Serotonin-induced hypophagia is mediated via α2 and β2 adrenergic receptors in neonatal layer-type chickens

Update on Feeding Regulation by Ghrelin in Birds: Focused on Brain Network

Ghrelin is known to be a feeding stimulatory hormone in mammals, but in birds, in contrast to mammals, the feeding behavior is regulated in inhibitory manners. This is because the neuropeptides associated with the regulation in the brain are different from those in mammals, i.e., it has been shown that, in chickens, a corticotropin-releasing hormone family peptide, urocortin, which is a feeding-inhibitory peptide, is mainly involved in the inhibitory mechanism. However, feeding is also regulated by various neurotransmitters in the brain, and recently, their interaction with the mechanisms underlying feeding inhibition by ghrelin in birds has been intensively studied and clarified. This review summarizes these findings.

Possible interaction of central noradrenergic, serotoninergic and oxytocin systems with nesfatin-1 induced hypophagia and feeding behavior in newborn broiler

There are some differences between mammals and birds in terms of central food intake regulation. In avian species, the hypophagic role of nesfatin-1 has not been investigated with other neurotransmitters. Therefore, this study aimed to determine the alteration of feeding behavior following intracerebroventricular (ICV) injection of nesfatin-1 and its possible interaction with central noradrenergic, serotoninergic, and oxytocin systems in newborn broiler chicks. In experiment 1, birds received ICV injection of phosphate-buffered saline (PBS), prazosin (α₁ receptors antagonist, 10 nmol), nesfatin-1 (40 ng), and co-administration of prazosin and nesfatin-1. Experiments 2-10 were similar to experiment 1, except that yohimbine (α₂ receptors antagonist, 13 nmol), metoprolol (β₁ receptors antagonist, 24 nmol), IC1118,551 (β₂ receptors antagonist for, 5nmol), SR59230R (β₃ receptors antagonist, 20 nmol), fluoxetine (serotonin reuptake inhibitor, 10 µg), PCPA (serotonin synthesis inhibitor, 1.5 µg), 8-OH-DPAT (5-HT₁A receptors agonist, 15.25 nmol), SB242084 (5-HT₂C receptors antagonist,1.5 µg) and tocinoic acid (oxytocin receptors antagonist, 2 µg) were injected instead of prazosin. Immediately after the injection, food consumption and behavioral traits were recorded. Nesfatin-1 decreased food consumption (P < 0.05). Nesfatin-1 along with ICI118551 decreased food consumption (P < 0.05). The nesfatin-1- induced hypophagia were reduced by the simultaneous injection of PCPA and nesfatin-1 (P < 0.05). Nesfatin-1induced hypophagia were decreased by the simultaneous injection of SB242084 (P < 0.05). The nesfatin-1 -induced hypophagia were abolished by the simultaneous injection of the tocinoic acid and nesfatin-1 (P < 0.05). ICV injection of the nesfatin-1 decreased the number of steps, jumps, exploratory food, and pecks (P < 0.05) with no effect on drink pecks (P > 0.05). Nesfatin-1 significantly decreased standing time and increased both sitting time and rest time (P < 0.05). Nesfatin-1 could play an important role in feeding behavior, and its hypophagic effects were mediated by β₂ adrenergic, 5-HT₂C serotoninergic, and oxytocin receptors in neonatal chickens.

Intracerebroventricular injection of taurine induces hypothermia through modifying monoaminergic pathways in chicks

Brain monoamines are reported to regulate body temperature and food intake. The objective of this study was to investigate the mechanism of brain monoamine metabolism in taurine-induced hypothermia and appetite suppression. In Experiment 1, 5-day-old male Julia layer chicks (n = 10) were subjected to intracerebroventricular (ICV) injection with saline or taurine (5 μmol/10 μL). In Experiment 2, the chicks were ICV injected with saline, taurine, fusaric acid (dopamine-β-hydroxylase inhibitor: 558 nmol), or taurine with fusaric acid. In Experiment 3, the chicks were ICV injected with saline, taurine, para-chlorophenylalanine (PCPA, tryptophan hydroxylase inhibitor: 400 nmol), or taurine with PCPA. In Experiment 4, the chicks were ICV injected with saline, taurine, clorgyline (monoamine oxidase inhibitor: 81 nmol), or taurine with clorgyline. Central taurine lowered rectal temperature at 30 min post-injection and increased norepinephrine in the brainstem and its metabolite 3-methoxy-4-hydroxyphenylglycol in both the diencephalon and brainstem. Similarly, taurine treatment induced increases in serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid in the diencephalon. Fusaric acid completely and PCPA partially, but not clorgyline, attenuated taurine-induced hypothermia. The anorexigenic effect of taurine was partially attenuated by PCPA, but not fusaric acid nor clorgyline. In conclusion, central taurine activates dopamine-β-hydroxylase and tryptophan hydroxylase to produce norepinephrine and 5-HT, and then induces hypothermia, but 5-HT alone may be linked with taurine-induced anorexia in chicks.

Neuropeptide Y modifies a part of diencephalic catecholamine but not indolamine metabolism in chicks depending on feeding status

The role of the monoaminergic system in the feeding behavior of neonatal chicks has been reported, but the functional relationship between the metabolism of monoamines and appetite-related neuropeptides is still unclear. This study aimed to investigate the changes in catecholamine and indolamine metabolism in response to the central action of neuropeptide Y (NPY) in different feeding statuses and the underlying mechanisms. In Experiment 1, the diencephalic concentrations of amino acids and monoamines following the intracerebroventricular (ICV) injection of NPY (375 pmol/10 μl/chick), saline solution under ad libitum, and fasting conditions for 30 min were determined. Central NPY significantly decreased L-tyrosine concentration, the precursor of catecholamines under feeding condition, but not under fasting condition. Central NPY significantly increased dopamine metabolites, including 3,4-dihydroxyphenylacetic acid and homovanillic acid (HVA). The concentration of 3-methoxy-4-hydroxyphenylglycol was significantly reduced under feeding condition, but did not change under fasting condition by NPY. However, no effects of NPY on indolamine metabolism were found in either feeding status. Therefore, the mechanism of action of catecholamines with central NPY under feeding condition was elucidated in Experiment 2. Central NPY significantly attenuated diencephalic gene expression of catecholaminergic synthetic enzymes, such as tyrosine hydroxylase, L-aromatic amino acid decarboxylase, and GTP cyclohydrolase I after 30 min of feeding. In Experiment 3, co-injection of α-methyl-L-tyrosine, an inhibitor of tyrosine hydroxylase with NPY, moderately attenuated the orexigenic effect of NPY, accompanied by a significant positive correlation between food intake and HVA levels. In Experiment 4, there was a significant interaction between NPY and clorgyline, an inhibitor of monoamine oxidase A with ICV co-injection which implies that co-existence of NPY and clorgyline enhances the orexigenic effect of NPY. In conclusion, central NPY modifies a part of catecholamine metabolism, which is illustrated by the involvement of dopamine transmission and metabolism under feeding but not fasting conditions.

5-Hydroxytryptophan Suppresses the Abdominal Fat Deposit and Is Beneficial to the Intestinal Immune Function in Broilers

Background

Serotonin (5-HT), a monoaminergic neurotransmitter, involves in the regulation of many physiological functions. In the present study, the effects of 5-hydroxytryptophan (5-HTP), the precursor of 5-HT, on lipid metabolism and intestinal immune function in broiler chickens were investigated in chickens.

Methods

Two hundred broilers were divided randomly into two groups and fed separately with a corn-soybean basal diet (CD) or the basal diet supplemented with 0.2% 5-HTP.

Results

The results showed that 5-HTP reduced (P < 0.05) feed intake and the abdominal fat pad weight. 5-HTP treatment tended to upregulate the mRNA level of adiponectin receptor 1 (ADP1R) and ADP2R in abdominal fat but had no significant influence on their protein levels (P > 0.05). In 5-HTP-chickens, lipopolysaccharide exposure decreased secretory immunoglobulin A (sIgA) concentrations in serum and the duodenal contents. Expression of mRNA encoding interleukin (IL), tumor necrosis factor-α (TNF-α), and transforming growth factor-β (TGF-β) decreased after 5-HTP treatment; however, LPS increased expression significantly in 5-HTP-treated chickens compared with CD chickens. In 5-HTP-chickens, the phosphorylation of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) were reduced, but the phosphorylation of ribosomal p70S6 kinase (p70S6K) was increased in the duodenum.

Conclusion

In summary, the result suggests that dietary 5-HTP supplementation reduces accumulation of abdominal fat and is beneficial to intestinal immune function.

Interaction between leptin and glutamatergic system on food intake regulation in neonatal chicken: role of NMDA and AMPA receptors

Objective: The aim of the current study was to determine the possible interaction of the central leptin and Glutamatergic systems on feeding behavior in neonatal 3-hours food deprived (FD₃) broilers chickens.Methods: In experiment 1, FD₃ chicken received intracerebroventricular (ICV) injection of control solution (group i) and 2.5, 5 and 10 µg of Leptin (groups ii-iv). In experiment 2, FD₃ chicken were ICV injected with (group i) control solution and groups ii-iv with 2.5, 5 and 10 nmol of AG-490 (JAK₂ antagonist). In experiment 3, injections were (i) control solution, (ii) Leptin (10 µg), (iii) AG-490 (2.5 nmol) and (iv) Leptin + AG-490. In experiment 4, broiler chickens were ICV injected with (i) control solution, (ii) Leptin (10 µg), (iii) MK-801 (NMDA glutamate receptors antagonist; 15 nmol) and (iv) Leptin + MK-801. Experiments 5-9 were similar to experiment 1, except chicken were ICV injected with CNQX (AMPA receptor antagonist, 390 nmol), UBP-302 (Kainate receptor antagonist, 390 nmol), AIDA (mGluR1 antagonist, 2 nmol), LY341495 (mGluR2 antagonist, 150 nmol) and UBP1112 (mGluR3 antagonist, 2 nmol) instead of MK-801. Then, food intake was measured until 120 min after injection.Results: ICV injection of leptin (2.5, 5 and 10 µg) significantly decreased food intake in a dose dependent manner (p < 0.05). Also, ICV injection of the JAK₂ antagonist (2.5, 5 and 10 nmol) had hyperphagic effect in chicken (p < 0.05). Co-administration of leptin + AG-490, partially decreased leptin-induced hypophagia in broiler chicken (p < 0.05). In addition, co-injection of leptin + MK-801 significalty inhibited leptin-induced hypophagia in neonatal chicken (p < 0.05). Also, co-administration of leptin + CNQX partially attenuated hypophagic effect of leptin in chicken (p < 0.05).Conclusion: The results of present study suggest that leptin has hypophagic effect in neonatal chicken and this effect is probably mediated via NMDA and AMPA glutamatergic receptors.

Dietary phytase and myo-inositol supplementation are associated with distinct plasma metabolome profile in broiler chickens

Phytase enzyme is used as a dietary supplement in broiler nutrition to improve phosphorous bioavailability. Phytase deliberates phosphate groups from phytic acid and produces myo-inositol after total dephosphorylation. Myo-inositol is a bioactive compound having beneficial modulatory effects on metabolism in humans. However, it is not well understood if and how phytic acid degradation products, particularly myo-inositol, can modulate metabolism in broiler chicken. The purpose of this study was to investigate effects of dietary supplements of phytase and myo-inositol on the blood plasma metabolome profile of broiler chickens. Broilers were provided a nutrient-adequate control diet or the same diet supplemented with either 3.5 g myo-inositol or 500, 1500 or 3000 units of phytase, per kilogram of feed (grower diet). Broilers were group-housed in floor pens (eight pens per diet) and provided one of the treatment diets for 22 days. Then, blood was collected from one bird per pen, resulting in eight replicated measurements per diet. A targeted metabolomics approach was applied to the heparin plasma. Body weight of the birds was not significantly affected by the treatments. Plasma myo-inositol concentrations were significantly increased by myo-inositol supplementation and phytase supplementation at 500 and 1500 units/kg. Metabolites generally affected by phytase supplementation belonged to the groups of acyl-carnitines, phosphatidylcholines, sphingomyelins, lysophosphatidylcholine, biogenic amines and amino acids. Compared to the control diet, phytase supplements had significantly higher plasma concentrations of kynurenine and creatinine, but lower concentrations of histamine and cis-4-hydroxyproline. Myo-inositol supplementation significantly increased plasma concentrations of dopamine and serotonine. While some metabolites were similarly affected by myo-inositol and phytase supplementation, others were distinctly differently affected. We conclude that myo-inositol, either as a directly added supplement or indirectly released from phytate upon phytase supplementation, can affect specific metabolic pathways. Additional effects found on phytase supplementation may be related to intermediary phytate degradation products. Results are indicative for innovative hypothesis to be tested in future experiments, for instance, with regard to relationships between phytase or myo-inositol supplements and bird immunity or behaviour.

Enteroendocrine profile of α-transducin and α-gustducin immunoreactive cells in the chicken (Gallus domesticus) gastrointestinal tract

The enteroendocrine profile and distribution patterns of the taste signaling molecules, α-gustducin (Gαgust) and α-transducin (Gαtran) protein subunits, were studied in the gastrointestinal (GI) tract of the chicken (Gallus domesticus) using double labeling immunohistochemistry. Gαtran or Gαgust immunoreactivity was observed in enteroendocrine cells (EEC) expressing different peptides throughout the entire GI tract with different density. In the proventriculus tubular gland, Gαtran or Gαgust/gastrin (GAS) immunoreactive (-IR) cells were more abundant than Gαtran/or Gαgust containing glucagon-like peptide-1 (GLP-1) or peptide YY (PYY), whereas only few Gαtran or Gαgust cells co-stored ghrelin (GHR) or 5-hydroxytryptamine (5-HT). In the pyloric mucosa, many Gαtran or Gαgust-IR cells co-expressed GAS or GHR, with less Gαtran or Gαgust cells containing GLP-1, PYY, or 5-HT. In the small intestine, a considerable subset of Gαtran or Gαgust-IR cells co-expressed 5-HT in the villi of the duodenum and ileum, PYY in the villi of the jejunum, CCK or GLP-1 in the villi of the ileum, and GHR in the duodenum crypts. In the large intestine, many Gαtran or Gαgust-IR cells contained 5-HT or GLP-1 in the villi of the rectum, whereas some Gαtran/Gαgust-IR cells co-expressed PYY- or CCK-, and few Gαtran/Gαgust-IR cells were positive for GHR-IR. In the cecum, several Gαtran or Gαgust-IR cells were IR for 5-HT. Finally, many Gαtran/Gαgust cells containing 5-HT were observed in the villi and crypts of the cloaca, whereas there were few Gαtran or Gαgust/CCK-IR cells. The demonstration that Gα-subunits are expressed in the chicken GI enteroendocrine system supports the involvement of taste signaling machinery in the chicken chemosensing processes.