Spontaneous Neuronal Plasticity in the Contralateral Motor Cortex and Corticospinal Tract after Focal Cortical Infarction in Hypertensive Rats

Abstract

Objectives: In this study, we investigated the spontaneous neural plasticity on the contralateral side in hypertensive rats, including the expression of nerve growth factors (synaptophysin [SYN] and growth-associated protein 43 [GAP-43]), and the association between nerve fiber sprouting and redistribution, and the recovery of motor functions following sensorimotor cortical infarction. Methods: Initially, Sprague-Dawley rats were induced with renal hypertension by the bilateral renal arteries clips method. Further, they were induced with cerebral ischemia by the middle cerebral artery electrocoagulation method; 70 male rats completed the study. We compared the changes in the corticospinal tract (CST) and the expressions of SYN and GAP-43 on the contralateral side in rats with cerebral infarction using immunohistochemical staining, western blot, and biotinylated dextran amine (BDA) tracing analyses. The recovery of motor function in rats after cortical infarction was evaluated by the foot-fault and beam-walk tests. Results: The motor behavior tests revealed that the motor function of rats could recover to various degrees after focal cortical infarction. Compared with the sham-operated group, the SYN and GAP-43 levels increased in the motor cortex of the opposite hemisphere within 28 days after middle cerebral artery occlusion (MCAO). The increase in SYN and GAP-43 expressions presented differently in layers Ⅱ, Ⅲ, and Ⅴ. The amount of BDA-positive fibers also increased significantly in the denervated cervical spinal gray matter on day 56 post-MCAO. Conclusions: The increases in SYN and GAP-43 on the contralateral side of the motor cortex could promote CST sprouting and rewiring in the spinal cord gray matter and also spontaneous motor function recovery after cortical infarction.