Assessing spiradoline-like discriminative effects of DuP 747: influence of route of administration

DuP 747, trans-3,4-dichloro-N-methyl-N-[2-(pyrrolidin-1-yl)-1,2,3,4- tetrahydronaphthalen-1-yl]benzeacetamide methanesfonate, is a recently synthesized analgesic drug that binds with high affinity and selectivity to the kappa-opioid receptor. In order to determine if DuP 747 has kappa-like discriminative effects it was tested for stimulus generalization in rats trained to discriminate between SC injections of saline and 3.0 mg/kg of spiradoline, a potent kappa-opioid agonist. A range of drug doses was administered by each of several routes 30 min before a test session. Spiradoline occasioned orderly dose-dependent increases in spiradoline-appropriate lever selection after SC or IP administration, with ED50s of 0.65 and 1.75 mg/kg, respectively. In contrast, DuP 747 (1.0-30 mg/kg) occasioned little spiradoline-appropriate lever selection when administered SC, but was generalized from spiradoline partially when administered IP (ED50 = 5.9 mg/kg) or PO (ED50 = 59 mg/kg). The 5-hydroxy-desmethoxy metabolite of DuP 747, administered SC (0.3-10 mg/kg), occasioned selection of the saline-appropriate lever only. That DuP 747 had little spiradoline-like activity after SC administration suggests that a metabolite of DuP 747 was responsible for the spiradoline-appropriate responding that followed IP and PO administration of the drug, apparently a metabolite Other than 5-hydroxy-desmethoxy-DuP 747.