When someone sustains a spinal cord injury (SCI), one of the most difficult issues to deal with is that there is no "cure" at the present time. One would think that, with the "explosion in scientific knowledge" we hear about almost every day, SOMEONE would be doing SOMETHING to find a cure for people with SCI. If we can achieve the impossible in other areas, like transplanting entire organs and organ systems from one person to another and isolating human genes, why can't we figure out why the spinal cord does not repair itself and then do something to correct this biological problem? Compared to a lot of the scientific puzzles that HAVE been solved, it shouldn't be all that difficult...
There are really two separate issues involved in this assumption:
- Is the scientific question, "Why won't the spinal cord regenerate?" easy to answer?
- What's being done to find a cure?
Let's look at these issues and put them into the context of what scientists have been doing about SCI over the past half century.
Before World War II, an injury to the spinal cord was considered to be a fatal condition. If you did not die as a direct result of the injury, you probably would die within a few weeks or months from complications, such as a kidney infection, respiratory problems, or badly infected skin sores.
Fortunately, an improved understanding of SCI led to better patient management, enabling many people to survive their injuries and the initial period afterwards. In addition, the discovery of penicillin and sulfa drugs made common, but life-threatening complica-tions like kidney and skin infections manageable conditions rather than potential killers.
Because the spinal cord carries vital information to the brain, the muscles and many organs, the fact that SCI is now a survivable injury is a miracle itself. However, this miracle leads to another pressing need - to find a way to reverse, or at least diminish, the devastating physical effects of the injury.
The Search For the Cure
The 1980's and 1990's have been an exciting time for people interested in spinal cord injury repair and Regeneration. Both in terms of treat-ment techniques and general knowledge about nervous system function, the progress that has occurred in recent years is encouraging.
The search for a cure involves one of the most complex parts of the human body. The spinal cord is an integral part of the body's most specialized system, the Central Nervous System (CNS). The CNS consists primarily of the brain and spinal cord.
A major role of the spinal cord is to carry mes-sages to and from all parts of the body and the brain. Some of these messages control sensation, such as knowing your finger is touching a hot stove, while others regulate movement. The spinal cord also carries mes-sages that regulate autonomic functions such as heart rate and breathing - over which we generally do not exert voluntary control.
The spinal cord carries these messages through a network of nerves which link the cells of the spinal cord to target cells in all other systems of the body. An individual nerve cell is called a Neuron, each with receptive branching fibers called dendrites. The Axon, carrying an output signal, extends from the cell body, and is covered by a protective fatty substance called a Myelin sheath which helps the impulse travel efficiently.
A Nerve Impulse from one neuron is picked up by the Dendrite of the next nerve cell in the pathway at a specialized connection called a Synapse. An electrochemical reaction causes the impulse to "jump" across the synapse and the signal stimulates the second nerve cell and the impulse then travels down its axon. The message is picked up and transmitted by a series of neurons until the connection is complete.
There are millions of nerve cells within the spinal cord itself. Some of these Lower Motor Neurons receive Motor commands from the brain and send their signals directly to the muscles. Other spinal cord neurons form relay pathways for information travelling up or down the length of the spinal cord. Still other spinal cord neurons remain intact and form intricate circuits below the level of injury. Because cells below the injury are no longer under voluntary control, they cannot be utilized as effectively and may cause unintentional movements such as spasms.
Regeneration
Most of the cells in the human body have the ability to repair themselves after an injury. If you cut your finger, often you have a visible laceration for a few days or weeks, followed by the formation of a scar. In time, you may not be able to tell that the cut had occurred. This indicates that skin cells regenerate, just like cells in the blood vessels, organs and many other tissues. Peripheral nerves (nerve fibers outside the brain and spinal cord), such as those located in your fingertips, also regenerate, although this process is different from that in the skin and other organs.
For years, scientists have focused on the big mystery: "Why doesn't the central nervous system regenerate?" This question is even more perplexing because we know that central nerves in lower animal species CAN regenerate. There are no definite answers to this mystery yet, but scientists are exploring the questions in many ways.
Basic Cell Research
An important avenue of research is to look at normal cell function in the CNS of mammals. Scientists investigating this area of research are attempting to identify and describe cellular interactions in properly working systems. In addition, they are working with SCI models in an attempt to identify and explain what occurs after an injury.
Through cell research, scientists are trying to identify the following:
1. What substances are present in the CNS which "switch off" CNS nerve growth in mammals?
- It has been shown that regeneration occurs in lower animals, as well as in mammalian fetuses in the very early stages of development. At some point in development, the cells appear to lose the ability to regenerate. This loss may be related to the maturation of the nerve cells or to changes in other nervous system cells past which axons must regenerate.
2. What growth inhibiting factors, present in the CNS of mammals, prevent nerve cells from regenerating and reestablishing connections (synapses)?
- Scientists have identified some proteins in the myelin sheath surrounding spinal cord axons which inhibit nerve cell growth. Additionally, other regeneration-inhibiting proteins have been identified on the surfaces of cells that form the nervous system equivalent of a "scar". Some scientists believe that nerve cells can be encouraged to regrow and re-establish Functional synapses by removing or altering this cellular "scar". Antibodies generated against some of these proteins can neutralize the inhibitors and allow growth to occur. The ability of central nerves to regenerate in lower animals is thought to be due to the lack of inhibitors in their CNS.
3. Can growth stimulating substances can be introduced into the mammalian CNS to encourage nerve growth and synapse development?
- Investigators are attempting to alter the Environment around the injury site to encourage nerve cell growth and repair. As described above, our peripheral nerves can regenerate. This is due to the presence of cell proteins that stimulate rather than inhibit nerve growth. When these cells or the factors they produce such as "growth factors that nourish nerve cells are introduced into the CNS, central nerve regrowth can occur. Finding ways to effectively introduce these cells or substances to achieve functional recovery is a major goal of "cure" research today.
