Experimental Syringomyelia in the Rat: Histopathology of Spinal Cord and Kinematic Analysis of Locomotion

ABSTRACT

The neurotoxic effects of excitatory amino acids(EAAs) in the brain are well documented, but their toxicity in the spinal cord has not been thoroughly studied. Intraspinal microinjections of quisqualic acid(QA) were done to evaluate its neurotoxic effects on neurons in the adult rat spinal cord. Animals were divided into four groups based on times of post-QA injections, ranging from 7-49 days. Total volume injected in each group ranged from 0.3 to 2.0microL of QA and normal saline(vehicle) were injected in lower thoracic and upper lumbar spinal cord. Kinematic analysis of recovery process was performed using a computerized motion analysis system after intraspinal injection of QA and saline. Our results showed that unilateral injections of QA produced either unilateral or bilateral neuronal degenerations during the survival period. This was accompanied by an inflammatory reaction and initiation of pathological process leading to spinal cavitation in 23 of 25 animals. Segments affected by QA injections showed darkly stained, hypertrophied neuronal profiles, and an increased expression of glial fibrillary acidic protein(GFAP). Immunostaining for GFAP was especially intense in the areas of neuronal degeneration and around the border of spinal cavities. The kinematic analysis of locomotion in the right hindlimb showed a decrease in gait height(pre-injection level 2.07+/-0.12cm) at post QA injection 1 week(1.53+/-0.09cm), but returned to pre-injection level at 5 weeks(1.83+/-0.15cm). There was no statistical difference in the gait distance before and after QA injections. Results of this study have shown that the intraspinal injection of QA may be a suitable model to study cellular events of EAA-induced neurotoxicity on spinal neurons and the pathological process of spinal cavitation following neuronal degeneration. Computerized motion analysis system was useful for detection of the neurological deficits from minor spinal cord injury.