Cocaine is a naturally occurring alkaloid with psychomotor stimulant and local anesthetic properties. Due to its strongly reinforcing properties in man it is widely abused in this country. Cocaine abuse has become a major public health problem. The mechanisms underlying cocaine's reinforcing properties are not well understood but appear to involve central dopamine neurons and, via dopamine receptors, their projection fields. Studying the biochemical mechanisms of action of cocaine in animals has been hindered by the complex nature of the intact brain systems including the multiple dopamine systems in the CNS. In intact animal systems, however, it is clear that chronic cocaine alters dopaminergic functioning. The present studies will directly examine cellular mechanisms by which cocaine interacts with CNS dopamine containing neurons in a novel isolated system. Re-aggregate tissue cultures will be used which contain neurochemically-defined cells from fetal mouse brain which have been dissected, dissociated and recombined to form highly organized structures in which innervating and target cells make appropriate functional connections. The advantage of this re-aggregating tissue system is that cells from discrete areas of the brain can be cultured either alone or in combination with the appropriate targets and in the presence and absence of appropriate innervation. Two major sets of experiments will be performed in this model system. The first set will examine the effects of various cocaine exposure paradigms (acute and chronic) on the biochemical pharmacology (e.g., dopamine release, dopamine turnover, dopamine receptor/effecter functioning) of the dopamine neurons in the reaggregate systems (i.e., aggregates with and without appropriate targets). The second set of experiments will take advantage of the inherent developmental nature of the reaggregate systems. The effects of cocaine exposure during development of the reaggregates systems on the phenotypic expression of D1 and D2 receptors and their coupling to effector systems (e.g., adenylate cyclase) will be examined. Issues of tissue specificity, dose effects, and 'critical periods' will be studied. The results of these experiments will enhance significantly the understanding of the mechanisms of action of cocaine in mature, and in developing, dopamine-containing neuronal systems in the brain and may provide important directions for examining cocaine effects in more complex systems.
