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.? 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