Radiotracer imaging of dopaminergic transmission in neuropsychiatric disorders

This article will review the capabilities and accomplishments of radiotrace r imaging with single photon emission computed tomography (SPECT) and posit ron emission tomography (PET) to measure pre-, post-, and "intra-synaptic" aspects of dopaminergic (DAergic) neurotransmission. The presynaptic site c an be labeled with probes for the dopamine transporter (DAT) or the synthet ic enzyme aromatic L-amino acid decarboxylase ("dopa decarboxylase"). The p ostsynaptic sites can be labeled with probes for either the dopamine D-1 re ceptor (D1R) or the dopamine D-2 receptor (D2R). The "synaptic" measurement s are made indirectly by measurements of the interaction/displacement of re ceptor tracers by endogenous dopamine (DA). Agents are used which either re lease (e.g., amphetamine) or deplete (e.g., alpha-methyl-paratyrosine (AMPT ), an inhibitor of tyrosine hydroxylase) tissue stores of DA. The applicati on of these paradigms will be reviewed with special emphasis to neuropsychi atric diseases such as schizophrenia and idiopathic Parkinson's disease (IP D).