Antidepressant-like Effects of δ Opioid Receptor Agonists in Animal Models

Recently, delta opioid receptor agonists have been proposed to be attractive targets for the development of novel antidepressants. Several studies revealed that single treatment of delta opioid receptor agonists produce antidepressant-like effects in the forced swimming test, which is one of the most popular animal models for screening antidepressants. In addition, subchronic treatment with delta opioid receptor agonists has been shown to completely attenuate the hyperemotional responses found in olfactory bulbectomized rats. This animal model exhibits hyperemotional behavior that may mimic the anxiety, aggression, and irritability found in depressed patients, suggesting that delta opioid receptor agonists could be effective in the treatment of these symptoms in depression. On the other hand, prototype delta opioid receptor agonists produce convulsive effects, which limit their therapeutic potential and clinical development. In this review, we presented the current knowledge regarding the antidepressant-like effects of delta opioid receptor agonists, which include some recently developed drugs lacking convulsive effects.