The effect of cannabinoid receptors on extinction memory in fear conditional model in rat

Previous studies have shown that endocannabinoid system have many effects include emotional, motivational behavior, regulation of movement, endocrine function, nociception, thermoregulation, sensory perception, memory and mood, cognition, pain perception, energy balance and extinction learning. They are released from postsynaptic neurons, on-demand to elevated levels of intracellular calcium and activate presynaptic cannabinoid (CB1) receptors and suppress transmitter release either transiently or persistently. Also the primary function of the e CB system is to gate and regulate neurotransmitter release, particularly GABA and glutamate. CB1 receptors mainly distribute in mammals brain and in brain sites which play in emotional memory like medial prefrontal cortex (mPFC), Basolateral amygdale (BLA) and hippocampus. Extinction consists of the learned inhibition of retrieval of previously acquired memories. The formation of these aversive memories and fear extinction has been studied according to the Pavlovian learning paradigm. This associative learning process consists of the pairing of a neutral conditioned stimulus (CS) with an aversive unconditioned stimulus (US) eliciting a conditioned fear response. The CS can be a cue (e.g. a tone) or a context (e.g. a room). Fear extinction consists of a new inhibitory learning after repeated or prolonged CS presentations, without the US, which causes a gradual decrease in the magnitude of the conditioned response. The amygdala, prefrontal cortex and hippocampus have all been implicated in the acquisition, consolidation and retrieval of extinction of conditioned fear. The results show the crucial involvement of the CB1 receptor in the BLA, mPFC and hippocampus in the extinction because the CB1 receptor antagonist impairs extinction. Administration of the CB1 receptor antagonist into the BLA before conditioning or before/after the first extinction trial blocks extinction. Findings demonstrated which intra-IL administration of the CB1 agonist WIN 55,212-2 facilitates the extinction of fear-potentiated startle. The e CB system plays an important role in the regulation of fear memories. Also, some studies demonstrate that after an aversive training experience the endogenous cannabinoid anandamide is released into the BLA, hippocampus, and mPFC and normally plays a role in the formation of a strong memory trace. In this review, we try to discuses about of the effects of cannabinoid receptors on extinction memory in fear conditional model in rat.

Keywords:

Extinction , Cannabinoid , Hippocampus , Prefrontal cortex , Amygdale