Development and Experimentation of a rTMS Device for Rats

Neuropathic pain (NP) is related to the presence of hyperalgesia, allodynia and spontaneous pain, affecting 7–10% of the general population. Repetitive transcranial magnetic stimulation (rTMS) is being applied for NP relief especially in patients with refractory pain. Objective: As NP response to existing treatments is often insufficient, we aimed to develop a magnetic stimulator and customized coils and evaluate rTMS treatment over the nociceptive response of rats submitted to a NP model. Methods: The magnetic stimulator and the butterfly coils were developed in the Biomedical Engineering lab of Hospital de Clínicas de Porto Alegre. The device generated pulses with a 1 ms pulse width in a 1 Hz frequency. A total of 106 adult (60-days old) male Wistar rats were divided into 9 experimental groups: control (C), control plus sham rTMS (C + s.rTMS), control plus rTMS (C + rTMS), sham neuropathic pain (s.NP), sham neuropathic pain plus sham rTMS (s.NP + s.rTMS), sham neuropathic pain plus rTMS (s.NP + rTMS), neuropathic pain (NP), neuropathic pain + sham rTMS (NP + s.rTMS) and neuropathic pain plus rTMS (NP + rTMS). NP establishment was achieved 14 days after the surgery for chronic constriction injury (CCI) of the sciatic nerve, and rats were treated with daily 5-min sessions of rTMS for 8 consecutive days. Nociceptive behavior was assessed by von Frey and Hot Plate tests at baseline, after NP establishment and post-treatment. Results: The measurement of magnetic field intensity 2.5 mm and 5.0 mm from the coil center on the 90º axis showed 160 mT and 125 mT respectively. rTMS treatment promoted a partial reversal of the mechanical allodynia and a total reversal of the thermal hyperalgesia induced by CCI. Conclusions: We presume that low-frequency rTMS is a potential tool for NP treatment, possibly due to the modulation of plasticity and promotion of an analgesic effect.