• Energy Research

A common finding in resistance to change research with food-maintained operant behavior is that the persistence of behavior depends on the rate of reinforcement delivered in the context in which the behavior occurs. The present experiment evaluated the effects of rate of response-dependent alcohol delivery on the resistance to change of rats' alcohol self-administration in the face of disruption produced by extinction and a range of doses of naltrexone (1.0, 3.0, 10.0 mg/kg, subcutaneous). Rats responded for a 10% alcohol solution in a multiple schedule of reinforcement arranging a higher rate of alcohol delivery (variable interval 15 s) in the presence of one stimulus and a lower rate of alcohol delivery (variable interval 45 s) in the presence of another stimulus. Baseline response rates and resistance to extinction were higher in the presence of the stimulus associated with higher rates of alcohol delivery. This finding is consistent with studies of the resistance to change of food-maintained behavior. The rate of alcohol delivered in the components, however, did not systematically affect resistance to disruption by naltrexone. One interpretation of this finding from the perspective of behavioral momentum theory is that naltrexone may decrease the impact of alcohol-associated stimuli on the persistence of drinking by reducing sensitivity to the relative reinforcement conditions arranged in the presence of different stimuli.

The generalized matching law quantitatively describes the relation between relative response allocation and relative reinforcement allocation in a choice situation and has accounted well for drug-maintained choice behavior. Earlier studies applying the generalized matching law to alcohol-maintained choice, however, have produced somewhat atypical findings (e.g. poor fits, negative sensitivity values). These findings may be the result of the procedures used in the earlier alcohol studies (e.g. two-bottle choice procedure, variations in relative concentration of alcohol, volume consumed as dependent variable). This experiment examined the applicability of the generalized matching law to alcohol self-administration using procedures more similar to those typically used with other reinforcers. A free-operant choice procedure arranging concurrent variable-interval schedules of alcohol reinforcement was used to vary rates of alcohol deliveries produced by two response options. Results showed that the generalized matching law provided a good description of changes in the relative allocation of behavior with changes in the relative rate of alcohol delivery. Thus, the atypical results in earlier studies were likely a result of the procedures used. These results suggest that the parameters of the generalized matching law may provide useful quantitative measures of the impact biological and environmental variables on alcohol-associated choice behavior.

An extensive body of research using concurrent‐chains schedules of reinforcement has shown that choice for one of two differentially valued food‐associated stimuli is dependent upon the overall temporal context in which those stimuli are embedded. The present experiments examined whether the concurrent chains procedure was useful for the study of behavior maintained by alcohol and alcohol‐associated stimuli. In Experiment 1, rats responded on concurrent‐chains schedules with equal variable‐interval (VI) 10‐s schedules in the initial links. Across conditions, fixed‐interval schedules in the terminal links were varied to yield 1:1, 9:1, and 1:9 ratios of alcohol delivery. Initial‐link response rates reflected changes in terminal‐link schedules, with greater relative responding in the rich terminal link. In Experiment 2, terminal‐link schedules remained constant with a 9:1 ratio of alcohol delivery rates while the length of two equal duration initial‐link schedules was varied. Preference for the rich terminal link was less extreme when initial links were longer (i.e., the initial‐link effect), as has been previously reported with food reinforcers. This result suggests that the conditioned reinforcing value of an alcohol‐associated stimulus depends on the temporal context in which it is embedded. The concurrent‐chains procedure and quantitative models of concurrent chains performance may provide a useful framework within which to study how contextual variables modulate preference for drug‐associated conditioned reinforcers.

Amphetamines are the second most highly abused illicit drugs worldwide, yet there is no pharmacological treatment for amphetamine abuse and dependence. Preclinical studies and, more recently, human studies, suggest that the opioid receptor antagonist, naltrexone, might be useful in the treatment of amphetamine abuse. Naltrexone, an opioid receptor antagonist, is currently used for the treatment of alcohol dependence. The aim of this study was to explore the ability of naltrexone to modify self-administration of amphetamine or ethanol in rhesus monkeys. Monkeys were trained to respond to intravenous injections of either D-amphetamine (0.003 mg/kg/injection) or ethanol (0.05 g/kg/injection) on a fixed ratio 30 schedule. Naltrexone (0.01-1 mg/kg) was administered intramuscularly 30 min before the start of treatment test sessions. Naltrexone dose-dependently decreased both amphetamine and ethanol self-administration. These findings support the potential use of naltrexone as therapy for amphetamine and polydrug abuse.