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.