocanabinoide na antinocicepçao induzida pela estimulação Elétrica Transcutânea do nervo -TENS

Abstract

The pathological pain affects 30% of the world population. Aiming their control, many interventions are used, which involving pharmacological and non-pharmacological treatments. Thus, a non-pharmacological strategy used has been Transcutaneous Electrical Nerve Stimulation (TENS), a method that use the electric current to induce analgesia. However, the mechanisms involved in the antinociceptive effect induced by TENS are not fully elucidated. With the discovery of the endocannabinoid system and studies demonstrated that its system have an important role in the modulation of pain, the present study aimed to investigate the involvement of this system in TENS antinociceptive effect at central and peripheral levels. For such, male Swiss mice weighing 25 to 30g, were underwent to a pain model using tumor cells of Ehrlich, injected into the paw. After that, in order to evaluate the analgesic effect of low and high TENS frequency in the mechanical allodynia induced by the cells, the animals were stimulated for both frequencies for 20 minutes, which were applied by electrodes in the right hind paw. The nociceptive threshold was measured by the von Frey hairs test. To evaluate the involvement of the endocannabinoid system, were pre administered by intra plantar (i.pl.), intrathecal (i.t.) and intra dorsolateral Periaqueductal Gray Matter (i.d.l.PAG) via, the antagonist for cannabinoid receptors type 1 (CB1), the AM 251 and the inhibitor of the enzyme responsible for the degradation of the endocannabinoid anandamide (AEA), the MAFP. Furthermore, were also used the Western blot analysis to investigate the expression of CB1 receptors and immunofluorescence analysis to quantify and co-locate these receptors. Our results found that both frequencies used reverted significantly (P < 0.05) the mechanical allodynia induced by Ehrlich tumor cells. In addition, this effect was reversed by AM251 and prolonged by MAFF, both pre injected by i.pl., i.t. and i.d.l.PAG routes. In addition to these results, the Western Blot analysis showed an increase in expression of CB1 receptors after the application of TENS, in both frequencies, in paw subcutaneous tissues and d.l.PAG, 3 hours after injection Erlinch cells. A similar result was found after immunofluorescence analysis, which found an increase in the number of CB1 receptors after stimulation with TENS, in the dorsal horn of the spinal cord and d.l.PAG. Thus, this study concludes that the endocannabinoid system may be involved in the antinociceptive effect induced by TENS, in both low and high frequency, at central and peripheral levels and suggests that this effect occurs by the activation of the descending inhibitory pain pathway, mainly by release of endocannabinoids and activation of CB1 receptors.