Metaplastic modulation of insular cortex in vivo LTD induced by conditioned taste aversion extinction

Memory formation and extinction are supported by activity-dependent changes in synaptic plasticity that shape memory persistence and attenuation. These processes are tightly regulated by homeostatic mechanisms. Metaplasticity, a form of such regulation, modulates synaptic plasticity based on the history of previous activity. Our laboratory has previously demonstrated that conditioned taste aversion (CTA) training blocks the expression of in vivo long-term potentiation (LTP) and depression (LTD) in the basolateral amygdala to insular cortex (BLA-IC) pathway. Nevertheless, evidence on how memory extinction affects subsequent expression of LTD, a mechanism linked to memory attenuation, remains still elusive. The present study aimed to analyze whether CTA extinction modifies the expression of in vivo LTD in the BLA-IC projection. Animals received low-frequency stimulation to induce in vivo IC-LTD after CTA extinction. Our results demonstrate that CTA extinction reduces the blockade of LTD induced by CTA training in the BLA-IC pathway and reverts the CTA-induced enhancement in synaptic excitability within this circuit to levels comparable to those observed in animals without prior CTA training. These results support the notion that extinction of aversive memories exerts a modulatory effect on synaptic plasticity expression in the adult neocortex.