Inhibition of drinking by naltrexone in the rat: interaction with the dopamine D-1 antagonist SCH 23390 and the D-2 antagonist sulpiride.
The involvement of dopamine receptors in water intake was investigated in the rat deprived of water for 24 hr. A 0.03 mg/kg dose of SCH 23390 markedly enhanced naltrexone (0.1 and 10.0 mg/kg)-induced hypodipsia, whilst the drug alone significantly decreased water intake at doses of 0.01 to 3.0 mg/kg, accompanied by marked motor dysfunction. Sulpiride (20.0 and 40.0 mg/kg) did not markedly affect water intake and naltrexone-induced hypodipsia. Consistent with previous results, apomorphine (0.3 mg/kg) alone was without marked effects, while it produced a marked potentiation of naltrexone (1.0 and 10.0 mg/kg)-induced hypodipsia. SCH 23390 (0.003 mg/kg) and sulpiride (40.0 mg/kg) completely antagonized the enhancing effects of apomorphine on naltrexone-induced hypodipsia. Similar effects were also seen in the latency to begin drinking. In contrast to the effects on naltrexone-induced hypodipsia, it appears that both dopamine D-1 and D-2 receptors play a key role in the effects of apomorphine on naltrexone-induced hypodipsia in the rat.
Ukai
M
M
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Meijo University, Nagoya, Japan.
Nakayama
S
S
Kameyama
T
T
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004327:Drinking Behavior / Q000187:drug effects*; D008297:Male; D009271:Naltrexone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology*; D013469:Sulpiride / Q000494:pharmacology*
D001552:Benzazepines; D011954:Receptors, Dopamine; D009271:Naltrexone; D013469:Sulpiride; D001058:Apomorphine