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Table 1 Tolerance induced by morphine but not naloxone in MOR-KO mice that had been transfected with the dsAAV2-MORS196A-EGFP gene

From: Antinociceptive effects of morphine and naloxone in mu-opioid receptor knockout mice transfected with the MORS196A gene

  ED50 of morphine
(mg/kg)
ED50 of naloxone
(mg/kg)
Acute effect 4.4 ± 1.0 8.4 ± 1.2
Sub-chronic effect 7.2 ± 1.1 (×1.63) 8.4 ± 1.2
  1. The ED50 values of morphine and naloxone that inhibit the tail-flick responses were determined using the up-and-down method 3 weeks after gene transfer. The mice were then sub-chronically treated with morphine (10 mg/kg) or naloxone (10 mg/kg) subcutaneously twice a day for 4 days. ED50 values were then redetermined. Data are means ± the standard error of the mean (SEM) (n = 6).