Drugs
Synapse Activity Decreases. These brain scans highlight dopamine receptors, with areas of highest density shown in red. The meth abuser has severely reduced receptor levels. Other drugs, including alcohol, cocaine, and heroin, have the same effect.
Aging
An overwhelming number of studies have reported age-related changes in dopaminesynthesis, binding sites, and number of receptors. Studies using positron emission tomography (PET) in living human subjects have shown a significant age-related decline in dopamine synthesis, notably in the striatum and extrastriatal regions (excluding themidbrain).
Significant age-related decreases in dopamine receptors D1, D2, and D3 have also been highly reported.
A general decrease in D1 and D2 receptors has been shown, and more specifically a decrease of D1 and D2 receptor binding in the caudate nucleus and putamen.
A general decrease in D1 receptor density has also been shown to occur with age. Significant age-related declines in dopamine receptors, D2 and D3
were detected in theanterior cingulate cortex wikipedia.org , frontal cortex, lateral temporal cortex,hippocampus, medial temporal cortex, amygdala, medial thalamus, and lateral thalamus.
One study also indicated a significant inverse correlation between dopamine binding in the occipital cortex and age.
Postmortem studies also show that the number of D1 and D2 receptors decline with age in both the caudate nucleus and the putamen, although the ratio of these receptors did not show age-related changes.
The loss of dopamine with age is thought to be responsible for many neurological symptoms that increase in frequency with age, such as decreased arm swing and increasedrigidity.
Changes in dopamine levels may also cause age-related changes in cognitive flexibility.