(A) Dose effect of i.t. morphine on MIS and MIA in 30 min.
(B) Time course of morphine on MIS and MIA.
(C) Induction of acute MIA tolerance with morphine (100 mg/kg, s.c.) or saline. Mice had returned to the basal nociceptive latencies 24 hr after injection.
(D) Acute MIA tolerance was tested with i.t. morphine 24 hr after s.c. morphine treatment.
(E) I.t. morphine induced comparable scratches in acute MIA tolerant and control mice.
(F) Induction of chronic MIA tolerance by daily injection of morphine (10 mg/kg, s.c.) and MIA was examined daily.
(G) After 5 days of systemic morphine injection, i.t. morphine also showed antinociceptive tolerance.
(H) I.t. morphine induced comparable scratches in chronic MIA tolerant and control mice. In all experiments, the dose of i.t. morphine is 0.3 nmol. n = 6~8 per group. MIA results are expressed as % maximum possible effect (MPE). *p < 0.05. Error bars represent standard error of the mean.