Food deprivation and acquisition of intravenous cocaine self-administration in rats: effect of naltrexone and haloperidol.
In order to create optimal conditions for the acquisition of i.v. cocaine self-administration in the rat, three groups of rats were deprived of food to different extents in order to obtain body weight reductions of 5 to 15, 15 to 25 and 25 to 35% of the pre-experimental body weights, and were tested for five consecutive 6-hr sessions in a continuous reinforcement procedure for self-administration of cocaine (0.12 mg/ml) or saline. Self-administration interacted with weight loss and indicated that: 1) a minimum level of 15 to 25% weight loss was required to obtain cocaine self-administration; 2) weight loss-induced potentiation of cocaine self-administration resulted from an interaction of increased nonspecific lever pressing activity and increased reinforcing effects of the compound; and 3) optimal differentiation between cocaine- and saline-induced responding was obtained at 15 to 25% weight loss. Daily pretreatment during the five test sessions, with 0.1 to 1.0 mg/kg of naltrexone or 43 to 375 micrograms/kg of haloperidol, dose-dependently decreased the number of cocaine (0.12 mg/ml) self-injections. Naltrexone pretreatment, and to a lesser extent haloperidol pretreatment, appeared to affect cocaine self-administration in a specific manner; both treatments affected responding on the reinforced lever, but not responding on the nonreinforced lever. Self-administration of 0.06 mg/ml of cocaine tended to be decreased by naltrexone (1 mg/kg) and haloperidol (375 micrograms/kg); whereas self-administration induced by 0.25 mg/ml of cocaine was not significantly affected by naltrexone or haloperidol. Both treatments failed to affect self-administration of saline.(ABSTRACT TRUNCATED AT 250 WORDS)
De Vry
J
J
Rudolf Magnus Institute for Pharmacology, Medical Faculty, University of Ultrecht, The Netherlands.
Donselaar
I
I
Van Ree
J M
JM
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D003042:Cocaine / Q000494:pharmacology*; D005508:Food Deprivation; D006220:Haloperidol / Q000494:pharmacology*; D008297:Male; D009271:Naltrexone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012054:Reinforcement, Psychology; D012646:Self Administration
D009271:Naltrexone; D003042:Cocaine; D006220:Haloperidol