The D4 dopamine receptor (DRD4) activates ERK1/2 and Akt via the transactivation of platelet-derived growth factor receptor-beta (PDGFRbeta). However, the mechanism by which this process occurs is not understood. In this thesis, site-specific PDGFRbeta phosphorylation was examined, and molecular and pharmacological methods were employed to investigate the role of various candidate mediators in this pathway. DRD4 stimulation results in the phosphorylation of the PDGFRbeta at the PI3K and PLCgamma binding sites. Pharmacological analysis reveals that DRD4-mediated Akt phosphorylation requires PI3K. Experiments involving the overexpression of beta-arrestin mutants, kinase-inactive c-src and csk, which negatively modulates src activity, indicate that these proteins do not participate in this transactivation cascade. Pharmacological studies suggest that calmodulin and PKCdelta act both upstream and downstream of the PDGFRbeta in DRD4-stimulated ERK1/2 phosphorylation. Although this present study supports a role for these proteins in DRD4-PDGFRbeta transactivation, further experiments are required to determine how these proteins are activated.