Transcranial direct current stimulation combined with exercise modulates the inflammatory profile and hyperalgesic response in rats subjected to a neuropathic pain model: Long-term effects.

Background: Behavioral alterations, like mechanical and thermal hyperalgesia, and modulation of biomarkers in the peripheral and central nervous systems (CNS) are markers of chronic pain. Transcranial direct current stimulation (tDCS) with exercise is a promising therapy for pain due to its neuromodulatory capacity.

Objective: To assess the individual effects of tDCS, exercise, and the two combined on the nociceptive response and BDNF, IL-1β, and IL-4 levels in the CNS structures of rats in a chronic pain model.

Methods: For 8 consecutive days after the establishment of chronic neuropathic pain by inducing a constriction injury to the sciatic nerve (CCI), the rats received tDCS, exercise, or both treatments combined (20 min/day). The hyperalgesic response was assessed by von Frey and hot plate tests at baseline, 7, and 14 days after CCI surgery and immediately, 24 h, and 7 days after the end of treatment. The BDNF, IL-1β, and IL-4 levels were assessed in the cerebral cortex, brainstem, and spinal cord by enzyme-linked immunosorbent assay at 48 h and 7 days after the end of treatment.

Results: The CCI model triggered marked mechanical and thermal hyperalgesia. However, bimodal tDCS, aerobic exercise, and the two combined relieved nociceptive behavior for up to 7 days following treatment completion.

Conclusions: Bimodal tDCS, aerobic exercise, or both treatments combined promoted analgesic effects for neuropathic pain. Such effects were reflected by cytokine modulation throughout the spinal cord-brainstem-cerebral cortex axis.