Convulsant activity of a non-peptidic delta-opioid receptor agonist is not required for its antidepressant-like effects in Sprague-Dawley rats.

RATIONALE: Non-peptidic delta-opioid receptor agonists possess antidepressant-like activity in the forced swim assay in the rat. These compounds have also previously been shown to possess convulsant properties in mice.
OBJECTIVE: The aim of the present study was to examine whether such convulsions occurred in rats and to investigate if delta-mediated convulsant activity was necessary for the mediation of delta-opioid agonist-induced antidepressant-like activity.
METHODS: The peripheral administration of delta-opioid receptor agonists to male Sprague-Dawley rats was followed by a period of observation for convulsant activity. Following this period and 60 min after delta-opioid agonist administration, rats were tested in the forced swim assay.
RESULTS: The non-peptidic delta-opioid receptor agonists (+)-4-[(R)-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-methoxyphenyl)methyl]-N,N-diethylbenzamide (SNC80) and (+)-4-[(R)-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-hydroxyphenyl)methyl]-N,N-diethylbenzamide dihydrochloride [(+)BW373U86] both produced dose-dependent convulsant activity in rats and decreased immobility in the forced swim assay. The delta-opioid receptor antagonist naltrindole prevented the convulsant activity of (+)BW373U86 and its effects in the forced swim assay. This suggested a delta-opioid mechanism for both effects. Midazolam prevented convulsions but did not prevent activity in the forced swim assay. Rats tolerant to the convulsive effects of (+)BW373U86 still displayed antidepressant-like effects.
CONCLUSION: delta-Mediated convulsions do occur in rats and can be prevented without affecting the delta-mediated effects in the forced swim assay. Therefore the convulsant activity of (+)BW373U86 and possibly other non-peptidic delta-agonists is not required for activity in the forced swim assay.