The interaction of bombesin and corticotropin-releasing hormone on ingestive behavior in the domestic fowl

Hypothalamic mechanism of corticotropin-releasing factor's anorexigenic effect in Japanese quail (Coturnix japonica)

Central administration of corticotropin-releasing factor (CRF), a 41-amino acid peptide, is associated with anorexigenic effects across various species, with particularly potent reductions in food intake in rodents and chickens (Gallus gallus domesticus), a species for which the most is known. The purpose of the current study was to determine the hypothalamic mechanism of CRF-induced anorexigenic effects in 7 day-old Japanese quail (Coturnix japonica), a less-intensely-selected gallinaceous relative to the chicken that can provide more evolutionary perspective. After intracerebroventricular (ICV) injection of 2, 22, or 222 pmol of CRF, a dose-dependent decrease in food intake was observed that lasted for 3 and 24 h for the 22 and 222 pmol doses, respectively. The 2 pmol dose had no effect on food or water intake. The numbers of c-Fos immunoreactive cells were increased in the paraventricular nucleus (PVN) and lateral hypothalamic area (LHA) at 1 h post-injection in quail injected with 22 pmol of CRF. The hypothalamic mRNA abundance of proopiomelanocortin, melanocortin receptor subtype 4, CRF, and CRF receptor sub-type 2 was increased at 1 h in quail treated with 22 pmol of CRF. Behavior analyses demonstrated that CRF injection reduced feeding pecks and jumps and increased the time spent standing. In conclusion, results demonstrate that the anorexigenic effects of CRF in Japanese quail are likely influenced by the interaction between CRF and melanocortin systems and that injection of CRF results in species-specific behavioral changes.

Glucagon-related peptides and the regulation of food intake in chickens

The regulatory mechanisms underlying food intake in chickens have been a focus of research in recent decades to improve production efficiency when raising chickens. Lines of evidence have revealed that a number of brain‐gut peptides function as a neurotransmitter or peripheral satiety hormone in the regulation of food intake both in mammals and chickens. Glucagon, a 29 amino acid peptide hormone, has long been known to play important roles in maintaining glucose homeostasis in mammals and birds. However, the glucagon gene encodes various peptides that are produced by tissue‐specific proglucagon processing: glucagon is produced in the pancreas, whereas oxyntomodulin (OXM), glucagon‐like peptide (GLP)‐1 and GLP‐2 are produced in the intestine and brain. Better understanding of the roles of these peptides in the regulation of energy homeostasis has led to various physiological roles being proposed in mammals. For example, GLP‐1 functions as an anorexigenic neurotransmitter in the brain and as a postprandial satiety hormone in the peripheral circulation. There is evidence that OXM and GLP‐2 also induce anorexia in mammals. Therefore, it is possible that the brain‐gut peptides OXM, GLP‐1 and GLP‐2 play physiological roles in the regulation of food intake in chickens. More recently, a novel GLP and its specific receptor were identified in the chicken brain. This review summarizes current knowledge about the role of glucagon‐related peptides in the regulation of food intake in chickens.

Intracerebroventricular administration of novel glucagon-like peptide suppresses food intake in chicks

Glucagon-related peptides such as glucagon, glucagon-like peptide-1, and oxyntomodulin suppress food intake in mammals and birds. Recently, novel glucagon-like peptide (GCGL) was identified from chicken brain, and a comparatively high mRNA expression level of GCGL was detected in the hypothalamus. A number of studies suggest that the hypothalamus plays a critical role in the regulation of food intake in mammals and birds. In the present study, we investigated whether GCGL is involved in the central regulation of food intake in chicks. Male 8-day-old chicks (Gallus gallus) were used in all experiments. Intracerebroventricular administration of GCGL in chicks significantly suppressed food intake. Plasma glucose level was significantly decreased by GCGL, whereas plasma corticosterone level was not affected. Central administration of a corticotrophin-releasing factor (CRF) receptor antagonist, α-helical CRF, attenuated GCGL-suppressed food intake. It seems likely that CRF receptor is involved in the GCGL-induced anorexigenic pathway. All our findings suggest that GCGL functions as an anorexigenic peptide in the central nervous system of chicks.

The mechanism underlying the central glucagon-induced hyperglycemia and anorexia in chicks

We investigated the mechanism underlying central glucagon-induced hyperglycemia and anorexia in chicks. Male 8-day-old chicks (Gallus gallus) were used in all experiments. Intracerebroventricular administration of glucagon in chicks induced hyperglycemia and anorexia from 30 min after administration. However, the plasma insulin level did not increase until 90 min after glucagon administration, suggesting that glucose-stimulated insulin secretion from pancreatic beta cells may be suppressed by central glucagon. The plasma corticosterone concentration significantly increased from 30 min to 120 min after administration, suggesting that central glucagon activates the hypothalamic pituitary adrenal (HPA) axis in chicks. However, central administration of corticotropin-releasing factor (CRF), which activates the HPA axis in chicken hypothalamus, significantly reduced not only food intake but also plasma glucose concentration, suggesting that CRF and the activation of the HPA axis are related to the glucagon-induced anorexia but not hyperglycemia in chicks. Phentolamine, an α-adrenergic receptor antagonist, significantly attenuated the glucagon-induced hyperglycemia, suggesting that glucagon induced hyperglycemia at least partly via α-adrenergic neural pathway. Co-administration of phentolamine and α-helical CRF, a CRF receptor antagonist, significantly attenuated glucagon-induced hyperglycemia and anorexia. It is therefore likely that central administration of glucagon suppresses food intake at least partly via CRF-induced anorexigenic pathway in chicks.

The avian subpallium: new insights into structural and functional subdivisions occupying the lateral subpallial wall and their embryological origins

The subpallial region of the avian telencephalon contains neural systems whose functions are critical to the survival of individual vertebrates and their species. The subpallial neural structures can be grouped into five major functional systems, namely the dorsal somatomotor basal ganglia; ventral viscerolimbic basal ganglia; subpallial extended amygdala including the central and medial extended amygdala and bed nuclei of the stria terminalis; basal telencephalic cholinergic and non-cholinergic corticopetal systems; and septum. The paper provides an overview of the major developmental, neuroanatomical and functional characteristics of the first four of these neural systems, all of which belong to the lateral telencephalic wall. The review particularly focuses on new findings that have emerged since the identity, extent and terminology for the regions were considered by the Avian Brain Nomenclature Forum. New terminology is introduced as appropriate based on the new findings. The paper also addresses regional similarities and differences between birds and mammals, and notes areas where gaps in knowledge occur for birds.

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

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

Differential thresholds of neuromedins B-, C-, and bombesin-induced anorexia and crop-emptying rate in chicks

Neuromedin B (NMB) and neuromedin C (NMC) are homologs of bombesin and are distributed throughout both the brain and gastrointestinal tract. The physiological roles of these bombesin-like peptides in chicks (Gallus gallus) have not been documented. Therefore, the purpose of the present study was to measure the effects of these bombesin-like peptides on food intake, crop-emptying rate and body temperature in chicks, and then to compare these effects with those of bombesin. Intracerebroventricular (ICV, 5 nmol) and intraperitoneal (IP, 300 nmol/kg) injections of NMB, NMC, and bombesin significantly decreased food deprivation-induced food intake. When ICV injected (5 nmol), all three peptides significantly reduced crop-emptying rate. IP injection of NMC and bombesin (300 nmol/kg) also reduced crop-emptying rate while NMB did not. The magnitude of food intake suppression and crop-emptying rate reduction were greater for bombesin than NMB and NMC. ICV and IP injections of NMB, NMC and bombesin did not affect cloacal temperature. In sum, the present study suggests that central and peripheral NMB and NMC are associated with reduced food intake and crop-emptying of chicks, but these effects are weaker than those of bombesin.

Central and peripheral alytesin cause short-term anorexigenic effects in neonatal chicks

We studied the effects of alytesin, a natural analogue of bombesin, on appetite-related responses and behaviors in neonatal chicks. Chicks responded to both intracerebroventricular (ICV) and peripheral injections of alytesin with short-term reduced feed intake. ICV alytesin caused reduced short-term water intake when feed was present, but we determined this effect was secondary to feed intake since an effect on water intake was not detected in feed-restricted alytesin-treated chicks. The anorexigenic effect of both ICV and peripheral alytesin may be mediated at the hypothalamus, since all hypothalamic nuclei studied; regio lateralis hypothalami, nucleus dorsomedialis hypothalami, nucleus paraventricularis magnocellularis, nucleus perventricularis hypothalami, nucleus infundibuli hypothalami and the nucleus ventromedialis hypothalami, were activated as evident by increased c-Fos immunoreactivity. Central alytesin did not cause increased behaviors that were unrelated to ingestion and did not cause anxiety-related behavior patterns. Additionally, central alytesin did not affect pecking efficacy. We conclude that both ICV and peripheral alytesin injections induce anorexigenic effects in chicks, and the hypothalamus is involved. While the anorexigenic effects of alytesin and bombesin appear to be conserved across species, the two peptides may differ in other behavioral responses and central mechanisms of action.

Central administration of neuromedin U suppresses food intake in chicks

The appetite-suppressive action of brain-gut peptides is similar in both chickens and mammals. In mammals, the brain-gut peptide neuromedin U (NMU) suppresses food intake via hypothalamic neuropeptides, corticotropin-releasing factor (CRF), oxytocin, and arginine-vasopressin. In chickens, central administration of CRF, oxytocin, or arginine-vasotocin (AVT, a nonmammalian equivalent of arginine-vasopressin) suppresses food intake. However, the anorexigenic action of NMU in chickens has not yet been identified. In the present study, we analyzed the effects of the central administration of NMU on food intake and hypothalamic mRNA levels of CRF, AVT and mesotocin (a nonmammalian equivalent of oxytocin) in chicks. Intracerebroventricular administration of NMU in chicks significantly suppressed food intake and induced wing-flapping behavior. NMU also significantly upregulated mRNA expression of CRF and AVT, but did not influence mRNA expression of mesotocin in the hypothalamus. These results suggest that NMU functions as an appetite-suppressive peptide via CRF and AVT in the central nervous system in chicks.

Central administration of glucagon suppresses food intake in chicks

Food intake in chickens is regulated in a manner similar to that in mammals. Corticotropin-releasing factor (CRF), which increases the plasma corticosterone concentration, plays an important role as a mediator of many appetite-suppressive peptides in the central nervous system in both species. Central administration of glucagon suppresses food intake in rats. However, the anorexigenic action of glucagon in chicks has not yet been identified. In the present study, we investigated the effects of central administration of glucagon on food intake in chicks. Intracerebroventricular administration of glucagon in chicks significantly suppressed food intake and significantly induced hyperglycemia. In contrast, peripheral administration of the same dose of glucagon did not influence food intake and plasma glucose concentration. These results suggest that glucagon functions in chicks as an appetite-suppressive peptide in the central nervous system. Intracerebroventricular administration of glucagon in chicks also significantly increased CRF mRNA expression and plasma corticosterone concentration, suggesting that CRF acts as a downstream molecule for a glucagon-induced appetite-suppressive pathway in chicks. It is likely that the induction of hyperglycemia by central administration of glucagon is involved in its anorexigenic action, because peripheral administration of glucose in chicks suppressed food intake. These results suggest that CRF- and/or hyperglycemia-mediated pathways are involved in the anorexigenic action of glucagon in chicks.

Central ghrelin acts as an anti-dipsogenic peptide in chicks

The aim of this study was to look at whether ghrelin has an anti-dipsogenic effect, as seen in the eel, when administered centrally in neonatal chicks. Intracerebroventricular (ICV) injection of chicken ghrelin inhibited water intake (WI) in chicks under both ad libitum and 17-h water-deprived drinking conditions at doses ranging from 0.01 to 0.1nmol/chick. This inhibitory effect was observed when 0.1nmol of rat ghrelin was injected. On the other hand, 0.1nmol des-acyl rat ghrelin did not reduce WI. To examine the mechanism underlying the effect of ghrelin on WI, chicken B-type (or brain) natriuretic peptide (BNP), an anti-dipsogenic peptide in mammals, was injected at doses ranging from 0.1 to 1nmol/chick. BNP did not affect WI in chicks under both normal and water-deprived drinking conditions. These findings indicate that ghrelin acts as an anti-dipsogenic peptide through the GHS receptor in the chicken.

The corticotropin-releasing factor system as a mediator of the appetite-suppressing effects of stress in fish

A characteristic feature of the behavioural response to intensely acute or chronic stressors is a reduction in appetite. In fish, as in other vertebrates, the corticotropin-releasing factor (CRF) system plays a key role in coordinating the neuroendocrine, autonomic, and behavioural responses to stress. The following review documents the evidence implicating the CRF system as a mediator of the appetite-suppressing effects of stress in fish. Central injections of CRF or the related peptide, urotensin I (UI), or pharmacological treatments or stressors that result in an increase in forebrain CRF and UI gene expression, can elicit dose-dependent reductions in food intake that are at least partially reversed by pre-treatment with a CRF receptor antagonist. In addition, the appetite suppressing effects of various environmental, pathological, physical, and social stressors are associated with elevated levels of forebrain CRF and UI gene expression and with an activation of the hypothalamic-pituitary-interrenal (HPI) stress axis. In contrast, although stressors can also be associated with an increase in caudal neurosecretory system CRF and UI gene expression and an endocrine role for CRF-related peptides has been suggested, the physiological effects of peripheral CRF-related peptides on the gastrointestinal system and in the regulation of appetite have not been investigated. Overall, while CRF and UI appear to participate in the stress-induced changes in feeding behaviour in fish, the role of other know components of the CRF system is not known. Moreover, the extent to which the anorexigenic effects of CRF-related peptides are mediated through the hypothalamic feeding center, the HPI axis and cortisol, or via actions on descending autonomic pathways remains to be investigated.

Distribution of corticotropin-releasing factor-immunoreactive neurons in the central nervous system of the domestic chicken and Japanese quail

In birds, as in mammals, corticotropin-releasing factor (CRF) is present in a number of extrahypothalamic brain regions, indicating that CRF may play a role in physiological and behavioral responses other than the control of adrenocorticotropin hormone release by the pituitary. To provide a foundation for investigation of the roles of CRF in the control of avian behavior, the distribution of CRF immunoreactivity was determined throughout the central nervous system of the domestic chicken (Gallus domesticus) and Japanese quail (Coturnix japonica). The distribution of CRF-immunoreactive (-ir) perikarya and fibers in the chicken and quail brain was found to be more extensive than previously reported, notably in the telencephalon. Numerous CRF-ir perikarya and fibers were present in the hyperstriatum, hippocampus, neostriatum, lobus parolfactorius, and archistriatum, as well as in the nucleus taeniae, nucleus accumbens, and bed nucleus of the stria terminalis, which exhibited the strongest immunolabeling in the telencephalon. The presence of dense populations of CRF-ir perikarya in the medial lobus parolfactorius, nucleus of the stria terminalis, and paleostriatum ventrale, apparently giving rise to CRF-ir projections to the mesencephalic reticular formation, the parabrachial/pericerulear region, and the dorsal vagal complex, suggests that these telencephalic areas may constitute part of the avian "central extended amygdala." These results have important implications for understanding the role of extrahypothalamic CRF systems in emotional responses in birds.