Many lines of evidence suggest a role for dopamine in neuropsychiatric disorders such as PD, schizophrenia, attention deficit hyperactivity disorder (ADHD), and drug abuse. The first evidence for dopamine's involvement in these disorders came from either postmortem histological/neurochemical studies or the observation that the drugs used to treat these disorders either increased or blocked dopamine neurotransmission in the brain. Since the advent of neuroimaging techniques such as positron emission topography (PET), a majority of the current human studies use this technique to further define the role of dopamine in these disorders.
PET enables the direct measurement ofcomponents of dopamine neurotransmission in the living human brain by using radiotracers, which label dopamine receptors, dopamine transporters, and precursors of dopamine or compounds that have specificity for the enzymes that degrade dopamine. Certain types of PET
studies also provide information on regional brain metabolism or blood flow, thus, PET can be used to assess the functional consequences of changes in brain dopamine activity.
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