Enhanced cingulate LTP in morphine treated mice. (A) LTP was induced with the spike-timing protocol in ACC neurons in wild-type mice (n = 7). (B) Enhanced potentiation was observed in morphine treated mice (n = 8). The insets show averages of six EPSCs at baseline responses (1) and 30 min (2) after LTP induction (arrow). The dashed line indicates the mean basal synaptic response. (C) There was a significant increase in LTP in morphine treated mice compared to saline treated group.