Methylamine induced hypophagia is mediated via dopamine D1 and D2 receptors in neonatal meat chicks

The role of central neurotransmitters in appetite regulation of broilers and layers: similarities and differences

The importance of feeding as a vital physiological function, on the one hand, and the spread of complications induced by its disorder in humans and animals, on the other hand, have led to extensive research on its regulatory factors. Unfortunately, despite many studies focused on appetite, only limited experiments have been conducted on avian, and our knowledge of this species is scant. Considering this, the purpose of this review article is to examine the role of central neurotransmitters in regulating food consumption in broilers and layers and highlight the similarities and differences between these two strains. The methodology of this review study includes a comprehensive search of relevant literature on the topic using appropriate keywords in reliable electronic databases. Based on the findings, the central effect of most neurotransmitters on the feeding of broilers and laying chickens was similar, but in some cases, such as dopamine, ghrelin, nitric oxide, and agouti-related peptide, differences were observed. Also, the lack of conducting a study on the role of some neurotransmitters in one of the bird strains made it impossible to make an exact comparison. Finally, it seems that although there are general similarities in appetite regulatory mechanisms in meat and egg-type chickens, the long-term genetic selection appropriate to breeding goals (meat or egg production) has caused differences in the effect of some neurotransmitters. Undoubtedly, conducting future studies while completing the missing links can lead to a comprehensive understanding of this process and its manipulation according to the breeding purposes of chickens.

Central dopaminergic, serotoninergic, as well as GABAergic systems mediate NMU-induced hypophagia in newborn chicken

AIM

Dopaminergic, serotoninergic, and GABAergic systems influence feeding; however, it is unknown how these chemicals interact with neuromedin U (NMU)-induced feeding in birds. In the current study, ten trials were conducted to determine the links between the above-mentioned systems and NMU.

MATERIALS AND METHODS

In the foremost experimentation, chickens were given intracerebroventricularly injections of NMU (0.1, 1, and 10 µg). NMU (10 µg), SCH23390 (5 nmol), a D1 receptor antagonist, and NMU + SCH23390 were administered in the second experiment. In subsequent experiments, instead of SCH23390, were applied AMI-193 (5 nmol D2 receptor antagonist), NGB2904 (6.4 nmol D3 receptor antagonist), L-741,742 (6 nmol D4 receptor antagonist), 6-OHDA (2.5 nmol dopamine inhibitor), SB242084 (5-HT2c receptor antagonist, 1.5 μg), 8-OH-DPAT (5-HT1A receptor agonist, 15.25 nmol), picrotoxin (GABAA receptor antagonist, 0.5 μg), and CGP54626 (GABAB receptor antagonist, 20 ng). Then, cumulative intake of food was recorded for 2 h.

RESULTS

According to the results, NMU reduced feeding when compared to the control group (p < 0.05). The NMU-induced hypophagia was reduced with co-injection of NMU and SCH23390 (p < 0.05). Hypophagia was diminished with NMU and AMI-193 (p < 0.05). NMU + NGB2904 and NMU + L-741,742 co-injections had no influence (p > 0.05). 6-OHDA reduced the hypophagia (p < 0.05). NMU and SB242084 decreased the hypophagia (p < 0.05), whereas NMU and 8-OH-DPAT had no effect (p > 0.05). The effects were amplified with picrotoxin (p < 0.05). NMU with CGP54626 had no influence on the hypophagia (p > 0.05).

CONCLUSION

Thus, NMU-induced hypophagia is probably mediated by D1/D2, 5-HT2c, and GABAA receptors in neonatal chicks.

Possible effects of the central adrenergic and dopaminergic receptors on hypophagia induced by neuromedin S in neonatal layer-type chicks

The current study was aimed to determine the possible effects of the central adrenergic and dopaminergic receptors in neuromedin S (NMS)-induced hypophagia in neonatal layer-type chickens. In the first experiment, control solution, and NMS (0.25, 0.5, and 1 nmol), were injected (intracerebroventricular (ICV)) in chickens. In the second experiment, birds were injected with a control solution,SCH23390 (D₁receptor antagonist, 5 nmol), NMS (1 nmol), and a combination of the SCH23390 + NMS. Experiments 3-11 were similar to experiment 2, except that chickens were injected withAMI-193 (D₂receptor antagonist, 5 nmol), NGB2904(D₃receptor antagonist, 6.4 nmol), L-741,742(D₄receptor antagonist, 6 nmol), 6-OHDA(6-hydroxydopamine, 2.5 nmol),Prazosin(α₁receptor antagonist, 10 nmol),Yohimbine(α₂receptor antagonist, 13 nmol),Metoprolol(β₁receptor antagonist receptor, 24 nmol),ICI 118,551 (β₂receptor antagonist, 5 nmol),SR 59230R (β₃ receptor antagonist, 20 nmol) instead ofSCH23390. Then, cumulative food intake was recorded at 30, 60, and 120 min following the injection. According to the results, food intake was significantly decreased after ICV injection of NMS in a dose -dependent manner (P < 0.05). Also, the co-injection of the SCH23390 + NMS significantly attenuated NMS-induced hypophagia (P < 0.05). The co-administration of AMI-193 + NMS significantly reduced NMS- induced hypophagia (P < 0.05). In addition, the co-injection of ICI 118,551 + NMS and 6-OHDA + NMS considerably decreased NMS-induced food consumption (P < 0.05). However, NGB2904, L-741742, Prazosin, Yohimbine, Metoprolol and SR 59230R had no effect on hypophagia induced by NMS (P > 0.05). These results demonstrated thatNMS- induced hypophagia might be mediated by D₁/D₂ dopaminergic andβ₂adrenergic receptors in neonatal layer-type chickens.

Mediatory role of the dopaminergic system through D1 receptor on glycine-induced hypophagia in neonatal broiler-type chickens

The present study aimed to examine the mediatory role of the dopaminergic system in the food intake induced by intracerebroventricular (ICV) injection of glycine in neonatal 3-h feed-deprived (FD3) meat-type chickens. In the first and second experiments, birds were ICV injected using low and high doses of glycine (50, 100 and 200 nmol) and strychnine (50, 100 and 200 nmol), respectively. In experiments 3-9, the behaviorally subeffective doses of dopamine (10 nmol), 6-OHDA (2.5 nmol), SCH 23,390 (D1 antagonist; 5 nmol), AMI-193 (D2 antagonist; 5 nmol), NGB2904 (D3 antagonist; 6.4 nmol) and L-741,742 (D4 antagonist; 6 nmol) were, respectively, co-administrated with glycine (200 nmol) in FD3 5-day-old chicks to investigate possible interplay of dopamine receptors in glycine-induced feeding behavior. Then, cumulative food intake based on body weight percentage (%BW) was determined at 30, 60 and 120 min after the injection. According to the results, dopamine significantly boosted the hypophagia induced by glycine at all-time intervals (p ≤ 0.001). These results combined with the previous findings suggest an interplay between dopamine and glycine in chicken's brain in which D1 receptor-mediated food intake induced by glycine.

Central and peripheral methylamine-induced hypophagia is mediated via nitric oxide and TAAR1 in neonatal layer-type chicken

The aim of the current study was to determine effects of intracerebroventricular (ICV) and intraperitoneal (i.p.) administration of Methylamine (MET) and possible interactions with nitric oxide (NO) and TAAR₁ pathways in 24-h fasted (FD₂₄) and ad libitum layer-type chicken. In experiment 1, FD₂₄ chicken ICV injected with MET (15, 30, 45, 60 and 75 μg). In experiment 2, ICV injection of MET (15, 30, 45, 60 and 75 μg) was injected in the ad libitum birds. Experiments 3-4 were similar to experiments 1-2, except chicken i.p. injected with MET (15, 30, 45, 60 and 75 mg/kg). In experiment 5, FD₂₄ birds ICV injected with l-NAME (NO synthesis inhibitor, 100 nmol), MET (75 μg) and co-injection of l-NAME + MET. Experiment 6 was similar to experiment 5, except, ad libitum birds received injections. In experiment 7, FD₂₄ chicken i.p. injected with l-NAME (100 mg/kg), MET (75 mg/kg) and co-injection of l-NAME + MET. In experiment 8, FD₂₄ birds ICV injected with RO5256390 (selective TAAR₁ agonist, 10, 20 and 40 μg). In experiment 9, ad libitum birds ICV injected with RO5256390 (10, 20 and 40 μg). In experiment 10, FD₂₄ birds ICV injected with RO5256390 (10 μg), MET (75 μg) and their co-injection. Experiment 11 was similar to experiment 10, except, ad libitum birds received ICV injections. In experiment 12, FD₂₄ chicken i.p. injected with RO5256390 (2.5, 5 and 10 mg/kg). In experiment 13, FD₂₄ chicken i.p. injected with RO5256390 (2.5 mg/kg), MET (75 mg/kg) and RO5256390 + MET. Then cumulative food intake was determined until 120 min after injection. According to the results, ICV injection of MET decreased food intake in FD₂₄ and ad libitum chicken (P < 0.05). MET (i.p.) diminished food consumption in fasted (P < 0.05) but not in ad libitum chicken (P> 0.05). Co-injection of the l-NAME + MET significantly decreased MET-induced hypophagia in FD₂₄ and ad libitum chicken (P < 0.05). MET-induced hypophagia (i.p.) weakened by l-NAME in FD₂₄ chicken (P < 0.05). RO5256390 decreased food intake in FD₂₄ and ad libitum chicken (P < 0.05). Co-injection of RO5256390 + MET increased MET-induced hypophagia in FD₂₄ and ad libitum chicken (P < 0.05). RO5256390 decreased food intake in FD₂₄ chicken (P < 0.05). Co-injection of the RO5256390 + MET amplified MET-induced hypophagia in FD₂₄ chicken (P < 0.05). Based on the findings, MET-induced hypophagia is mediated via NO and TAAR₁ pathways on food intake in layer chicken.

Methylamine Activates Glucose Uptake in Human Adipocytes Without Overpassing Action of Insulin or Stimulating its Secretion in Pancreatic Islets

Background: Methylamine, a natural soluble amine present in foods, is known to be a substrate of primary amine oxidase (PrAO) widely expressed in animal tissues. Methylamine has been reported to activate glucose transport in fat cells and to facilitate glucose disposal in rabbits but the interests and limits of such insulin-mimicking actions have not been further explored. This work aimed to perform a preclinical study of the inter-individual variations of these biological properties to study the putative link between PrAO activity and insulin resistance. Methods: Methylamine was tested on human adipocyte preparations and in rabbit pancreatic islets to determine its influence on glucose uptake and insulin release, respectively. PrAO activity and related responses were determined in adipose tissues obtained from two cohorts of non-obese and obese women. Results: Adipose tissue PrAO activity was negatively correlated with insulin resistance in high-risk obese women. PrAO-dependent activation of glucose uptake was negatively correlated with body mass index and reflected the decrease of insulin responsiveness of human fat cells with increasing obesity. Methylamine exhibited antilipolytic properties in adipocytes but was unable to directly activate insulin secretion in isolated pancreatic islets. Conclusions: PrAO activation by its substrates, e.g., methylamine, increases glucose utilization in human adipocytes in a manner that is linked to insulin responsiveness. Methylamine/PrAO interaction can therefore contribute to adipose tissue enlargement but should be considered as potentially useful for diabetes prevention since it could limit lipotoxicity and facilitate glucose handling, at the expense of favoring healthy fat accumulation.

Hypophagic effects of insulin are mediated via NPY1/NPY2 receptors in broiler cockerels

Neuropeptide Y (NPY) plays a mediatory role in cerebral insulin function by maintaining energy balance. The current study was designed to determine the role of insulin in food intake and its interaction with NPY receptors in 8 experiments using broiler cockerels (4 treatment groups per experiment, except for experiment 8). Chicks received control solution or 2.5, 5, or 10 ng of insulin in experiment 1 and control solution or 1.25, 2.5, or 5 μg of receptor antagonists B5063, SF22, or SML0891 in experiments 2, 3, and 4 through intracerebroventricular (ICV) injection, respectively. In experiments 5, 6, and 7, chicks received ICV injection of B5063, SF22, SML0891, or co-injection of an antagonist + insulin, control solution, and insulin. In experiment 8, blood glucose was measured. Insulin, B5063, and SML0891 decreased food intake, while SF22 led to an increase in food intake. The hypophagic effect of insulin was also reinforced by injection of B560, but ICV injection of SF22 destroyed this hypophagic effect of insulin and increased food intake (p < 0.05). However, SML0891 had no effect on decreased food intake induced by insulin (p > 0.05). At 30 min postinjection, blood sugar in the control group was higher than that in the insulin group (p < 0.05). Therefore, the NPY1 and NPY2 receptors mediate the hypophagic effect of insulin in broiler cockerels.

Consequence of dopamine D2 receptor blockade on the hyperphagic effect induced by cannabinoid CB1 and CB2 receptors in layers

1. Endocannabinoids (ECBs) and their receptors play a regulatory function on several physiological processes such as feed-intake behaviour, mainly in the brain. This study was carried out in order to investigate the effects of the dopaminergic D1 and D2 receptors on CB1/CB2 ECB receptor-induced hyperphagia in 3-h feed-deprived neonatal layer chickens. 2. A total of 8 experiments were designed to explore the interplay of these two modulatory systems on feed intake in neonatal chickens. In Experiment 1, chickens were intracerebroventricular (ICV) injected with control solution, l-DOPA (levo-dihydroxyphenylalanine as precursor of dopamine; 125 nmol), 2-AG (2-arachidonoylglycerol as CB₁ receptor agonist; 2 µg) and co-administration of l-DOPA (125 nmol) plus 2-AG (2 µg). Experiments 2-4 were similar to Experiment 1 except birds were injected with either 6-OHDA (6-hydroxydopamine as dopamine synthesis inhibitor; 150 nmol), SCH23390 (D1 receptor antagonist; 5 nmol) and AMI-193 (D2 receptor antagonist; 5 nmol) instead of l-DOPA, respectively. Additionally, Experiments 5-8 followed the previous ones using the same dose of l-DOPA, 6-OHDA and dopamine antagonists except that birds were injected with CB65 (CB2 receptor agonist; 5 µg) instead of 2-AG. Coadministrations were at the same dose for each experiment. Cumulative feed intakes were measured until 120 min after each injection. 3. ICV administration of 6-OHDA and AMI-193 significantly attenuated 2-AG-induced hyperphagia. Interestingly, the hyperphagic effect of CB65 was significantly attenuated by administration of l-DOPA, whereas the administration of 6-OHDA and AMI-193 together amplified the hyperphagic effect of CB65. 4. It was concluded that cannabinoid-induced feeding behaviour is probably modulated by dopamine receptors in neonatal layer-type chickens. It seems that their interaction may be mediated by the D2-dopamine receptor.