Dopamine D(2) receptors and ingestive behavior: brainstem mediates inhibition of intraoral intake and accumbens mediates aversive taste behavior in male rats.
BACKGROUND
One of the factors that terminate the ingestion of an intraorally infused solution of sucrose may be an increase in the perceived aversiveness of its taste.


OBJECTIVE
We tested the hypothesis that dopamine D(2), as opposed to D(1), receptors in the brainstem or nucleus accumbens inhibit intraoral intake by enhancing the aversiveness of the taste of the infused solution.


METHODS
Male rats were infused intraorally with a 2 M sucrose solution (1 ml/min) and intake and the display of gapes and chin rubs, i.e. taste-related aversive behavior, was measured. Gapes and chin rubs were also measured in rats during and 40 s after brief intraoral infusion (1 ml/min during 20 s) of a 0.3 mM solution of quinine HCl. The full D(1) receptor agonist dihydrexidine (0.1-3.0 mg/kg) and antagonist SCH-23390 (0.03-0.1 mg/kg), the D(2) receptor agonist quinpirole (0.3 mg/kg) and antagonist raclopride (1.7 mg/kg) were injected IP. Quinpirole (14-55 microg) and raclopride (5 microg) were also infused into the fourth brain ventricle. In addition, quinpirole (2 or 10 microg) was infused into the shell region of the nucleus accumbens.


RESULTS
IP dihydrexidine and quinpirole inhibited the intraoral intake of sucrose and pretreatment with raclopride, but (in the case of dihydrexidine) not SCH-23390, attenuated this effect. Injection of quinpirole into the fourth ventricle produced raclopride-reversible inhibition of intraoral intake but did not stimulate the display of gapes and chin rubs. Infusion of quinpirole into the shell region of the nucleus accumbens had the opposite effects. The intake of sucrose was suppressed by the addition of quinine HCl but this suppression was unaffected by dopamine agonist or antagonist treatment.


CONCLUSIONS
It is suggested that brainstem dopamine D(2) receptors mediate suppression of consummatory ingestive behavior and that D(2) receptors in the shell region of the nucleus accumbens mediate the display of gapes and chin rubs, but that neither of these D(2) receptor populations mediate the hedonic evaluation of taste.
Sederholm
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F
Section of Applied Neuroendocrinology, Karolinska Institutet, Novum, 141 57 Huddinge, Sweden.
Johnson
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AE
Brodin
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U
Södersten
P
P
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D001552:Benzazepines / Q000494:pharmacology; D001933:Brain Stem / Q000187:drug effects / Q000502:physiology*; D018491:Dopamine Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D004326:Drinking; D005247:Feeding Behavior / Q000187:drug effects / Q000502:physiology*; D007274:Injections, Intraperitoneal; D007276:Injections, Intraventricular; D008297:Male; D009714:Nucleus Accumbens / Q000187:drug effects / Q000502:physiology*; D010617:Phenanthridines / Q000494:pharmacology; D019257:Quinpirole / Q000494:pharmacology; D020891:Raclopride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000187:drug effects / Q000502:physiology*; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000502:physiology*; D017552:Solitary Nucleus / Q000502:physiology; D013395:Sucrose / Q000008:administration & dosage; D013649:Taste / Q000187:drug effects / Q000502:physiology*
D001552:Benzazepines; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D010617:Phenanthridines; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D019257:Quinpirole; C061532:dihydrexidine; D020891:Raclopride; D013395:Sucrose