DOI
https://doi.org/10.25772/TSS0-G006
Defense Date
2010
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Pharmacology & Toxicology
First Advisor
Aron Lichtman
Abstract
While there is currently active debate over possible therapeutic applications of marijuana and cannabis-based compounds, consistently their primary drawbacks have been the psychoactive properties, dependence, and abuse potential. Prolonged administration of ∆9-tetrahydrocannabinol (THC), the primary psychoactive constituent in marijuana, demonstrates both tolerance and physical withdrawal in both preclinical and clinical studies. Repeated THC administration also produces CB1 receptor adaptations in the form of reduced activation of receptors, along with a downregulation of membrane surface receptors, in many brain regions involved in THC-associated behaviors. The increased need for drug to maintain therapeutic effects, and a withdrawal syndrome following discontinuation of use, are common risk factors in drugs of abuse. Recently, compounds have been developed that prolong the availability of the major naturally occurring endogenous cannabinoids, anandamide (AEA) and 2-arachidonoylglycerol (2-AG), through inhibition of their catabolic breakdown by fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively. The overall objectives of this research are to elucidate the physiologic roles of these two endogenous ligands and to determine if either can produce beneficial therapeutic effects without negative cannabis-like CNS effects. Therefore, we tested the impact of acute and prolonged blockade of FAAH and MAGL on a variety of cannabinoid-mediated behaviors and on precipitated cannabinoid withdrawal. Despite that acute blockade of FAAH and MAGL produce similar efficacy in reducing nociceptive responses, and both can reduce THC-induced somatic withdrawal, sustained blockade of these enzymes leads to remarkably different adaptations in CB1 receptor functioning. Namely, prolonged elevations in brain 2-AG leads to marked antinociceptive tolerance, cross-tolerance to exogenous cannabinoid agonists, and physical dependence. In contrast, sustained elevations in brain anandamide continues to dampen pain responses without apparent signs of physical withdrawal, loss of CB1 receptor activation as measured by [35S]GTPγS, or receptor downregulation as measured by [3H]CP,55940. These results suggest that chronic 2-AG elicits greater compensatory changes in CB1 receptor functions than anandamide. With similar efficacy in most therapeutic endpoints tested, and evidence of reduced impact on long-term function of the endocannabinoid system, these results distinguish FAAH as a more promising therapeutic target to treat pain and other conditions than MAGL.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
May 2010