Dopamine D3 and D3 Receptors
Dopamine influences movement, learning, attention, and emotion. Excess activity at dopamine receptors has been linked to the disorder, schizophrenia. Some drugs, such as cocaine, block the reuptake of dopamine, as well as norepinephrine and serotonin. The extra neurotransmitter molecules then remain in the synapse, which then intensifies their normal mood altering effects, which produces a euphoric rush. This is the “high” associated with the use of cocaine. When cocaine levels drop, the absence of these neurotransmitters then causes a “crash”.
Dopamine can either be present in deficient or excessive amounts, which can both cause disease. Dopamine deficiency in the striatum or substantia nigra results in Parkinson's-like symptoms. In this case, movement becomes slow and rigid, accompanied by muscle tremor. Certain drugs, such as L-DOPA have been created to supplement the quantity of dopamine in the brain. An excessive amount of dopamine is affiliated with schizophrenia, characterized by altered behavior, and delusions.
The dopamine D3 receptor is a potential site for anti-psychotic drug action and may be involved in the patho-physiology of schizophrenia.
Dopamine D3 receptor (DRD3) gene variants have been implicated in the pathogenesis of psychiatric disorders. Many studies, however, have failed to replicate the association of dopamine D3 receptors with schizophrenia. A possible reason for this may lie in the definition of phenotype, which is traditionally based on psychiatric diagnosis. In a study that was done, professionals investigated the possibility that variants of the dopamine D3 gene might be associated with symptomatology in a sample of subjects affected by major psychoses. Two hundred and eleven patients that were affected by major psychoses were assessed by the Operational Criteria Checklist for Psychotic Illness (OPCRIT) and were also typed for the dopamine D3 variants using polymerase chain reaction techniques. Mania, depression, delusion, and disorganization were the four symptomatologic factors used as phenotype definitions. Dopamine D3 variants were not associated with these symptomatologic factors, and consideration of possible stratification effects, such as sex and psychiatric diagnosis, did not reveal any association either.
Sources:
Dec. 13, 2005. bio.davidson.edu.
Dec. 13, 2005. ncbi.nlm.nih.gov.
Dec. 13, 2005. interscience.wiley.com. © 1999 Wiley-Liss, Inc.
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