title: Variable-ratio schedules of timeout from avoidance: effects of d-amphetamine and morphine.
abstract: Rats were trained on concurrent schedules in which pressing one lever postponed shock and pressing the other lever produced periods of signaled timeout from avoidance on variable-ratio schedules. These procedures generated high rates of timeout-reinforced responding and provided a baseline for studying the effects of drugs on behavior maintained by different types of negative reinforcement (shock postponement vs. timeout). Morphine (2.5 to 10.0 mg/kg) reduced behavior maintained by timeout at doses that increased or had no effect on avoidance responding. In contrast, d-amphetamine (0.125 to 2.0 mg/kg) produced large increases in timeout responding at doses that had minimal effect on avoidance in rats trained on variable-interval and variable-ratio schedules. Thus, the event-dependent effects of morphine, observed in previous studies in which timeout responding was maintained at low rates by interval schedules, were replicated with high timeout rates maintained by variable-ratio schedules. The effects of d-amphetamine could also be described as "event dependent" because timeout responding was stimulated more than avoidance regardless of the maintenance schedule or baseline rate.
authors.affiliation: Department of Psychology, University of North Carolina, Wilmington 28403.
authors.forename: M
authors.initials: M
authors.lastname: Galizio
authors.forename: A R
authors.initials: AR
authors.lastname: Allen
mesh_terms: D000818:Animals; D001143:Arousal / Q000187:drug effects; D001288:Attention / Q000187:drug effects*; D001362:Avoidance Learning / Q000187:drug effects*; D003913:Dextroamphetamine / Q000494:pharmacology*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology; D051381:Rats; D012055:Reinforcement Schedule
chemical_list: D009271:Naltrexone; D009020:Morphine; D003913:Dextroamphetamine