Papers of the Week

The anterior cingulate cortex (ACC) is a key cortical region for pain perception and emotion. Different forms of synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), have been reported in the ACC. Synaptic tagging of LTP plays an important role in hippocampus-related associative memory. In this study, we demonstrate that synaptic tagging of LTD is detected in the ACC of adult male and female mice. This form of tagged LTD requires the activation of metabotropic glutamate receptor subtype 1 (mGluR1). The induction of tagged LTD is time-related with the strongest tagged LTD appearing when the interval between two independent stimuli is 30 min. Inhibitors of mGluR1 blocked the induction of tagged LTD, however, blocking N-methyl-d-aspartate (NMDA) receptors did not affect the induction of tagged LTD. Nimodipine, an inhibitor of L-type voltage-gated calcium channels (VGCCs), also blocked tagged LTD. In an animal model of amputation, we found that tagged LTD was either reduced or completely blocked. Together with our previous report of tagged LTP in the ACC, this study strongly suggests that excitatory synapses in the adult ACC are highly plastic. The biphasic tagging of synaptic transmission provides a new form of heterosynaptic plasticity in the ACC which has functional and pathophysiological significance in phantom pain. The anterior cingulate cortex (ACC) is a key cortical region for pain perception and chronic pain. Previous studies have reported a novel form of long-term heterosynaptic potentiation in the ACC. In this study, we discovered a long-term depression (LTD) form of synaptic tagging in the ACC of adult male and female mice. This form of tagged LTD requires the activation of metabotropic glutamate receptors (mGluRs). In an animal model of amputation, tagged LTD is reduced or completely blocked. Our results strongly suggest that brain cortices of adult mice are highly plastic and show biphasic tagging of plasticity. These findings of tagged LTD may provide a new direction for future treatment of phantom pain and amputation-related emotional disorders.