Role of kappa-opioid receptors in the effects of salvinorin A and ketamine on attention in rats.

Two drugs that alter perception and cognition in humans—salvinorin A (a kappa-opioid receptor agonist) and ketamine (an NMDA receptor antagonist)—produced similar disruptions in attention and motivation in rats tested on a food-motivated attention task. Both drugs increased omission errors (signs of reduced motivation) and slowed correct response latencies (processing deficits). Pre-feeding before testing produced a subtly different pattern, suggesting the drug effects were not purely motivational. A kappa-opioid receptor blocker (JDTic) prevented all effects of salvinorin A and some effects of ketamine. Binding studies showed ketamine also activates kappa-opioid receptors, though less potently than salvinorin A. These findings suggest kappa-opioid receptors may contribute to cognitive disruptions seen in conditions like schizophrenia.

Study at a glance

Abstract

Disruptions in perception and cognition are characteristic of psychiatric conditions such as schizophrenia. Studies of pharmacological agents that alter perception and cognition in humans might provide a better understanding of the brain substrates of these complex processes. One way to study these states in rodents is with tests that require attention and visual perception for correct performance. We examined the effects of two drugs that cause disruptions in perception and cognition in humans-the kappa-opioid receptor (KOR) agonist salvinorin A (salvA; 0.125-4.0 mg/kg) and the non-competitive NMDA receptor antagonist ketamine (0.63-20 mg/kg)-on behavior in rats using the 5-choice serial reaction time task (5CSRTT), a food-motivated test that quantifies attention. We also compared the binding profiles of salvA and ketamine at KORs and NMDA receptors. SalvA and ketamine produced the same pattern of disruptive effects in the 5CSRTT, characterized by increases in signs often associated with reduced motivation (omission errors) and deficits in processing (elevated latencies to respond correctly). Sessions in which rats were fed before testing suggest that reduced motivation produces a subtly different pattern of behavior. Pretreatment with the KOR antagonist JDTic (10 mg/kg) blocked all salvA effects and some ketamine effects. Binding and function studies revealed that ketamine is a full agonist at KORs, although not as potent or selective as salvA. SalvA and ketamine have previously under-appreciated similarities in their behavioral effects and pharmacological profiles. By implication, KORs might be involved in some of the cognitive abnormalities observed in psychiatric disorders such as schizophrenia.