Chronic morphine recruits the cAMP/PKA pathway for MOR inhibition of GABA synaptic currents. A, B, Representative IPSCs (top) and group data (bottom) of the DAMGO inhibition in control and in the presence of AACOCF3 or 4-AP in neurons of the saline group (A) and the morphine group (B). C, DAMGO effects on IPSCs in the presence of H89 from neurons of the saline group and of the morphine group without or with addition of AACOCF3 or 4-AP. D, DAMGO effects in similar experiment groups but in the presence of the AC inhibitor SQ22536 (50 μm). E, Summarized data of the DAMGO effects on IPSCs in the saline group (open columns) and in the morphine group (filled columns). *p < 0.05, **p < 0.01. Calibration: 100 pA and 50 ms. KT, KT5720.