Parkinson’s disease is a neurological disorder that affects around 1 million individuals in the United States, most of whom are older than 50. The condition is characterized by slowness of movement, muscular rigidity, tremors and postural instability.

The dopamine discovery and subsequent treatments

In the late 1950s, it was discovered that the dopamine levels in the brains of Parkinson’s patients decreased. This was followed in the 1960s by the development of an effective treatment in the form of the drug levodopa, which is converted to dopamine in the brain. At present, levodopa is combined with another drug, called carbidopa, which reduces the peripheral breakdown of levodopa. This allows greater levels to reach the brain and reduces the side effects. Newer drugs are also playing an important role in the treatment of this disorder. Examples are dopamine inhibitors and dopamine agonists, which interact directly with the dopamine receptors that can be found in the brain.

Genes and MPTP

Although almost all cases of Parkinson’s disease occur sporadically, genetic studies have demonstrated several heritable gene abnormalities in certain families. Currently, it is thought that these heritable factors influence the vulnerability of some individuals to environmental factors, such as pesticides, which increase the risk of developing the condition.

In the late 1970s, a chemical substance called MPTP was discovered to cause Parkinson’s symptoms in drug addicts. This stimulated intensive research on the causes of the disorder. MPTP was accidentally synthesized by drug designers who were trying to create a heroin-like compound. It was found to be converted in the brain into a substance that destroys dopamine receptors.

Where in the brain?

In the past decades, it has been shown that specific regions in the basal ganglia, collections of cell bodies deep lying deep in the brain, are abnormally overactive in Parkinson’s patients. It has also been found that surgical destruction of these overactive nuclei, called the palladium and the subthalamic nucleus, can greatly reduce the symptoms of Parkinson’s disease. This surgical procedure, called pallidotomy, has known a resurgence in the past decade, along with chronic deep-brain stimulation.

These techniques are quite successful for treating patients who have experienced significant worsening of symptoms and are troubled by the development of drug-related involuntary movements.

Lately, there have also been further attempts to treat such patients with the implantation of cells, such as fetal cells that are capable of producing dopamine. Another option that is currently being explored, is replacement therapy with stem cells.