Cortical electrical stimulation in female rats with a cervical spinal cord injury to promote axonal outgrowth

Electrical stimulation (ES) to promote corticospinal tract (CST) repair after spinal cord injury (SCI) is underinvestigated. This study is the first to detail intracortical ES of the injured CST. We hypothesize that cortical ES will promote CST collateralization and regeneration, prevent dieback, and improve recovery in an SCI rat model. The CST was transected at the the fourth cervical level in adult female Lewis rats trained in a stairwell grasping task. Animal groups included (a) ES333 (n=14; 333Hz, biphasic pulse for 0.2-ms duration every 500 ms, 30 pulses per train); (b) ES20 (n=14; 20Hz, biphasic pulse for 0.2-ms duration every 1 s, 60 pulses per train); (c) SCI only (n=10); and (d) sham (n=10). ES of the injured forelimb's motor cortex was performed for 30min immediately prior to SCI. Comparisons between histological data were performed with a 1-way ANOVA or Kruskal-Wallis test, and grasping scores were compared using repeated-measures 2-way ANOVA. Significantly more axonal collateralization was found in ES333 animals compared with controls (p<.01). Axonal dieback analysis revealed ES20 rats to have consistently more dieback than the other groups at all points measured (p<.05). No difference in axonal regeneration was found between groups, nor was there any difference in functional recovery. Cortical ES of the injured CST results in increased collateral sprouting and influences neuroplasticity depending on the ES parameters used. Further investigation regarding optimal parameters and its functional effects is required.