The influence of cost manipulation on water contrafreeloading induced by repeated exposure to quinpirole in the rat.
BACKGROUND
Quinpirole (QNP), a D2/D3 dopaminergic receptor agonist, was found to elicit an apparently antieconomical drinking behavior called contrafreeloading (CFL). The perseverative operant responding observed may represent a compulsive-like behavior prompted by sensitization to the effects of QNP.


OBJECTIVE
In the present study, we investigated the effect of different response costs on instrumental behavior and CFL in rats repeatedly treated with QNP (0.5 mg/kg i.p.). Moreover, we studied the consummatory components of ingestive behavior in no-choice paradigms and the role of learned operant conditioning in free drinking.


METHODS
In experiment 1, rats were trained to perform under three different fixed ratio schedules of reinforcement (FR1, FR3, and FR10) and were given a choice between operant and free access to water. In experiment 2, rats were divided into four groups, each one resembling experiment 1 in one or more features, with no choice available and water consumption measured at an interval of 0-60 min.


RESULTS
(a) Increasing FR significantly reduced CFL % in saline -- but not in QNP-injected groups; (b) under free-drinking conditions, QNP caused a progressive hypodipsic effect which was, however, contrasted by maintaining cues formerly contingent on operant access to water; and (c) under CFL conditions QNP-treated rats drank more than under free access conditions.


CONCLUSIONS
QNP confers rigidity in responding for water, impeding adaptation to different contingencies for access to the resource. In QNP-treated rats, CFL behavior appears adaptive as far as it allows animals to partially circumvent the hypodipsic effect of the drug.
Milella
Michele S
MS
Department of Human Physiology and Pharmacology Vittorio Erspamer, University of Rome Sapienza, Rome, Italy.
Amato
Davide
D
Badiani
Aldo
A
Nencini
Paolo
P
D000818:Animals; D002755:Choice Behavior / Q000187:drug effects; D003216:Conditioning, Operant / Q000187:drug effects*; D018491:Dopamine Agonists / Q000494:pharmacology*; D004327:Drinking Behavior / Q000187:drug effects*; D007274:Injections, Intraperitoneal; D008297:Male; D009042:Motivation; D009771:Obsessive-Compulsive Disorder / Q000139:chemically induced; D019257:Quinpirole / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D012528:Satiety Response / Q000187:drug effects*; D013239:Stereotyped Behavior / Q000187:drug effects
D018491:Dopamine Agonists; D019257:Quinpirole