Separation of the convulsions and antidepressant-like effects produced by the delta-opioid agonist SNC80 in rats

Rationale: Delta-opioid agonists produce a number of behavioral effects, including convulsions, antinociception, locomotor stimulation, and antidepressant-like effects. The development of these compounds as treatments for depression is limited by their convulsive effects. Therefore, determining how to separate the convulsive and antidepressant-like characteristics of these compounds is essential for their potential clinical use. Objective: The present study tests the hypothesis that the rate of delta-opioid agonist administration greatly contributes to the convulsive properties, but not the antidepressant-like effects, of delta-opioid agonists. Materials and methods: The delta-opioid agonist SNC80 (1, 3.2, and 10 mg kg^-1 or vehicle) was administered to Sprague-Dawley rats by intravenous infusion over different durations of time (20 s, 20, or 60 min). Convulsions were measured by observation prior to determining antidepressant-like effects in the forced swim test. Results: Slowing the rate of SNC80 administration minimized delta agonist-induced convulsions without altering the effects of SNC80 in the forced swim test. Conclusions: These data suggest that delta agonist-induced antidepressant properties are independent of convulsive effects, and that it may be possible to eliminate the convulsions produced by delta agonists, further promoting their potential clinical utility.