Regulation of Energy Balance in Birds by the Neuroendocrine Hypothalamus

A bird's-eye overview of molecular mechanisms regulating feed intake in chickens-with mammalian comparisons

In recent decades, a lot of research has been conducted to explore poultry feeding behavior. However, up to now, the processes behind poultry feeding behavior remain poorly understood. The review generalizes modern expertise about the hormonal regulation of feeding behavior in chickens, focusing on signaling pathways mediated by insulin, leptin, and ghrelin and regulatory pathways with a cross-reference to mammals. This overview also summarizes state-of-the-art research devoted to hypothalamic neuropeptides that control feed intake and are prime candidates for predictors of feeding efficiency. Comparative analysis of the signaling pathways that mediate the feed intake regulation allowed us to conclude that there are major differences in the processes by which hormones influence specific neuropeptides and their contrasting roles in feed intake control between two vertebrate clades.

Early Feeding Strategy Mitigates Major Physiological Dynamics Altered by Heat Stress in Broilers

Heat stress is one of the stressors that negatively affect broiler chickens, leading to a reduction in production efficiency and profitability. This reduction affects the economy in general, especially in hot and semi-hot countries. Therefore, improving heat tolerance of broiler chicks is a key to sustained peak performance, especially under adverse environmental heat stress conditions. The present study investigated three early feed withdrawal regimes (FWD) as a potential mitigation for thermal stress exposure. A total of 240 unsexed one-day-old Cobb-500 chicks were randomly recruited to one of four experimental groups using a completely randomized design (10 birds × 6 replicates). The experimental groups included the control group with no feed withdrawal (control), while the other three groups were subjected to early feed withdrawal for either 24 h on the 5th day of age (FWD-24), 12 h on the 3rd and 5th day of age (FWD-12), or 8 h on the 3rd, 4th, and 5th day of age (FWD-8), respectively. Production performance was monitored throughout the experiment. Meanwhile, blood and liver samples were taken at the end of the experimental period to evaluate major physiological dynamic changes. Our findings demonstrated that under chronic heat stress conditions, FWD treatments significantly improved broilers' production performance and enhanced several physiological parameters compared with the control. Serum levels of thyroid hormones were elevated, whereas leptin hormone was decreased in FWD groups compared with the control. Moreover, serum total protein, globulin, and hemoglobin levels were higher, while total cholesterol and uric acid were lower in the FWD groups. Furthermore, FWD groups showed significantly higher antioxidant marker activity with a significantly lower lipid peroxidation level. Immunoglobulin levels, lysozyme, complement factor C3, and liver heat shock protein 70 (HSP70) concentration were also elevated in FWD compared with the control. Also, serum interleukin-1β (IL-1β) and interferon-gamma (IFN-γ) significantly increased with FWD. Based on our findings, early feed withdrawal can be applied as a promising non-invasive nutritional strategy for broilers reared under chronic heat stress conditions. Such a strategy promotes the alleviation of the deleterious effects of heat stress on broiler performance, immunity, and redox status, owing to the onset of physiological adaptation and the development of thermotolerance ability.

Leptin administration does not influence migratory behaviour in white-throated sparrows (Zonotrichia albicollis)

Migratory flights by birds are among the most energetically demanding forms of animal movement, and are primarily fueled by fat as an energy source. Leptin is a critical fat-regulation hormone associated with energy balance in non-avian species but its function in birds is highly controversial. Prior research indicated the effects of leptin differed between birds in migratory condition or not, but no research has assessed the effect of leptin on migratory behaviour itself. In this study, our objective was to determine if leptin affects migratory restlessness and fat deposition in migratory songbirds. We used photoperiod manipulation to induce spring migratory condition, and measured migratory restlessness in leptin-injected and saline-injected white-throated sparrows (Zonotrichia albicollis). Leptin treatment had no effect on migratory restlessness nor fat deposition, providing evidence that leptin does not influence avian migratory motivation or behaviour. Our results also further support the idea that birds in a hyperphagic migratory condition may be insensitive to leptin.

Experimental ghrelin administration affects migratory behaviour in a songbird

Twice a year, billions of birds take on drastic physiological and behavioural changes to migrate between breeding and wintering areas. On migration, most passerine birds regularly stop over along the way to rest and refuel. Endogenous energy stores are not only the indispensable fuel to complete long distance flights, but are also important peripheral signals that once integrated in the brain modulate crucial behavioural decisions, such as the decision to resume migration after a stopover. A network of hormones signals metabolic fuel availability to the brain in vertebrates, including the recently discovered gut-hormone ghrelin. Here, we show that ghrelin takes part in the control of migratory behaviour during spring migration in a wild migratory passerine. We manipulated blood concentrations of ghrelin of 53 yellow-rumped warblers (Setophaga coronata coronata) caught during stopover and automatically radio-tracked their migratory behaviour following release. We found that injections of acylated and unacylated ghrelin rapidly induced movements away from the release site, indicating that the ghrelin system acts centrally to mediate stopover departure decisions. The effects of the hormone manipulation declined within 8 h following release, and did not affect the overall rate of migration. These results provide experimental evidence for a pivotal role of ghrelin in the modulation of behavioural decisions during migration. In addition, this study offers insights into the regulatory functions of metabolic hormones in the dialogue between gut and brain in birds.

Cocaine- and amphetamine-regulated transcript peptide- and dopamine-containing systems interact in the ventral tegmental area of the zebra finch, Taeniopygia guttata, during dynamic changes in energy status

The mesolimbic dopamine (DA)-pathway regulates food-reward, feeding-related behaviour and energy balance. Evidence underscores the importance of feeding-related neuropeptides in modulating activity of these DA neurons. The neuropeptide, CART, a crucial regulator of energy balance, modulates DA-release, and influences the activity of ventral tegmental area (VTA) DAergic neurons in the mammalian brain. Whether CART- and DA-containing systems interact at the level of VTA to regulate energy balance, however, is poorly understood. We explored the interaction between CART- and DA-containing systems in midbrain of the zebra finch, Taeniopygia guttata, an interesting model to study dynamic changes in energy balance due to higher BMR/daytime body temperature, and rapid responsiveness of the feeding-related neuropeptides to changes in energy state. Further, its midbrain DA-neurons share similarities with those in mammals. In the midbrain, tyrosine hydroxylase-immunoreactive (TH-i) neurons were seen in the substantia nigra (SN) and VTA [anterior (VTAa), mid (VTAm) and caudal (VTAc)]; those in VTA were smaller. In the VTA, CART-immunoreactive (CART-i)-fibers densely innervated TH-i neurons, and both CART-immunoreactivity (CART-ir) and TH-immunoreactivity (TH-ir) responded to energy status-dependent changes. Compared to fed and fasted birds, refeeding dramatically enhanced TH-ir and the percentage of TH-i neurons co-expressing FOS in the VTA. Increased prepro-CART-mRNA, CART-ir and a transient appearance of CART-i neurons was observed in VTAa of fasted, but not fed birds. To test the functional interaction between CART- and DA-containing systems, ex-vivo superfused midbrain-slices were treated with CART-peptide and changes in TH-ir analysed. Compared to control tissues, CART-treatment increased TH-ir in VTA but not SN. We propose that CART is a potential regulator of VTA DA-neurons and energy balance in T. guttata.

The AMPK-mTOR signaling pathway is involved in regulation of food intake in the hypothalamus of stressed chickens

Glucocorticoids (GCs) can stimulate the appetite and AMPK in broilers. The activation of hypothalamic mTOR has been proposed as an important anorexigenic signal. However, inhibitory effect of AMPK activity on appetite and AMPK downstream signaling pathway under stress has not been reported. In this study, we performed an intracerebroventricular (icv) injection of compound C, an AMPK inhibitor, in GC-treated birds to explore the regulatory mechanism on appetite and AMPK downstream signaling pathway. A total of 48 7-day-old broilers, which had received an icv cannula, were randomly subjected to one of two treatments: subcutaneous injection of dexamethasone (DEX) or saline. After 3 days of continuous DEX injection, chicks of each group received an icv injection with either compound C (6 μg/2 μL) or vehicle (dimethyl sulfoxide, 2 μL). The results showed that body weight gain was reduced by the DEX treatment. Compared with the control, icv injection of compound C reduced feed intake at 0.5-1.5 h. In the DEX-treated group, the inhibitory effect of compound C on appetite remained apparent at 0.5-1 h. The DEX treatment increased the gene expression of liver kinase B1 (LKB1), neuropeptide Y (NPY), and decreased p-mTOR protein level. In stressed broilers, inhibition of AMPK relieved the decreased mTOR activity. A significant interaction was noted in DEX and compound C on protein expression of phospho-AMPK. Taken together, in stressed broilers, the central injection of compound C could inhibit central AMPK activity and reduce appetite, in which the AMPK/mTOR signaling pathway might be involved.

Neuropeptide Y and maternal behavior in the female native Thai chicken

Maternal care behaviors in birds include incubation and rearing behaviors. During incubating period, the hens stop laying and eating less due to food restriction as a natural fasting when compared with the rearing hens, resulting in low production of eggs and chicks. Neuropeptide Y (NPY), a neurotransmitter/neuromodulator, is very well known to be involved in food intake regulation in birds and mammals. The objective of this study is to elucidate the association between NPY and maternal behaviors in the female native Thai chicken. The distributions of NPY-immunoreactive (-ir) neurons and fibers in the brain of the incubating (INC), nest-deprived (ND), and replaced-egg-with-chicks (REC) hens at day 6 were determined utilizing immunohistochemistry technique. The results revealed that the distributions of NPY-ir neurons and fibers were observed within the septalis lateralis, nucleus rotundus, and nucleus dorsolateralis anterior thalami, with predominantly located within the the nucleus paraventricularis magnocellularis (PVN). NPY-ir fibers were located throughout the brain and the densest NPY-ir fibers were distributed in a discrete region lying close to the ventriculus tertius (third ventricle) through the hypothalamus. Changes in the number of NPY-ir neurons within the PVN of the INC, ND, and REC hens were compared at different time points (at days 6 and 14). Interestingly, the number of NPY-ir neurons within the PVN was significantly higher (P < 0.05) in the INC hens when compared with those of the ND and REC hens at day 14 but not day 6. In addition, the number of NPY-ir neurons within the PVN of the INC hens was significantly increased (P < 0.05) from day 6 to day 14 but not the ND and REC hens. These results indicated, for the first time, the asscociation between NPY and maternal behaviors in the femle native Thai chicken. Change in the number of NPY-ir neurons within the PVN during the transition from incubating to rearing behavior suggested the possible role of NPY in the regulation of the maternal behaviors in this equatorial species. In addition, the native Thai chicken might be an excellent animal model for the study of this phenomenon.

Concurrent changes in photoperiod-induced seasonal phenotypes and hypothalamic CART peptide-containing systems in night-migratory redheaded buntings

This study tested the hypothesis whether hypothalamic cocaine-and amphetamine-regulated transcript (CART)-containing systems were involved in photoperiod-induced responses associated with spring migration (hyperphagia and weight gain) and reproduction (gonadal maturation) in migratory songbirds. We specifically chose CART to examine neural mechanism(s) underlying photoperiod-induced responses, since it is a potent anorectic neuropeptide and involved in the regulation of changes in the body mass and reproduction in mammals. We first studied the distribution of CART-immunoreactivity in the hypothalamus of migratory redheaded buntings (Emberiza bruniceps). CART-immunoreactive neurons were found extensively distributed in the preoptic, lateral hypothalamic (LHN), anterior hypothalamic (AN), suprachiasmatic (SCN), paraventricular (PVN), dorsomedialis hypothalami (DMN), inferior hypothalamic (IH), and infundibular (IN) nuclei. Then, we correlated hypothalamic CART-immunoreactivity in buntings with photostimulated seasonal states, particularly winter non-migratory/non-breeding (NMB) state under short days, and spring premigratory/pre-breeding (PMB) and migratory/breeding (MB) states under long days. There were significantly increased CART-immunoreactive cells, and percent fluorescent area of CART-immunoreactivity was significantly increased in all mapped hypothalamic areas, except the SCN, PVN, AN, and DMN in photostimulated PMB and MB states, as compared to the non-stimulated NMB state. In particular, CART was richly expressed in the medial preoptic nucleus, LHN, IH and IN during MB state in which buntings showed reduced food intake and increased night-time activity. These results suggest that changes in the activity of the CART-containing system in different brain regions were associated with heightened energy needs of the photoperiod-induced seasonal responses during spring migration and reproduction in migratory songbirds.

Effect of Stereotaxic Surgery of the Third Ventricle on Growth Performance in Neonatal Chicks

Feeding behavior and energy metabolism are precisely regulated by humoral and/or neural factors in the central nervous system. In particular, nuclei, such as the arcuate nucleus, ventromedial hypothalamic nucleus, and lateral hypothalamic area located near the third ventricle of the hypothalamus are the centers of feeding and energy metabolism in various vertebrate species, including chickens. In this study, we evaluated the effects of cannulation of the third ventricle on chick growth and feeding behavior in the neonatal stage, to develop a method for local and chronic central nervous system-mediated energy metabolism. Referring to the chick brain atlas, a guide cannula was inserted into the third ventricle of the chick under anesthesia immediately after hatching using a stereotaxic instrument. The chicks that recovered from anesthesia were bred for 11 days under normal feeding management conditions, and then feed intake amount, body weight gain, and metabolic tissue weight were measured. The effects of direct stimulation of the third ventricle with 2-deoxy-D-glucose on the expression level of the immediate-early gene, cFOS, and feed intake in 5-day-old chicks were also evaluated. There were no differences in feed intake, body weight gain, and metabolic tissue weight between 11-day-old cannulated and control chicks. The expression of cFOS mRNA in the ventromedial hypothalamic nucleus was higher than that in the amygdala after the third ventricular administration of 2-deoxy-D-glucose. Additionally, direct third ventricular injection of 2-deoxy-D-glucose attenuated the feeding behavior of chicks for a while. Overall, we speculate that the technique is effective for local and/or chronic stimulation of the nucleus near the third ventricle of the chick hypothalamus, which is important for feed and energy metabolism regulation.

Effects of dietary energy level on appetite and central adenosine monophosphate-activated protein kinase (AMPK) in broilers

Adenosine monophosphate-activated protein kinase (AMPK) acts as a sensor of cellular energy changes and is involved in the control of food intake. A total of 216 1-d-old broilers were randomly allotted into 3 treatments with 6 replicates per treatment and 12 broilers in each cage. The dietary treatments included 1) high-energy (HE) diet (3,500 kcal/kg), 2) normal-energy (NE) diet (3,200 kcal/kg), and 3) low-energy (LE) diet (2,900 kcal/kg). The present study was conducted to investigate the effects of dietary energy level on appetite and the central AMPK signal pathway. The results showed that a HE diet increased average daily gain (ADG), whereas a LE diet had the opposite effect (P < 0.05, N = 6). The average daily feed intake (ADFI) of the chickens fed the LE diet was significantly higher than that of the control (P < 0.05, N = 6). Overall, the feed conversion rate gradually decreased with increasing dietary energy level (P < 0.05, N = 6). Moreover, the chickens fed the LE and HE diets demonstrated markedly improved urea content compared with the control group (P < 0.0001, N = 8). The triglyceride (TG) content in the LE group was obviously higher than that in the HE group but showed no change compared with the control (P = 0.0678, N = 8). The abdominal fat rate gradually increased with increased dietary energy level (P = 0.0927, N = 8). The HE group showed downregulated gene expression levels of liver kinase B1 (LKB1), neuropeptide Y (NPY), cholecystokinin (CCK), and glucocorticoid receptor (GR) in the hypothalamus compared with the control group (P < 0.05, N = 8). However, LE treatment significantly increased the mRNA level of AMP-activated protein kinase α2 (AMPKα2) compared with other groups (P = 0.0110, N = 8). In conclusion, a HE diet inhibited appetite and central AMPK signaling. In contrast, a LE diet activated central AMPK and appetite. Overall, the central AMPK signal pathway and appetite were modulated in accordance with the energy level in the diet to regulate nutritional status and maintain energy homeostasis in birds.

Identification of hypothalamic genes in associating with food intake during incubation behavior in domestic chicken

The molecular mechanism underlying in the onset and maintenance of incubation behavior are not fully understood, and it is still unknown the reason why White Leghorn, a layer strain, hens never display incubation behavior. Therefore, to explore specific hypothalamic genes regulating incubation behavior, cap analysis of gene expression (CAGE) were applied to comparison between incubating Silkie and laying White Leghorn hens. In addition, mRNA expression of some differentially expressed genes (DEGs) and melanocortinergic appetite genes including agouti-related peptide (AgRP) and pro-opiomelanocortin (POMC) was also analyzed on Silkie hens under natural anorexia and starvation. The CAGE identified 217 hypothalamic DEGs in incubating Silkie hens, and that of two, transthyretin (TTR) and prolactin-releasing peptide (PrRP), suggested as appetite gene, were markedly up- and down-regulated in incubating hens, respectively. In addition, AgRP and POMC expression also increased in incubating bird. mRNA expression of TTR, PrRP, and appetite genes were not differed significantly by starvation, although TTR mRNA expression was relatively high in fasting hens. Consequently, transcriptome by CAGE identified a number of hypothalamic genes differentially expressed by incubation behavior in Silkie hens. Of these, it is suggested that TTR and PrRP may, at least in part, be related to adaptation to natural anorexia in incubating Silkie chickens.

Insulin receptor localization in the embryonic avian hypothalamus

The hypothalamus is a brain region critical for the homeostatic regulation of appetite and energy expenditure. Hypothalamic neuronal activity that is altered during development can produce permanent physiological changes later in life. For example, circulating hormones such as insulin have been shown to influence hypothalamic neuronal projections, leading to altered metabolism in adult rodents. While insulin signaling in the post-hatch chicken has been shown to mirror that of mammals, the developmental role of insulin in the avian embryonic hypothalamus remains largely unexplored. Here we present the earliest known evidence for insulin receptor (InsR) expression in embryonic avian hypothalamic nuclei governing energy homeostasis. RT-PCR analysis reveals InsR mRNA in E8, E10, and E12 neurons while western blot data demonstrate protein expression in E12 avian whole brain and hypothalamic lysates. Immunohistochemical analysis of avian hypothalamic brain slices demonstrates a shift in InsR localization from paraventricular expression in E8 to a more defined concentration of InsR in developmental regions resembling the ventromedial hypothalamus (VMH) and arcuate nucleus (ARC) in E12 time points. In addition, InsR expression appears in a heterogeneous pattern, suggesting receptor localization to subpopulations of avian hypothalamic neurons as early as E8. With increasing evidence suggesting energy homeostasis pathways may be altered via the gestational environment, it is important to understand how insulin signaling may affect embryogenesis. Our research provides evidence for the earliest known embryonic expression of InsR protein in the avian hypothalamus and may suggest a developmental role for insulin signaling in the early patterning of metabolic pathways in the central nervous system.

Insulin immuno-neutralization decreases food intake in chickens without altering hypothalamic transcripts involved in food intake and metabolism

In mammals, insulin regulates blood glucose levels and plays a key regulatory role in appetite via the hypothalamus. In contrast, chickens are characterized by atypical glucose homeostasis, with relatively high blood glucose levels, reduced glucose sensitivity of pancreatic beta cells, and large resistance to exogenous insulin. The aim of the present study was to investigate in chickens the effects of 5 h fasting and 5 h insulin immuno-neutralization on hypothalamic mRNA levels of 23 genes associated with food intake, energy balance, and glucose metabolism. We observed that insulin immune-neutralization by administration of anti-porcine insulin guinea pig serum (AI) significantly decreased food intake and increased plasma glucose levels in chickens, while 5 h fasting produced a limited and non-significant reduction in plasma glucose. In addition, 5 h fasting increased levels of NPY, TAS1R1, DIO2, LEPR, GLUT1, GLUT3, GLUT8, and GCK mRNA. In contrast, AI had no impact on the levels of any selected mRNA. Therefore, our results demonstrate that in chickens, food intake inhibition or satiety mechanisms induced by insulin immuno-neutralization do not rely on hypothalamic abundance of the 23 transcripts analyzed. The hypothalamic transcripts that were increased in the fasted group are likely components of a mechanism of adaptation to fasting in chickens.

DNA methylation and expression of proopiomelanocortin (POMC) gene in the hypothalamus of three-week-old chickens show sex-specific differences

Increased availability and improved sequence annotation of the chicken (Gallus gallus f. domestica) genome have sparked interest in the bird as a model system to investigate translational embryonic development and health/disease outcomes. However, the epigenetics of this bird genome remain unclear. The aim of this study was to determine the levels of gene expression and DNA methylation at the proopiomelanocortin (POMC) gene in the hypothalamus of 3-week-old chickens. POMC is a key player in the control of the stress response, food intake, and metabolism. DNA methylation of the promoter, CpG island, and gene body regions of POMC were measured. Our data illustrate the pattern, variability, and functionality of DNA methylation for POMC expression in the chicken. Our findings show correlation of methylation pattern and gene expression along with sex-specific differences in POMC. Overall, these novel data highlight the promising potential of the chicken as a model and also the need for breeders and researchers to consider sex ratios in their studies.

Comparative transcriptome analysis of hypothalamus-regulated feed intake induced by exogenous visfatin in chicks

Background

The intracerebroventricular injection of visfatin increases feed intake. However, little is known about the molecular mechanism in chicks. This study was conducted to assess the effect of visfatin on the feeding behavior of chicks and the associated molecular mechanism.

Results

In response to the intraventricular injection of 40 ng and 400 ng visfatin, feed intake in chicks was significantly increased, and the concentrations of glucose, insulin, TG, HDL and LDL were significantly altered. Using RNA-seq, we identified DEGs in the chick hypothalamus at 60 min after injection with various doses of visfatin. In total, 325, 85 and 519 DEGs were identified in the treated chick hypothalamus in the LT vs C, HT vs C and LT vs HT comparisons, respectively. The changes in the expression profiles of DEGs, GO functional categories, KEGG pathways, and PPI networks by visfatin-mediated regulation of feed intake were analyzed. The DEGs were grouped into 8 clusters based on their expression patterns via K-mean clustering; there were 14 appetite-related DEGs enriched in the hormone activity GO term. The neuroactive ligand-receptor interaction pathway was the key pathway affected by visfatin. The PPI analysis of DEGs showed that POMC was a hub gene that interacted with the maximum number of nodes and ingestion-related pathways, including POMC, CRH, AgRP, NPY, TRH, VIP, NPYL, CGA and TSHB.

Conclusion

These common DEGs were enriched in the hormone activity GO term and the neuroactive ligand-receptor interaction pathway. Therefore, visfatin causes hyperphagia via the POMC/CRH and NPY/AgRP signaling pathways. These results provide valuable information about the molecular mechanisms of the regulation of food intake by visfatin.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4644-7) contains supplementary material, which is available to authorized users.

Obese super athletes: fat-fueled migration in birds and bats

Migratory birds are physiologically specialized to accumulate massive fat stores (up to 50-60% of body mass), and to transport and oxidize fatty acids at very high rates to sustain flight for many hours or days. Target gene, protein and enzyme analyses and recent -omic studies of bird flight muscles confirm that high capacities for fatty acid uptake, cytosolic transport, and oxidation are consistent features that make fat-fueled migration possible. Augmented circulatory transport by lipoproteins is suggested by field data but has not been experimentally verified. Migratory bats have high aerobic capacity and fatty acid oxidation potential; however, endurance flight fueled by adipose-stored fat has not been demonstrated. Patterns of fattening and expression of muscle fatty acid transporters are inconsistent, and bats may partially fuel migratory flight with ingested nutrients. Changes in energy intake, digestive capacity, liver lipid metabolism and body temperature regulation may contribute to migratory fattening. Although control of appetite is similar in birds and mammals, neuroendocrine mechanisms regulating seasonal changes in fuel store set-points in migrants remain poorly understood. Triacylglycerol of birds and bats contains mostly 16 and 18 carbon fatty acids with variable amounts of 18:2n-6 and 18:3n-3 depending on diet. Unsaturation of fat converges near 70% during migration, and unsaturated fatty acids are preferentially mobilized and oxidized, making them good fuel. Twenty and 22 carbon n-3 and n-6 polyunsaturated fatty acids (PUFA) may affect membrane function and peroxisome proliferator-activated receptor signaling. However, evidence for dietary PUFA as doping agents in migratory birds is equivocal and requires further study.

Understanding variation in migratory movements: A mechanistic approach

Spatial and temporal fluctuations in resource availability have led to the evolution of varied migration patterns. In order to appropriately time movements in relation to resources, environmental cues are used to provide proximate information for timing and the endocrine system serves to integrate these external cues and behavioral and physiological responses. Yet, the regulatory mechanisms underlying migratory timing have rarely been compared across a broad range of migratory patterns. First, we offer an updated nomenclature of migration using a mechanistic perspective to clarify terminology describing migratory types in relation to ecology, behavior and endocrinology. We divide migratory patterns into three types: obligate, nomadic, and fugitive. Obligate migration is characterized by regular and directed annual movements between locations, most commonly for breeding and overwintering, where resources are predictable and sufficient. Nomadic migrations occur less predictably than do obligate migrations as animals make use of potentially rich but ephemeral resources that occur unpredictably in space or time. Fugitive migrations move animals away from an area in response to severe disruption of environmental conditions and occur as part of an emergency life history stage. We also consider partially migratory populations, which include a mix of sedentary and migratory individuals; the movement patterns of partial migrants are expected to fall into one of the three types above. For these various forms of migration, we review our understanding of the environmental cues and endocrine mechanisms that underlie the expression of a migratory state. Several common hormonal mechanisms exist across the varied migratory forms, but there are also important areas where further investigations are needed in order to gain broad insight into the origin of movements and the diversity of migratory patterns. We propose that taking a comparative approach across the migratory types that considers endocrine mechanisms will advance a new understanding of migration biology.

The physiological and neuroendocrine correlates of hunger in the Red Junglefowl (Gallus gallus)

The ability to regulate food intake is critical to survival. The hypothalamus is central to this regulation, integrating peripheral signals of energy availability. Although our understanding of hunger in rodents is advanced, an equivalent understanding in birds is lacking. In particular, the relationship between peripheral energy indices and hypothalamic 'hunger' peptides, agouti-related protein (AgRP), pro-opiomelanocortin (POMC) and neuropeptide Y (NPY) is poorly understood. Here, we compare AgRP, POMC and NPY RNA levels in the hypothalamus of Red Junglefowl chicks raised under ad libitum, chronic restriction and intermittent feeding regimens. Hypothalamic gene expression differed between chronically and intermittently restricted birds, confirming that different restriction regimens elicit different patterns of hunger. By assessing the relationship between hypothalamic gene expression and carcass traits, we show for the first time in birds that AgRP and POMC are responsive to fat-related measures and therefore represent long-term energy status. Chronically restricted birds, having lower indices of fat, show elevated hunger according to AgRP and POMC. NPY was elevated in intermittently fasted birds during fasting, suggesting a role as a short-term index of hunger. The different physiological and neuroendocrine responses to quantitative versus temporal feed restriction provide novel insights into the divergent roles of avian hunger neuropeptides.

Endogenous Nitric Oxide and Dopamine Regulate Feeding Behavior in Neonatal Layer-type Chickens

Evidence from animal studies suggests that endogenous nitric oxide and dopamine (DA) have a regulatory role in the rewarding system, but their interaction(s) have not been studied in avian species. In this study, 4 experiments were performed to determine the effects of central administration of L-arginine (nitric oxide precursor; 200 nmol), NG-nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor; 100 nmol), amphetamine (an indirect DA agonist; 125 pmol) and DA (40 pmol) on feeding behavior in neonatal layer-type chickens (each experiment included 4 groups, n=12 birds in each group). Prior to the initiation of the treatments, birds were fasted for 3 hours (FD3). In experiment 1, chickens received intracerebroventricular (ICV) injection of saline, L-NAME (100 nmol), amphetamine (125 pmol), and combination of L-NAME + amphetamine. In experiment 2, chickens received the ICV injection of saline, L-arginine (200 nmol), amphetamine (125 pmol) and their combination. In experiment 3, chickens received ICV injection of saline, L-arginine (200 nmol), DA (40 pmol) and L-arginine + DA. In experiment 4, chickens received ICV injection of saline, L-NAME (100 nmol), DA (40 pmol) and L-NAME + DA. Thereafter, the cumulative food intake (on the basis of metabolic body weight) was recorded until 2-h post injection. The results showed that ICV injection of amphetamine or DA significantly decreased food intake (P<0.05). Also, co-administration of L-NAME + amphetamine attenuated the hypophagic effect of amphetamine (P<0.05), while combined administration of L-NAME and DA had no effect on DA-induced hypophagia. Additionally, the hypophagic effect of amphetamine was significantly amplified by L-arginine (P<0.05), but the combination of L-arginine and DA did not alter feeding behavior which was induced by DA. These results suggest an interaction between DAergic and nitrergic systems via a presynaptic mechanism on food intake regulation in layer-type chicken.

Modification of feeding circuits in the evolution of social behavior

Adaptive trade-offs between foraging and social behavior intuitively explain many aspects of individual decision-making. Given the intimate connection between social behavior and feeding/foraging at the behavioral level, we propose that social behaviors are linked to foraging on a mechanistic level, and that modifications of feeding circuits are crucial in the evolution of complex social behaviors. In this Review, we first highlight the overlap between mechanisms underlying foraging and parental care and then expand this argument to consider the manipulation of feeding-related pathways in the evolution of other complex social behaviors. We include examples from diverse taxa to highlight that the independent evolution of complex social behaviors is a variation on the theme of feeding circuit modification.

Glucocorticoids induced high fat diet preference via activating hypothalamic AMPK signaling in chicks

Glucocorticoids (GCs) stimulate appetite, contributing to enhanced fat deposition. Our present study was conducted to determine whether GCs could evoke an appetite specifically for fat-rich diets in chicks. Chicks were subjected to a subcutaneous injection of corticosterone (CORT, 2mg/kg body weight/day) or corn oil (control), and food preference was tested. The results showed that CORT-chicks consumed more high-fat diet (HFD) compared with controls. In HFD-fed chicks, hypothalamic phosphorylated AMP-activated protein kinase α (AMPKα) and neuropeptide Y (NPY) mRNA levels were increased by CORT treatment. Activating AMPK with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside, an AMPK activator, via intracerebroventricular injection further enhanced the CORT-induced HFD consumption and concurrently up-regulated NPY mRNA levels and phosphorylated AMPKα and acetyl-coenzyme A carboxylase levels. The dramatic increase in HFD consumption and upregulation of NPY mRNA levels and phospho-AMPKα levels induced by peripheral CORT injection was not altered by intracerebroventricular infusion of compound C (4-16μg), an AMPK inhibitor. In conclusion, CORT challenge caused a HFD preference by enhancing the AMPK pathway in the hypothalamus.

Influence of leptin and GABAB-receptor agonist and antagonist on neurons of the hypothalamic infundibular nucleus in the chicken

In birds and mammals, the neuroendocrine regulation of energy balance is conserved in many aspects. Despite significant similarities between the two groups, differences in the regulatory mechanisms were detected. The present study was performed to carry out investigations of the influence of human leptin and GABA_B-receptor agonist and antagonist on the firing rate of neurons of the Nucleus infundibuli hypothalami in brain slices from juvenile chickens. For the first time, we demonstrated a clear, dose-related change in the firing rate of hypothalamic neurons in juvenile chickens after the acute application of recombinant human leptin (1, 10, and 100 nM). All investigated neurons increased their subsequent firing rate. Application of GABA_B-receptor agonist baclofen (1 µM) blocked, while antagonist CGP 35348 (10 µM) increased the spontaneous neuronal activity. Simultaneous application of baclofen and leptin reduced the effect observed from single leptin application. This was not found after simultaneously application of leptin and CGP. Altogether, our results indicate that in bird brain slices, and exemplarily in those of the chicken, hypothalamic neurons show mammalian-like responsiveness after acute leptin and GABA application. GABA_B-mechanisms involved in GABA release play a likely important role in the leptin-mediated effects on NI neurons via functional leptin receptors.

Changes in brain peptides associated with reproduction and energy homeostasis in photosensitive and photorefractory migratory redheaded buntings

Present study examined the expression of brain peptides associated with the reproduction and energy homeostasis (GnRH/GnIH, NPY/VIP), and assessed their possible functional association in the photosensitive (non-breeding, pre-breeding), photostimulated (breeding) and photorefractory (post-breeding) migratory redheaded buntings (Emberiza bruniceps), using double-labeled immunohistochemistry. Particularly, we measured immunoreactive (-ir) cell numbers, per cent cell area and cell optical density (OD) in the preoptic area (GnRH-I), midbrain (GnRH-II), paraventricular nucleus (GnIH), dorsomedial hypothalamus, DMH and infundibular complex, INc (NPY and VIP), and lateral septal organ (VIP) of buntings kept under natural photoperiods at the wintering latitude (26°55'N). There was a significant seasonal difference in GnRH-I, not GnRH-II, with reduced -ir cells in the photosensitive and photorefractory buntings, and notably with increased cell OD between the refractory and non-breeding states with no increase in testis size. Also, increased cell OD of GnIH neurons in non-breeding state indicated its role in the maintenance of small testes during the post-refractory period. Overall, seasonal changes in GnRH-I and GnIH were found consistent with their suggested roles in reproductive regulation of absolute photorefractory birds. Further, there was a significant seasonal change in cell OD of NPY neurons in DMH, not the INc. In contrast, VIP immunoreactivity was seasonally altered, with a significantly higher VIP-ir cells in breeding than the pre-breeding state. Finally, close proximity between perikarya with fibres suggested functional interactions between the GnRH and GnIH, and NPY and VIP. Thus, seasonal plasticity of brain peptides is perhaps the part of neural regulation of seasonal reproduction and associated energy homeostasis in migratory songbirds.

Effect of dexamethasone on hypothalamic expression of appetite-related genes in chickens under different diet and feeding conditions

BACKGROUND

Glucocorticoids (GCs) are involved in the control of appetite in birds and mammals. The effect of GCs on feed intake in birds depends on their dietary energy level. But the regulation mechanism of GCs on appetite is still unclear in chickens facing to different energy level. An experiment was conducted to investigate the effect of dexamethasone (DEX) on hypothalamic expression of appetite-related peptides in chickens fed high/low fat diet and under fasting/feeding condition.

RESULTS

An interaction between DEX injection and dietary energy level was found on hypothalamic corticotropin-releasing hormone (CRH) gene expression in fasted chickens (P < 0.05). The chickens, given a DEX injection and a low fat diet treatment, had the highest CRH mRNA levels than any of the fasted chickens given treatments (P < 0.05). Under fasting conditions, the DEX treatment significantly increased hypothalamic neuropeptide Y (NPY) and GC receptors mRNA levels (P < 0.05). Under re-feeding conditions, DEX treatment significantly decreased hypothalamic expression levels of NPY and agouti-related peptide (AgRP) but significantly increased the level of hypothalamic CRH expression (P < 0.05).

CONCLUSION

A regulatory network formed by NPY, AgRP and CRH is associated with the appetite-control by GCs. The result suggests that the regulation of GCs on orexigenic neuropeptides expression is dependent at least partially on dietary energy level and feeding state.

Developmental expression of Kv1 voltage-gated potassium channels in the avian hypothalamus

Specialized hypothalamic neurons integrate the homeostatic balance between food intake and energy expenditure, processes that may become dysregulated during the development of diabetes, obesity, and other metabolic disorders. Shaker family voltage-gated potassium channels (Kv1) contribute to the maintenance of resting membrane potential, action potential characteristics, and neurotransmitter release in many populations of neurons, although hypothalamic Kv1 channel expression has been largely unexplored. Whole-cell patch clamp recordings from avian hypothalamic brain slices demonstrate a developmental shift in the electrophysiological properties of avian arcuate nucleus neurons, identifying an increase in outward ionic current that corresponds with action potential maturation. Additionally, RT-PCR experiments identified the early expression of Kv1.2, Kv1.3, and Kv1.5 mRNA in the embryonic avian hypothalamus, suggesting that these channels may underlie the electrophysiological changes observed in these neurons. Real-time quantitative PCR analysis on intact microdissections of embryonic hypothalamic tissue revealed a concomitant increase in Kv1.2 and Kv1.5 gene expression at key electrophysiological time points during development. This study is the first to demonstrate hypothalamic mRNA expression of Kv1 channels in developing avian embryos and may suggest a role for voltage-gated ion channel regulation in the physiological patterning of embryonic hypothalamic circuits governing energy homeostasis.

Peripheral Insulin Doesn't Alter Appetite of Broiler Chicks

An experiment was conducted to investigate the effect of peripheral insulin treatment on appetite in chicks. Six-d-age chicks with ad libitum feeding or fasting for 3 h before injection received a subcutaneous injection of 0, 1, 3, 5, 10, or 20 IU of insulin or vehicle (saline). The results showed peripheral insulin treatment (1 to 20 IU) did not alter significantly the feed intake in chicks under either ad libitum feeding or fasting conditions within 4 h (p>0.05). Compared with the control, plasma glucose concentration was significantly decreased after insulin treatment of 3, 5, 10, and 20 IU for 4 h in chicks with ad libitum feeding (p<0.05). In fasted chicks, 10 and 20 IU insulin treatments significantly decreased the plasma glucose level for 4 h (p<0.05). Peripheral insulin treatment of 10 IU for 2 or 4 h did not significantly affect the hypothalamic genes expression of neuropeptide Y, proopiomelanocortin, corticotropin-releasing factor and insulin receptors (p>0.05). All results suggest peripheral administration of insulin has no effect on appetite in chicks.

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

Recently, methylamine has been found as an endogenous amine, which is controlling food intake in mammals. However, there is no evidence about the effect of methylamine on feeding behavior in poultry. So, the present study was designed to evaluate the effect of intracerebroventricular (ICV) injection of methylamine and involvement of central methylamine/dopaminergic systems on feeding behavior in neonatal meat type chicks. In experiment 1, chicks were ICV injected with different doses of methylamine (0.48, 0.96, 1.44, 1.92 and 2.40 μmol). In experiment 2, chicks received a dose of either the control solution, 2.40 μmol methylamine, 125 nmol L-DOPA (dopamine precursor) or a combination of methylamine plus L-DOPA. Experiments 3-7 were similar to experiment 2 except that 150 nmol 6-OHDA (dopamine synthase inhibitor), 5 nmol SCH23390 (D1 receptor antagonist), 5 nmol AMI-193 (D2 receptor antagonist), 6.4 nmol NGB2904 (D3 receptor antagonist) and 6 nmol L-741, 742 (D4 receptor antagonist) were used instead of 125 nmol L-DOPA, respectively. Cumulative food intake was determined until 2 h post-injection. According to the results, methylamine significantly decreased food intake in a dose dependent manner (p < 0.05). The inhibitory effect of methylamine on food intake was significantly attenuated by 6-OHDA, SCH23390 and AMI-193 (P < 0.05), but NGB2904 and L-741, 742 had no effect on food intake induced by methylamine. In addition, hypophagic effect of methylamine significantly amplified by L-DOPA (P < 0.05). These results suggest that methylamine decrease food intake and there is an interaction between methylamine and dopaminergic system via D1 and D2 receptors in chickens.

Acquired alterations of hypothalamic gene expression of insulin and leptin receptors and glucose transporters in prenatally high-glucose exposed three-week old chickens do not coincide with aberrant promoter DNA methylation

Background

Prenatal exposures may have a distinct impact for long-term health, one example being exposure to maternal ‘diabesity’ during pregnancy increasing offspring ‘diabesity’ risk. Malprogramming of the central nervous regulation of body weight, food intake and metabolism has been identified as a critical mechanism. While concrete disrupting factors still remain unclear, growing focus on acquired epigenomic alterations have been proposed. Due to the independent development from the mother, the chicken embryo provides a valuable model to distinctively establish causal factors and mechanisms.

Aim

The aim of this study was to determine the effects of prenatal hyperglycemia on postnatal hypothalamic gene expression and promoter DNA methylation in the chicken.

Methods and Findings

To temporarily induce high-glucose exposure in chicken embryos, 0.5 ml glucose solution (30 mmol/l) were administered daily via catheter into a vessel of the chorioallantoic egg membrane from days 14 to 17 of incubation. At three weeks of postnatal age, body weight, total body fat, blood glucose, mRNA expression (INSR, LEPR, GLUT1, GLUT3) as well as corresponding promoter DNA methylation were determined in mediobasal hypothalamic brain slices (Nucleus infundibuli hypothalami). Although no significant changes in morphometric and metabolic parameters were detected, strongly decreased mRNA expression occurred in all candidate genes. Surprisingly, however, no relevant alterations were observed in respective promoter methylation.

Conclusion

Prenatal hyperglycemia induces strong changes in later hypothalamic expression of INSR, LEPR, GLUT1, and GLUT3 mRNA. While the chicken provides an interesting approach for developmental malprogramming, the classical expression regulation via promoter methylation was not observed here. This may be due to alternative/interacting brain mechanisms or the thus far under-explored bird epigenome.

Modulation of opioid-induced feeding behavior by endogenous nitric oxide in neonatal layer-type chicks

The current study was designed to evaluate the effects of central administration of L-arginine (The precursor of nitric oxide), N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, selective opioid receptor agonists and involvement of central nitrergic/opioidergic systems on feeding behavior in neonatal layer-type chicks. The results of this study showed that the intracerebroventricular (ICV) injection of L-arginine (400 and 800 nmol) significantly decreased food intake (P < 0.001) but the injection of 200 nmol L-arginine had no effect on cumulative food intake in FD3 chickens (P > 0.05). The ICV injection of L-NAME (200 and 400 nmol) increased food intake (P < 0.001) but 100 nmol of L-NAME had no significant effect (P > 0.05). On the other hand, the co-injection of 100 nmol L-NAME significantly attenuated the anorexigenic effect of 800 nmol L-arginine (P < 0.001). Moreover, the food intake of chicks was significantly decreased by ICV injection of DAMGO (μ-opioid receptor agonist, 125 pmol) (P < 0.001) while both DPDPE (δ-opioid receptor agonist, 40 pmol) and U-50488H (κ-opioid receptor agonist, 30 nmol) significantly stimulated food intake (P < 0.001). In addition, the hypophagic effect of DAMGO was significantly amplified by administration of L-arginine (P < 0.001) while the administration of L-NAME attenuated the hypophagic effect of DAMGO (P < 0.001). In contrast, co-injection of L-arginine or L-NAME with DPDPE had no effect on the hyperphagia induced by DPDPE as well as the hyperphagic effect of U-50488H on food intake was not affected by concurrent injection of L-arginine or L-NAME (P > 0.05). These results suggest that nitrergic and opioidergic systems have an important role on feeding behavior in the CNS of neonatal layer-type chicks and it seems that interaction between them is mediated by μ-opioid receptor.

Glucocorticoids increase NPY gene expression via hypothalamic AMPK signaling in broiler chicks

Glucocorticoids (GCs) induce profound hyperphagia in birds. However, the neuronal regulatory network underlying GC-provoked hyperphagia is unclear. To determine whether any cross talk occurs among hypothalamic GC receptors (GRs), AMP-activated protein kinase (AMPK), and GCs in the regulation of appetite, we performed an intracerebroventricular injection of mifepristone (a GR inhibitor) and compound C (an AMPK inhibitor) on GC-treated male chicks. The results indicate that central GC administration increased the expression of GR and neuropeptide Y mRNA, as well as phosphorylated AMPKα(Thr172) and acetyl-coenzyme A carboxylase(Ser79). Blocking AMPK significantly attenuated GC-induced hyperphagia. Blocking GR significantly attenuated part of the AMPK signaling pathway and GC-induced hyperphagia. Thus, the results suggest that GCs cause hyperphagia via the AMPK-neuropeptide Y signaling pathway.

Neural correlates of migration: activation of hypothalamic clock(s) in and out of migratory state in the blackheaded bunting (Emberiza melanocephala)

BACKGROUND

Many vertebrates distinguish between short and long day lengths using suprachiasmatic nuclei (SCN). In birds particular, the mediobasal hypothalamus (MBH) is suggested to be involved in the timing of seasonal reproduction. This study investigated the response of SCN and MBH to a single long day, and the role of MBH in induction of the migratory phenotype in night-migratory blackheaded buntings.

METHODOLOGY/PRINCIPAL FINDINGS

Experiment 1 immunocytochemically measured c-fos in the SCN, and c-fos, vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) in the MBH of buntings exposed to a 20 h light period. Long light period induced significantly stronger c-fos expression, measured as number of c-fos-like immunoreactive (c-fos-lir) cells, in MBH, but not in the SCN. Within the MBH, c-fos-lir cells were significantly denser in the inferior hypothalamic nucleus (IH) and infundibular nucleus (IN), but not in the dorsomedial hypothalamus (DMH). IH and IN also had significantly increased number of VIP and NPY labeled cells. DMH had significantly increased number of VIP labeled cells only. Experiment 2 assayed c-fos, VIP and NPY immunoreactivities in the middle of day and night in the MBH of buntings, after seven long days (day active, non-migratory state) and after seven days of Zugunruhe (night active, migratory state) in long days. In the migratory state, the number of c-fos-lir cells was significantly greater only in DMH; VIP-lir cells were denser in all three MBH regions suggesting enhanced light sensitivity at night. The denser NPY-lir cells only in IN in the non-migratory state were probably due to premigratory hyperphagia.

CONCLUSIONS/SIGNIFICANCE

In buntings, SCN may not be involved in the photoperiod-induced seasonal responses. MBH contains the seasonal clock sensitive to day length. VIP and NPY are parts of the neuroendocrine mechanism(s) involved, respectively, in sensing and translating the photoperiodic message in a seasonal response.

Reproductive neuropeptides: prevalence of GnRH and KNDy neural signalling components in a model avian, gallus gallus

Diverse external and internal environmental factors are integrated in the hypothalamus to regulate the reproductive system. This is mediated through the pulsatile secretion of GnRH into the portal system to stimulate pituitary gonadotrophin secretion, which in turn regulates gonadal function. A single subpopulation of neurones termed 'KNDy neurones' located in the hypothalamic arcuate nucleus co-localise kisspeptin (Kiss), neurokinin B (NKB) and dynorphin (Dyn) and are responsive to negative feedback effects of sex steroids. The co-ordinated secretion from KNDy neurones appears to modulate the pulsatile release of GnRH, acting as a proximate pacemaker. This review briefly describes the neuropeptidergic control of reproduction in the avian class, highlighting the status of reproductive neuropeptide signalling systems homologous to those found in mammalian genomes. Genes encoding the GnRH system are complete in the chicken with similar roles to the mammalian counterparts, whereas genes encoding Kiss signalling components appear missing in the avian lineage, indicating a differing set of hypothalamic signals controlling avian reproduction. Gene sequences encoding both NKB and Dyn signalling components are present in the chicken genome, but expression analysis and functional studies remain to be completed. The focus of this article is to describe the avian complement of neuropeptidergic reproductive hormones and provide insights into the putative mechanisms that regulate reproduction in birds. These postulations highlight differences in reproductive strategies of birds in terms of gonadal steroid feedback systems, integration of metabolic signals and seasonality. Also included are propositions of KNDy neuropeptide gene silencing and plasticity in utilisation of these neuropeptides during avian evolution.

Decreased expression of the satiety signal receptor CCKAR is responsible for increased growth and body weight during the domestication of chickens

Animal domestication has resulted in changes in growth and size. It has been suggested that this may have involved selection for differences in appetite. Divergent growth between chickens selected for egg laying or meat production is one such example. The neurons expressing AGRP and POMC in the basal hypothalamus are important components of appetite regulation, as are the satiety feedback pathways that carry information from the intestine, including CCK and its receptor CCKAR (CCK1 receptor). Using 16 generations of a cross between a fast and a relatively slow growing strain of chicken has identified a region on chromosome 4 downstream of the CCKAR gene, which is responsible for up to a 19% difference in body weight at 12 wk of age. Animals possessing the high-growth haplotype at the locus have lower expression of mRNA and immunoreactive CCKAR in the brain, intestine, and exocrine organs, which is correlated with increased levels of orexigenic AGRP in the hypothalamus. Animals with the high-growth haplotype are resistant to the anorectic effect of exogenously administered CCK, suggesting that their satiety set point has been altered. Comparison with traditional breeds shows that the high-growth haplotype has been present in the founders of modern meat-type strains and may have been selected early in domestication. This is the first dissection of the physiological consequences of a genetic locus for a quantitative trait that alters appetite and gives us an insight into the domestication of animals. This will allow elucidation of how differences in appetite occur in birds and also mammals.

Alpha-melanocyte stimulating hormone plays an important role in the regulation of food intake by the central melanocortin system in chicks

Proopiomelanocortin (POMC, a precursor of melanocortin peptides) neurons in the hypothalamus play an important role in the central regulation of food intake in mammals. There is evidence that human melanocortin peptides alpha-, beta- and gamma2-melanocyte-stimulating hormone (α-, β- and γ2-MSH) significantly decreased food intake in chickens. However, the amino acid sequences of β- and γ2-MSH of chickens are different from those of humans whereas the amino acid sequence of α-MSH is conserved between these species. In the present study, we examined the effects of the central administration of α-, chicken β-, and chicken γ2-MSH on food intake in chicks. Central administration of α-MSH significantly suppressed food intake in chicks. In contrast, β- and γ2-MSH did not influence food intake in chicks. Central administration of HS014, a melanocortin 4 receptor antagonist, significantly reversed the anorexigenic action of α-MSH, suggesting that this action is mediated by the melanocortin 4 receptor in chicks as well as in mammals. These results suggest that α-MSH may play an important role in the regulation of food intake by the central melanocortin system in chicks.

Comparisons of insulin related parameters in commercial-type chicks: Evidence for insulin resistance in broiler chicks

The aim of this study is to elucidate whether insulin acts differentially within the central nervous system (CNS) of two types of commercial chicks to control ingestive behavior. Male layer and broiler chicks (4-day-old) were intracerebroventricularly (ICV) injected with saline or insulin under satiated and starved conditions. Feed intake was measured at 30, 60 and 120 min after treatment. Secondly, blood and hypothalamus were collected from both chick types under ad libitum feeding and fasting for 24 h. Plasma insulin concentration was measured by time-resolved fluoro-immunoassay. Hypothalamic insulin receptor mRNA expression levels were measured by quantitative RT-PCR. The ICV injection of insulin significantly inhibited feed consumption in layer chicks when compared with saline (P<0.05), but not broiler chicks (P>0.1). Plasma insulin concentration of both chick types significantly decreased following 24 h of fasting, while insulin concentrations in the broiler chicks were significantly higher compared to the layers fed under ad libitum conditions. Hypothalamic insulin receptor mRNA expression levels were significantly lower (P<0.05) in broiler chicks than in layer ones under ad libitum feeding. Feed deprivation significantly decreased insulin receptor mRNA levels in layer chicks (P<0.01), but not in broiler chicks (P>0.1). Moreover, plasma insulin concentrations correlated negatively with hypothalamic insulin receptor protein expression in the two types of chicks fed ad libitum (P<0.05). These results suggest that insulin resistance exists in the CNS of broiler chicks, possibly due to persistent hyperinsulinemia, which results in a down-regulation of CNS insulin receptor expression compared to that in layer chicks.

Transcriptional and pathway analysis in the hypothalamus of newly hatched chicks during fasting and delayed feeding

Background

The hypothalamus plays a central role in regulating appetite and metabolism. However, the gene networks within the hypothalamus that regulate feed intake and metabolism, and the effects of fasting on those pathways are not completely understood in any species. The present experiment evaluated global hypothalamic gene expression in newly hatched chicks using microarray analysis to elucidate genes and pathways regulated by feeding, fasting, and delayed feeding. Ten groups of chicks were sampled over four days post-hatch, including fed, fasted, and 48 h fasted followed by access to feed for 4 h, 24 h, and 48 h. Hypothalamic samples were collected for microarray analysis (n = 4). Expression patterns of selected genes were confirmed by quantitative real-time PCR. Pathway analysis of the microarray results predicted a network of genes involved in neuropeptide or neurotransmitter signaling. To confirm the functionality of this predicted gene network, hypothalamic neurons from fed and fasted chicks were isolated and cultured in the presence of neuropeptide Y, somatostatin, α-melanocyte stimulating hormone, norepinephrine, and L-phospho-serine. Results confirmed functional relationships among members of the predicted gene network. Moreover, the effects observed were dependant upon the nutritional state of the animals (fed vs. fasted).

Results

Differences in gene expression (≥ 1.6 fold) were detected in 1,272 genes between treatments, and of those, 119 genes were significantly (P < 0.05) different. Pathway Miner analysis revealed that six genes (SSTR5, NPY5R, POMC, ADRB2, GRM8, and RLN3) were associated within a gene network. In vitro experiments with primary hypothalamic neurons confirmed that receptor agonists involved in this network regulated expression of other genes in the predicted network, and this regulation within the network was influenced by the nutritional status and age of the chick.

Conclusions

Microarray analysis of the hypothalamus during different nutritional states revealed that many genes are differentially regulated. We found that functional interactions exist among six differentially regulated genes associated within a putative gene network from this experiment. Considering that POMC, an important gene in controlling metabolism, was central to this network, this gene network may play an important role in regulation of feeding and metabolism in birds.

Corticotropin-releasing factor is a downstream mediator of the beta-melanocyte-stimulating hormone-induced anorexigenic pathway in chicks

Proopiomelanocortin (POMC, a precursor of anorexigenic neuropeptides) neurons in hypothalamus suppresses food intake in both mammals and chickens. In mammals, several lines of evidence suggest that POMC-derived anorexigenic peptides upregulate mRNA levels of anorexigenic peptides such as corticotropin-releasing factor (CRF) and thyrotropin-releasing factor and downregulate mRNA levels of orexigenic peptides such as orexin and melanin-concentrating hormone. However, the POMC-induced anorexigenic pathway in chickens has not been well characterized. In the present study, we investigated how POMC neurons regulate mechanisms of food intake using an anorexigenic peptide, beta-melanocyte-stimulating hormone (beta-MSH), derived from the post-transcriptional cleavage of POMC. Central administration of beta-MSH in chicks significantly suppressed food intake, and importantly, this suppression was accompanied by a significant upregulation of CRF mRNA levels. Furthermore, the CRF type 2 receptor antagonist alpha-helical CRF significantly reversed the anorexigenic action of beta-MSH. These findings indicate that CRF and its receptor, CRF type 2 receptor, act as the major mediators in beta-MSH-induced anorexigenic action in chicks. beta-MSH significantly increased orexin mRNA levels and did not alter mRNA levels of thyrotropin-releasing factor and melanin-concentrating hormone in chicks, suggesting that the beta-MSH-induced anorexigenic pathway in chicks is different from that in mammals. Increases in orexin mRNA levels were accompanied by significant decreases in plasma glucose concentration, suggesting that orexin mRNA might be stimulated by beta-MSH-induced hypoglycemia. Thus, this study demonstrates the direct evidence that CRF is a critical downstream target in the beta-MSH-induced anorexigenic pathway in chicks.

Circulating prolactin and corticosterone concentrations during the development of migratory condition in the Dark-eyed Junco, Junco hyemalis

Endogenous plasma prolactin and baseline corticosterone concentrations were measured in Dark-eyed Juncos (Junco hyemalis, n=27) photostimulated into migratory condition to look at how these hormones may be linked to the development of migratory condition. In addition to the commonly used assay for corticosterone, a recombinant-derived European starling prolactin assay validated for Dark-eyed juncos was used to measure endogenous prolactin in order to detect small but significant changes in plasma prolactin levels. In response to transfer from short (10.5L:13.5D) to long (18L:6D) days, the birds increased in body mass, fat score, daily food intake, and nocturnal migratory locomotor activity (Zugunruhe). On short-days, both hormones were low (corticosterone mean=2.89ng/mL+/-0.48 SE; prolactin mean=6.43ng/mL+/-1.31 SE). But, within 14 days of photostimulation both hormones increased significantly (Day 14: corticosterone mean=5.71ng/mL+/-0.77 SE; prolactin mean=19.67ng/mL+/-2.81 SE), rising further by Day 48 (corticosterone mean=8.41ng/mL+/-0.72; prolactin mean=112.67ng/mL+/-9.18 SE). On Day 48, birds with the most fat (fat score=3) had significantly higher corticosterone levels than those with less fat (fat score=2). This pattern, albeit not statistically significant, was similar for prolactin. These results illustrate that, independent of the seasonal peak in prolactin associated with the onset of photorefractoriness, plasma prolactin levels can rise, in concert with corticosterone, as birds come into spring migratory condition, providing some support for earlier hypotheses that these two hormones play an integral role in the development of migratory condition. Whether similar changes in plasma prolactin occur with respect to autumn migration, as does baseline corticosterone, has yet to be determined.

Type-dependent differential expression of neuropeptide Y in chicken hypothalamus (Gallus domesticus)

Neuropeptide Y (NPY) is one of the most important orexigenic agents in central regulation of feeding behavior, body weight and energy homeostasis in domestic chickens. To examine differences in the hypothalamic NPY between layer-type and meat-type of chickens, which are two divergent kinds of the domestic chickens in feeding behavior and body weight, we detected mRNA levels of NPY in hypothalamic infundibular nucleus (IN), paraventricular nucleus (PVN) and lateral hypothalamic area (LHA) of these two types of chickens using one-step real time RT-PCR. The meat-type chicken had more food daily (about 1.7 folds) and greater body weights (about 1.5 folds) and brain weights than the layer-type chicken at the age of 14 d. In the meat-type of chicken, NPY mRNA levels of the IN and PVN were significantly greater than those of the LHA, and were not significantly different between the IN and PVN. However, in the layer-type of chicken, NPY mRNA levels were significantly greater in the IN than those in the LHA and PVN, and were not significantly different between the PVN and LHA. In all these hypothalamic regions, the layer-type of chicken had significantly higher NPY mRNA levels than the meat-type chicken did. These results suggest the expression of NPY in the hypothalamus has a type-dependent pattern in domestic chickens.