Experimental study on the protection of spinal motoneurons by using glatiramer acetate based on a rat model of nerve stumps

Objective To determine the activation of glial cells after brachial plexus injury (BPI), and to explore whether glatiramer acetate (GA) can improve the survival rate of spinal motoneurons of nerve stumps by inhibiting the activation of glial cells. Methods A nerve stumps model of 76 SD rats after BPI was established by operation, and the rats were randomly divided into GA group (n=38) and control group (n=38). After operation, GA group was given subcutaneous injection of GA, and control group was given subcutaneous injection of normal saline of equal volume. The following indexes were detected at 5 time points on the 1st, 3rd, 7th, 14th, and 28th day after operation and administration. The cerebrospinal fluid（CSF）of rats was collected and the levels of tumor necrosis factor -α(TNF-α), interleukin-6 (IL-6) and brain-derived neurotrophic factor (BDNF) in CSF were measured by ELISA. The C5 stump and spinal cord were removed. The spinal cord was stained with Nissl to observe the histopathological changes. Immunohistochemistry and western blot were used to detect the astrocyte activation marker [glial fibrillary acidic protein (GFAP)] and microglia activation marker [ionic calcium adaptor protein-1 (Iba-1)] in spinal cord, and western blot was used to detect the synaptophysin (SYP) in spinal cord also. HE staining and immunohistochemical staining were used for detecting axonal growth marker [growth-associated protein 43 (GAP-43)] and Schwann cell marker S100 in nerve stump, and toluidine blue staining was used to observe myelinated nerve fiber density of regenerated nerve. Results The nerve stump model of all rats after BPI was successfully established. Compared with the control group at each time point after surgery and administration, TNF-α and IL-6 levels decreased and BDNF increased in the GA group (P＜0.05)；the survival percentage of motorneurons in the injured anterior horn increased in GA group (P＜0.05)；the expressions of GFAP and Iba-1 decreased and the expression of SYP increased in the GA group (P＜0.01); the positive rates of GAP43 and S100 immunohistochemical staining per unit area of stump increased in GA group except for the first day (P＜0.05); and the myelinated nerve fibers density in the stump increased in the GA group (P＜0.05). In addition, HE staining of stump roots showed that the neural structure of the control group was chaotic and that of the GA group was orderly. Conclusion After BPI, glial cells are activated, the functional status of nerve stump and the number of spinal motoneurons in anterior horn of spinal cord decrease. GA-protected spinal motoneurons and their nerve stump functions are improved and maintained, and GA can inhibit the activation of microglia and astrocytes.