March 30, 2009

Spinal Cord Stimulation May Ease Parkinson’s Symptoms

Illustration of neurons

Electrical stimulation of the spinal cord improves mobility in rodents that have the symptoms of Parkinson's disease, according to a new study. The technique, if effective in people, could provide a less invasive alternative to deep brain stimulation, which involves surgically implanting tiny electrodes into brain regions that control movement.

Parkinson's is a neurodegenerative disease that affects 1.5 million people in the United States. It's characterized by muscle stiffness, tremors, slow movement and impaired balance. It develops when brain cells that produce the neurotransmitter dopamine mysteriously begin to die. The loss of dopamine-producing neurons causes abnormal activity in the brain regions that control movement.

The first line of treatment for Parkinson's disease is L-dopa, a drug that restores dopamine. Unfortunately, L-dopa becomes less effective over time. When drugs fail, some patients turn to deep brain stimulation, in which a pacemaker-like device blocks abnormal neuronal signals by sending pulses to specific brain regions through surgically implanted electrodes. The treatment is effective for many patients, but the operation is invasive and targets very small brain structures.

Some of the faulty electrical signals in Parkinson's patients resemble those seen in epilepsy. Stimulating nerves outside the brain to suppress those faulty signals can successfully control epileptic seizures. A research team led by Dr. Romulo Fuentes and Dr. Miguel Nicolelis of Duke University reasoned that a similar technique might be used in Parkinson's patients. Their technique, called dorsal column stimulation, involves surgically implanting tiny electrodes on the dorsal column of the spinal cord, which connects to regions of the brain responsible for movement. Their work was funded by NIH's National Institute of Neurological Disorders and Stroke (NINDS) and National Institute of Mental Health (NIMH), among others.

In a study published in Science on March 20, 2009, the researchers first tested their technique in mice with acute symptoms of Parkinson's disease. To induce the symptoms, the researchers temporarily blocked dopamine production in mice that were genetically modified to prevent their brain cells from recycling used dopamine.

Seconds after a high-frequency electrical stimulation, the mice began to walk and move normally. When the scientists coupled the electrical stimulation with L-dopa (the dopamine replacement treatment), the combined treatment was more effective than either alone. Only 20% of the typical drug dose restored normal movement.

The scientists also tested the technique in another animal model that more closely mimics chronic Parkinson's disease: rats lacking about 80% of their dopamine-producing neurons. The spinal cord stimulation greatly improved these rats' impaired motor function as well.

Spinal cord stimulation represents a shift in how researchers aim to treat people with Parkinson's disease. Rather than focusing on small regions of the brain, the new approach is thought to stimulate large areas of the cortex, the brain's outermost layer. If these findings are confirmed in humans, the procedure could dramatically improve treatment for the disease by making electrical therapy safer and more broadly available.

—by Nancy Van Prooyen

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