Age-dependent reduction of ghrelin- and motilin-induced contractile activity in the chicken gastrointestinal tract

Daily feeding frequency affects feed intake and body weight management of growing layers

The objective of this study was to investigate the effect of feeding behavior on feed intake and body weight in growing layers and the underlying mechanisms, thereby providing a scientific foundation for optimal feeding practices in growing layers' management. A total of 144 Hy-line brown growing layers of 10 wk old and similar body weight, were divided into 3 treatment groups with different feeding frequency and equal cumulative daily feeding amount: the once-a-day feeding group (F1) was fed at 9:00 am every day, with feeding amount of 150 g/layer; the twice-a-day feeding group (F2) were fed at 9:00 am and 13:00 pm every day, with each feeding amount of 75 g/layer; the 4 times-a-day feeding group (F4) were fed at 9:00 am, 11:00 am, 13:00 pm, and 15:00 pm every day, with each feeding amount of 37.5 g/layer. Pre-experiment lasted for 1 wk and formal experiment lasted for 8 wk. The results indicated that the daily feed intake and body weight were decreased (P < 0.05) while feed conversion ratio was not affected (P > 0.05) as daily feeding times increased. The glandular stomach proportion was significantly increased in twice-a-day feeding group, while liver proportion and ileum length were significantly increased in 4 times-feeding group (P < 0.05). Additionally, 4 times-feeding daily resulted in a significant elevation of blood glucose levels, which may have suppressed feed intake (P < 0.05). In 4 times-feeding group, the plasma triglyceride levels increased as feeding times, accompanied by a notable up-regulation in the mRNA level of appetite-suppressing gene, hypothalamic pro-opiomelanocortin (POMC) and glandular stomach ghrelin. This modulation effectively suppressed the subsequent feed intake and body weight. Therefore, 4 times feeding daily is recommended in growing layers' management, because it reduced the feed cost without affecting the feed conversion efficiency.

Pheasant motilin, its distribution and gastrointestinal contractility-stimulating action in the pheasant

Previously, pheasant motilin was identified as a 22-amino acid peptide with a sequence of FVPFFTQSDI QKMQEKERIK GQ. In the present study, the distribution of pheasant motilin mRNA was determined and compared with that of ghrelin, a motilin-related peptide. The effects of pheasant motilin on the cognate gastrointestinal (GI) muscle strips were also examined in an in vitro contraction study. The expression of pheasant motilin mRNA was highest in the small intestine (duodenum, jejunum and ileum), moderate in the colon and very low in the brain, lung, heart, pancreas, esophagus, proventriculus, gizzard and caecum, and this distribution was in contrast with that of ghrelin mRNA. Pheasant motilin caused contraction of the cognate GI tract in a region-dependent manner, similar to chicken motilin. The contraction in the small intestine was large and was not affected by atropine. In contrast, contraction in the proventriculus was small and was decreased by atropine. The crop and colon were insensitive to pheasant motilin. Neither GM109 nor MA2029, mammalian motilin receptor antagonists inhibited the contractions of pheasant motilin. Erythromycin was ineffective in the pheasant ileum, although it caused contraction of the rabbit duodenum. These results indicate that pheasant motilin caused contraction through an action on smooth muscles in the small intestine and an action on enteric cholinergic nerves in the proventriculus. This high responsiveness of the small intestine suggests that motilin is a regulator of small intestinal motility in avians, and the characteristic of the motilin receptor in the pheasant might be different from that in mammals, as is that in chickens.

Motilin Comparative Study: Structure, Distribution, Receptors, and Gastrointestinal Motility

Motilin, produced in endocrine cells in the mucosa of the upper intestine, is an important regulator of gastrointestinal (GI) motility and mediates the phase III of interdigestive migrating motor complex (MMC) in the stomach of humans, dogs and house musk shrews through the specific motilin receptor (MLN-R). Motilin-induced MMC contributes to the maintenance of normal GI functions and transmits a hunger signal from the stomach to the brain. Motilin has been identified in various mammals, but the physiological roles of motilin in regulating GI motility in these mammals are well not understood due to inconsistencies between studies conducted on different species using a range of experimental conditions. Motilin orthologs have been identified in non-mammalian vertebrates, and the sequence of avian motilin is relatively close to that of mammals, but reptile, amphibian and fish motilins show distinctive different sequences. The MLN-R has also been identified in mammals and non-mammalian vertebrates, and can be divided into two main groups: mammal/bird/reptile/amphibian clade and fish clade. Almost 50 years have passed since discovery of motilin, here we reviewed the structure, distribution, receptor and the GI motility regulatory function of motilin in vertebrates from fish to mammals.

Capromorelin, a ghrelin receptor agonist, increases feed intake and body weight gain in broiler chickens (Gallus gallus domesticus)

Ghrelin is a hormone that induces orexigenic effects in mammals. However, in avian species, there is scant and conflictive results on the effect of ghrelin on feed intake (FI). Therefore, we evaluated the effect of a ghrelin receptor agonist (capromorelin) on FI, ADG, water intake (WI), animal behavior and concentrations of ghrelin, glucose, growth hormone (GH) and insulin in broiler chickens. One-day-old male broilers were reared as recommended by the industry. At 4 wk of age (experimental day 0; D0), birds were blocked by weight and randomly assigned to 3 treatments in 2 identical trials. Control birds received a vehicle control solution containing 0 mg/kgBW/d of capromorelin. Birds in treatments 2 and 3 received capromorelin at target doses of 6 or 12 mg/kgBW/d of capromorelin (n = 27). FI and WI were measured 3 times a day at 0700 h (Period 1; P1), 1200 h (P2) and 1700 h (P3), while BW was recorded daily. Blood samples were collected on D-1 and D5. Bird behavior (pecking, sitting and standing) was evaluated for 9 h on D2. Data were analyzed using a randomized complete block design with repeated measures over time. Orthogonal polynomial contrasts were used to determine linear and quadratic effects of increasing levels of capromorelin. Polynomial contrasts showed that capromorelin doses linearly increased FI (P = 0.002) and ADG (P = 0.019). There were no treatment, day or treatment x d interactions on glucose, ghrelin and GH concentrations. However, there was a treatment x d interaction (P = 0.041) on insulin concentrations. Concentrations of insulin were higher on D5 for the 0 and 12 mg/kgBW/d treatments as compared with D-1. Polynomial contrasts showed that capromorelin doses linearly increased number of pecks/h (P = 0.018). Per hour FI and WI was higher during P1 (i.e., 0700-1200) as compared to P2 and P3 (P < 0.001). Our observations suggest that capromorelin linearly increases feed intake; thus, the same effect of that reported in mammalian species.

Integration of lncRNA and mRNA profiles to reveal the protective effects of Codonopsis pilosula extract on the gastrointestinal tract of mice subjected to D‑galactose‑induced aging

Codonopsis pilosula is a type of traditional Chinese medicine that exerts an anti‑aging effect and can regulate the gastrointestinal (GI) system. The aim of the present study was to investigate the underlying molecular mechanisms responsible for the anti‑aging effects of Codonopsis pilosula in the GI tract of mice with D‑galactose‑induced aging. First, a successful mouse model of aging was established, and Codonopsis pilosula water extract was then used for treatment. The anti‑aging effects of Codonopsis pilosula on the GI tract were then detected from the perspectives of tissue structure, physiological function and cell ultrastructure. Finally, in order to explore the underlying molecular mechanisms, the expression profiles of lncRNAs and mRNAs in the stomach and intestine were examined using microarray technology. A total of 117 (41 lncRNAs and 76 mRNAs) and 168 (85 lncRNA sand 83 mRNAs) differentially expressed genes associated with the anti‑aging effects of Codonopsis pilosula were identified in the stomach and intestine, respectively. Through integrated analysis of the stomach and intestine, 4 hub RNAs, including 1 lncRNA (LOC105243318) and 3 mRNAs (Fam132a, Rorc and 1200016E24Rik) were identified, which may be associated with the anti‑aging effects of Codonopsis pilosula in the GI tract of aging mice. The Kyoto Encyclopedia of Genes and Genomes analysis revealed that the metabolic pathway was an important pathway underlying the anti‑aging effects of Codonopsis pilosula in the GI tract. On the whole, in the present study, 4 hub RNAs associated with these effects and their regulatory networks were found in the GI tract of aging mice. In addition, the metabolic pathway was found to play an important role in these anti‑aging effects in the GI tract.

Motilin- and ghrelin-induced contractions in isolated gastrointestinal strips from three species of frogs

Ghrelin (GHRL) and motilin (MLN), gut peptides isolated from the mucosa of the stomach and duodenum, respectively, stimulate gastrointestinal (GI) motility in mammals and birds. However, the functions of MLN and GHRL in amphibian GI tracts have not been examined in detail. To clarify the regulation of GI motility by the two peptides, the effects of human MLN and rat GHRL on contractility of isolated GI strips from three species of frogs, the black-spotted pond frog (pond frog; Pelophylax nigromaculata), bullfrog (Lithobates catesbeiana) and Western clawed frog (Xenopus; Xenopus tropicalis), were examined in in vitro experiments. The GI tract of each frog was divided into the stomach, upper intestine, middle intestine and lower intestine. Human MLN caused contractions of the stomach in the pond frog and upper intestine in the bullfrog and Xenopus, but other GI regions were insensitive to human MLN. Erythromycin did not cause contraction of the upper intestine of the bullfrog and Xenopus. Rat GHRL did not cause contraction of the stomach and small intestines in the pond frog and bullfrog, but it caused a concentration-dependent contraction in the stomach and upper intestine of Xenopus, while des-acyl rat GHRL did not cause any contraction of them. In conclusion, human MLN caused the contraction of the stomach or upper intestine in the three species of frogs, but GHRL was effective only in the stomach and upper intestine of Xenopus. On the basis of these data, MLN but not GHRL causes the GI region-dependent contractions in the frogs.

Evaluation of the Relationship between Adipose Metabolism Patterns and Secretion of Appetite-Related Endocrines on Chicken

Simple Summary

The weight of an animal conforms to a certain growth pattern. Among others, feed, environment, and body composition, in addition to genetics, affect the animal’s feed consumption and body weight. Under normal circumstances, the body weight of an animal is mainly affected by feed intake, and body composition may significantly influence feed intake. Therefore, this report sets out the effects of fat accumulation on lipid metabolism and appetite, and finally introduces the effects of feeding patterns on animal feed intake.

Abstract

In addition to the influence of genes, the quality of poultry products is mainly controlled by the rearing environment or feed composition during rearing, and has to meet human use and economical needs. As the only source of energy for poultry, feed considerably affects the metabolic pattern of poultry and further affects the regulation of appetite-related endocrine secretion in poultry. Under normal circumstances, the accumulation of lipid in adipose reduces feed intake in poultry and increases the rate of adipose metabolism. When the adipose content in cells decreases, endocrines that promote food intake are secreted and increase nutrient concentrations in serum and cells. By regulating the balance between appetite and adipose metabolism, the poultry’s growth and posture can maintain a balanced state. In addition, increasing fiber composition in feed can effectively increase poultry welfare, body weight, lean composition and antioxidant levels in poultry. According to this, the concept that proper fiber content should be added to feed should be considered for better economic benefits, poultry welfare and meat productivity.

Identification of pheasant ghrelin and motilin and their actions on contractility of the isolated gastrointestinal tract

Motilin and ghrelin were identified in the pheasant by molecular cloning, and the actions of both peptides on the contractility of gastrointestinal (GI) strips were examined in vitro. Molecular cloning indicated that the deduced amino acid sequences of the pheasant motilin and ghrelin were a 22-amino acid peptide, FVPFFTQSDIQKMQEKERIKGQ, and a 26-amino acid peptide, GSSFLSPAYKNIQQQKDTRKPTGRLH, respectively. In in vitro studies using pheasant GI strips, chicken motilin caused contraction of the proventriculus and small intestine, whereas the crop and colon were insensitive. Human motilin, but not erythromycin, caused contraction of small intestine. Chicken motilin-induced contractions in the proventriculus and ileum were not inhibited by a mammalian motilin receptor antagonist, GM109. Neither atropine (a cholinergic receptor antagonist) nor tetrodotoxin (a neuron blocker) inhibited the responses of chicken motilin in the ileum but both drugs decreased the responses to motilin in the proventriculus, suggesting that the contractile mechanisms of motilin in the proventriculus was neurogenic, different from that of the small intestine (myogenic). On the other hand, chicken and quail ghrelin did not cause contraction in any regions of pheasant GI tract. Since interaction of ghrelin and motilin has been reported in the house musk shrew, interaction of two peptides was examined. The chicken motilin-induced contractions were not modified by ghrelin, and ghrelin also did not cause any contraction under the presence of motilin, suggesting the absence of interaction in both peptides. In conclusion, both the motilin system and ghrelin system are present in the pheasant. Regulation of GI motility by motilin might be common in avian species. However, absence of ghrelin actions in any GI regions suggests the avian species-related difference in regulation of GI contractility by ghrelin.

A novel 86-bp indel of the motilin receptor gene is significantly associated with growth and carcass traits in Gushi-Anka F2 reciprocal cross chickens

1. A previous whole-genome association analysis has identified the motilin receptor gene (MLNR), which regulates gastrointestinal motility and gastric emptying, as a candidate gene related to chicken growth.2. MLNR mRNA was expressed in all tissues tested, and the expression level in digestive tissues was greater than in other tissues. Expression levels in the pancreas, duodenum and glandular stomach at day old and one, two and three weeks of age indicated a possible correlation with the digestive system. This suggested that the MLNR gene plays a central role in gastrointestinal tract function and affects the growth and development of chickens. Moreover, there was a significant difference in expression in the glandular stomach tissue between Ross 308 and Gushi chickens at six weeks of age.3. Re-sequencing revealed an 86-bp insertion/deletion polymorphism in the downstream region of the MLNR gene. The mutation locus was genotyped in 2,261 individuals from nine different chicken breeds. MLNR expression levels in the glandular stomach of chickens with DD genotypes were greater than those in chickens with the ID and II genotypes. The DD genotype was the most dominant genotype in commercial broiler's (Ross 308 and Arbor Acres broilers), and the D allele frequency in these breeds exceeded 91%. The deletion mutation tended towards fixation in commercial broilers.4. Association with growth and carcass traits analysed in a Gushi-Anka F₂ intercrossed population, showed that the DD genotype was significantly associated with the greatest growth and carcass trait values, whereas values associated with the II genotype were the lowest in the F₂ reciprocal cross chickens.5. The results suggest that the mutation is strongly associated with growth related traits and it is likely to be useful for marker-assisted selection of chickens.

Ghrelin serves as a signal of energy utilization and is involved in maintaining energy homeostasis in broilers

Ghrelin, one of the most important appetite regulating peptides, is involved in the regulation of energy homeostasis. The anorexia effect of ghrelin in chickens is contrary to that of ghrelin in mammals. In the present study, the effects of feeding status and dietary energy level on plasma total ghrelin levels and expression were studied in broilers. The gene expression of ghrelin and its receptor GHS-R1a were measured in the hypothalamus, proventriculus, duodenum, liver, and abdominal fat pad. The results showed that ghrelin mRNA and GHS-R1a mRNA are moderately expressed in liver and abdominal fat. Ghrelin secretion was increased by fasting and refeeding. The gene expression of ghrelin and GHS-R1a in the hypothalamus, proventriculus, liver, and abdominal fat pad were changed by feeding status and dietary energy level. The results suggest that ghrelin is a signal of energy utilization in chickens. The abundant expression of ghrelin and GHS-R1a in liver and abdominal fat pad may be associated with energy balance.

Regulation of Gastrointestinal Motility by Motilin and Ghrelin in Vertebrates

The energy balance of vertebrates is regulated by the difference in energy input and energy expenditure. Generally, most vertebrates obtain their energy from nutrients of foods through the gastrointestinal (GI) tract. Therefore, food intake and following food digestion, including motility of the GI tract, secretion and absorption, are crucial physiological events for energy homeostasis. GI motility changes depending on feeding, and GI motility is divided into fasting (interdigestive) and postprandial (digestive) contraction patterns. GI motility is controlled by contractility of smooth muscles of the GI tract, extrinsic and intrinsic neurons (motor and sensory) and some hormones. In mammals, ghrelin (GHRL) and motilin (MLN) stimulate appetite and GI motility and contribute to the regulation of energy homeostasis. GHRL and MLN are produced in the mucosal layer of the stomach and upper small intestine, respectively. GHRL is a multifunctional peptide and is involved in glucose metabolism, endocrine/exocrine functions and cardiovascular and reproductive functions, in addition to feeding and GI motility in mammals. On the other hand, the action of MLN is restricted and species such as rodentia, including mice and rats, lack MLN peptide and its receptor. From a phylogenetic point of view, GHRL and its receptor GHS-R1a have been identified in various vertebrates, and their structural features and various physiological functions have been revealed. On the other hand, MLN or MLN-like peptide (MLN-LP) and its receptors have been found only in some fish, birds and mammals. Here, we review the actions of GHRL and MLN with a focus on contractility of the GI tract of species from fish to mammals.

Does motilin peptide regulate gastrointestinal motility of zebrafish? An in vitro study using isolated intestinal strips

Motilin (MOT), a 22-amino-acid peptide hormone produced in the duodenal mucosa, stimulates gastrointestinal motility in mammals and birds, and it is a mediator of interdigestive motor complexes. Recently, expression of MOT-like peptide (MOTLP) and its receptor mRNAs was identified in zebrafish. The aim of the present study was to determine whether the zebrafish MOTLP (zfMOTLP, HIAFFSPKEMRELREKE) affects zebrafish gastrointestinal motility, with comparison to the effect of human MOT, in which five amino acids are identical to zfMOTLP at positions 5, 9, 15, 16, and 17. zfMOTLP caused small contractions of the rabbit duodenum and chicken ileum but, the sensitivity was about 3000-times lower than that of human MOT. zfMOTLP-induced contraction in the rabbit duodenum was decreased by pretreatment of the MOT receptor antagonist GM109, indicating that zfMOTLP could bind to the MOT receptor. zfMOTLP (3-100nM) increased the intracellular Ca²⁺ concentration in zfMOT receptor-expressing HEK293 cells, but human MOT did not cause responses even at 100nM. In in vitro study using isolated zebrafish gastrointestinal strips, zfMOTLP caused only small contractions even at high doses (1-10μM). zfMOT receptor mRNA is detected in the gastrointestinal tract and brain to almost the same extent, and the expression level (40-70 copies/100ng total RNA) is much lower than that in the chicken gastrointestinal tract. These results suggest that the MOTLP/MOT receptor system is present in zebrafish, but its physiological role for regulation of gastrointestinal motility might be not significant due to the weak contractile activity and low expression level of the receptor.

The chicken is an interesting animal for study of the functional role of ghrelin in the gastrointestinal tract

Ghrelin has been identified in vertebrates from fish to mammals, and it has multiple biological activities including gastrointestinal (GI) motor-stimulating action. In some non-mammalian vertebrates, we examined the effects of ghrelin on contractility of the isolated GI tract as well as the mRNA expression of growth hormone secretagogue-receptor 1a (GHS-R1a) to determine whether the motor-stimulating action of ghrelin is common in vertebrates. The expression level of GHS-R1a mRNA differed depending on the species and on the GI region (stomach, small intestine, and colon). GI region-dependent expression of GHS-R1a mRNA was remarkable in chickens, and the expression levels changed depending on age. In a functional study, ghrelin did not cause contraction of unstimulated GI strips in fish (goldfish and rainbow trout) or amphibians (bullfrog and Japanese fire belly newts) even using their homologous ghrelin. In avian species, ghrelin caused contraction of the unstimulated GI tract of the chicken but not of the Japanese quail, and the responses to ghrelin in the chicken GI tract decreased with aging. Our in vitro studies show that the motor-stimulating action of ghrelin is not conserved across vertebrates and that the chicken is a unique animal species for evaluation of the GI-stimulating action of ghrelin of different age.

Molecular cloning of motilin and mechanism of motilin-induced gastrointestinal motility in Japanese quail

Motilin, a peptide hormone produced in the upper intestinal mucosa, plays an important role in the regulation of gastrointestinal (GI) motility. In the present study, we first determined the cDNA and amino acid sequences of motilin in the Japanese quail and studied the distribution of motilin-producing cells in the gastrointestinal tract. We also examined the motilin-induced contractile properties of quail GI tracts using an in vitro organ bath, and then elucidated the mechanisms of motilin-induced contraction in the proventriculus and duodenum of the quail. Mature quail motilin was composed of 22 amino acid residues, which showed high homology with chicken (95.4%), human (72.7%), and dog (72.7%) motilin. Immunohistochemical analysis showed that motilin-immunopositive cells were present in the mucosal layer of the duodenum (23.4±4.6cells/mm(2)), jejunum (15.2±0.8cells/mm(2)), and ileum (2.5±0.7cells/mm(2)), but were not observed in the crop, proventriculus, and colon. In the organ bath study, chicken motilin induced dose-dependent contraction in the proventriculus and small intestine. On the other hand, chicken ghrelin had no effect on contraction in the GI tract. Motilin-induced contraction in the duodenum was not inhibited by atropine, hexamethonium, ritanserin, ondansetron, or tetrodotoxin. However, motilin-induced contractions in the proventriculus were significantly inhibited by atropine and tetrodotoxin. These results suggest that motilin is the major stimulant of GI contraction in quail, as it is in mammals and the site of action of motilin is different between small intestine and proventriculus.

Effects of ghrelin and motilin on smooth muscle contractility of the isolated gastrointestinal tract from the bullfrog and Japanese fire belly newt

Ghrelin has been identified in some amphibians and is known to stimulate growth hormone release and food intake as seen in mammals. Ghrelin regulates gastrointestinal motility in mammals and birds. The aim of this study was to determine whether ghrelin affects gastrointestinal smooth muscle contractility in bullfrogs (anuran) and Japanese fire belly newts (urodelian) in vitro. Neither bullfrog ghrelin nor rat ghrelin affected longitudinal smooth muscle contractility of gastrointestinal strips from the bullfrog. Expression of growth hormone secretagogue receptor 1a (GHS-R1a) mRNA was confirmed in the bullfrog gastrointestinal tract, and the expression level in the gastric mucosa was lower than that in the intestinal mucosa. In contrast, some gastrointestinal peptides, including substance P, neurotensin and motilin, and the muscarinic receptor agonist carbachol showed marked contraction, indicating normality of the smooth muscle preparations. Similar results were obtained in another amphibian, the Japanese fire belly newt. Newt ghrelin and rat ghrelin did not cause any contraction in gastrointestinal longitudinal muscle, whereas substance P and carbachol were effective causing contraction. In conclusion, ghrelin does not affect contractility of the gastrointestinal smooth muscle in anuran and urodelian amphibians, similar to results for rainbow trout and goldfish (fish) but different from results for rats and chickens. The results suggest diversity of ghrelin actions on the gastrointestinal tract across animals. This study also showed for the first time that motilin induces gastrointestinal contraction in amphibians.

Gastrointestinal hormones and gut motility

PURPOSE OF REVIEW

To summarize the recent findings.

RECENT FINDINGS

Studies of changes in the plasma levels confirm the earlier concepts, but offer little proof of causal effect. It is increasingly realized that peptides produced in the gut have a paracrine role or an indirect effect via the gut-brain axis. Interest in prokinetic peptide agonists remains high despite the failure of two candidate drugs, but relamorelin and camicinal offer new hope.

SUMMARY

We review the original studies published since January 2013 on peptides produced in the gut and with an effect on gastrointestinal motility.

Correlation of ghrelin concentration and ghrelin, ghrelin-O-acetyltransferase (GOAT) and growth hormone secretagogue receptor 1a mRNAs expression in the proventriculus and brain of the growing chicken

To determine mechanisms for age-related decrease of GHS-R1a expression in the chicken proventriculus, changes in mRNA expression of ghrelin and ghrelin-O-acetyltransferase (GOAT) as well as ghrelin concentrations in the proventriculus and plasma were examined in growing chickens. Changes in expression levels of ghrelin, GOAT and GHS-R1a mRNAs were also examined in different brain regions (pituitary, hypothalamus, thalamus, cerebellum, cerebral cortex, olfactory bulb, midbrain and medulla oblongata). Ghrelin concentrations in the proventriculus and plasma increased with aging and reached plateaus at 30-50 days after hatching. High level of ghrelin mRNA decreased at 3 days after hatching, and it became stable at half of the initial level. Expression levels of GHS-R1a and GOAT decreased 3 or 5 days after hatching and became stable at low levels. Significant negative correlations were found between plasma ghrelin and mRNA levels of GOAT and GHS-R1a. Expression levels of ghrelin mRNA were different in the brain regions, but a significant change was not seen with aging. GHS-R1a expression was detected in all brain regions, and age-dependent changes were observed in the pituitary and cerebellum. Different from the proventriculus, the expression of GOAT in the brain increased or did not change with aging. These results suggest that decreased GHS-R1a and GOAT mRNA expression in the proventriculus is due to endogenous ghrelin-induced down-regulation. Expression levels of ghrelin, GOAT and GHS-R1a in the brain were independently regulated from that in the proventriculus, and age-related and region-dependent regulation pattern suggests a local effect of ghrelin system in chicken brain.