The role of GABAergic system on the inhibitory effect of ghrelin on food intake in neonatal chicks
ABSTRACT Ghrelin is a gut-brain peptide that has a stimulatory effect on food intake in mammals. In contrast, this peptide decreases food intake in neonatal chicks when injected intracerebroventricularly (ICV). In mammals, neuropeptide Y (NPY) mediates the orexigenic effect of ghrelin whereas in chicks it appears that corticotrophin releasing factor (CRF) is partially involved in the inhibitory effect of ghrelin on food intake. Gamma aminobutyric acid (GABA) has a stimulatory effect on food intake in mammals and birds. In this study we investigated whether the anorectic effect of ghrelin is mediated by the GABAergic system. In Experiment 1, 3h-fasted chicks were given an ICV injection of chicken ghrelin and picrotoxin, a GABA(A) receptors antagonist. Picrotoxin decreased food intake compared to the control chicks indicating a stimulatory effect of GABA(A) receptors on food intake. However, picrotoxin did not alter the inhibitory effect of ghrelin on food intake. In Experiment 2, THIP hydrochloride, a GABA(A) receptor agonist, was used in place of picrotoxin. THIP hydrochloride appeared to partially attenuate the decrease in food intake induced by ghrelin at 30 min postinjection. In Experiment 3, the effect of ICV injection of chicken ghrelin on gene expression of glutamate decarboxylase (GAD)(1) and GAD(2), GABA synthesis enzymes in the brain stem including hypothalamus, was investigated. The ICV injection of chicken ghrelin significantly reduced GAD(2) gene expression. These findings suggest that ghrelin may decrease food intake in neonatal chicks by reducing GABA synthesis and thereby GABA release within brain feeding centers.
SourceAvailable from: Shahin Hassanpour[Show abstract] [Hide abstract]
ABSTRACT: Appetite regulates by a complex system of central and peripheral signals which interact in order to modulate ingestion response. A number of peptides comprise a complex network that regulates feeding behavior in vertebrates. This review is focused on the main neurotransmitters and peptides that influence feeding responses in mammals and birds. On the basis of literature review, there are several evidences that neurotransmitters have different effects on food intake between mammals and birds. Also, central regulation of food intake regulates via different mechanisms in animals. So, the aim of this review was to investigate comparative food-intake regulation mechanisms in mammals and birds.
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ABSTRACT: The purpose of this study was to examine the effects of intracerebroventricular injection of metoprolol (a b 1 adrenergic receptor antagonist), ICI 118,551 (a b 2 adrenergic receptor antagonist), and SR 59230R (a b 3 adrenergic receptor antagonist) on ghrelin-induced food and water intake by 3-h food-deprived (FD 3) cockerels. The chickens were randomly allocated to 4 treatment groups with 8 replicates in each group. A cannula was surgically implanted into the lateral ventricle of the brain. In experiment 1, chickens received the b 1 adrenergic receptor antagonist (24 nmol) before injection of the ghrelin (0.6 nmol). In experiment 2, chickens received the b 2 adrenergic receptor antagonist (5 nmol) before injection of the ghrelin (0.6 nmol). In experiment 3, birds were injected with ghrelin (0.6 nmol) after the b 3 adrenergic receptor antagonist (20 nmol). Cumulative food and water intake were recorded 3-h post injection and analyzed by two-way analysis of variance. According to the results, ghrelin injection reduced food and water intake by broiler cockerels (p B 0.05). The effect of ghrelin on food intake was significantly attenuated by pretreatment with the b 2 receptor antagonist (p B 0.05). Furthermore, the b 2 receptor antagonist had no effect on water intake induced by ghrelin. Also, pretreatment with the b 1 and b 3 receptors antagonists had no effect on ghrelin-induced food and water intake. These results suggest that the effect of ghrelin on cumulative food intake by cockerels is mediated via b 2 adrenergic receptors.
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ABSTRACT: Ghrelin (Grh) is an endogenous ligand of the growth hormone secretagogue receptor. In neonatal chicks, central Ghr induces anxiogenic-like behavior but strongly inhibits food intake. The intermediate medial mesopallium (IMM) of the chick forebrain has been identified to be a site of the memory formation, and the modulation of the GABAA receptors that are present here modifies the expression of behavior. Thus, the GABAergic system may constitute a central pathway for Ghr action in regulating the processes of food intake and stress-related behaviors. Therefore, we investigated if the effect of systemic administration of bicuculline (GABAA receptor antagonist) and diazepam (benzodiazepine receptor agonist) on the anxiety in an Open Field test and inhibition in food intake induced by Grh (30 pmol) when injected into IMM, were mediated by GABAergic transmission. In Open Field test, bicuculline was able to block the anxiogenic-like behavior induced by Ghr, whereas diazepam did not produce it. However, the co-administration of bicuculline or diazepam plus Ghr did not show any change in food intake at 30, 60 and 120min after injection compared to Ghr alone. Our results indicate for the first time that Ghr, injected into the forebrain IMM area, induces an anxiogenic-like behavior, which was blocked by bicuculline but not diazepam, thus suggesting that Ghr plays an important role in the response pattern to acute stressor, involving the possible participation of the GABAergic system. Nevertheless, as neither drug affected the hypophagia induced by intra-IMM Ghr, this suggests that it may be mediated by different mechanisms. Copyright © 2014. Published by Elsevier Inc.Hormones and Behavior 12/2014; 67. DOI:10.1016/j.yhbeh.2014.11.015 · 4.51 Impact Factor