Fig. 7. Effect of intrathecal pretreatment with MK-801 on dynorphin A (1–17)-mediated pain-like response. Groups of mice were treated intrathecal with a noncompetitive N -methyl-d-a spartic acid receptor antagonist, MK-801 (1 nmol/mouse), or vehicle 30 min before the intrathecal injection of dynorphin A (1–17) (30 pmol). Immediately after the intrathecal injection of dynorphin A (1–17), the number of licking or biting behaviors was counted (A ), and the duration of licking or biting behaviors was measured (B ) for 20 min after the intrathecal injection of dynorphin A (1–17). Dunnett test: $$ P < 0.01, $$$ P < 0.001, versus  saline-dynorphin A (1–17) group.