Effects of the Kappa Agonist U69,593 on Naltrexone’s Discriminative Stimulus Effect in Subjects Given Chronic, Intermittent Sucrose Access

Abstract

Naltrexone (NTX) is a non-specific opioid antagonist that is comparable to naloxone (Narcan). Avena, Hoebel & colleagues (2004) demonstrated that rats given access to a chronic, intermittent sucrose solution have increased endorphin function. Our previous research has shown that rats given access to a 25% sucrose solution can discriminate NTX (0.1 mg/kg - 3.2 mg/kg) from saline in an operant procedure. We wondered if NTX’s discriminative stimulus effects are mediated by kappa-opioid receptors. To examine this, we used U69,593, a kappa-opioid receptor agonist in multiple discrimination testing procedures.