Dopamine is one of many chemicals called neurotransmitters that are used by the brain and nervous system to communicate. It is responsible for relaying messages related to wakefulness, concentration, appetite, motivation, memory and feelings of reward. Dopamine is also the biochemical precursor of two other neurotransmitters -- epinephrine and norepinephrine.
Synthesis
Dopamine is synthesized from the amino acid tyrosine. This amino acid is abundant in meats, dairy products and soy. Tyrosine undergoes a series of enzymatic modifications to yield dopamine. Cells that use dopamine as a neurotransmitter are referred to as dopaminergic. The amount of dopamine that can be made is limited by the activity of the first enzyme in the synthesis chain -- tyrosine hydroxylase. Because of this, taking tyrosine supplements has little to no effect on brain levels of dopamine.
Localization
Dopaminergic cells represent a very small percentage of the neurons in the nervous system, accounting for only 0.0005 percent of the cell population. Three major pathways utilize dopaminergic neurotransmission in the central nervous system: the mesostriatal pathway, the mesocortical pathway and the tuberoinfundibular pathway.
Dopamine Storage and Release
Dopamine that is to be used in communicating neuronal impulses is packaged safely into proteins called vesicular monoamine transporters, or VMATs. When the cell is stimulated, it releases several of these dopamine-containing VMATs, which will transport the neurotransmitter out of the cell. After dopamine has done its job, it is either re-packaged and transported back into the cell to be reused or degraded by special enzymes.
Oxidative Stress
When there is more dopamine present inside of a cell than there are vesicles to store it in, oxidative stress can occur and cause damage or death to the cell. It is thought that dopamine overload causes biochemical damage to cellular mitochondria that provide the cell with all of the energy it requires to function. Damage to these cellular organs results in death of the cell.
Parkinson's Disease
Parkinson's disease is a movement disorder caused by the degeneration and death of dopaminergic neurons in an area of the brain called the substantia nigra; this area is part of the mesostriatal pathway. Although it is not clear exactly what goes wrong to trigger the death of striatal cells, research has shown that excess dopamine can cause the mitochondrial stress and protein aggregations that contribute to the pathology of the disease.
References
- "Journal of Computational Neuroscience"; Dynamics of Tyrosine Hydroxylase Mediated Regulation of Dopamine Synthesis; P Kaushik, et al.; April 2007
- "Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd Edition)"; Eric Nestler, Seven Hyman and Robert Malenka; 2009
- Dana Foundation: Rethinking Dopamine's Role in Parkinson's Disease
- "Parkinsonism & Related Disorders"; Toxic Effects of Dopamine Metabolism in Parkinson's Disease; N. Hattoria, et al.; January 2009
