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EXPERIMENTAL STUDY ON BRACHIAL PLEXUS INJURY INDUCED BY RADIATION IN RATS

Objective To explore the changes of morphology and ventricornual motor neuronsin SD rats’ ventral horn of spinal cord after radiated as the therapy protocol for breast cancer, to discover the rule of radiationinduced injury of brachialplexus, and also if there exits the reversible conversion in neurons. Methods Twenty SD rats were selected. The left side of the rats was used as the radiation side, and the right side as the control side. The RIBPI animal models were established by divideddose of radiation. Using 2 Gy/time and 5 times/week, a total administered dose reached 30 Gy after 3 weeks. The behaviour of the rats was observed after radiation. At 3, 5, 7 and 9 weeks after the last radiation (n=4), the wet weights of biceps brachii muscle, upperlimb circumference and compound action potential were examined; the pathological changes of biceps brachiimuscle, the morphological changes, counts of the motor neurons in ventral horn and axons of bilateral spinal cord were observed by HE staining, argentums staining and toluidine blue staining. Results The rats showed lameness and a “claw hand” 3 weeks after radiation. Compared with control side, thewet weights of biceps brachii muscle and upperlimb circumference were significantly reduced, meanwhile, the compound action potential significantly decreased, and its latent period was also significantly prolonged 3, 5, 7 and 9 weeks (Plt;0.05). The histological observation: Musculocutaneous nerve showed decreased medullated fibers, heterogeneous ditribution and decreased density, thin myelin sheath, damaged nerve structure and collagen hyperplasia; biceps brachii muscle showed degeneration, fiber breakage and inflammatory cell infiltration; The account of motor neurons in ventral horn was significantly decreased in the radiation side with time extending, the sign of cell death, such as, the neurons crimple, and karyolysis were observed(Plt;0.05). Conclusion Large dose of X-ray can inducedbrachial plexus injury, and the lameness, a “claw hand”, biceps brachii muscle atrophy and the compound action potential abnormality. The account of motor neurons in ventral horn was significantly decreased. The motor neurons showed oxonal degeneration and myelinec degeration.