Effects of μ-, δ- and κ-opioid receptor agonists on methamphetamine-induced self-injurious behavior in mice

Opioid receptor agonists can differentially modify the behavioral effects of direct/indirect dopamine receptor agonists, such as methamphetamine, cocaine and apomorphine. However, the effects of opioid receptor agonists on high-dose methamphetamine-induced behavior have not yet been clarified. Therefore, the present study was undertaken to investigate the effects of μ (morphine)-, δ (SNC80)- and κ (U50,488H)-opioid receptor agonists on methamphetamine-induced self-injurious behavior and locomotor activity in mice. Methamphetamine (20 mg/kg) induced severe self-injurious behavior. In a combination test, some opioid receptor agonists significantly attenuated methamphetamine-induced self-injurious behavior, with potencies in the order morphine > buprenorphine (μ-opioid and κ-opioid receptor agonist/antagonist) > U50,488H, as maximum effects. These results suggest that the stimulation of μ- and κ-opioid receptors plays an inhibitory role in high-dose methamphetamine-induced stereotypic self-injurious behavior in mice, without affecting locomotor activity.