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Self-administration of the anandamide transport inhibitor AM404 by squirrel monkeys
Charles W Schindler1, Maria Scherma2, Godfrey H Redhi3
1Preclinical Pharmacology Section, Behavioral Neuroscience Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, 251 Bayview Boulevard, Baltimore, MD, 21224, USA. cschind@helix.nih.gov.
Rationale:
N-(4-hydroxyphenyl)-arachidonamide (AM404) is an anandamide transport inhibitor shown to reduce rewarding and relapse-inducing effects of nicotine in several animal models of tobacco dependence. However, the reinforcing/rewarding effects of AM404 are not clear.
Objectives:
We investigated whether AM404 maintains self-administration behavior or reinstates extinguished drug seeking in squirrel monkeys.
Methods And Results:
In monkeys with a history of anandamide or cocaine self-administration, we substituted injections of AM404 (1-100 microg/kg/injection). Using a 10-response, fixed-ratio schedule, self-administration behavior was maintained by AM404. Dose-response curves had inverted U shapes, with peak response rates occurring at a dose of 10 microg/kg/injection. In anandamide-experienced monkeys, we also demonstrated self-administration of another anandamide transport inhibitor VDM11. In addition to supporting self-administration, priming injections of AM404 (0.03-0.3 mg/kg) reinstated drug-seeking behavior previously reinforced by cannabinoids (∆(9)-tetrahydrocannabinol (THC) or anandamide) or cocaine. Both AM404 self-administration behavior and reinstatement of drug seeking by AM404 were reduced by treatment with the cannabinoid CB1 receptor antagonist/inverse agonist rimonabant (0.3 mg/kg). Moreover, the reinforcing effects of AM404 were potentiated by the treatment with the fatty acid amide hydrolase (FAAH) inhibitor URB597 (0.3 mg/kg) suggesting a major role of anandamide in these effects. Finally, AM404 (0.3 mg/kg) potentiated the reinforcing effects of anandamide but not those of cocaine.
Conclusions:
In non-human primates, AM404 effectively reinforced self-administration behavior and induced reinstatement of drug-seeking behavior in abstinent monkeys. These effects appeared to be mediated by cannabinoid CB1 receptors. Therefore, compounds that promote actions of endocannabinoids throughout the brain by inhibiting their membrane transport may have a potential for abuse.