Dopamine, also known as 3,4-dihydroxyphenethylamine, is a monoamine neurotransmitter affecting dopamine receptors (D1-5). The majority of the body's dopamine is synthesized and used in the brain; however, dopamine effects many peripheral organs (e.g. heart, blood vessels) as well, and is also synthesized by the kidneys.
Dopamine is important in the reward-driven learning system; every reward studied involves dopamine being released from the brain. Dopamine is also heavily associated with motivation and locomotion. Many addictive drugs, including cocaine and amphetamine, act directly on the dopamine system. Dopamine has also been linked to Parkinson's disease, schizophrenia and ADHD.
Dopamine can structurally be classed as a phenethylamine (a monoamine chain attached to a benzene ring) molecule. It contains a catechol group attached to a monoamine chain. A monoamine chain is made up of an amine group attached to an ethane chain. This monoamine chain can be found in many neurotransmitters, including histamine, serotonin, adrenaline and noradrenaline. It's also found in many drugs, examples being tryptamines and phenethylamines.
The dopamine system
Dopamine receptors are found primarily in the central nervous system, as well as the cardio-pulmonary and renal systems. The dopamine receptors can be split into two categories. D1 and D5 receptors are part of the D1-like family, which are responsible for excitatory responses. D2-4 receptors are part of the D2-like family, which are responsible for inhibitory responses.
Drugs targeting the dopamine system
Many stimulant drugs exhibit an excitatory effect upon dopamine receptors. Among these are amphetamine, its analogues, and cocaine. Many psychedelic and entactogenic drugs also indirectly excite dopamine receptors. Antipsychotics (also commonly referred to as Neuroleptics) used in the treatment of a variety of psychiatric illnesses have inhibitory effects on dopamine receptors.
Dopamine and the reward system
The reward system is the body's method of regulating and controlling specific behaviors by inducing pleasurable effects. The mesolimbic pathway is a dopaminergic reward pathway in the brain that is associated with drug addiction. Drug addiction and misuse of the main classes of addictive drugs (opiates, stimulants, ethanol and nicotine) are due to increased dopamine transmission in the mesolimbic pathways.
Stimulant psychosis is a psychotic disorder induced by certain psychostimulant drugs, such as amphetamine, cocaine and methylphenidate. It usually occurs in recreational abuse, with large doses, but can occur due to therapeutic use. Symptoms include auditory and visual hallucinations, delusions and catatonia. It is theorized that the dopaminergic mesolimbic pathway is responsible for stimulant psychosis, as the stimulants involved all have agonist effects on dopamine receptors. This is supported by the fact that antipsychotic medication has antagonist effects on dopamine receptors.
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- ↑ Ayano, G. (2016). "Dopamine: Receptors, Functions, Synthesis, Pathways, Locations and Mental Disorders: Review of Literatures". Journal of Mental Disorders and Treatment. 2 (2). doi:10.4172/2471-271X.1000120. ISSN 2471-271X.
- ↑ Schultz, W. (August 2001). "Book Review: Reward Signaling by Dopamine Neurons". The Neuroscientist. 7 (4): 293–302. doi:10.1177/107385840100700406. ISSN 1073-8584.
- ↑ Hong, S. (2013). "Dopamine system: manager of neural pathways". Frontiers in Human Neuroscience. 7: 854. doi:10.3389/fnhum.2013.00854. ISSN 1662-5161.
- ↑ 5.0 5.1 Wise, R. A., Rompre, P. P. (1989). "Brain dopamine and reward". Annual Review of Psychology. 40: 191–225. doi:10.1146/annurev.ps.40.020189.001203. ISSN 0066-4308.
- ↑ Kelley, A. E., Berridge, K. C. (1 May 2002). "The Neuroscience of Natural Rewards: Relevance to Addictive Drugs". Journal of Neuroscience. 22 (9): 3306–3311. doi:10.1523/JNEUROSCI.22-09-03306.2002. ISSN 0270-6474.
- ↑ Badgaiyan, R. D. (2013). "A Novel Perspective on Dopaminergic Processing of Human Addiction". Journal of Alcoholism and Drug Dependence. 1 (1): 1000e101. doi:10.4172/2329-6488.1000e101. ISSN 2329-6488.
- ↑ Chronic Amphetamine Use and Abuse
- ↑ Bracha, H. S. (July 1989). "Is there a right hemi-hyper-dopaminergic psychosis?". Schizophrenia Research. 2 (4–5): 317–324. doi:10.1016/0920-9964(89)90022-4. ISSN 0920-9964.
- ↑ Brady, K. T., Lydiard, R. B., Malcolm, R., Ballenger, J. C. (December 1991). "Cocaine-induced psychosis". The Journal of Clinical Psychiatry. 52 (12): 509–512. ISSN 0160-6689.