Parkinson's Disease - Introduction

Other Changes. The PD disease process also appears to impair nerve endings in the heart to cause dysautonomia--changes in the autonomic (also called sympathetic) nervous system. Such changes may impair the release of norepinephrine, a hormone that regulates blood pressure, pulse rate, perspiration, and other automatic responses to stress. Evidence suggests this may be responsible for the abrupt drops in blood pressure when standing that occur in PD. Further research is underway to determine if the loss of nerve terminals is confined to the heart or if it affects other organs as well.

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Biologic Factors

Apoptosis and Alpha Synuclein. Important research now suggests that three molecules are critical in the development of inherited PD: alpha synuclein, parkin, and ubiquitin, which all interact in the normal brain. Abnormally high levels of alpha synuclein, which is produced in dopamine-rich nerve cells, may play a central role. Normally, two other molecules, parkin and ubiquitin, are involved in the natural self-destruction of synuclein--a natural process of programmed cell death called apoptosis. If this process goes awry, for instance with a defective parkin gene, then apoptosis fails to occur. If synuclein is not eliminated in these cells, it builds up and becomes toxic to dopamine. In such cases, synuclein accumulates in Lewy bodies, the deposits of fibrous tissue found in all patients with PD.

Another protein, beta amyloid, also increases the build-up of synuclein. Beta amyloid is a known factor in Alzheimer's disease, and may help explain the co-existence between Alzheimer's and Parkinson's disease in many patients.

Lewy Bodies. The fibrous deposits known as Lewy bodies are the hallmark signs of Parkinson's disease. They are found in the substantia nigra, the place in the brain where dopamine is first released. It is not clear whether Lewy bodies are the major killers of the nerve cells or whether they are simply a byproduct of the degenerative process. They are found not only in the brains of patients with Parkinson's disease, but, in rare cases, may show up in cells in other parts of the body (e.g., the heart, intestine), causing severe disabling symptoms. These substances are also present in other diseases that cause dementia, such as Alzheimer's, and can occur in people without neurologic symptoms.

The Mitochondria and Oxygen-Free Radicals. Some research has observed that certain Parkinson's patients have a significantly low levels of complex I, an enzyme found in the mitochondria, sausage-like structures that are the primary source of energy within cells. Some theories suggest that low amounts of complex I may make nerve cells vulnerable to the assault of oxygen free radicals (also called oxidants). Oxidants are unstable molecules that bind to other molecules in the body. They are normally produced by the natural chemical processes in the body. If the body is subjected to environmental stresses, however, they can be over-produced. And, in excess, they can damage any cell, including nerve cells in the brain, and even interferes with their DNA.