[Changes in neural networks by conditional transgenic approach: a key to our comprehension of neuro-psychiatric disorders in the basal ganglia system].

The striatum, the first relay of the basal ganglia system, is critically involved in motor functions and motivational processes. The dorsal striatum is central to the motor control and motor learning and the ventral striatum or nucleus accumbens is essential for motivation, the reward system and reinforcement by drugs. This system is dysfunctional in movement disorders such as Parkinson's disease and Huntington's disease and in psychiatric disorders including drug addiction. The striatum consists of two populations of neurons projecting at the origin of two distinct paths in the circuit of basal ganglia, and of different populations of interneurons. These two populations of efferent neurons, striatopallidal and striatonigral neurons, are characterized by their projection sites and their differential expression in dopamine receptors and neuropeptides. Their roles in motor control and motivational processes and in the mechanisms of neuroadaptation in the system's pathologies remain mostly unknown. To identify these specific functions, we have developed new animal models wearing molecular or cell "lesions" by a conditional transgenic approach to target a specific population of neurons. By this approach, we demonstrated the inhibitory role of the population of striatopallidal neurons in the motor control and in the process of drug addiction, identified new genes selectively expressed by striatopallidal neurons that could be the target for future therapies and identified the potential role of this population of neurons disturbances in attention-deficit hyperactivity disorder (ADHD).