title: Apomorphine markedly potentiates naltrexone-induced hypodipsia in the rat.
abstract: This article describes the effects of apomorphine on naltrexone-induced decreases in water intake of the rat deprived of water for 24 h. Apomorphine alone at reasonable doses (0.03, 0.1, 0.3 and 1.0 mg/kg) failed to affect water intake of the rat, but a higher dose (3.0 mg/kg) abolished water intake completely, accompanied by marked stereotypy. Naltrexone (0.1, 1.0 and 10.0 mg/kg) produced a dose-dependent reduction in water intake. A 0.3-mg/kg dose of apomorphine which is considered to activate preferentially presynaptic dopamine autoreceptors enhanced markedly naltrexone (1.0 and 10.0 mg/kg)-induced decreases in water intake. Only apomorphine at 1.0 mg/kg caused a significant prolongation of the latency to start drinking. Apomorphine (0.3 mg/kg), naltrexone (0.1, 1.0 and 10.0 mg/kg) or their combinations did not produce a marked effect on locomotor activity in the rat. These results suggest that apomorphine is capable of potentiating naltrexone-induced decreases in water intake through the mediation of presynaptic dopamine autoreceptors without causing motor dysfunction.
authors.affiliation: Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Meijo University, Nagoya, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Ukai
authors.forename: S
authors.initials: S
authors.lastname: Nakayama
authors.forename: T
authors.initials: T
authors.lastname: Kameyama
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D004326:Drinking / Q000187:drug effects*; D008297:Male; D009271:Naltrexone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009271:Naltrexone; D001058:Apomorphine