The purpose of the NIMH Psychoactive Drug Screening Program is to provide pharmacological and functional screening of novel synthetic compounds and natural products for potential use as PET (positron emission tomography) ligands for functional brain imaging, research tools or probes for basic and clinical research, and therapeutic agents for mental disorders. The objectives of the contract are to receive and test coded samples (synthetic compounds, small molecules, gene products, and natural product extracts) in broad-based human and rodent CNS (central nervous system) receptor and enzyme binding assays, to test active samples in secondary functional assays, and to provide an electronic data file for each of the screened compounds. Approximately 60% of these samples are to be tested in human recombinant receptor assays. Samples for screening can include, but are not limited to, novel chemical entities, structural analogs of lead compounds, genes or gene products, small molecules, enzyme inhibitors, and natural products. It is anticipated that NIMH- approved and coded samples will be submitted from NIH- or federally- funded research programs and other academic research laboratories. It is expected that the screening information derived from this program will provide individual investigators with conceptual or structural leads for the design and/or development of new chemical entities, small molecules, gene products, tissue- or cell-specific drug delivery systems, therapeutic entities, or PET/SPECT ligands for human brain imaging.