Quinpirole- and amphetamine-induced hyperdipsia: influence of fluid palatability and behavioral cost.
Daily administration of moderate doses of amphetamine or of the dopaminergic D2 agonist quinpirole is associated with the development of excessive, non-regulatory drinking. Here we compared the influence of manipulating fluid palatability and behavioral cost on the development of this drinking augmentation. Experiment 1 was based on the phenomenon of contrafreeloading (CFL): animals work for a resource even though the same resource is freely available. The effects of 15 daily injections of amphetamine (1.0 and 1.7 mg/kg i.p. ) or quinpirole (0.1 and 0.56 mg/kg i.p.) were evaluated in mildly water-deprived rats. For the first 6 days the rats obtained water by lever pressing (FR3) only; over the following 9 days water was also freely available (CFL). Initially, 0.56 mg/kg quinpirole reduced lever pressing for water. A complete recover of responding was then obtained, and was followed by a progressive increment in the amount water obtained by lever pressing during the CFL phase (from 10 to 50%). Amphetamine did not affect percent CFL, but at the highest dose (1.7 mg/kg) reduced total water intake during the last 3 days of treatment. In experiment 2 the rats had free access to two bottles, one of which contained tap water, and the other contained either an ethanol (6%) or a sucrose (5%) solution. After habituation to this regimen, the rats received 10 daily i.p. injections of vehicle, amphetamine (1.0 or 3 mg/kg), or quinpirole (0.1 or 0.56 mg/kg). Quinpirole 0.56 mg/kg enhanced daily fluid intake under both sucrose and ethanol conditions, but selectively reduced ethanol preference. The higher amphetamine dose reduced fluid intake and sucrose preference. In conclusion, chronic exposure to a dopaminergic D2 agonist, but not to amphetamine, produced an increment of drinking that was resistant to manipulation of either palatability or the behavioral cost of the fluid.
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Institute of Medical Pharmacology, University of Rome 'La Sapienza', P. le A. Moro 5, 00185, Rome, Italy.
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D000428:Alcohol Drinking; D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects; D019422:Dietary Sucrose / Q000008:administration & dosage; D018491:Dopamine Agonists / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004326:Drinking / Q000187:drug effects*; D007274:Injections, Intraperitoneal; D008297:Male; D009042:Motivation; D019257:Quinpirole / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000187:drug effects; D013649:Taste / Q000187:drug effects*
D019422:Dietary Sucrose; D018491:Dopamine Agonists; D017448:Receptors, Dopamine D2; D019257:Quinpirole; D000661:Amphetamine