Effects of adrenoceptor agonists and antagonists on morphine-induced Straub tail in mice

Abstract

Straub-tail behavior was induced by subcutaneous injection of different doses (10–60 mg/kg) of morphine to mice. The maximum response was obtained with 20–40 mg/kg of the drug. The response induced by morphine (40 mg/kg) was decreased by intraperitoneal administration of different doses of clonidine (0.05–0.1 mg/kg). Pretreatment of animals with yohimbine (1–4 mg/kg ip) reversed the inhibitory action of clonidine. Yohimbine did not elicit any response by itself. Administration of prazosin (0.25, 0.5, and 1 mg/kg) reduced the morphine response. The combination of prazosin with yohimbine (1 mg/kg), but not with clonidine (0.05 mg/kg), caused a potentiated inhibition of the morphine effect. Phenylephrine (2–6 mg/kg ip) did not elicit any effect by itself and also did not alter the response induced by morphine or morphine plus clonidine. Dobutamine (2.5–10 mg/kg ip), atenolol (2.5–10 mg/kg ip), salbutamol (2.5–10 mg/kg ip), and propranolol (2.5–10 mg/kg ip) did not alter morphine-induced Straub-tail behavior in mice. In conclusion, activation of α 2-adrenergic pathways contributes to morphine-induced Straub tail, while α 1- and β 2-adrenergic may not be involved in this phenomenon.