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Dopamine is believed to be involved in motivation, reward, and reinforcement.[1] Dopamine also plays an essential role in the control and coordination of movement.[1]
Dopamine receptors all influence the activity of the second messenger, cyclic AMP, which is involved in many biochemical processes within a neurone.[2] Dopamine receptor subtypes D1 and D5 increase the levels of cyclic AMP, whereas D2, D3, and D4 subtypes decrease the levels of cyclic AMP.[2] Thus, depending on which receptor subtype the neurotransmitter binds with on the postsynaptic neurone, dopamine can increase or decrease cellular activity.[2]
Dopamine, and its actions within the CNS, is critical to the underlying disease state of many conditions, including Parkinson’s disease, which is characterised by a dearth of dopamine, and schizophrenia, which appears to be caused by an overactivity of dopamine within certain brain regions.[3] Furthermore, many addictive substances work by altering the effect of dopamine within the brain.[1] For instance, the drug cocaine appears to act by inhibiting the reuptake of dopamine, which leads to an increased concentration of dopamine in the synapse, prolonging its action.[1]
Delusion – a disturbance in thought leading to false beliefs.
Hallucination – a false sensory perception, such as hearing voices or seeing things that are not there.
Prolactin – a hormone, produced and released into the bloodstream by the pituitary gland, that is involved in the secretion of milk and breast growth; unusually high amounts are responsible for impotence and loss of libido in both men and women.
References:
[1] Purves D, Augustine GJ, Fitzpatrick D, et al. (eds). Neuroscience. 4th edition. Sinauer Associates ,2008.