Two days ago, National Public Radio's All Things Considered broadcast a segment in its series This I believe with Mohammed Ali's contribution entitled "I Am Still The Greatest". The great boxing champion is suffering from Parkinson's disease. But that did not stop him to deliver his testimonial. Despite his condition, Muhammad Ali has risen to even greater championship after his boxing career ended, becoming a relentless ambassador for humanitarian causes and for more research in better treatments for this horribly destructive disease.
Parkinson's Disease is a degenerative disease of the central nervous system, resulting in severe tremor of limbs, motor arrest, and disruption of speech. Its cause is unknown, though a subset of people with the disease are known to carry an inherited genetic mutation that may predispose degeneration.
Nerve cells located in the basal ganglia, a group of forebrain structures situated nose-ward under the cerebral cortex, control our fine movements. They provide feedback to the nerve cells in the motor areas of the cerebral cortex that connect with nerve cells in the ventral horn of the spinal cord. The spinal nerve cells, known as motor neurons, innervate muscle fibers and control limb movement.
Basal ganglia functionality depends on a set of nerve cells located in a structure behind the basal ganglia, known as substantia nigra. In Parkinson's disease, the substantia nigra cells degenerate over decades and eventually die. The loss of their input to the basal ganglia perturbs motor control.
The nerve cells in the substantia nigra use the neurotransmitter dopamine to communicate with the nerve cells in the basal ganglia. Replacing the lost dopamine with the systemic administration of the drug levodopa ameliorates the symptoms. However, over time the brain develops increasing tolerance to the drug, and even high doses cannot control tremors anymore. Efforts pioneered by A. Björklund in Sweden at grafting into the brain undifferentiated cells induced to produce dopamine showed promising results in animal studies, but have not proved unequivocally successful in humans to date.
When medication eventually fails, surgically removing specific parts of the basal ganglia or inter-brain structures also involved in fine motor control may improve the condition (Çoban and others, 2009). In the last decade, however, deep brain stimulation has gained popularity. The method is less invasive and has produced superb outcome. It entails electrical stimulation of nerve cells in the basal ganglia or the inter-brain using thin implanted micro-electrode wires. The electrical impulses are thought to disrupt the persistent nerve cell activity causing the tremors. As a potential further improvement of this procedure, a research study published recently in the journal Science showed that the electrical stimulation of spinal cord nerve fibers with micro-electrodes, threaded between the vertebrae to touch the outer spinal cord where bundles of nerve fibers run that convey sensory information to the brain, may suffice to subdue tremors in Parkinsonian mice (Fuentes and others, 2009). The promising findings were reported on Mar. 19, 2009, in Julie Steenhuysen's post entitled "Spinal cord device helped mice with Parkinson's" on Reuters and Sandra Blakeslee's article entitled "Spinal Shocks Ease Parkinson’s in Mice" in The New York Times. If this procedure proved successful in people, brain surgery would be rendered unnecessary.
If Parkinson's disease runs in your family, you may be interested in gene chip tests for a predisposition available from 23andMe.
- Some patients with Parkinson's Disease benefitted from having fetal midbrain tissue rich in dopamine-producing nerve cells grafted into the dopamine-depleted basal ganglion known as striatum. However, dyskinesias, that is severe bouts of involuntary movements, hampered recovery despite major improvements in motor control. Using radioactively labeled markers and Positron Emission Tomography, Politis and others (2010) recently showed that the grafts produce extraordinary amounts of the neurotransmitter serotonin, suggesting that excessive serotonergic innervation of the striatum causes the dyskinesias. Hence, medication with long-lasting serotonin antagonists may subdue the undesired effect in grafted patients, and the use of grafts that lack great amounts of serotonergic nerve cells in future surgery may improve outcome in implantation therapy (07/03/10).
- If you are considering stem cell therapy, you may find the information on the International Society for Stem Cell Research site helpful (07/26/10).
- Today, Diane Rehm interviewed Miguel Nicolelis on her show with the title "Miguel Nicolelis: 'Beyond Boundaries'". Dr. Nicolelis is a lead investigator in this research and discusses his fascinating insights (03/16/11).
- Çoban A, Hanagasi HA, Karamursel S, Barlas O (2009) Comparison of unilateral pallidotomy and subthalamotomy findings in advanced idiopathic Parkinson's disease. Br J Neurosurg 23:23-29.
- Fuentes R, Petersson P, Siesser WB, Caron MG, Nicolelis MA (2009) Spinal cord stimulation restores locomotion in animal models of Parkinson's disease. Science 323:1578-1582.
- Politis M, Wu K, Loane C, Quinn NP, Brooks DJ, Rehncrona S, Bjorklund A, Lindvall O, Piccini P (2010) Serotonergic neurons mediate dyskinesia side effects in Parkinson's patients with neural transplants. Sci Transl Med 2(38):38ra46.