Asymmetrical synaptic cooperation between cortical and thalamic inputs to the amygdale.

Fear conditioning, a form of associative learning is thought to involve the induction of an associative long-term potentiation of cortical and thalamic inputs to the lateral amygdala. Here, we show that stimulation of the thalamic input can reinforce a transient form of plasticity (E-LTP) induced by weak stimulation of the cortical inputs. This synaptic cooperation occurs within a time window of 30 min, suggesting that synaptic integration at amygdala synapses can occur within large time windows. Interestingly, we found that synaptic cooperation is not symmetrical. Reinforcement of a thalamic E-LTP by subsequent cortical stimulation is only observed within a shorter time window. We found that activation of endocannabinoid CB1 receptors is involved in the time restriction of thalamic and cortical synaptic cooperation in an activity-dependent manner. Our results support the hypothesis that synaptic cooperation can underlie associative learning and that synaptic tagging and capture is a general mechanism in synaptic plasticity.