| Group 1: Naïve (without any treatment) | | Group 2: Saline single injection or 1 injection each day for 8 days, s.c. (data combined as there was no difference between the two groups) | | Group 3: MorX1 (morphine10 mg/kg, one injection, s.c.) | | Group 4: Sal X8 (saline, 8 injections, 1 injection each day, for 8 days, s.c.) | | Group 5: MorX8 (morphine10 mg/kg, 1 injection each day × 8 days, s.c.) | | Group 6: Esc, morphine escalating dose (10, 20, 20, 40, 40, 80, 160 mg/kg, s.c.) | | Group 7: PP24h, acute implantation of placebo pellet, sacrificed 24 h later | | Group 8: PM24h, acute implantation of morphine pellet (25 mg), sacrificed 24 h later | | Group 9: PP7d, chronic implantation of placebo pellets (on day 1 and day 4) and sacrificed on day 7 | | Group 10: PM7d, chronic implantation of morphine pellets (25 mg) (on day 1 and day 4) and sacrificed on day 7 | |
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