The disruptive effects of the CB1 receptor antagonist rimonabant on extinction learning in mice are task-specific.
BACKGROUND
Disruption of CB(1) receptor signaling through the use of CB(1) (-/-) mice or the CB(1) receptor antagonist rimonabant (SR141716) has been demonstrated to impair extinction of learned responses in conditioned fear and Morris water maze tasks. In contrast, CB(1) (-/-) mice exhibited normal extinction rates in an appetitively motivated operant conditioning task.


OBJECTIVE
The purpose of this study was to test whether rimonabant would differentially disrupt extinction learning between fear-motivated and food-motivated tasks.


METHODS
Separate groups of C57BL/6J mice were trained in two aversively motivated tasks, conditioned freezing and passive avoidance, and an appetitively motivated operant conditioning task at a fixed ratio (FR-5) schedule of food reinforcement. After acquisition, the respective reinforcers in each task were withheld, and an intraperitoneal injection of vehicle or rimonabant was given 30 min before each extinction session.


RESULTS
Rimonabant (3 mg/kg) treatment significantly disrupted extinction in both the conditioned freezing and passive avoidance tasks but failed to affect extinction rates in the operant conditioning task, whether using daily or weekly extinction sessions. Interestingly, rimonabant (3 mg/kg) prevented the significant increases in lever pressing (i.e., extinction burst) that occurred during the first extinction session of the operant conditioning task.


CONCLUSIONS
These results support the hypothesis that the CB(1) receptor plays a vital role in the extinction of aversive memories but is not essential for extinction of learned responses in appetitively motivated tasks.
Niyuhire
Floride
F
Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA 23298-0613, USA.
Varvel
Stephen A
SA
Thorpe
Andrew J
AJ
Stokes
Rene J
RJ
Wiley
Jenny L
JL
Lichtman
Aron H
AH
D000818:Animals; D001070:Appetitive Behavior; D001362:Avoidance Learning / Q000187:drug effects; D003216:Conditioning, Operant / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005108:Extinction, Psychological / Q000187:drug effects*; D005239:Fear; D046352:Freezing Reaction, Cataleptic; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D008568:Memory / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D009043:Motor Activity / Q000187:drug effects; D010880:Piperidines / Q000494:pharmacology*; D011720:Pyrazoles / Q000494:pharmacology*; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors*; D012054:Reinforcement, Psychology; D000077285:Rimonabant
D010880:Piperidines; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D000077285:Rimonabant