Involvement of CRF on the anorexic effect of GLP-1 in layer chicks

Glucagon-like peptide-1 (GLP-1) is recognized as an anorexic peptide in the brain of chicks. However, the mechanism underlying the inhibition of feeding has not been well studied. It is reported that GLP-1 activates neurons containing corticotrophin-releasing factor (CRF) in the brain of mammals. Since CRF is also an anorexic peptide, it is possible that the anorexic effect of GLP-1 is mediated by CRF in chicks. The present study was carried out to test this. First, we determined plasma corticosterone (CORT) concentrations after intracerebroventricular (ICV) injection of GLP-1 and found that this treatment increased CORT release in layer chicks. The CORT-releasing effect was partly attenuated by co-injection of astressin, a CRF receptor antagonist, demonstrating that GLP-1 stimulated CORT secretion by activation of CRF neurons. CRF neurons also appear to be involved in mediating the inhibition of food intake by GLP-1 because this effect was also partly attenuated by astressin. Furthermore, we demonstrated that the anorexic effect of GLP-1 was weaker in broiler than layer chicks. The present results suggest that the anorexic effect of GLP-1 might be mediated by CRF neurons in the chick brain and that the sensitivity of the inhibitory response to GLP-1 differs between chick strains.     

Intracerebroventricular injection of glucagon-like peptide-1 changes lipid metabolism in chicks

Glucagon-like peptide-1 (GLP-1), derived from proglucagon, is thought to act as a negative regulator of energy homeostasis in mammals, since intracerebroventricular (ICV) injection of GLP-1 inhibits feeding behavior and enhances energy expenditure. The anorexigenic effect of GLP-1 is also observed in chicks, but whether brain GLP-1 enhances energy expenditure has not been investigated. The aim of the present study was to clarify the effect of ICV injection of GLP-1 on energy expenditure as well as metabolic changes in chicks. The injection of GLP-1 did not affect energy expenditure calculated from oxygen consumption and carbon dioxide production. On the other hand, the injection of GLP-1 significantly decreased respiratory quotient, suggesting that brain GLP-1 shifted the use of energy sources from carbohydrates to lipids. In support of this, ICV injection of GLP-1 increased plasma non-esterified fatty acid concentration while plasma glucose concentration was decreased. In conclusion, GLP-1 appears to act in the brain as a metabolic modulator rather than as a regulator of total energy expenditure in chicks.     

Beta 3-adrenergic receptor is involved in feeding regulation in chicks

We examined whether the brain beta 3-adrenergic receptor (B3-AR) is involved in the feeding regulation of chicks. Intracerebroventricular (ICV) injection of BRL37344, a B3-AR agonist, reduced food intake of chicks under ad libitum, but not fasting, feeding conditions. The ICV injection of BRL37344 did not affect chick posture or locomotion activity suggesting that BRL37344 inhibited feeding without induction of sleep-like behavior as caused by norepinephrine. Furthermore, the rectal temperature increased following the ICV injection of BRL37344. Intraperitoneal administration of BRL37344 did not reduce food intake under ad libitum feeding condition. The present study demonstrated that the brain B3-AR is involved in the inhibition of feeding in chicks. We also suggested that activation of the brain affects the energy metabolism in chicks.     

Central administration of alpha-melanocyte-stimulating hormone changes lipid metabolism in chicks

Alpha-melanocyte-stimulating hormone (MSH) is well known as an anorexigenic peptide in the brain of mammals. In addition to this, brain alpha-MSH enhances heat production (HP), indicating that the peptide acts as a catabolic factor in the regulation of energy metabolism. The anorexigenic effect of alpha-MSH is also observed in chicks (Gallus gallus), but no information has been available for its effect on HP. The present study was performed to examine whether intracerebroventricular (ICV) injection of alpha-MSH increases HP in chicks. The injection of alpha-MSH (10 and 100 pmol) did not affect oxygen consumption, carbon dioxide production and HP during the 1 h post-injection period. This result was supported by another result that ICV injection of alpha-MSH did not affect locomotion activity in chicks. In contrast, the respiratory quotient was significantly lowered by the ICV injection of MSH. We also found that alpha-MSH significantly increased plasma non-esterified fatty acid concentrations. In summary, brain alpha-MSH appears to exert generally catabolic effects on lipid metabolism in the chick, but does not appear to be involved in the regulation of HP.     

Peripheral or central administration of nitric oxide synthase inhibitor affects feeding behavior in chicks

We investigated the effect of peripheral or central administration of N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, on food intake in layer and broiler chicks (Gallus gallus). The intraperitoneal administration of L-NAME significantly decreased food intake in both broiler and layer chicks while the administration of D-NAME, an inactive form of L-NAME, had no effect. The intracerebroventricular (ICV) injection of L-NAME did not affect food intake in broiler chicks. However, ICV injection of L-NAME increased food intake in layer chicks while the injection of D-NAME had no effect. In addition to this, L-NAME-induced feeding was negated with the co-injection of L-arginine, suggesting that NO acts as a feeding-inhibitor signal in the brain of layer chicks. The present study revealed that administration of NO synthase inhibitor affected food intake in chicks, but the effect might be changed by chick strain and position of the injection.     

Anorexigenic effects of central neuropeptide S involve the hypothalamus in chicks (Gallus gallus)

Neuropeptide S (NPS) affects appetite-related processes in mammals. However, its role in avian biology is unreported. We hypothesized that intracerebroventricular (ICV) NPS would cause anorexigenic effects in chicks (Gallus gallus). To evaluate this, Cobb-500 chicks were centrally injected with multiple doses (0, 0.313, 0.625 and 1.250 mug) of NPS. NPS-treated chicks responded with decreased feed and water intake. The effect on water intake was secondary to feed intake, because fasted NPS-treated chicks did not reduce water intake. ICV NPS injection also reduced plasma corticosterone concentration. We monitored behavior and found decreased ingestive and exploratory pecking, jumping, locomotion, and increased time spent in deep rest. We hypothesized that the anorexigenic effects were hypothalamic in origin and quantified c-Fos reactivity in the lateral hypothalamus (LH), paraventricular nucleus (PVN) and ventromedial hypothalamus (VMH) after NPS treatment. NPS was associated with decreased c-Fos reactivity in the LH, increased reactivity in the PVN and had no effect in the VMH. When NPS was injected directly into the LH and PVN, chicks responded with decreased feed and water intake, suggesting that effects were directly mediated by these nuclei. We conclude that ICV NPS causes anorexigenic effects in chicks, without directly affecting water intake, and the hypothalamus is involved.     

Distribution of proglucagon mRNA and GLP-1 in the brainstem of chicks

Glucagon-like peptide-1 (GLP-1), structurally similar to glucagon, synthesized from the precursor proglucagon, is a well known anorexigenic peptide in the brain of several animal species. However, there are no previous reports concerning GLP-1-containing neurons in the chick brain. The aim of the present study was to investigate the distribution of proglucagon mRNA and GLP-1-immunoreactive (GLI) perikarya in various regions of the chick brain. We detected proglucagon mRNA in the brainstem, and to a lesser extent in the telencephalon. In the brainstem, a study using immunohistochemistry revealed that GLI perikarya were present in the nucleus motorius nervi facialis pars dosalis, nucleus motoris dorsalis nervi vagi and nucleus tractus solitarii. Furthermore, we found that proglucagon mRNA expression in the brainstem decreased after 24 h fasting. The present findings support the idea that endogenous GLP-1 is involved in feeding behavior of chicks.     

Central oxyntomodulin causes anorexigenic effects associated with the hypothalamus and alimentary canal in chicks (Gallus gallus)

Several peptides that are derived from proglucagon including glucagon, glucagon-like peptide-1 (GLP-1), and oxyntomodulin (OXM) cause satiety in mammals. Glucagon and GLP-1 also cause satiety in the avian, but the effects of OXM on avian appetite-related processes are not reported. Thus, this study was conducted to elucidate whether OXM induces satiety in chicks and to determine its mechanism of induction. Intracerebroventricular (ICV) OXM, in a linear-dose dependent manner, potently decreased feed and water intake. However, we found that the effect on water intake was secondary to a reduction in feed intake. Chicks treated with ICV OXM had decreased c-Fos immunoreactivity in the regio lateralis hypothalami, but the nucleus infundibuli hypothalami (homologue to the mammalian arcuate nucleus) had increased c-Fos immunoreactivity. ICV OXM also caused total alimentary canal transit time to be decreased. We conclude that changes in the hypothalamus and gut may contribute to anorexigenic effects after ICV OXM in chicks. Through divergent evolution of birds and mammals, the central anorexigenic effects of OXM may have been conserved.     

Neuropeptide Y-induced feeding is dependent on GABAA receptors in neonatal chicks

In mammals and birds, neuropeptide Y (NPY) and gamma-aminobutyric acid (GABA) are found in brain areas known to be involved in the control of ingestive behavior and act to increase voluntary food intake. In rats, significant evidence suggest a functional and behavioral interaction between NPY and GABA mediated transmission in various brain regions, including the arcuate and paraventricular nuclei of the hypothalamus which can be important in the regulation of feeding behavior. In the present study, the effect of intracerebroventricular (ICV) administration of NPY and GABA receptor antagonists on food intake was examined in neonatal chicks. The ICV injection of NPY strongly stimulated food intake while co-administration of NPY and picrotoxin, a GABA_A antagonist, (but not CGP54626, a GABA_B antagonist) weakened food intake induced by NPY. These results suggest that central NPY stimulates food intake in neonatal chicks by interaction with the GABAergic system via GABA_A receptors.     

The Stimulatory Effect of Cerebral Intraventricular Injection of cNPY on Precocial Feeding Behavior in Neonatal Chicks (Gallus domesticus)

Neuropeptide Y (NPY) is one of the most potent stimulants of food intake in many animals. Most of the supporting evidence for the effects of NPY has been gathered in mammalian species using porcine NPY. To investigate the effects of NPY on precocial feeding initiation in chicks, we firstly used chicken NPY (cNPY) to study its role in food intake and spontaneous activities in 3-day-old male chicks. Food intake was monitored at different times after intracerebroventricular (ICV) injection of cNPY (2.5, 5.0 or 10.0 μg/10 μL) and anti-cNPY antibody (anti-cNPY) (1:9000, 1:3000 or 1:1000 in dilution). cNPY given at different doses significantly increased food intake at 30 min, 60 min, 90 min and 120 min after injection. Chicks treated with 5.0 μg/10 μL of cNPY showed a maximal 4.48 fold increase in food intake comparing to the control at 30 min. There is still more than 2 fold increase in food intake at 120 min after injection of cNPY. Food intake was significantly inhibited by a single ICV injection of anti-cNPY diluted to 1:9000 (60% inhibition), 1:3000 (92% inhibition), and 1:1000 (95% inhibition) at 30 min with 1:1000 being the maximally effective concentration. The inhibitory effects of anti-cNPY (diluted to1:9000, 1:3000, 1:1000) at 120 min post ICV injection were 22%, 42% and 46%, respectively. But ICV of anti-cNPY (1:3000 in dilution) did not block the orexigenic effect of 2.5 μg/10 μL of cNPY. ICV injection of different concentrations of cNPY increases locomotor activity in a dose-dependent manner while ICV anti-cNPY greatly decreased the distance moved by each chick compared to control groups. Taken together, our results demonstrated that cNPY has a promoting effect on chick food intake and locomotor activity, and that endogenous cNPY might play a positive role in regulating precocial feeding behavior in newly hatched chicks.     

大鼠脑室注射高渗氯化钠和蔗糖诱导饮水行为和脑内c—fos的表达

用ＳＤ种系清醒大鼠,观察脑室注射高渗物质引起的饮水及ｃ－ｆｏｓ在脑内的表达部位。实验结果表明,脑室内微量注射１．５ｍｏｌ／Ｌ、３ｍｏｌ／Ｌ ＮａＣｌ或３ｍｏｌ／Ｌ蔗糖均可诱导饮水反应,并在前脑的终板血管器官、正中视前核和下丘脑视上核与室旁核中见到Ｆｏｓ样免疫反应阳性细胞,同样在后脑的最后区、臂旁外侧核与孤束核中也能见到Ｆｏｓ样免疫反应阳性细胞,同样在后脑的最后区、臂旁外侧核与孤束核中也能见到Ｆｏｓ     

The anorexic effect of alpha-melanocyte-stimulating hormone is mediated by corticotrophin-releasing factor in chicks

Alpha-melanocyte-stimulating hormone (alpha-MSH) is recognized as an anorexic peptide in the brain of vertebrates, but its mechanism of action has not been identified in birds. Therefore, we investigated whether the anorexic effect of alpha-MSH is mediated by corticotrophin-releasing factor (CRF) in the domestic chick. Firstly, we found that intracerebroventricular (i.c.v.) injection of alpha-MSH dose dependently increased plasma corticosterone (CORT) concentration. This effect was partly attenuated by co-injection of astressin, a CRF receptor antagonist, demonstrating that alpha-MSH stimulated CORT secretion by activating CRF neurons. The alpha-MSH-elicited CORT release was not attenuated by the injection of agouti-related protein, an endogenous melanocortin-4 (MC4) receptor antagonist, suggesting that alpha-MSH stimulated CRF neurons through MC4 receptor-independent pathways. Finally, we found that the anorexic effect of alpha-MSH was partly attenuated by astressin. The present results suggest that the anorexic effect of alpha-MSH in the chick brain is mediated in part by activation of CRF neurons.     

Glucagon-Like Peptide 1 (GLP-1) Can Reverse AMP-Activated Protein Kinase (AMPK) and S6 Kinase (P70S6K) Activities Induced by Fluctuations in Glucose Levels in Hypothalamic Areas Involved in Feeding Behaviour

The anorexigenic peptide, glucagon-like peptide-1 (GLP-1), reduces glucose metabolism in the human hypothalamus and brain stem. The brain activity of metabolic sensors such as AMP-activated protein kinase (AMPK) responds to changes in glucose levels. The mammalian target of rapamycin (mTOR) and its downstream target, p70S6 kinase (p70S6K), integrate nutrient and hormonal signals. The hypothalamic mTOR/p70S6K pathway has been implicated in the control of feeding and the regulation of energy balances. Therefore, we investigated the coordinated effects of glucose and GLP-1 on the expression and activity of AMPK and p70S6K in the areas involved in the control of feeding. The effect of GLP-1 on the expression and activities of AMPK and p70S6K was studied in hypothalamic slice explants exposed to low- and high-glucose concentrations by quantitative real-time RT-PCR and by the quantification of active-phosphorylated protein levels by immunoblot. In vivo, the effects of exendin-4 on hypothalamic AMPK and p70S6K activation were analysed in male obese Zucker and lean controls 1 h after exendin-4 injection to rats fasted for 48 h or after re-feeding for 2–4 h. High-glucose levels decreased the expression of Ampk in the lateral hypothalamus and treatment with GLP-1 reversed this effect. GLP-1 treatment inhibited the activities of AMPK and p70S6K when the activation of these protein kinases was maximum in both the ventromedial and lateral hypothalamic areas. Furthermore, in vivo s.c. administration of exendin-4 modulated AMPK and p70S6K activities in those areas, in both fasted and re-fed obese Zucker and lean control rats.     

Inhibitory effect of ghrelin on food intake is mediated by the corticotropin-releasing factor system in neonatal chicks

It is known that, in rats, central and peripheral ghrelin increases food intake mainly through activation of neuropeptide Y (NPY) neurons. In contrast, intracerebroventricular (ICV) injection of ghrelin inhibits food intake in neonatal chicks. We examined the mechanism governing this inhibitory effect in chicks. The ICV injection of ghrelin or corticotropin-releasing factor (CRF), which also inhibits feeding and causes hyperactivity in chicks. Thus, we examined the interaction of ghrelin with CRF and the hypothalamo-pituitary-adrenal (HPA) axis. The ICV injection of ghrelin increased plasma corticosterone levels in a dose-dependent or a time-dependent manner. Co-injection of a CRF receptor antagonist, astressin, attenuated ghrelin-induced plasma corticosterone increase and anorexia. In addition, we also investigated the effect of ghrelin on NPY-induced food intake and on expression of hypothalamic NPY mRNA. Co-injection of ghrelin with NPY inhibited NPY-induced increase in food intake, and the ICV injection of ghrelin did not change NPY mRNA expression. These results indicate that central ghrelin does not interact with NPY as seen in rodents, but instead inhibits food intake by interacting with the endogenous CRF and its receptor.     

Neuropeptide regulation of feeding in catfish, Ictalurus punctatus: a role for glucagon-like peptide-1 (GLP-1)?

Glucagon-like peptide 1 is a compound known to cause reduced food intake in mammals, though its action on feed intake in fish is unknown. The clear differences in the effects of GLP-1 on mammalian and teleostean glucose homeostasis suggest that we cannot assume a similar action of GLP-1 on feeding in mammals and fish. In this study the effects and specificity of centrally administered GLP-1 on feed intake were examined. It was demonstrated that intracerebroventricular (ICV) injection of glucagon-like peptide 1 (GLP-1) in the channel catfish (Ictalurus punctatus) is a potent inhibitor of feed intake with a dose of 0.25 ng g(-1) body wt. reducing feed intake by 50%. The weak response to intraperitoneal (i.p.) and intravenous (i.v.) injection treatments with GLP-1 suggests the major effects on feed intake are centrally mediated. GLP-1 action on feed intake was not antagonized by ICV injection of exendin(9-39). Immunoneutralization of GLP-1 by ICV injection of antisalmon GLP-1 antisera did not affect feed intake over 48 h, while ICV injection of GLP-1 at a dose of 30 ng g(-1) body wt. reduced feed intake for over 20 h. Additionally, there is some evidence that GLP-1 caused gastric evacuation. We conclude that GLP-1 is a potent inhibitor of feeding in fish, but its involvement in feed intake regulation under physiological conditions remains to be clarified.     

下丘脑室旁核注射GLP-1 对糖尿病大鼠中枢GLP-1 受体表达

目的:探讨下丘脑室旁核(hypothalamic paraventricular nucleus,PVN)注射GLP-1(胰高血糖素样肽-1)对糖尿病大鼠胃排空的影响及机制。方法:30只Wistar大鼠随机分为正常对照组(NC组)、糖尿病组(DM组)和GLP-1干预组(GLP-1组),每组各10只。DM组和GLP-1组腹腔注射链脲佐菌素,三组大鼠均PVN区埋置套管,恢复7d,GLP-1组微量注射0.5μg/0.5μl的GLP-1,NC组和DM组大鼠PVN区微量注射等体积生理盐水。甲基纤维素-酚红灌胃法检测胃排空;半定量RT-PCR检测大鼠下丘脑GLP-1RmRNA的表达。结果:DM组胃排空率较NC组明显升高(P<0.05),GLP-1组胃排空明显低于DM组(P<0.05),GLP-1组和NC组差异无统计学意义(P>0.05)。GLP-1组下丘脑GLP-1RmRNA的表达明显高于DM组和NC组(P<0.05),并与胃排空率成负相关(P<0.05)。DM组和NC组差异无统计学意义(P>0.05)。结论:PVN区注射GLP-1可以抑制糖尿病大鼠早期胃排空加速,作用机制可能和促进下丘脑GLP-1受体表达有关。     

Attenuation of lipopolysaccharide anorexia by antagonism of caudal brain stem but not forebrain GLP-1-R

The central glucagon-like peptide-1 (GLP-1) system has been implicated in the control of feeding behavior. Here we explore GLP-1 mediation of the anorexic response to administration of systemic LPS and address the relative importance of caudal brain stem and forebrain GLP-1 receptor (GLP-1-R) for the mediation of the response. Fourth-intracerebroventricular delivery of the GLP-1-R antagonist exendin-(9-39) (10 microg) did not itself affect food intake in the 24 h after injection but significantly attenuated the otherwise robust (approximately 60%) reduction in food intake obtained after LPS (100 microg/kg) treatment. This result highlights a role for caudal brain stem GLP-1-R in the mediation of LPS anorexia but does not rule out the possibility that forebrain receptors also contribute to the response. Forebrain contribution was addressed by delivery of the GLP-1-R antagonist to the third ventricle with the caudal flow of cerebrospinal fluid blocked by occlusion of the cerebral aqueduct. Exendin-(9-39) delivery thus limited to forebrain did not attenuate the anorexic response to LPS. These data suggest that LPS anorexia is mediated, in part, by release of the native peptide acting on GLP-1-R within the caudal brain stem.     

Estradiol modulates the anorexic response to central glucagon-like peptide 1

Estrogens suppress feeding in part by enhancing the response to satiation signals. Glucagon-like peptide 1 (GLP-1) acts on receptor populations both peripherally and centrally to affect food intake. We hypothesized that modulation of the central GLP-1 system is one of the mechanisms underlying the effects of estrogens on feeding. We assessed the anorexic effect of 0, 1, and 10 μg doses of GLP-1 administered into the lateral ventricle of bilaterally ovariectomized (OVX) female rats on a cyclic regimen of either 2 μg β-estradiol-3-benzoate (EB) or oil vehicle 30 min prior to dark onset on the day following hormone treatment. Central GLP-1 treatment significantly suppressed food intake in EB-treated rats at both doses compared to vehicle, whereas only the 10 μg GLP-1 dose was effective in oil-treated rats. To follow up, we examined whether physiologic-dose cyclic estradiol treatment influences GLP-1-induced c-Fos in feeding-relevant brain areas of OVX females. GLP-1 significantly increased c-Fos expression in the area postrema (AP) and nucleus of the solitary tract (NTS), and the presence of estrogens may be required for this effect in the paraventricular nucleus of the hypothalamus (PVN). Together, these data suggest that modulation of the central GLP-1 system may be one of the mechanisms by which estrogens suppress food intake, and highlight the PVN as a region of interest for future investigation.     

Feeding responses to central administration of several somatostatin analogs in chicks

Somatostatin is well known as an inhibitor of growth hormone release from the anterior pituitary. Its effects are exerted via 5 subtypes of receptors, which are named SSTR1 through 5. We recently reported that intracerebroventricular (ICV) injection of somatostatin stimulates feeding behavior in chicks. However, the specific receptors which mediate this orexigenic effect have not been identified in chicks. Thus, the purpose of the present study was to identify the receptor subtypes involved in somatostatin-induced feeding using 5 somatostatin analogs. Chicks that received vapreotide and octreotide (less than 3 nmol), which are agonist of SSTR2 and SSTR5, increased their food intake. Additionally, chicks ICV injected with BIM23056 or L-817,818 (SSTR3 and SSTR5 agonists, respectively) also had increased food intake. However, ICV injection of the SSTR4 agonist L-803,087 did not cause an orexigenic effect, suggesting that SSTR4 might not be important in somatostatin-induced feeding behavior. In summary, results from this study may be interpreted as SSTR2, SSTR3 and SSTR5 are related to somatostatin-associated feeding behavior in chicks.     

Nesfatin-1 influences the excitability of glucosensing neurons in the hypothalamic nuclei and inhibits the food intake

Nesfatin-1 is a recently discovered neuropeptide that has been shown to decrease food intake after lateral, third, or fourth brain ventricle, cisterna magna administration, or PVN injection in ad libitum fed rats. With regards to the understanding of nesfatin-1 brain sites of action, additional microinjection studies will be necessary to define specific nuclei, in addition to the PVN, responsive to nesfatin-1 to get insight into the differential effects on food intake. In the present study, we evaluated nesfatin-1 action to modulate food intake response upon injection into the specific hypothalamic nuclei (PVN, LHA and VMN) in freely fed rats during the dark phase. We extend previous observations by showing that the nesfatin-1 (50 pmol) injected before the onset of the dark period significantly reduced the 1 to 5 h cumulative food intake in rats cannulated into the PVN, LHA, but not in rats cannulated into the VMN. Glucosensing neurons located in the hypothalamus are involved in glucoprivic feeding and homeostatic control of blood glucose. In order to shed light on the mechanisms by which nesfatin-1 exerts its satiety-promoting actions, we examined the effect of nesfatin-1 on the excitability of hypothalamic glucosensing neurons. Nesfatin-1 excited most of the glucose-inhibited (GI) neurons and inhibited most of the glucose-excited (GE) neurons in the PVN. Of 34 GI neurons in the LHA tested, inhibitory effects were seen in 70.6% (24/34) of GI neurons. The main effects were excitatory after intra-VMN administration of nesfatin-1 in GE neurons (27/35, 77.1%). Thus, our data clearly demonstrate that nesfatin-1 may exert at least a part of its physiological actions on the control of food intake as a direct result of its role in modulating the excitability of glucosensing neurons in the PVN, LHA and VMN.