Cannabinoid agonists differentially substitute for the discriminative stimulus effects of Delta(9)-tetrahydrocannabinol in C57BL/6J mice.
BACKGROUND
A variety of behavioral procedures have been developed to assess cannabinoid activity in mice; however, the feasibility of establishing Delta(9)-THC as a discriminative stimulus in mice has not been documented.


OBJECTIVE
One goal was to establish Delta(9)-THC as a discriminative stimulus in mice; after having done so, another goal was to examine the in vivo mechanism of action of Delta(9)-THC with other cannabinoids and noncannabinoids.


METHODS
C57BL/6J mice (n = 8) were trained to discriminate Delta(9)-THC (10 mg/kg i.p.) from vehicle while responding under a fixed ratio 30 schedule of food presentation.


RESULTS
Mice satisfied the discrimination criteria in 18-98 (median = 67) sessions and the discriminative stimulus effects of Delta(9)-THC were dose-dependent (ED(50) = 2.6 mg/kg). CP 55940 and WIN 55212-2 dose-dependently increased Delta(9)-THC-appropriate responding to 100% (ED(50) = 0.032 and 0.45 mg/kg, respectively), whereas methanandamide and a variety of noncannabinoids (cocaine, ethanol, and ketamine) produced a maximum of 34% Delta(9)-THC-appropriate responding. The cannabinoid CB(1) antagonist SR 141716A (rimonabant) surmountably antagonized the discriminative effects of Delta(9)-THC, CP 55940, and WIN 55212-2; methanandamide did not significantly modify the Delta(9)-THC discriminative stimulus.


CONCLUSIONS
The discriminative stimulus effects of Delta(9)-THC, CP 55940, and WIN 55212-2 are mediated by the same (i.e., CB(1)) receptors, whereas the effects of methanandamide or a metabolite of methanandamide are mediated at least in part by non-CB(1) receptors. The discriminative stimulus effects of Delta(9)-THC in mice could be used to evaluate mechanisms of cannabinoid activity with approaches (e.g., inducible knockouts) currently unavailable in nonmurine species.
Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA. mcmahonl@uthscsa.edu.
Lance R
LR
McMahon
Brett C
BC
Ginsburg
R J
RJ
Lamb
D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D048588:Benzoxazines / Q000494:pharmacology; D002186:Cannabinoids / Q000819:agonists*; D003511:Cyclohexanols / Q000494:pharmacology; D003627:Data Interpretation, Statistical; D004193:Discrimination Learning / Q000187:drug effects; D004192:Discrimination, Psychological / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000494:pharmacology*; D004347:Drug Interactions; D006213:Hallucinogens / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists; D012055:Reinforcement Schedule; D000077285:Rimonabant
D001095:Arachidonic Acids; D048588:Benzoxazines; D002186:Cannabinoids; D003511:Cyclohexanols; D006213:Hallucinogens; D009025:Morpholines; D009281:Naphthalenes; D010880:Piperidines; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; C088155:methanandamide; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D013759:Dronabinol; C054649:3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol; D000077285:Rimonabant