According to "Harrison's Principles of Internal Medicine," dopamine is an essential neurotransmitter found in the substantia nigra of the midbrain. As a neurotransmitter in the central nervous system, or CNS, it is produced in presynaptic neurons and stimulates receptors in postsynaptic neurons in order to send electrochemical signals along neural tracts. In the rest of the body, dopamine acts as a neurohormone involved in the "fight-or-flight" response.
History
A Swedish scientist, Dr. Arvid Carlsson, M.D., Ph.D., won the Nobel Prize for the discovery of dopamine in the 1950s, according to the Nobel Prize Foundation. Dr. Carlsson's research introduced to the scientific community the nature of dopamine as a neurotransmitter involved in CNS signal transduction. His intricate experiments proved the relationship between decreases of dopamine and Parkinson's disease, paving the way for future treatment of the neurological disorder.
Significance
The relationship of dopamine with several neurological conditions, such as schizophrenia and Parkinson's disease, is compelling. An imbalance of this single neuromodulator can result in audio and visual hallucinations as seen in schizophrenia, depression and anxiety, movement and cognitive dysfunction present in Parkinson's disease, and emotional disturbances.
According to "Harrison's Principles of Internal Medicine," dopamine is critical to cardiac resuscitation in hypovolemic shock. In conditions of low blood volume and cardiac arrest, dopamine is the drug of choice due to its inotropic effects such as strengthening of heart muscle contractions.
Function
Dopamine plays an important role in motor function, balance, emotional response, cognition, motivation and pleasure sensation. This neurotransmitter governs the signaling throughout the limbic system along four neuronal pathways, according to the book "Hardcore Neuroscience."
In the tuberoinfundibular pathway, dopamine is referred to as Prolactin-inhibiting factor due to its role in prolactin inhibition within the anterior pituitary gland.
Within the nigrostriatal pathway, dopamine is transmitted from the substantia nigra to the striatum region of the brain, involved in movement and sensation. The dopamine coursing the mesocortical tract controls emotional and motivational responses. The mesolimbic pathway travels to the pleasure center of the brain, known as the nucleus accumbens. The dopamine within this neural tract is associated with addiction and hallucinations.
Functions within the rest of the body are related to dopamine's catecholamine effects, which are through the stimulation of the sympathetic nervous system, according to the authors of "Harrison's Principles of Internal Medicine" and "Hardcore Neuroscience." Dopamine results in an increase in heart rate, blood pressure, perspiration and muscle strength.
Metabolism
Dopamine is the precursor to the catecholamines involved in the "fight-or-flight" response called noradrenaline, or norepinephrine, and adrenaline, otherwise known as epinephrine.
Derived from the amino acid tyrosine, dopamine production is catalyzed by dopa decarboxylase reactions. After reuptake in the postsynaptic neurons, it is then metabolized by monamine oxidase, according to the book "National Medical Series: Biochemistry."
Dopamine Imbalance Conditions
Imbalances in dopamine levels are associated with conditions such as drug addictions, alcoholism, schizophrenia, Parkinson's disease, attention deficit hyperactivity disorder or ADHD, paranoia, tumors such as pheochromocytomas and prolactinemia.
References
- "National Medical Series: Biochemistry," 4th ed.; Victor Davidson, Ph.D & Donald Sittman, Ph.D; 1999
- "Download of Psychiatry"; Saxby Pridmore, M.D.; 2006
- "Harrison's Principles of Internal Medicine," 17th ed.; Anthony Fauci, M.D., et al.; 2008
- "Hardcore Neuroscience"; Kevin Wang, M.D., et al.; 2006
- "Harvard Review of Psychiatry"; Neurobiologic Processes in Drug Reward and Addiction; Byron Adinoff, M.D.; Nov-Dec 2004
