DOI
https://doi.org/10.25772/930T-TT05
Defense Date
2013
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Psychology
First Advisor
Aron Lichtman
Second Advisor
Joseph Porter
Abstract
Cannabinoid agonists, including marijuana containing delta-9-tetrahydrocannabinol (THC), are found rewarding by humans. In addition to human self-reports and experimental studies that show marijuana is rewarding, contributions from preclinical studies also have implicated cannabinoid receptors in reward-motivated behavior. One way to assess these preclinical effects of cannabinoids is intracranial self-stimulation (ICSS), where an animal performs a response to receive electrical stimulation of a specific brain area or circuit known to be involved in reward. Drugs of abuse, such as psychomotor stimulants, facilitate responding for ICSS. While a few studies have shown facilitating effects of cannabinoids in rats, several have shown the opposite effect, and no studies so far have evaluated cannabinoids in mouse ICSS. Furthermore there are no studies evaluating specific inhibitors of endocannabinoid catabolic enzymes in ICSS in any species. In these studies we assessed the cannabinoid agonist THC, as well as the fatty acid amide hydrolase (FAAH) inhibitor, PF-3845, the monoacylglycerol lipase (MAGL) inhibitor JZL184, and the combined FAAH/MAGL inhibitor SA-57 in ICSS of the medial forebrain bundle in C57BL/6 mice. Additionally, we assessed the psychomotor stimulant cocaine as a positive control to facilitate ICSS. These studies were complimented with spontaneous locomotor activity and food-maintained operant experiments to assess the sensitivity of ICSS to cannabinoids. Additionally, brain endocannabinoid levels were measured in brain regions associated with the mesolimbic system after enzyme inhibitor treatments. THC, JZL184, and SA-57 all produced time-dependent reductions in ICSS that were mediated through CB1 receptors, as they were blocked by pre-treatment with the CB1 antagonist rimonabant, but not with the CB2 antagonist SR144528. PF-3845 also reduced ICSS, but did so independent of CB1 and CB2 receptors, and only with one dose (30.0 mg/kg) that has not been assessed previously in vivo. We showed that ICSS was more sensitive to the rate-reducing effects of cannabinoids than other measures of behavior with motor components including spontaneous locomotor activity and operant nose-poking for food, and that the reduction of ICSS produced by both JZL184 and SA-57 is accompanied by increases in 2-AG in mesolimbic brain areas. Thus, cannabinoids do not facilitate ICSS in C57BL/6 mice over a range of doses and pre-treatment times, similar to most studies with rats. These data suggest that cannabinoids may produce rewarding effects through non-mesolimbic areas of the brain.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
October 2013