Novel events in dopamine receptor signaling and regulation
Abstract
The dopamine receptor system, including D1 and D2 receptors, represents a critical component of the nervous system. It is involved in such functions as cognition, motor control, reward and motivation, and often dysfunction can lead to disease. This thesis presents novel investigations involving the evaluation of two distinctive GPCR modulation mechanisms. First, we evaluated the pharmacological profiles of the enantiomers of a dopamine D1 receptor full agonist, doxanthrine (DOX) at D1 and α 2C adrenergic receptors. (+)-DOX displayed greater potency and intrinsic activity than (-)-DOX in a heterologous D1 receptor expression system and endogenously expressed D1 system. Studies with the endogenously expressing D1 cells revealed that (-)-DOX was a weak partial agonist that reduced the activity of (+)-DOX and dopamine. (-)-DOX displayed greater potency than (+)-DOX at α2C adrenergic receptors. These findings demonstrate a reversed stereoselectivity for the enantiomers of DOX at D 1 and α2C receptors and have implications for the therapeutic utility of doxanthrine. Second, we characterized the ability of the D 2 receptor to interact physically with the cannabinoid CB 1 (CB1) receptor through receptor dimerization. Both receptors are co-expressed in the basal ganglia and evidence suggests that CB1 and D2 receptors may oligomerize, providing unique pharmacology. Limited information exists on the regulation of CB1 and D 2 receptor dimers. We employed a novel technique, multicolor bimolecular fluorescence complementation (BiFC) to examine the subcellular localization of D2-D2 homodimers and CB1-D2 heterodimers. Multicolor BiFC was used to explore the effects of chronic ligand treatment on receptor dimerization. Chronic agonist treatment resulted in increased formation of CB1-D2 heterodimers relative to the D2-D2 homodimers. The effects of the D2 agonist, quinpirole were restricted to the intracellular compartment. Conversely, treatment with the CB1 receptor agonist, CP55,940 produced increases in both membrane and intracellular CB1-D2 heterodimers. The effects of CB1 activation were examined further by combining multicolor BiFC with a constitutively active CB1 receptor mutant. These studies demonstrated that the expression of the CB1 mutant increased intracellular CB1-D2 heterodimer formation. In summary, agonist-induced modulation of CB1-D 2 oligomerization may have physiological implications in diseases such as Parkinson’s disease and drug abuse.^
Degree
M.S.
Advisors
Val J. Watts, Purdue University.
Subject Area
Biology, Neuroscience
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