Motor cortex stimulation in rats with chronic constriction injury

Motor cortex stimulation (MCS) has gained a significant role in treatment of neuropathic pain. In order to evaluate effect of MCS in experimental animals we applied MCS to rats with neuropathic pain, which was evoked by chronic constriction injury (CCI) to the left sciatic nerve. Pain thresholds of both hind limbs were measured before, immediately after MCS, 1 h after MCS and 1 day after MCS. Effect of the stimulation was studied with respect to laterality (contralateral and ipsilateral MCS) and duration (short-term 10-min and long-term 1-h stimulation). It was found out that in control rats MCS did not affect thermal nociceptive thresholds. However, in CCI animals following results were obtained: difference score (difference in paw withdrawal latency between ligated and non-ligated hind limb) significantly decreased after both short- and long-term contralateral MCS; the difference score after the long-term ipsilateral MCS (related to the ligated hind limb) was not significantly different from that of intact animals; the effects of the contralateral short-term and the ipsilateral long-term stimulation faded within 1 h after the end of MCS, while the effect of the contralateral long-term MCS remained 1 h after the end of the MCS and faded within 24 h. It is concluded that MCS in experimental animals exerts similar effects as in human suffering from neuropathic pain and that the effect might be evoked from both cerebral cortices.