Comparison between pentobarbital- and muscimol-induced feeding in satiated sheep.
Twenty sheep were used to study the mechanisms by which the intracerebral administration of pentobarbital and of muscimol induces feeding in ruminants. Injections of 1 mumol calcium induced a weak feeding response at 1 h postinjection compared with control values (108 vs. 63 g, p less than 0.05). Injections of 78 mumol pentobarbital and of 100 nmol muscimol elicited strong feeding responses (p less than 0.01). A preinjection of 1 mumol calcium reduced the response to pentobarbital by about 40% but did not affect the response to muscimol. Administration of 1.1 mmol sodium chloride reduced the effect to pentobarbital by about 60% but only partially decreased the effect to muscimol. Administration of picrotoxin, a GABA antagonist, slightly decreased the feeding response to pentobarbital and to muscimol. Administration of gamma-vinyl GABA, an inhibitor of the enzyme GABA transaminase, did not affect feeding behavior of sheep at any of the doses tested (0-10 mumol). Injections of gamma-vinyl GABA followed by equimolar injections of GABA failed to provoke any feeding response. The data suggest that pentobarbital and muscimol may induce feeding by acting on a similar hypothalamic receptor complex but by different mechanisms. The lack of effect of GABA itself remains unexplained.
Seoane
J R
JR
Département de zootechnie, Faculté de sciences de l'agriculture et de l'alimentation, Université Laval, Cité Universitaire, Québec, Canada.
Bédard
L
L
Caron
N
N
D000614:Aminocaproates / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004435:Eating / Q000187:drug effects*; D007276:Injections, Intraventricular; D008297:Male; D009118:Muscimol / Q000008:administration & dosage / Q000494:pharmacology*; D010424:Pentobarbital / Q000008:administration & dosage / Q000494:pharmacology*; D010852:Picrotoxin / Q000494:pharmacology; D012756:Sheep; D012964:Sodium / Q000494:pharmacology; D020888:Vigabatrin; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D000614:Aminocaproates; D002118:Calcium; D009118:Muscimol; D010424:Pentobarbital; D010852:Picrotoxin; D012964:Sodium; D020888:Vigabatrin; D005680:gamma-Aminobutyric Acid