Changes In The Expressions Of Bcl-2 And Bax In Spinal Cord Following Spinal Cord Transection In Rat

Objective: To study the changes in the expressions of Bcl-2 and Bax proteins in spinal cord at different sites and time following spinal cord transection in female Sprague-Daeley (SD) rats.Methods: Female SD rats (n=20) weighing on average 200 g (180-220 g) were used to prepare transection spinal cord injury (tSCI) models. After receiving transection injury at T9(the 9th thoracic segment) spinal cord, rats were killed at 3 days, 7 days, 14 days, or 21 days . The spinal cord was removed en bloc and examined at four segments: 0-10 mm and 10-20 mm rostral to the center of transection, 0-10 mm and 10-20 mm caudal to the center of injury. Five normal rats were killed and got the same four segments as the normal control group. The expressions of Bcl-2 and Bax proteins in the specimens of spinal cord were detected with immunohistochemistry of avidin biotin peroxidase complex (ABC) method. The numbers of Bcl-2 and Bax positive cells in the gray matter on the ventral side and dorsal side to the central canal were respectively counted for each section. All data were expressed as x±S and analyzed using the computer program SPSS 11.0 for windows. Differences were considered to be statistically significant at the level of P<0. 05.Results: 1. After tSCI, the bilateral posterior limbs of rats are completely paraplegic, and the recovery of motor function begins at 14days after tSCI. 2. In normal control group, the positive expressions of Bcl-2 protein are mainly distributed in the gray matter on the ventral side to the central canal. After tSCI, at 3 days, the Bcl-2 positive cells increased significantly and reached peak, at 7 days decreased to thenormal level, then kept lightly increased level till 21 days. The Be1-2 positive cells in caudal side to tSCI are more than these in rostral side. The Bcl-2 positive cells in extremital side to tSCI are more than these in proximal side. After tSCI, in the white matter the expression of Bcl-2 are increased dramatically compared to the normal control group. 3. The positive expressions of Bax protein in the normal group are extensively distributed in the abdominal horn, in the intermediate zone and in the posterior horn of spinal cord. After tSCI, the Bax positive cells increased till 7 days, then decreased to the normal level, and these changes are mainly occurred in the dorsal side to the central canal. In the dorsal side, the Bax positive cells in caudal side to tSCI are more than these in rostral side, these in proximal side more than in extremital side. In the ventral side of the gray matter and in the white matter the expression changes of Bax are little. 4. After tSCI, the ratio of Bax and Bcl-2 increased, and at 7 days reached the apex, then decreased below the normal level, and the ratio of the proximal side is higher than that of the extremital side. 5. After tSCI, the transection terminals began to degenerate to form cavitations and at 3 days the transect area of cavitations reached to the biggest, then changed little. The areas between the rostral side and the caudal side had no difference.Conclusions: l.The expression rules of Bcl-2 and Bax after tSCI: the expression of Bcl-2 is increased and reaches peak at 3 days, then decreases and maintains lightly increased level till 21 days; the expression of Bax is also increased and reaches peak at 7 days, then decreases and maintains the normal level till 21 days. Bax in the serious injury parts and Bcl-2 in the light injury parts increase greatly. 2. Bcl-2 and Bax are all participating in the pathology changes of spinal cord following injury. 3. Bcl-2 has the role of anti-apoptosis, and can abate the secondary injury after tSCI, while Bax has the reverse role. 4. Within 7 days after tSCIthe endogenetic expression of Bcl-2 protein is insufficient against apoptosis. So, general therapeutic measures should be taken as early as possible. 5. The expression changes of Bax are more active. So, to treat SCI, inhibiting Bax expression is possible more effective than increasing Bcl-2 expression. 6. After injury, the expression of Bcl-2 in white matter increases greatly. This suggests that the glial cells may take part in the rehabilitate process.