Parkinson's disease slows down the voluntary movement of muscles. It causes hands and arms to shake when they are at rest, and it leads to the signature "Parkinsonian gait," a tentative, stooped walk with little or no arm swing. Dopamine is a neurotransmitter that mediates nerve signals that control voluntary muscle movement. Parkinson's disease arises when brain levels of dopamine significantly decline due to the death of nerve cells in the brainstem that produce this neurotransmitter.
The Facts
Parkinson's disease involves the gradual loss of control of voluntary muscle movements with symptoms that include tremors of the hands, arms and head; muscle rigidity; and deteriorating balance. Scientists believe the disease is brought on by a combination of environmental factors such as toxins or viruses and genetic predisposition. Parkinson's disease is correlated with a decline in brain levels of the neurotransmitter dopamine. For reasons that are not clearly understood, cells in the brainstem that produce dopamine begin to die. Symptoms of Parkinson's become evident after the death of about 60 percent to 80 percent of the dopamine-producing cells.
Treatment
One method of treating Parkinson's disease focuses on elevating dopamine brain levels by simultaneous administration of the drugs levodopa and carbidopa. MayoClinic.com explains that levodopa is an oral drug that can penetrate the brain, where it is then converted to dopamine. Carbidopa functions to delay the conversion of levodopa to dopamine until the levodopa has passed into the brain. In this way, carbidopa also protects the patient from experiencing nausea.
Considerations
Levodopa can successfully replace some of the dopamine that the patient has lost due to the death of dopamine-producing cells in the brainstem, but as time passes and the disease gets progressively worse, levodopa becomes less effective at controlling symptoms. The patient's doctor must then adjust the dose regimen.
Potential
In the July 4, 2002, issue of "Nature," Dr. Ronald McKay and his colleagues at the National Institute of Neurological Disorders and Stroke discuss the use of mouse embryonic stem cells to produce dopamine nerve cells called neurons. McKay concludes that the dopamine-producing neurons generated by the stem cells have the same properties as the dopamine neurons that reside naturally in the brainstem. Therefore, he suggests that embryonic stem cells are a potential treatment for Parkinson's disease.
The Future
One of the goals of Parkinson's disease research is to find new ways to increase dopamine levels in the brain. New drugs that might be able to do this are being evaluated in clinical trials. One such drug is called GM1 ganglioside, which might be able to increase dopamine brain levels by partially regenerating damaged dopamine-producing nerve cells in the brainstem.
References
- Healthcommunities.com: Neurology Channel: Parkinson's Disease: Overview: Signs and Symptoms
- National Institute of Neurological Disorders and Stroke: Parkinson's Disease: Hope Through Research
- MedlinePlus: Parkinson's Disease
- MayoClinic.com: Parkinson's disease: Treatment and Drugs
- PubMed: Dopamine neurons derived from embryonic stem cells function in an animal model of Parkinson's disease
