Levodopa therapy - the gold standard in Parkinson's disease (PD) treatment - causes disabling motor complications (dyskinesias) that are largely resistant to available drugs. Studies on anti-dyskinetic therapies have paid little attention to the endocannabinoid neurotransmitter system, despite: (1) the striking abundance of cannabinoid receptors in the basal ganglia;(2) its ability to regulate basal ganglia function;(3) experimental evidence for anti-dyskinetic properties of cannabinoid drugs. So far, clinical studies addressing the therapeutic efficacy of cannabinoid receptor agonists on levodopa-induced dyskinesias (LID) have produced conflicting results. Lack of knowledge of the molecular mechanisms underlying the antidyskinetic properties of these agents and the consequent inappropriate pharmacological manipulation of the endocannabinoid system may contribute to these inconsistencies. Furthermore, little information is available on the antidyskinetic potentials of indirect cannabinoid agonists (FAAH inhibitors), which have been shown recently to ameliorate hyperkinetic disorders. Previous work from our lab carried out in rats with unilateral 6- OHDA lesions (an animal model of PD) indicates that application of direct cannabinoid agonists alleviates LID via activation of CB1 cannabinoid receptors and concomitant desensitization of TRPV1 receptors through a phosphatase-operated mechanism. On the other hand, FAAH inhibitors reduce LID through a CB1-independent mechanism requiring pharmacological blockade of TRPV1 receptors and activation of peroxisome proliferators-activated receptors (PPARs). These observations suggest that direct and indirect cannabinoid agonists alleviate LID via CB1- and non-CB1-dependent mechanisms, respectively, and that TRPV1 and PPAR receptors play a critical role in these responses. Biochemical, pharmacological and behavioral approaches will be used to test this hypothesis.
The first aim will investigate the molecular mechanisms of the antidyskinetic effects of the direct cannabinoid agonist WIN55212-2;it will focus on the cross talk between CB1 and TRPV1 receptors and the role played by the phosphates calcineurin and DARPP-32 in this interaction.
The second aim will analyze the antidyskinetic effects of the FAAH inhibitor URB597, the contribution of signaling lipids elevated by URB597 in these responses and the ability of TRPV1 and PPAR receptor antagonists to modulate these effects.
The third aim will address the efficacy of earlier treatment with direct and indirect cannabinoid agonists to prevent or delay the expression of dyskinesias, and possible differences in the development of tolerance to their behavioral effects. In conclusion, our study will identify the mechanisms of action of different cannabinoid agents, investigate their efficacy upon chronic administration and characterize novel targets for antidyskinetic therapies using a pre- clinical experimental setting.
Several preclinical and clinical studies indicate that cannabinoid drugs reduce the motor complications (dyskinesias) induced by long-term use of medications for Parkinson's disease. This proposal investigates the mechanisms of action and pharmacological targets of different cannabinoid agents and evaluates their efficacy in reducing levodopa- induced dyskinesias in a rat model of Parkinson's disease. The study will identify new and more effective therapeutic strategies for the treatment of levodopa-associated motor complications.
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