Figure 1. Time-course of static mechanical sensitivity.

A: Schematic representation of the experimental paradigm. Rats received i.p. injections of vincristine (0.1 mg/kg/day) during 2 cycles of 5 days. Analgesic treatment started at D15, and was performed for 5 days until D19. The analgesic effect of oxycodone or morphine was tested on D15 and D19, with a time-course of 30, 60 and 90 minutes after injection. These injections are illustrated by black triangles. At D15, all groups of vincristine-treated rats presented static mechanical allodynia (B) and hyperalgesia (C), as compared to control rats and the baseline (BL). B: Static mechanical allodynia measured using the electronic Von Frey test. The measured static mechanical allodynia was totally reversed after a single injection of morphine or oxycodone, although only oxycodone maintained a strong analgesic effect at D19. C: Static mechanical hyperalgesia measured by the “Pinch Test”. Oxycodone induced an analgesic effect in vincristine-oxycodone treated rats after a single injection, and maintained its analgesic effect at D19. All data are expressed as mean ± SEM. (n = 7 vincristine-morphine treated rats; n = 6 saline-morphine treated rats), (n = 7 vincristine-oxycodone treated rats; n = 6 saline-oxycodone treated rats), and (n = 7 vincristine-saline treated rats; n = 6 saline-saline treated rats). *p<0.05, **p<0.01, ***p<0.001: vincristine-oxycodone treated rats vs. vincristine-morphine treated rats; † p<0.05, †† p<0.01, ††† p<0.001: vincristine-oxycodone treated rats vs. vincristine-saline treated rats; §§ p<0.01, §§§ p<0.001: vincristine-morphine treated rats vs. vincristine-saline treated rats. For figure clarity, the statistical significance symbols for the vincristine vs. saline groups are not shown.