The main focus of Dr. Henry Huang's research is the development of new and improved Positron Emission Tomography (PET) radioligands. PET ligand development is a process that involves the interplays of chemistry, biology, pharmacology and pharmacokinetics, and it requires a good understanding of all these scientific disciplines. Over the years Dr. Huang has been involved in the development of new or improved PET radioligands for the dopamine, serotonin, glutamate and acetylcholine receptors and transporters in the brain. Development of PET radioligands includes the following stages: 1. design and synthesis of candidate ligands; 2. in vitro pharmacological experiments to determine binding affinities and selectivity. 3. design and execution of biological and pharmacological experiments in live animals including rodents and non-human primates to evaluate the ligands’ in vivo pharmacology and pharmacokinetics such as distribution, binding selectivity and specificity, metabolism, clearance, and blood and brain kinetics; 4. determination of dosimetry and toxicology; 5. clinical trials to determine the ligands’ suitability for applications in humans to image targeted receptors, proteins, or enzymes. PET imaging technique can be used to determine the concentrations of CNS receptors and transporters in discrete brain regions under normal conditions. It can also be used to probe the changes in the densities of certain receptors and transporters in diseases. Coupled with pharmacological manipulation or stimulation, PET imaging is capable of probing the abnormality in the neurotransmission system functions under diseased conditions. Further applications include determination of the receptor occupancy by marketed or experimental drugs and monitoring the outcome of drug treatment for diseases. In all these applications the key is the availability of an appropriate PET radioligand for a specific receptor, transporter, or enzyme. Therefore, development of PET radioligands is a critical component of PET imaging and will continue to be the major part of Dr. Huang's research. His current interest is the development of ligands for targets in the CNS encompassing many of the neurotransmission systems.