A genetic approach to study mechanisms of cocaine action

The brain dopamine system is thought to be the major target for the neuropharmacological actions of psychomotor stimulants such as cocaine. To investigate the mechanisms of cocaine action, we used a genetic approach, the gene-targeting technique, and generated D1 dopamine receptor mutant mice. Locomotor activity analysis in response to cocaine indicates that, in contrast to control mice which showed a dose-dependent increase in locomotion, D1 receptor mutant mice exhibited a dose-dependent decrease, suggesting that D1 receptors play an essential role in mediating such effects. Extracellular single unit recording of dopamine sensitive nucleus accumbens neurons in the D1 receptor mutant mice and control mice revealed a marked reduction in the inhibitory effects of cocaine and dopamine on the generation of action potentials, suggesting that D1 receptors play a fundamental role in cocaine- and dopamine-mediated neurophysiological effects within the nucleus accumbens. From these analyses, we conclude that the D1 dopamine receptor plays essential roles in mediating these effects of cocaine. In the future, the use of this powerful genetic approach will be essential for elucidating the molecular components of the signal transduction pathway leading to anatomical, cellular and behavioral changes upon cocaine administration and dopamine neurotransmission.