Cannabinoid CB1 receptors in the medial prefrontal cortex modulate the expression of contextual fear conditioning.
The ventral portion of the medial prefrontal cortex (vMPFC) has been related to the expression of contextual fear conditioning. This study investigated the possible involvement of CB1 receptors in this aversive response. Male Wistar rats were submitted to a contextual aversive conditioning session and 48 h later re-exposed to the aversive context in which freezing and cardiovascular responses (increase of arterial pressure and heart rate) were recorded. The expression of CB1 receptor-mRNA in the vMPFC was also measured using real time-PCR. In the first experiment intra-vMPFC administration of the CB1 receptor agonist anandamide (AEA, 5 pmol/200 nl) or the AEA transport inhibitor AM404 (50 pmol/200 nl) prior to re-exposure to the aversive context attenuated the fear-conditioned responses. These effects were prevented by local pretreatment with the CB1 receptor antagonist AM251 (100 pmol/200 nl). Using the same conditioning protocol in another animal group, we observed that CB1 receptor mRNA expression increased in the vMPFC 48 h after the conditioning session. Although AM251 did not cause any effect by itself in the first experiment, this drug facilitated freezing and cardiovascular responses when the conditioning session employed a lesser aversive condition. These results indicated that facilitation of cannabinoid-mediated neurotransmission in the vMPFC by local CB1 receptor activation attenuates the expression of contextual fear responses. Together they suggest that local endocannabinoid-mediated neurotransmission in the vMPFC can modulate these responses.
Lisboa
Sabrina F
SF
Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.
Reis
Daniel G
DG
da Silva
Andréia Lopes
AL
Corrêa
Fernando M A
FM
Guimarães
Francisco S
FS
Resstel
Leonardo B M
LB
D000818:Animals; D001095:Arachidonic Acids / Q000008:administration & dosage / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism*; D002243:Carbolines / Q000008:administration & dosage / Q000494:pharmacology; D003214:Conditioning, Classical; D004597:Electroshock; D063388:Endocannabinoids; D005239:Fear; D046352:Freezing Reaction, Cataleptic; D018756:GABA Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000494:pharmacology; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism*; D011720:Pyrazoles / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009435:Synaptic Transmission
D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D002243:Carbolines; D063388:Endocannabinoids; D018756:GABA Antagonists; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; C103505:AM 251; C035874:FG 7142; C078814:anandamide; C107594:N-(4-hydroxyphenyl)arachidonylamide