Reductions in ethanol, phencyclidine, and food-maintained behavior by naltrexone pretreatment in monkeys is enhanced by open economic conditions.
BACKGROUND
Previous results suggested that naltrexone had opioid-selective effects on behavior reinforced by orally delivered drugs and food. The present study explores the possibility that previous results were due to presentation of the reinforcers in a closed economy (all reinforcers earned by subjects) and that naltrexone's effect may be nonselective under conditions of an open economy (earned reinforcers supplemented by unearned).


OBJECTIVE
The purpose of this experiment was to compare the effect of naltrexone on ethanol-, phencyclidine-(PCP), and food-reinforced responding under several open-economy conditions and compare them with those from a previous report using a closed economy.


METHODS
Ethanol (8% w/v), PCP (0.25 mg/ml), and food were available under independent, concurrent, progressive-ratio (PR) schedules with water, and side positions were alternated daily. Three naltrexone doses (0.1, 0.3, and 1.0 mg/kg) were administered in a nonsystematic order for 5 days, with the 5-day pretreatment period serving as a control. Four economic conditions were compared: data for the closed economy were taken from a recently completed experiment using the same monkeys. The open-economy condition was varied by allowing free access to 1, 2 or 3 times the amount of drug or food that was earned during session later during a postsession time-out period.


RESULTS
In an open economy, naltrexone nonselectively suppressed ethanol, PCP, and food-maintained behavior, in contrast to results in the previous study which used a closed economy, wherein naltrexone did not significantly suppress food- or PCP self-administration. As the economy for PCP, ethanol, and food became more open, the suppressant effects of naltrexone increased and, in many animals, behavioral measures decreased to zero.


CONCLUSIONS
These results indicated that the economy under which drugs and food are self-administered is an important determinant of the effectiveness of naltrexone's ability to suppress drug- and food-reinforced behavior. The results also suggest that testing medications for drug abuse using a food control condition under a closed economy can bias the results toward a conclusion of selectivity of the treatment medication for drug-reinforced behavior.
Department of Psychiatry, University of Minnesota, Minneapolis 55455, USA. mcarroll@tc.umn.edu
M E
ME
Carroll
K P
KP
Cosgrove
U C
UC
Campbell
A D
AD
Morgan
J L
JL
Mickelberg
D000818:Animals; D002492:Central Nervous System Depressants / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects*; D004032:Diet; D000431:Ethanol / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005502:Food; D008253:Macaca mulatta; D008297:Male; D009271:Naltrexone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D010622:Phencyclidine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D012054:Reinforcement, Psychology
D002492:Central Nervous System Depressants; D018691:Excitatory Amino Acid Antagonists; D009292:Narcotic Antagonists; D000431:Ethanol; D009271:Naltrexone; D010622:Phencyclidine