I study psychoactive drugs such as amphetamine and cocaine for two main purposes: (1) to understand the alterations in the regulation of brain chemicals that can occur as a result of exposure to psychoactive drugs, and (2) to make use of possible animal models of psychiatric disorders. People who use stimulant drugs such as amphetamine and cocaine on a chronic basis can develop a psychosis that is similar to paranoid schizophrenia. This is of interest in light of our findings that chronic administration of amphetamine to rats can increase the utilization of dopamine, a brain neurotransmitter. To show this, we use microdialysis, a technique for analyzing neurotransmitter release in the brain. The alterations produced in transmitter utilization in the rat brain during chronic stimulant drug administration may be very similar to the changes occurring in the human brain exposed to stimulant drugs. These studies may provide insight into the biochemical changes occurring in the human brain that can contribute to the development of psychiatric disorders.