Establishment of a Rodent Model of Neural Injury After High Frequency Monopolar Stimulation of the Motor Cortex

Direct electrical motor cortex stimulation with short-train high-frequency stimulation (HFS) for motor evoked potentials (MEPs) has been used intraoperatively during supratentorial surgeries, but the safety threshold is poorly defined. The goal of this study is to establish a rat model for the investigation of neural damage in the cerebral cortex caused by high current HFS to aid in defining safety thresholds. We performed bilateral craniotomy on 12 rats. Cerebral sensory-motor cortex was stimulated with a high-frequency current for 100 times. The rats were sacrificed and the brains were sliced for Nissl, DAPI, and IBA-1 staining. Severe neural damage of the cerebral cortex was found in all cases, including markedly shrunken and pyknotic cells. IBA-1 staining revealed reactive microglia morphology in the lesion area. DAPI staining showed nucleus degeneration and deformation. The cell density were significantly lower within the lesion area compared to the contralateral side. This study has established a brain lesion model caused by HFS on rats. These results suggest HFS may carry a risk of serious neural damage if repeatedly applied to the same brain site. More experiments are needed to fully understand the safety threshold of direct cortical stimulation with HFS for clinical use.