Cure for Spinal Cord Injury Hampered by Animal Models
Christopher Reeve’s tragic accident in 1995, which left him paralyzed and confined to a wheelchair for the rest of his life, highlighted the desperate need for a cure for spinal cord injury. But a new study reveals that scientists may be significantly sidetracked by their reliance on animal experiments. A comprehensive review of traumatic spinal cord injury research, published in the most recent issue of the peer-reviewed journal Reviews in the Neurosciences, explores reasons why animal experiments are not reliably predictive of human outcomes.
PCRM neurologist Aysha Akhtar, M.D., M.P.H., reviewed years of spinal cord injury research to see how the use of animal models impacts progress. Her findings? The multitude of differences between animals and humans makes it extremely difficult for researchers to translate data from animal experiments into effective human treatments.
The evidence? Despite decades of research, scientists have yet to develop a single drug to cure spinal cord injury.
Dr. Akhtar’s paper outlines the many variations between laboratory-induced injuries in animals and human injuries, the difficulties in interpreting functional outcomes in animals, and the multitude of interspecies differences in physiology and anatomy. For example, researchers attempting to measure sensory function after injury can simply ask a human patient whether he feels a sharp or dull edge. In animals, however, they can rely only on their interpretation of the patient's behavior. If an injured animal doesn’t remove his paw from a hot plate, researchers can’t reliably know if this is because he’s not feeling the heat or if he's simply unable to move his paw, because traumatic spinal cord injury typically affects both sensory and motor function.
Spinal cord injury experiments on animals are particularly cruel. Researchers typically use mice and rats, but sometimes use dogs, cats, monkeys, and other animals. They injure the anesthetized animal’s spine or spinal cord, mostly by crushing, slicing, or burning. One common method is to expose the spinal cord or spine and drop a weight on the animal from different heights. Sometimes researchers immobilize the animal under the weight for a prolonged time.
The animals who aren’t immediately killed after the injuries are often kept alive for months, undergoing stressful tests to gauge their recovery and response to various treatments. The animals experience great pain; it is unknown how much, if any, painkillers are administered.
Although scientists have just begun to develop alternatives to the use of animals in spinal cord injury research, several techniques show great promise. Researchers at the University of Miami, for example, are collaborating on the Human Spinal Cord Injury Model Project, which uses imaging techniques, postmortem analysis, and nerve conduction methods to study human spinal cords. Other promising directions involve simulation modeling, studies on human nerve tissues and cells, and the study of human cadavers.
PCRM recently submitted a petition to the Food and Drug Administration calling for the mandatory use of nonanimal methods in drug development.