highly significantP < 0.001
After 60 min ( F (5,42) = 55.36, P < 0.001), the increase in percentage response was less significant ( P < 0.05) for morphine whilst it was highly significant ( P < 0.001) for PI-ME (150 and 200 mg/kg), the activity being retained in the latter case up to 90 min ( F (5,42) = 36.61, P < 0.001, not shown).