Figure 2.

Chronic morphine increases the potency of μ-opioid receptor (MOR) agonist. A, GABA IPSCs in the absence and presence of the MOR agonist DAMGO (1 μm) in neurons of saline and morphine groups. B, C, Summarized data of the DAMGO inhibition expressed as percentage of control (B) or current amplitude (C). D, Dose–response relationship for the IPSC-inhibiting effect of DAMGO in neurons from the saline-treated rats (open circles) and from the morphine-treated rats (filled circles). n = 6–7 cells for each data point. **p < 0.01. Calibration: A, 100 pA and 50 ms.