DOI
https://doi.org/10.25772/XT10-C161
Defense Date
2013
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Pharmacology & Toxicology
First Advisor
Aron Lichtman
Abstract
The effects of cannabinoids in reducing somatic signs of opioid withdrawal have been known for some time. In morphine dependent rodents, opioid withdrawal following precipitation with the mu opioid antagonist naloxone elicits robust withdrawal behaviors including jumps, paw flutters, head shakes, diarrhea and weight loss. Delta-9-tetrahydrocannabinol has been shown to reduce this opioid withdrawal in mice via activation of the cannabinoid type-1 (CB1) receptor and recently it has been shown that inhibition of the catabolic enzymes for endocannabinoids also reduce somatic signs of opioid withdrawal. Specifically, inhibition the enzyme fatty acid amide hydrolase (FAAH), the catabolic enzyme for the endocannabinoid N-arachidonoylethanolamide (AEA; anandamide) or inhibition of the enzyme monoacylglycerol lipase (MAGL), the catabolic enzyme for the endocannabinoid 2-arachindonoylglycerol (2-AG) has been shown to reduce opioid withdrawal in mice. However, FAAH inhibition only reduced a subset of withdrawal signs in mice and full MAGL inhibition which maximally reduced somatic withdrawal signs has been shown to produce THC-like effects and dependence potential. Additionally, the effects of endocannabinoid catabolic inhibitors on other aspects of withdrawal, such as the negative motivational effects, are not known. The objectives of this dissertation were to 1) assess the efficacy of dual inhibition of FAAH and MAGL on somatic signs of opioid withdrawal and 2) determine whether these treatments would produce cannabimimetic effects (hypomotility, catalepsy, antinociception and hypothermia); 3) develop other behavioral assays of opioid withdrawal; and 4) determine if endocannabinoid catabolic inhibitors would reduce the acquisition of opioid withdrawal induced conditioned place avoidance (CPA) as a measure of the negative motivational consequences of opioid withdrawal. We found that full inhibition of FAAH with the selective inhibitor PF-3845 and partial inhibition of MAGL with the selective inhibitor JZL184 reduced withdrawal-related jumps and the expression of diarrhea to a greater degree than either inhibitor alone and these effects were shown to be CB1 mediated. Additionally, we tested the novel dual FAAH/MAGL inhibitor SA-57 which has greater potency at inhibiting FAAH over MAGL and found that it similarly reduced withdrawal signs at doses that only partially elevated 2-AG while fully elevating AEA; furthermore, SA-57 did not produce cannabimimetic effects at these doses. We next assessed the effects of morphine withdrawal in five behavioral assays: marble burying, novelty-induced hypophagia, the light/dark box, a novel procedure developed to assess “escape behavior” and the CPA procedure. From these studies we selected the CPA procedure to further evaluate the effects of endocannabinoid catabolic inhibitors to determine their ability to reduce the negative motivational aspect of opioid withdrawal. We found that naloxone (0.056 mg/kg) produced robust CPA in morphine-pelleted, but not placebo-pelleted, mice and that this dose elicited minimal somatic withdrawal signs. Morphine pretreatment was shown to block withdrawal CPA and withdrawal jumping in mice while clonidine only blocked withdrawal CPA and these served as positive controls. We found that THC, JZL184, and SA-57 significantly reduced the percentage of mice that jumped during the conditioning session, demonstrating that these treatments blocked the somatic signs of withdrawal. However, none of these treatments significantly affected acquisition of the withdrawal CPA. These studies suggest that dual inhibition of FAAH/MAGL has enhanced effects on attenuating withdrawal-related jumps and diarrhea, but not the negative motivational aspects of morphine withdrawal as inferred by the Pavlovian CPA experiments.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
January 2014