For the mouse drug discrimination studies, anandamide (Organix, Inc., Woburn, MA), 2-AG (Organix), N-arachidonyl maleimide (NAM; provided by Cayman Chemical, Ann Arbor, Michigan), N-3-pyridinyl-4-[[3-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenyl]methyl]-1-piperidinecarboxamide (PF3845; provided by Pfizer, Kent, CT), and 4-nitrophenyl-4-(dibenzo[d][1,3]dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate (JZL184; provided by Dr. Benjamin Cravatt, The Scripps Research Institute, La Jolla, CA) were mixed in a vehicle of 5% ethanol, 5% emulphor (Rhone-Poulenc, Inc., Princeton, NJ) and 90% saline. THC [National Institute on Drug Abuse (NIDA), Rockville, MD] was also mixed with this vehicle (Experiment 1 in mice and in rat drug discrimination). Rimonabant (NIDA) and THC (Experiment 2 in mice) were mixed in 0.78% Tween-80 and 99.22% saline. For the mouse study, cyclohexylcarbamicacid 3′-carbamoyl-biphenyl-3-yl ester (URB597; Cayman Chemicals) was mixed in a vehicle of 1% dimethyl sulfoxide (DMSO)/1% Tween 80/98% saline, with addition of 0.2M NaOH buffer for a final ~ pH 8.0. For the rat study, URB597 (provided by Merck, Inc., & Co., Inc., Rahway, NJ) was first dissolved in DMSO under gentle heat at a concentration equivalent to 250 mg/ml and then diluted to test concentrations with a vehicle composed of 37% polyethylene glycol
