Figure 5.

Effect of δ₁ opioid receptor blockade on withdrawal jumping after acute and chronic morphine treatment. Mice subject to acute morphine treatment (left) were injected with a single morphine dose (50 mg/kg) whereas those subject to chronic morphine treatment (right) were injected t.i.d. for three days with escalating morphine doses (10, 20, and 40 mg/kg on treatment Days 1, 2, and 3, respectively) and a final 40 mg/kg morphine dose on Day 4. All mice were also injected with the δ₁ opioid receptor antagonist BNTX (0.5 mg/kg) 30 min prior to every morphine injection. Withdrawal was precipitated by naloxone (50 mg/kg) injection 3 h after completing acute and chronic morphine treatment. Antagonist control mice in both treatment paradigms were injected with saline instead of BNTX. There were no significant differences between saline and BNTX treated groups (P >0.05).