Figure 3.

Enhancement of synaptic transmission induced by withdrawal from fentanyl or morphine was reduced but not abolished by blockade of spinal NMDARs. In both graphs, areas of C-fiber-evoked field potentials were normalized to pre-drug values (dotted line) and plotted against time (minutes). A, Spinal superfusion with the NMDAR antagonist d-AP-5 (bottom white bar; 100 μm) failed to prevent enhancement of synaptic transmission induced by withdrawal, precipitated by topic application of the MOR antagonist CTOP (top white bar; 10 μm), after intravenous fentanyl (black bar; dosing as in Fig. 1B). B, As in A but with morphine infusion (black bar; dosing as in Fig. 1C).