Figure 3. Morphine delivery systems induce different withdrawal behaviors.

Male C57BL/6NCr mice (n=5) were implanted with a morphine sulfate pellet (25 mg), an osmotic pump (64 mg/mL, 1.0 μL/hour), or injected subcutaneously twice daily (20 mg/kg). Control mice received no treatment (“no naloxone”) or a naloxone injection without prior morphine treatment (“naloxone”). Withdrawal was induced at 1, 3, or 7 days post-implantation with an i.p. injection of 10 mg/kg naloxone. (A) After naloxone injection, mice were placed within a Plexiglas column and video-recorded for 20 minutes. Vertical jumps were assessed over the 20-minute period. (B) After completion of the jumping test, filter paper at the bottom of the column was weighed to measure feces and urine excreted. (C) Animal weight was compared before and after naloxone injection. Significance is shown as *p < 0.05 compared to non-morphine controls, #p < 0.05 compared to morphine S.C. injection, $p < 0.05 compared to osmotic pump within each timepoint, as determined by a two-way ANOVA with a Student-Newman-Keuls post hoc test. Bracketed groups indicate a significant difference between timepoints within the delivery method.