Figure 1.

μOR agonists inhibit CXCL12 signaling in glia-free neuronal cultures. A, Effect of 1 μm DAMGO (24 h) on ERK and Akt phosphorylation induced by CXCL12 (20 nm) in neurons; membranes were stripped and reprobed for total ERK/Akt to confirm equal loading. Cotreatment with the μOR (MOR) antagonist CTAP (1 μm) abolishes DAMGO inhibition (B). The bar graphs (C) represent the mean ± SEM of pERK or pAkt band densities represented with respect to control levels from five identical independent experiments. The CXCL12 stimulation at 5, 10, 15, and 30 min are all significantly higher than control levels (p < 0.05). CXCL12 stimulation at 15 and 30 min after DAMGO pretreatment is significantly lower than CXCL12 alone (p < 0.05). In D, neuronal cultures were treated with 1 μm morphine (or vehicle) in either the presence or absence of 1 μm CTAP for 24 h, followed by 20 nm CXCL12 for 5, 10, 15, or 30 min. pERK or pAkt levels were measured by immunoblotting. Total protein levels (ERK/Akt) were probed for loading control. The bar graphs (E, F) represent the mean ± SEM of pERK or pAkt band densities with respect to control levels from three identical independent experiments. The CXCL12 stimulation at 5, 10, 15, and 30 min are all significantly higher than control levels (p < 0.05). Morphine significantly blocks (p < 0.05) CXCL12-induced ERK/Akt phosphorylation at all time points.