An Applied Anatomical Study Of Corticospinal Tract In Adult Rats

PartⅠPrecise Localization of Corticospinal Tract in Spinal Cord in Adult RatsObjective: To detect the precise localization of corticospinal tract in medulla oblongata and white matter of spinal cord in adult rats. Methods: Anatomical localization of the corticospinal tract were revealed by using LFB staining method and protein kinase Cγimmunohistochemistry at coronal, sagittal and transverse sections of medulla oblongata and cervical, thoracic, lumbar and sacral segments of spinal cords in normal adult Sprague-Dawley rats. Results: The labeled myelinated nerve fibers were dark blue and clearly identified with surrounding hypochromatic nerve fibers in the pyramid, decussated to the ventral part of posterior funiculus in cervical, thoracic, lumbar and sacral segments of spinal cord. PKCγimmunoreactivities were brown and expressed in pyramid. Most of PKCγimmunoreactivities decussated posteriorly and projected to the dorsal part of contralateral side of medulla oblongata. In the spinal cord, the PKCγimmunoreactivities were located at the ventral part of dorsal funiculus in cervical, thoracic, lumbar segments of spinal cord and at the middle of dorsal funiculus in sacral segments. In addition, PKCγimmunoreactivities were also expressed in the neurons at dorsal horn of medulla oblongata and different segments of spinal cord. There were no PKCγimmunoreactivities in the ventral funiculus and the lateral funiculus of spinal cord. The distribution of LFB staining fibers and PKCγimmunoreactivities at medulla oblongata and white matter of spinal cord in adult rats were correspondence with the position and courser of corticospinal tract in rodents. Conclusions: Using LFB staining method and PKCγimmunohistochemical staining method can precisely reveal the anatomical localization of corticospinal tract in rats and provide the morphological foundation for studying the lesion and functional recovery of corticospinal tract.PartⅡEstablishment of Corticospinal Tract Semitransection Model in Adult RatsObjective: To establish corticospinal tract semitransection model in adult rats successfully. Methods: Tiltboard test, LFB staining, biotin dextran amine (BDA) tracing technique and PKCγimmunohistochemistry were utilized to assess the function and morphology of corticospinal tract semitransection model. Results: Forelimbs and hindlimbs at right sides were paralyzed after unilateral corticospinal tract semitransection. Tiltboard test showed the motor function of the opposite side of lesion side were limited. There was no LFB dense dye nerve fiber bundle in left pyramid at the level of injury. BDA tracing method and PKCγimmunohistochemistry showed only one bundle of BDA and PKCγpositive fibers decussated from right to left at the level of decussation of pyramid, then descended to sacral segments at the left part of dorsal funiculus of spinal cord. Under the level of injury, there were no BDA and PKCγlabeling nerve fibers decussated from left to right at the level of decussation of pyramid and descended at the right part of dorsal funiculus of spinal cord. Conclusions: Selectively semitransect the unilateral pyramidal tract at pyramid of medulla oblongata is easy to locate the position of corticospinal tract and the models are effective and reproducible. It is an ideal animal model for studying the plasticity and regeneration of corticospinal tract. BDA tracing technique and PKCγimmunohistochemistry are effective morphological assessments of corticospinal tract semitransection model. PartⅢThe Changes of Ultrastructure of Corticospinal Tract after Corticospinal Tract Semitransection in RatsObjective: To investigate the changes of ultrastructure of corticospinal tract after corticospinal tract semitransection in rats. Methods: Electron microscopy were utilized to determine the degeneration of the corticospinal tract at 4, 14, 28 days after corticospinal tract semitransection. Results: The early ultrastructural morphology revealed that the myelin sheath and axons of lesioned corticospinal tract were swelling and irregular in shape. Subsequently, during the extended periods, the ultrastructural changes were myelinoclasis, dissolvation in myelin sheath, and demyelination, shrink of cytoplasm, vacuolar degeneration, increase of organelles in axons progressively. These changes of lesioned corticospinal tract at cervical, thoracic, lumbar segments of spinal cord were more serious than those closed to lesion site. Conclusions: These results indicate that the myelin sheath and axons undergo progressive and extensive degeneration in lesioned corticospinal tract.