Abstract: Objective To investigate the structural and functional changes of lower motor neuron distal to the site of spinal cord injury in rats. Methods Seventies Sprague-Dawley rats were divided randomly into 6 groups: sham-operation group (controls, n=10) and 3 day group (n=10), 1 week group (n=10), 2 week group (n=10), 4 week group (n=15) and 8 week group (n=15) after spinal cord transaction at T10. Neuronal apoptosis and acetylcholinesterase (AChE) activity of spinal cord at L4- 6 were observed by using the terminal deoxynucleotidal transferase- mediated DUTP-biotin nick end labeling (TUNEL) method and the semiquantitative enzyme cytochemistry, respectively. Results The assessment of apoptosis by TUNEL labeling showed that fluorescent markers were observed occasionally in anterior horn distal to the site of injury. The optical density (OD) value of AchE positive motor neurons (area > 300 μm2) initially decreased about 3 days after transaction and then overshot 1 week or so. However, after that, the OD value decreased again, the lowest about 4 weeks. Then the OD value increased again, though at 8 weeks was still lower than that of controls (P<0.05). Conclusion The findings on indistinctive apoptosis provided the proof of no significant changes of lower motor neuron distal to the site of transection. Semiquantitative histochemical results about AChE reflected marked metabolic changes of motoneurons caudal to the transaction, which represented as part of functional reorganization.

Key words: spinal cord injury, transneuronal degeneration, functional reorganization