Fig. 4.
Modulation of increased nociceptive sensitivity by regulating the spinal GT and NMDAR activity.A, The baseline foot withdrawal latency was dose-dependently reduced on day 8 compared with that on day 0 in rats receiving either repeated boluses (B10, B20) or continuous infusion with morphine (C10, C20) for 7 d, indicating an increased nociceptive heat sensitivity.B, MK-801 (1 nmol · μl−1 · hr−1) blocked the increased nociceptive heat sensitivity when coadministered with morphine (20 nmol · μl−1 · hr−1) for 7 d (C20+MK). Similarly, coadministration (twice daily for 7 d) of 10 μg of morphine and 20 μg of PDC (B10+P) potentiated, whereas combined 10 μg of morphine and 20 μg of riluzole (B10+R) reduced, the increase in nociceptive heat sensitivity. **p < 0.01, compared with baseline foot withdrawal latencies on day 0 in the same group;+p < 0.05, compared with the corresponding morphine-alone group.