Influence of peripheral lipopolysaccharide (LPS) on feed intake, body temperature and hypothalamic expression of neuropeptides involved in appetite regulation in broilers and layer chicks.

1. This study examined the expression of genes related to appetite-regulating neuropeptides in the hypothalamus of broiler and layer chicks (Gallus gallus) after intraperitoneal (IP) injection of lipopolysaccharide (LPS). 2. Both broiler and layer chicks received (n = 10 per group) LPS at doses of 0 and 200 µg and feed intake was measured up to 6 h after injection. In a further experiment, (n = 8 per group) mRNA abundance of some hypothalamic neuropeptides was measured 2 h after injection. The rectal temperature of each chick was measured before and 2 h post-injection. 3. Feed intake was significantly decreased by LPS from 2 h after injection and thereafter, while the rectal temperature did not change. 4. LPS decreased the expression of appetite-enhancing neuropeptides: neuropeptide Y (NPY) and agouti-related peptide (AgRP) in broilers and, NPY in layer chicks. The expression of appetite-suppressing neuropeptides (corticotrophin-releasing factor (CRF), proopiomelanocortin (POMC) and, cocaine and amphetamine regulated-transcript (CART) was not changed in broilers, while CRF tended to decrease and POMC was significantly decreased in layers. The abundance of the cytokine tumour necrosis factor-alpha (TNF-α) did not change in broilers but was decreased in layers. 5. The findings indicated that the reduction in gene expression of hypothalamic appetite-enhancing neuropeptides NPY and AgRP is responsible for anorexia caused by LPS at a dose that did not influence body temperature.

Induction of hypothalamic GABA synthetic enzymes mRNA (Gad 1 and Gad 2) expression by negative energy balance in broiler and layer chicks.

Broiler and layer chicks have been selected for higher and lower food intake and body weight gain, respectively. It has recently been reported that glutamate decarboxylase (Gad1) mRNA, a gamma-aminobutyric acid (GABA) synthetic enzyme gene, is a reliable proxy for GABA release. Previous studies have revealed that GABAergic system has a stimulatory role on food intake in both mammals and birds. Over the recent years, evidence has identified the presence of GABAergic neurons as either the first- or second-order neurons within the various feeding nuclei of hypothalamus of laboratory rodents. They respond to the negative energy balance representing a critical role for GABA in the regulation of food intake. In the current study, the mRNA abundance of Gad 1 and Gad 2 was measured within the hypothalamus of both broiler and layer free fed, 12 h-fasted and 12 h-fasted / 3 h refed chicks. Furthermore, the effect of intracerebroventricular (ICV) injection of GABA was studied on food intake of chicks. The results indicated an increase in both Gad 1 and 2 expressions during fasting which tended to return to the baseline after refeeding. However, this increase was greater in broilers than in layers. The results also showed that ICV injection of GABA had no effect on food intake with the exception of an increase in free fed broilers. This study suggests a role for hypothalamic GABAergic system in birds that respond to negative energy balance, which seems to be more considerable in broilers than in layers.

Effect of central enterostatin on fat intake in neonatal chicks.

Enterostatin, a gut-brain pentapeptide cleaved from procolipase has been shown to inhibit fat intake in rodents after both peripheral and central administration. In this study, the effect of intracerebroventricular (ICV) injection of enterostatin on fat intake was investigated in neonatal chicks. In Experiment 1, 3-h-fasted chicks fed a low-fat diet were injected with the various doses of enterostatin. Experiment 2 was similar to experiment 1 except that the birds were fasted overnight. In Experiment 3, the 3-h-fasted and in Experiment 4, the overnight fasted chicks adapted to a high-fat diet received different doses of enterostatin. ICV injection of enterostatin caused a dose-dependent increase in high-fat diet intake in 3-h-fasted chicks whereas a decrease in high-fat intake was observed in chicks that were fasted overnight. However, low-fat diet intake was not affected by enterostatin in either 3-h or overnight fasted chicks. These results suggest that enterostatin acts within the brain of chicks to influence fat intake. It appears that in chicks, the eating effect of enterostatin has a biphasic nature similar to those seen in rodents.

Neuropeptide Y-induced feeding is dependent on GABAA receptors in neonatal chicks.

In mammals and birds, neuropeptide Y (NPY) and gamma-aminobutyric acid (GABA) are found in brain areas known to be involved in the control of ingestive behavior and act to increase voluntary food intake. In rats, significant evidence suggest a functional and behavioral interaction between NPY and GABA mediated transmission in various brain regions, including the arcuate and paraventricular nuclei of the hypothalamus which can be important in the regulation of feeding behavior. In the present study, the effect of intracerebroventricular (ICV) administration of NPY and GABA receptor antagonists on food intake was examined in neonatal chicks. The ICV injection of NPY strongly stimulated food intake while co-administration of NPY and picrotoxin, a GABA(A) antagonist, (but not CGP54626, a GABA(B) antagonist) weakened food intake induced by NPY. These results suggest that central NPY stimulates food intake in neonatal chicks by interaction with the GABAergic system via GABA(A) receptors.

The role of GABAergic system on the inhibitory effect of ghrelin on food intake in neonatal chicks.

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.

The role of central CB2 cannabinoid receptors on food intake in neonatal chicks.

The endocannabinoids (ECBs) have diverse physiological functions including the regulation of food intake and metabolism. In mammals, ECBs regulate feeding primarily through the CB1 receptors within the brain whereas the CB2 receptors are primarily involved in the regulation of immune function by direct action on peripheral immune cells and central glia. The central effect of ECBs on feeding behavior has not been studied in non-mammalian species. Therefore, the present study investigated the effect of CB65, a selective CB2 receptors agonist, on food intake in the neonatal chicks. In addition, the effect of astressin, a CRF receptor antagonist, on CB65-induced food intake was also investigated. Intracerebroventricular injection of the CB65 (1.25 µg) increased the food intake at 30- and 60-min post-injection significantly as compared to the control group. Pretreatment with a selective CB2 receptor antagonist, AM630, but not astressin, significantly attenuated the CB65-induced food intake. These results suggested that CB2 receptor agonists act on the brain to induce food intake.

Oxyntomodulin reduces expression of glucagon-like peptide 1 receptor in the brainstem of chickens.

Oxyntomodulin (OXM) is a peptide released from the gut and attenuates food intake by acting on hypothalamus. However, its role at the molecular level is not well studied. In the first section of this study, we analysed the effect of OXM on food intake behaviour after injecting into the lateral ventricle of chickens. The outcome showed that food intake decreased significantly after administering 4 nmol of OXM. In the second part, the expression of glucagon-like peptide 1 receptor (GLP-1R) in the brainstem was analysed by real-time RT-PCR. The results showed that expression of GLP-1R was reduced to 27% and 16% at 30 and 90 mins after injection of OXM respectively. In saline-injected chickens, no reduction in GLP-1R was seen. It can be concluded that OXM has a down regulatory effect on the responding receptor, GLP-1R and OXM in chicks has the same reductive effect on food intake as in the mammals.

Interaction between nociceptin/orphanin FQ (N/OFQ) and GABA in response to feeding.

Nociceptin/orphanin FQ (N/OFQ) and gamma aminobutyric acid (GABA) agonists have been shown to increase feed intake in mammals and birds. In this study, the effect of intracerebroventricular (icv) injection of the potent NOP receptor agonists Nociceptin (1-13) NH(2), the GABA(A) receptor antagonist bicuculline, and the GABA(A) receptor agonist muscimol on feed intake in cockerels was investigated. The icv injection of N/OFQ and muscimol increases feed intake. The effect of N/OFQ on feed intake was strongly blocked by the injection of bicuculline whereas the effect of muscimol was stimulated by N/OFQ. These results suggest that N/OFQ may act at GABA(A) receptors or increases overflow of GABA in the brain of chickens to stimulate feeding.

Feeding and locomotion responses to centrally injected nociceptin/orphanin FQ in chicks.

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the opioid receptor-like receptor or nociceptin receptor (NOP), has been shown to induce feeding, locomotion, anti-stress and anxiolytic effects in rodents after central nervous system injection. In this study, the effect of intracerebroventricular (icv) injection of N/OFQ on feeding and locomotion behavior was evaluated in male broiler-type chickens. The icv injection of N/OFQ caused a moderate but significant increase in feed intake similar to the classical opioid peptides in rats. It also increased feed pecking frequency and feeding time 1 h after injection. Stepping, wing flapping and preening were not affected by N/OFQ. These results suggest that N/OFQ can act within the central nervous system of chickens to increase feed intake.

Behavioral effects of intracerebroventricular injection of oxytocin in birds.

In addition to playing a role as a hormone, oxytocin (OT) can act as a neurotransmitter. In birds, mesotocin (MT) replaces OT. There is both direct and indirect evidence for behavioral effects of OT in rats and humans, but there have been no such studies performed in birds. The purpose of this study was to define the effect of intracerebroventricular (i.c.v.) injection of OT (0-10 microg) on locomotion and feeding behaviors of broiler cockerels. Stepping and wing flapping were increased dose-dependently, but OT decreased preening. The i.c.v. injection of OT also caused a dose-dependent decrease in feed intake, feeding time and pecking frequency. These results suggest that OT might play a unique role in inducing a state of arousal in chickens that resembles fear/anxiety and also in reducing feed intake by acting on MT and/or vasotocin receptors.

GABAergic control of food intake in the meat-type chickens.

This study examined the effects of intracerebroventricular injections of gamma-aminobutyric acid (GABA) agonists on short-term food intake in meat-type cockerels. In Experiment 1, birds were injected with various doses of muscimol, a GABA(A) agonist. In Experiment 2, the birds received bicuculline, a GABA(A) antagonist, prior to injection of muscimol. In Experiment 3, the effect of varying doses of baclofen, a GABA(B) agonist, on food intake was determined. The intracerebroventricular injection of muscimol caused a dose-dependent increase in food intake. This effect was significantly attenuated by pretreatment with bicuculline. Food intake was not affected by the intracerebroventricular injection of baclofen. These results suggest that GABA acts within the brain of broilers at a GABA(A), but not GABA(B), receptor to increase voluntary food intake.