Date of Award
basal ganglia, DARPP-32, dopamine receptors
The basal ganglia are a set of subcortical structures which integrate information from diverse brain areas to coordinate vital behaviors including movement, reward, and motivational processes. The striatum is the main input center of the basal ganglia which sends projections to the output nuclei via two pathways, the direct striatonigral pathway and the indirect striatopallidal pathway. These two pathways work together to modulate behavior and imbalance of these pathways can have profound physiological consequences. DARPP-32 is a dual function kinase/phosphatase inhibitor which has been shown to be a key mediator of signaling in both striatonigral and triatopallidal neurons. A variety of therapeutic agents and drugs of abuse can affect the phosphorylation of DARPP-32. Psychostimulants such as cocaine increase DARPP-32 phosphorylation at its main regulatory site, T34. Paradoxically, antipsychotics such as haloperidol also increase T34 phosphorylation to a similar degree. Despite this similar biochemical regulation, psychostimulants and antipsychotics have opposing behavioral and clinical effects. We hypothesized that these drugs act via the same biochemical pathway but in distinct populations of striatal neurons. To directly test this idea, we generated BAC transgenic mice which express epitope tagged DARPP-32 selectively in striatonigral and striatopallidal neurons using the D1 and D2 receptor promoters. We developed a protocol to immunoprecipitate DARPP-32 from drug treated mice and study phosphorylation in a cell-type specific manner. Using this new methodology we demonstrate that the increases in T34 phosphorylation with acute cocaine and haloperidol are restricted to striatonigral and striatopallidal neurons, respectively. Additionally, we show that the changes in DARPP-32 phosphorylation induced by a variety of drugs targeting the striatum have cell-type specific patterns. In a complimentary approach, we generated conditional knock-out mice in which DARPP-32 is selectively deleted in striatonigral or striatopallidal neurons. This allowed us to study the behavioral consequences of alteration in the direct and indirect pathways on psychostimulant and antipsychotic mediated locomotor behavior. These studies provided direct evidence for the theory that the direct and indirect pathways exert opposing influences on locomotor behavior. Additionally, we showed that dopamine can differentially modulate activity in these pathways resulting in a synergistic stimulation of locomotor activity.
Bateup, Helen S., "The Differential Contribution of Striatonigral and Striatopallidal Neurons in Mediating Responses to Therapeutic Agents and Drugs of Abuse: A Dual Role for DARPP-32" (2008). Student Theses and Dissertations. 16.