[Visualization of neurotransmitter receptors in the living human brain by position emission tomography (PET)]

Various brain imaging techniques have become available in the past decade. These include techniques to evaluate brain structure using X-ray computerized tomography or magnetic resonance imaging and techniques to assess brain functional activities (cerebral blood flow, brain energy metabolism and brain protein synthesis) using positron emission tomography (PET). PET also makes it possible for the first time to evaluate the states of various types of neurotransmitter receptors, such as dopamine D2 and D1, serotonin 5-HT2, muscarinic cholinergic, opiate, benzodiazepine and histamine H1, and to determine the state of monoamine oxidase (A and B) under in vivo conditions. These techniques cannot only be used to map "brain neurochemistry" in normal human beings, but they will also increase our knowledge by demonstrating neurochemical abnormalities in a wide range of neurological and psychiatric disorders or those that happen during normal aging. The PET techniques may be applicable to the development of new drugs in the pharmaceutical industry. We have been exploring the methodology of using 11C-labeled antagonists for mapping functional neurotransmitter receptors in human brain directly and noninvasively by PET. The present review article provides an outline of the conceptual and methodological progress over the past several years that has made it possible to visualize neurotransmitter receptors in the living human brain by PET on the basis of our original work.