IN-VIVO BRAIN RECEPTOR IMAGING

Brain receptors and their interactions with neurotransmitters and neur opharmacologic agents have been the subject of intense interest for se veral decades. Typically, studies of receptor binding have been carrie d out in vitro using postmortem brain tissues and selective ligands ra diolabeled with low-energy radionuclides such as H-3 or I-125. Quantit ative imaging of receptor sites in the living mammalian brain has rece ntly become feasible through the development of receptor ligands label ed with short-lived gamma- or positron-emitting radionuclides and suit able SPECT (single photon emission computed tomography) and PET (posit ron emission tomography) imaging equipment. This article describes the requirements for a successful radioligand that can be used for noninv asive in vivo imaging of neuroreceptors. Considerations of preparation , penetration through the blood brain barrier, in vivo pharmacology, a nd specific binding characteristics are discussed. Selected examples o f SPECT/PET tracers for labeling dopaminergic, serotonergic, opioid, m uscarinic, and benzodiazepine receptors are described, as well as thei r use in studies of receptor changes in health and disease. Also prese nted are new radioligands that selectively label presynaptic monoamine reuptake sites, and can be employed to detect neuronal damage.