Medical Health Encyclopedia

Dopamine. Dopamine deficiency is the hallmark feature in PD. It is one of three major neurotransmitters known as catecholamines, which help the body respond to stress and prepare it for the fight-or-flight response. Loss of dopamine negatively affects the nerves and muscles controlling movement and coordination, resulting in the major symptoms characteristic of Parkinson's disease. Dopamine also appears to be important for efficient information processing, and deficiencies may also be responsible for problems in memory and concentration that occur in many PD patients.

Although it is clear that dopamine deficiency is the primary defect in Parkinson's disease, it is not clear what causes dopamine loss. The culprit is less likely to be a single cause than a combination of genetic and biologic factors, which are triggered by some environmental assault.

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

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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.