PHILADELPHIA, PA June 7, 2001 - A study of how the severed spinal cord heals in rats shows a direct relationship between re-establishment of specific connections between the brain and spinal cord and recovery of hind-leg function, reports the June 1 issue of the journal Spine.

Spine-injured rats regain the ability to walk through regenerated connections between the lower brain and spinal cord--a pathway that cannot, unfortunately, restore leg muscle function in humans with spinal cord injury, write Dr. Yoshiaki Wakabayashi and colleagues of Tokyo Medical and Dental University.

Rats whose spinal cords are severed in infancy regain some function of their hind legs, and the researchers were looking for clues as to how this occurs. As in previous experiments, most rats whose spinal cords were cut at age two weeks had regained some walking ability five weeks later.

However, the restored function did not result from regeneration of direct pathway between the brain cortex and the spinal cord (corticospinal tracts), chemical and electrical studies suggested. Instead, rats that regained walking ability had regeneration of "subcortical" pathways originating from the brain stem.

These subcortical pathways seem better able to regenerate after injury than the "higher-level" corticospinal tracts. The difference in healing ability may reflect the fact that the subcortical pathways evolved earlier than the corticospinal tracts, the researchers suggest. Unlike in humans and other primates, the corticospinal pathways do not seem to be required for voluntary walking in rats.

Some experimental treatments have shown promise in spinal cord regeneration and recovery of function in humans. The new findings help to clarify how one form of spinal cord regeneration occurs. Future studies may be able to identify the specific growth factors or other variables that allow spinal cord regeneration in immature rats.

The results also show a direct relationship between regeneration of specific spinal cord tracts and restoration of walking ability. If the tracts between the brain and spinal cord can be re-established, recovery of function may be possible. In addition, the study shows the value of an electrical study--called muscle-evoked potentials--in confirming that specific spinal cord tracts have regenerated.
Recognized internationally as the leading journal in its field, Spine reports on today's most important diagnostic and therapeutic advances regarding spinal pain, deformity, and disability. Distinguished by its broad scope of coverage and emphasis on patient care, this popular biweekly has earned must-read status in the orthopaedic community. For more information, call 1-800-638-3030 or visit www.spinejournal.com.

---Lippincott Williams & Wilkins

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