Spinal cord injuries to the upper spinal cord (around T6 or even T10) can damage the nerve fibers that connect the brainstem and the spinal cord. Damage to the spinal cord at this level can make the patient susceptible to a potentially life-threatening condition known as autonomic dysreflexia.
Autonomic dysreflexia occurs if a patient has an upper spinal cord injury and receives some sort of strong stimulus to the lower part of the body, often the bladder or bowel. The strong sensory impulse travels up the spinal cord and evokes a response from the sympathetic nervous system. The sympathetic nervous system is a branch of the autonomic nervous system, which controls all those things that occur automatically (beating of your heart, breathing moment-to-moment adjustments of the blood pressure, etc.). The sympathetic branch of the autonomic nervous system is associated with those elements of the “fight or flight” response. If you are scared or surprised, your heart beats faster, face flushes, skeletal muscle become ready for action and so on. A strong sympathetic response will increase the heart rate and cause other blood vessels to constrict to redirect blood flow to the organs that are vital for survival under extreme conditions. In short, the blood pressure rises dramatically, but only transiently.
This widespread and strong sympathetic response causes widespread constriction of blood vessels, particularly in the muscles below the diaphragm. This causes hypertension (high blood pressure). The brain detects this by means of detectors in the arteries known as baroceptors in the arteries. The brain tries to defuse the situation by sending inhibitory impulses down the spinal cord, but these inhibitory signals never reach the constricted blood vessels because of the spinal cord injury. The brain has a back-up plan in which it tries to decrease peripheral blood pressure by slowing the heart rate. This, however, only works a bit and the hypertension continues.
This sudden increase in blood pressure and a decrease in heart rate is the hallmark of autonomic dysreflexia. Patients also tend to lose control of their bladder and bowel. If this all sounds unpleasant, it is.
Fortunately, a stem cell treatment for autonomic dysreflexia might be in the works. Armin Blesch, PhD, of the Spinal Cord Injury Center at Heidelberg University Hospital, in collaboration with colleagues from the University of California, San Diego, tested a treatment protocol for autonomic dysreflexia. Blesch and colleagues isolated neural stem cells from the brainstem of fetal rats. The goal was not the completely heal the spinal cord injury, but to provide some healing so that the compensatory impulses from the brain could find their way down to the abdominal area to relieve the hypertension.
Blesch tested spinal cord-injured rats that had received transplantations of the fetal brainstem stem cells with spinal cord-injured rats that had received no such treatment. Then Blesch and his colleagues compared the response of these animals when the lower portion of the body was heavily stimulated eight weeks after the stem cell transplantations.
According to Blesch: “Only the animals that received transplants of fetal cells derived from the brainstem had a resting heart rate and blood pressure that was similar to normal values,” Blesch said. “When we looked at their spinal cords, we found evidence that the transplanted cells may be serving as nerve relays to reconnect the brain with centers of control for cardiovascular function.”
This is a preclinical study, but it is an important proof-of-principle study that shows that complete healing of the spinal cord in not necessary to repair particular functions that can prevent a life-threatening condition such as autonomic dysreflexia.
Hopefully in humans, the neural stem cell line made by StemCells Inc, could work in patients with upper spinal cord injuries who are at risk for autonomic dysreflexia. Perhaps human clinical trials that address this very issue might be in the works.