Figure 3.

Effect of chronic morphine treatment on the phosphorylation of ERK and PEBP and the expression of PEBP in (A) CHO/μ cells and (B) SH-SY5Y cells. Cells were treated with 10 μM morphine (M36) or vehicle (Con) for 36 h and were then washed twice with culture medium and the withdrawal was preceded by precipitating the cells with 5 μM naloxone for 5 min (NLX-5) or 10 min (NLX-10). Data are presented as the mean ± standard error of the mean from three independent experiments. One-way analysis of variance was used followed by Dunnett’s post hoc test. ^**P<0.01 and ^***P<0.001, compared with the con. PEBP, phosphatidylethanolamine-binding protein; DAMGO, (D-Ala², MePhe⁴, Gly⁵-ol) enkephalin; ERK, extracellular signal-regulated kinase; CHO cells, Chinese hamster ovary cells; con, control.