Reversal of chronic stress-induced pain by transcranial direct current stimulation (tDCS) in an animal model

Transcranial direct current stimulation (tDCS) has been suggested as a therapeutic tool for pain syndromes. Although initial results in human subjects are encouraging, it still remains unclear whether the effects of tDCS can reverse maladaptive plasticity associated with chronic pain. To investigate this question, we tested whether tDCS can reverse the specific behavioral effects of chronic stress in the pain system, and also those indexed by corticosterone and interleukin-1 beta levels in serum and TNF alpha levels in the hippocampus, in a well-controlled rat model of chronic restraint stress (CRS). Forty-one adult male Wistar rats were divided into two groups control and stress. The stress group was exposed to CRS for 11 weeks for the establishment of hyperalgesia and mechanical allodynia as shown by the hot plate and von Frey tests, respectively. Rats were then divided into four groups control, stress, stress+sham tDCS and stress+tDCS. Anodal or sham tDCS was applied for 20 min/day over 8 days and the tests were repeated. Then, the animals were killed, blood collected and hippocampus removed for ELISA testing. This model of CRS proved effective to induce chronic pain, as the animals exhibited hyperalgesia and mechanical allodynia. The hot plate test showed an analgesic effect, and the von Frey test, an anti-allodynic effect after the last tDCS session, and there was a significant decrease in hippocampal TNF alpha levels. These results support the notion that tDCS reverses the detrimental effects of chronic stress on the pain system and decreases TNF alpha levels in the hippocampus. (c) 2012 Elsevier B.V. All rights reserved.