REPEATED ACQUISITION OF BEHAVIORAL CHAINS IN SQUIRREL-MONKEYS - COMPARISONS OF A MU-OPIOID, KAPPA-OPIOID AND DELTA-OPIOID AGONIST

Responding by squirrel monkeys was maintained by food presentation und er a repeated acquisition of behavioral chains procedure. Monkeys acqu ired a different three-response chain each session. Sequence completio ns were reinforced under a fixed-ratio 5 schedule, whereas errors prod uced a brief time out. Morphine (0.1-3.2 mg/kg) produced dose-related decreases in response rate at doses that had little or no effect on er rors. U50488H -N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide metha ne sulfonate hydrate} (0.018-0.56 mg/kg) yielded a steep dose-effect c urve, decreasing response rate only at high doses that also had little or no effect on errors. The delta opioid agonist BW373U86 (+/-)-4-((a lpha-R)-alpha-((2S*,5R*)-4-allyl-2,5 piperazinyl)-3-hydroxybenzyl)-N, N-diethylbenzamide dihydrochloride (0.0056-0.32 mg/kg) produced dose-r elated decreases in response rate and increased errors. The delta opio id receptor antagonist naltrindole (0.056-18 mg/kg) alone had no effec t on either the rate of responding or percent errors. The rate-decreas ing and error-increasing effects produced by BW373U86 were antagonized by naltrindole. BW373U86 alone at doses of greater than or equal to 0 .56 mg/kg produced brief tonic-clonic convulsions in all monkeys. Nalt rindole (1 mg/kg) also antagonized the convulsant effects of BW373U86. At doses at which naltrindole was an effective antagonist of BW373U86 , it failed to antagonize either morphine or U50488H. These results de monstrate that the delta opioid agonist BW373U86 produces effects on a cquisition that differ dramatically from prototypical mu and kappa opi oid agonists. These data suggest that the squirrel monkey is more sens itive to the disruptive effects of a delta agonist than to mu or kappa agonists in this experimental context.