Differential Behavioral Tolerance to the -Opioid Agonist SNC80 ([()-4-[(R)--[(2S,5R)-2,5-Dimethyl-4-(2-propenyl)-1- piperazinyl]-(3-methoxyphenyl)methyl]-N,N-diethylbenzamide) in Sprague-Dawley Rats

Nonpeptidic -opioid agonists produce a number of behaviors, such as antidepressant-like effects, locomotor stimulation, an-tinociception, and convulsions. To consider this class of com-pounds as potential therapeutics for humans, the effects of -opioid agonists after repeated administration must be evalu-ated. Therefore, the present study investigated the effects of repeated -opioid agonist, SNC80 ([()-4-[(R)--[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-methoxyphenyl)-methyl]-N,N-diethylbenzamide), administration on its antide-pressant-like effects in the forced swim test, locomotor activity, and convulsions in male Sprague-Dawley rats. Tolerance de-veloped rapidly to the convulsive and locomotor-stimulating effects of SNC80 but not to the antidepressant-like effects. In addition, tolerance was evaluated at the level of the receptor-