Prior to the end of the second world war, if a person survived a severe spinal cord injury (SCI), the injury still usually resulted in their early death. This was due to the numerous complications that can accompany this type of injury such as infections of the lungs and kidneys. Though the development and widespread use of new antibiotics (and other innovations) has greatly improved the life expectancy for injured persons since that time, medical science has still not been able to restore their bodies to more normal functioning. In the last few years however, this situation is finally beginning to change. Many promising new treatments for SCI are now in the experimental stage, and a few have already moved into human clinical testing. This signals a new era in the history of this awful and devastating injury.

To be able to understand how new treatments for SCI might work, I should explain a little about what happens to the spinal cord when it is injured and why this has such catastrophic medical consequences. First, it would be both instructive and convenient to view our spinal cord as sort of a superhighway between our brain and our body. There are two major lanes of "traffic" (nerve impulses) running North and South, and there are many "on ramps" and "off ramps" at regular intervals. The northbound lanes are many millions of single nerve fibers coming in from the body carrying traffic to our brain. Most of this nerve impulse "traffic" is sensory information, coming from our many sense organs that sample the world around or inside of us. The south bound lane is from the brain to the body and this nerve impulse traffic is largely "motor" information going to our muscles and organs. These lanes of millions of nerve fibers project the conscious or unconscious will of our brain to all parts of our body. The "on ramps" and "off ramps" are where nerve fibers enter the superhighway from the body - or get off of it heading to the body. These ramps are actually thousands of nerve fibers arranged in bundles entering or leaving the spinal cord on the left and the right side of each bony vertebral segment surrounding the spinal cord from the "tail bone" (sacrum) to the highest neck (cervical) bone.

When the vertebral column (spine) is crushed or bent in an extreme accident, the spinal cord inside is severely bruised and compressed, causing localized injury and death to many of the nerve cells and their fibers. There is bleeding in this local area of injury, and a slow healing process begins where a type of scar is formed, along with fluid-filled cysts and cavities where there was once healthy tissue. It is rare for a cord to be actually cut in two, though as we shall see, the functional consequences are the same.

Some of the injured nerve fibers survive intact but loose their electrical insulation (a fatty substance called myelin) over the very short distance of the injury zone. Nerve impulse traffic is blocked at this point. Therefore sensory or motor information never reaches the target tissue just as if these nerve fibers were cut in two. Many nerve fibers are so damaged at this local region that they actually go on to separate into two pieces. That part of the fiber separated from its nerve cell body (where the cell's nucleus is) always dies in about 48 - 72 hours and is lost forever. The remaining portion of the fiber does not begin to regrow at its tip to make new connections in mammals. The result is that major portions of the north and south bound lanes actually disappear, and these millions of fibers do not regenerate to restore nerve impulse traffic. There are two important lessons to be learned from this admittedly oversimplified description that are still worthwhile:
1.) The point along this superhighway where the damage occurs determines the level of functioning left to an injured person. If the damage occurs in the lower back, than incoming sensory information from the lower body and legs stops at the injury, and motor information to the legs is lost. Thus the individual is "paraplegic". What remains functional is the upper torso and arms. If the injury is at the neck, then control even of the arms and legs is lost, and there is no normal sensing of any portion of the body. This injury results in "quadriplegia". Since the nerves that control breathing at the diaphragm leave the spinal cord high in the neck, an injury to this region can even result in the loss of respiratory ability, and breathing has to be driven by artificial means.
2.) To restore spinal cord functioning, an experimental strategy might try to a.) produce regeneration of the remaining segment of a nerve fiber to make new connections on the other side of the injury, b.) prevent, or rescue, the damaged nerve fiber from proceeding on to separation, or perhaps even functionally reuniting the two segments so that both portions of the fiber survive, c.) facilitate nerve impulse traffic to cross the region of injury in intact fibers where they have lost their electrical insulation, and d.) to limit the delayed and slow degeneration of spinal cord tissue and the formation of nonfunctional scar (that is believed to be a barrier to nerve regeneration). Where nervous tissue is killed by the injury, medical science would like to find a replacement "graft" of nervous tissue to repopulate this region. While these scenarios may seem fanciful, in fact, these are the types of experimental treatments that are becoming a medical reality.

Once a pipe dream, researchers now are uncovering ways to repair spinal cord injuries. Current methods reduce the nerve cell damage or death that occurs in the hours following injury and increase the efficiency of surviving nerve cells. New evidence suggests that future treatments also may assist the regeneration of lost connections. Prospects include transplanting new nerve cells and supporting cells, delivering proteins that stimulate regeneration by the cells already in the spinal cord, and strategies to reduce inhibition of regeneration.

A gymnast cartwheels from one side of the balance beam to the other. As she flips, underneath the ripple of protective bones called vertebrae, nerve cells are passing brain messages through the spinal cord. The cells' chatter directs the coordinated movement of muscles that propel her body. If an accident, such as a fall off the beam, injures these cells, the communication line shuts down below the point of impact.
      Some 250,000 Americans have spinal cord injuries. The result can include paralysis, a loss of sensation or the ability to move.
      The spinal cord and brain, known as the central nervous system (CNS), is one main part of our nervous system. The other primary section is the peripheral nervous system (PNS), which includes the nerves that project to the limbs, heart, skin and other organs outside the brain. Both consist of nerve cells, or neurons, and supporting cells.
      Scientists have known for years that following an injury, many neurons in the PNS can repair themselves, but CNS neurons are incapable of rebuilding connections. In fact, certain cells in the CNS produce proteins that inhibit the appendages of neurons, known as axons, from regrowing. In the early 1980s, however, researchers demonstrated that the manipulation of the neuron's environment could promote cell regeneration in animals.

This finding is prompting:

New insight on the mechanisms that regulate repair.
Approaches for repairing damaged cells.
      In the last five years, researchers have unveiled techniques that modestly improve function in animals. One example involves the transplantation of cells taken from embryos, which are known to ignore the central nervous system's regeneration opponents. Researchers discovered that these cells can integrate into the spinal cord's broken communication line. In addition, when they grafted the cells into rats and cats with bruised spinal cords, close to the time of injury, some animals showed partial improved locomotion.
      Other researchers are making use of non-embryonic mature tissues. In one recent study, rats with completely severed spinal cords apparently showed limited functional improvement with multiple peripheral nerve section implants. The cells in the grafts initially include supporting cells, and cut axons. These axons degenerate, however, leaving behind a natural tube for the CNS axons to regrow through. In the study, the CNS axons grew across the grafts and apparently made connections with the neurons that move the legs. To create a better environment for growth, the scientists aimed the grafts into the gray matter -- the butterfly-shaped tissue in the center of the spinal cord -- which bypassed the spinal cord's inhibitory proteins (see illustration). The grafts were secured with a glue that contained cell injury reducing proteins known as growth factors.
      These natural factors, themselves, are an intense area of interest. Scientists are perfecting techniques to administer the proteins including specialized implants and genetically-modified cells that produce the factors. One study showed that rat cells, engineered to secrete a growth factor and then transplanted into the animal, regenerated some of the neuronal projections needed for walking. Researchers now are testing whether the growth improves function.
      Scientists also are examining the benefits of transplanting PNS supporting cells dislodged from their neighboring cells. These cells, called Schwann cells, naturally secrete their own growth factors and have membrane proteins that aid neuron growth. Recently, scientists successfully transplanted purified human Schwann cells into the severed spinal cords of rats and reported that some of the animals had a small improvement in function. More analysis is needed, however, to determine if effective connections were established.
      When the spinal cord is damaged, injured neurons cannot regenerate leaving their chain of communication from the brain to the muscles permanently interrupted. In one technique, researchers reconnected the severed spinal cord of rats with multiple nerve grafts from the peripheral nervous system. New connections apparently developed and after several months, some rats regained limited function of their hind limbs.