〔Abstract〕 To investigate the protective effects and mechanisms of acellular nerve allografts (ANA) on motor neurons in the spinal cord anterior horn of sciatic nerve injury ( SNI) rats . Methods SPF grade male SD rats were randomly divided into normal , model , ANA-bridged (bridge group) , and autologous nerve transplantation groups (autograft group) , with 6 rats in each group . The SNI rat model was established using the right sciatic nerve clamp method for 10mm . In the bridge group , the ANA was bridged to the two severed ends of the injured sciatic nerve , and in the autograft group , the autologous nerves were flipped head to tail and then bridged to the two se- vered ends . A spectrophotometer was applied to determine the DNA content in normal nerves and ANA . The foot- print test was used to determine the sciatic nerve function index (SFI) of the rats in each group , the wet weight ra- tio of the anterior tibialis muscle was calculated . The morphology and structure of the anterior horn motor neurons of the spinal cord of each group were observed by HE staining. The immunofluorescence and Western blot were used to detect Apaf-1 , Caspase-3 , Bcl-2 , Bax , and Cyt-C proteins expression in the L4-6 segment of the spinal cord . Results The DNA content in the ANA prepared in this study was significantly lower than that in normal nerves (P < 0. 05) . Compared with the normal group , the SFI and wet weight ratio of the anterior tibialis muscle were re- duced in the model group (P < 0. 001) ; compared with the model group , both SFI and wet weight ratio of the ante- rior tibialis muscle significantly increased in the bridge group and the autografts group ( P < 0. 05 , P < 0. 001) , and the SFI and wet weight ratio of the anterior tibialis muscle in the autograft group were higher than those in the bridge group (P < 0. 001 , P < 0. 01) . The results of HE staining showed that the motor neurons in the anterior horn of the spinal cord of the normal group were structurally intact and had clear cytosolic boundaries; the neurons in the model group were lysed and necrotic , with blurred cytosolic boundaries; the neurons in the bridge group were less lysed and necrotic , but the nuclear translocation phenomenon could still be seen; the neurons in the autograft group were morphologically and structurally intact with clear cytosolic boundaries . Compared with the normal group , the expression of Apaf-1 , Caspase-3 , Bax and Cyt-C proteins significantly increased in the model group (P < 0. 001 , P < 0. 01 , P < 0. 01 , P < 0. 05) , but the difference of Bcl-2 protein expression was not statistically sig- nificant. Compared with the model group , the expression of Apaf-1 , Caspase-3 , Bax , and Cyt-C proteins signifi- cantly decreased (P < 0. 001 , P < 0. 05) ; but the expression of Bcl-2 protein significantly increased in the bridge group and the autograft group (P < 0. 05) . The expression of Apaf-1 , Caspase-3 , Bax and Cyt-C proteins in the autografts group was lower than that in the bridge group (P < 0. 001 , P < 0. 05) . Conclusion ANA can exert a protective effect on motor neurons in the anterior horn of the spinal cord of SNI rats by improving the morphology and structure of neurons , increasing the expression of Bcl-2 protein , but decreasing the expression of Cyt-C , Bax , Caspase-3 , and Apaf-1 proteins in the spinal cord . The mechanism of ANA may be related to the Bcl-2/Cyt-C/ Apaf-1-mediated mitochondrial apoptosis signaling pathway .