Abstract
The lumbar spinal cords of lizards were transected, but after the initial paralysis most lizards recovered un-coordinated movements of hind limbs. At 25-45 days post-lesion about 50% of lizards were capable of walking with a limited coordination. Histological analysis showed that the spinal cord was transected and the ependyma of the central canal formed two enlargements to seal the proximal and distal ends of the severed spinal cord. Glial and few small neurons were formed while bridge axons crossed the gap between the proximal and the distal stumps of the transected spinal cord as was confirmed by retrograde tract-tracing technique. The bridging fibers likely derived from interneurons located in the central and dorsal grey matter of the proximal spinal cord stump suggesting they belong to the local central locomotory pattern generator circuit. The limited recovery of hind limb movements may derive from the regeneration or sprouting of short proprio-spinal axons joining the two stumps of the transected spinal cord. The present observations indicate that the study on spinal cord regeneration in lizards can give insights on the permissive conditions that favor nerve regeneration in amniotes.
Highlights
In most vertebrates, lesion of the spinal cord (SC) determines various degrees of paralysis, with notable exceptions in cyclostomes, some teleost fish, and aquatic salamanders [1,2,3,4,5,6], large injuries in the SC of mammals and birds determine permanent paralysis [7,8], and this result was reported for reptiles [9,10]
Eight lizards died between seven and 20 days post-amputation, probably in relation to the surgical intervention, but 17 animals survived until sacrifice for the histological analysis of the spinal cord
In these studies on lizards with complete or partially transected spinal cord, the animals begun to move their limbs again at 20–30 days post-transection, after the initial 10–15 days of complete paralysis. It is not clear from the above experiments whether the dorsal part degenerated while the ventral or motor region of the cord was still connecting the proximal with the distal stumps of the spinal cord, or whether this was due to regeneration of nerve tissue from the two SC stumps
Summary
Lesion of the spinal cord (SC) determines various degrees of paralysis, with notable exceptions in cyclostomes, some teleost fish, and aquatic salamanders [1,2,3,4,5,6], large injuries in the SC of mammals and birds determine permanent paralysis [7,8], and this result was reported for reptiles [9,10]. The histological analysis of the SC in lizards capable of recovering some movements of the hind limbs indicated that the SC lesion was incomplete [18] In these cases probably the intact nervous fibers were able to maintain some anatomical and physiological connectivity between the proximal and distal stumps adjacent to the interrupted SC. The reconnecting axons possibly re-activated the intrinsic circuits of the “central locomotor generator” present in the spinal cord [20,21,22,23], whihc was initially interrupted from the transection This process of recovery was previously described in the spinal cord of fish [2] and salamanders [3,4]
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