Spinal cord stimulation of dorsal columns in a rat model of neuropathic pain: evidence for a segmental spinal mechanism of pain relief.

Although spinal cord stimulation (SCS) of the dorsal columns is an established method for treating chronic neuropathic pain, patients still suffer from a substantial level of pain. From a clinical perspective it is known that the location of the SCS is of pivotal importance, thereby suggesting a segmental spinal mode of action. However, experimental studies suggest that SCS acts also through the modulation of supraspinal mechanisms, which might suggest that the location is unimportant. Here we investigated the effect of the rostrocaudal location of SCS stimulation and the effectiveness of pain relief in a rat model of chronic neuropathic pain. Adult male rats (n=45) were submitted to a partial ligation of the sciatic nerve. The majority of animals developed tactile hypersensitivity in the nerve lesioned paw. All allodynic rats were submitted to SCS (n=33) for 30 minutes (f=50 Hz; pulse width 0.2 ms). In one group (n=16) the electrodes were located at the level where the injured sciatic nerve afferents enter the spinal cord (T13), and in a second group (n=17) the electrodes were positioned at more rostral levels (T11) as verified by X-ray. A repositioning experiment of electrodes from T12 to T13 was performed in 2 animals. Our data demonstrate that SCS of the dorsal columns at the level where the injured fibers enter the spinal cord dorsal horn result in a much better pain-relieving effect than SCS at more rostral levels. From this we conclude that SCS in treatment of neuropathic pain acts through a segmental spinal site of action.