Transcranial direct-current stimulation reduces nociceptive behaviour in an orofacial pain model.

Background: Transcranial direct-current stimulation (tDCS) is a noninvasive method of brain stimulation suggested as a therapeutic tool for pain and is related to the reversal of maladaptive plasticity associated with chronic pain.

Objectives: This study investigated the effect of tDCS, a non-pharmacological therapy, on local mechanical hyperalgesia, and remote thermal hyperalgesia in rats submitted to orofacial inflammatory pain model, by facial von Frey and hot plate tests, respectively. In addition, we evaluated levels of BDNF, NGF, IL-10 and IL-6 in the brainstem and blood serum of these animals at 24 hours and 7 days after the end of tDCS treatment.

Methods: Rats were subjected to temporomandibular joint pain and treated with tDCS. The animals were divided into control, pain and pain + treatment groups. Mechanical and thermal hyperalgesia were evaluated at baseline, 7 days after administration of complete Freund's adjuvant, and immediately, 24 hours, and 7 days after the tDCS treatment. Neuroimmunomodulators levels were determined by ELISA. Statistical analyses were performed by (GEE)/Bonferroni (behavioural tests), three-way ANOVA/SNK (neurochemical tests) and Kruskal-Wallis (histological analysis).

Results: Transcranial direct-current stimulation reduced mechanical and thermal hyperalgesia (P < 0.01). We observed interaction between factors (pain and treatment) increasing brainstem BDNF (P < 0.01) and NGF (P < 0.05) levels. Furthermore, we found an increase in IL-6 and IL-10 levels in the brainstem at 24 hours and 7 days after tDCS, respectively.

Conclusion: We showed that tDCS reduces thermal and mechanical hyperalgesia induced by orofacial pain until 7 days after treatment. These findings demonstrate that tDCS was effective in the control of orofacial inflammatory pain.