Tetsuya Tachibana

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.

Intracerebroventricular injection of ghrelin and growth hormone releasing factor inhibits food intake in neonatal chicks

Growth hormone releasing factor (GRF) is known to stimulate feeding of rats. Ghrelin, a novel growth hormone (GH)-releasing acylated peptide, was recently isolated from rat stomach. It also stimulates the release of GH from the anterior pituitary through the GH secretagogue receptor (GHS-R) and feeding in the rat. We have investigated the effects of ghrelin and GRF on food intake of the neonatal chick. In Experiment 1, 0, 1.25, 2.5 and 5 microg of ghrelin were administered intracerebroventricularly (i.c.v.) to ad libitum fed birds. In Experiment 2, the effect of (i.c.v.) injection of 0, 1.25, 2.5 and 5 microg of GRF was investigated. Both peptides strongly inhibited food intake of the chick during the 2-h post-injection period. In the third experiment, 0, 0.5, 1 and 2 microg of ghrelin was injected i.c.v. in chicks previously deprived of food for 3 h. Food intake was again inhibited by ghrelin in a dose-dependent manner. These results suggest that the mechanisms for feeding of the neonatal chick through GH release are different from mammals.

Gonadotropin-inhibiting hormone stimulates feeding behavior in chicks.

Neuropeptides containing a C-terminal Arg-Phe-NH2 motif (RFamide peptides) are suggested to be involved in the control of feeding behavior in both invertebrates and vertebrates. Gonadotropin-inhibitory hormone (GnIH) is the first identified avian RFamide peptide that inhibits gonadotropin release from the pituitary. The GnIH precursor encodes one GnIH and its related peptides (GnIH-RP-1 and -RP-2) that shared the same C-terminal motif, Leu-Pro-Xaa-Arg-Phe-NH2 (Xaa = Leu or Gln) (LPXRFamide). GnIH neurons are localized in the paraventricular nucleus, with their fibers visible in multiple brain locations including the median eminence and brainstem. In this study, we therefore investigated the action of GnIH and its related peptides on feeding behavior. Intracerebroventricular (ICV) injection of GnIH, GnIH-RP-1 and GnIH-RP-2 significantly stimulated food intake in chicks. The chicken pentapeptide LPLRFamide, a degraded C-terminus of GnIH and GnIH-RP-1, did not stimulate feeding thereby demonstrating the importance of the N-terminus of GnIH and its related peptides for the orexigenic effect. Anti-GnIH antiserum suppressed appetite induced by fasting, but did not modify feeding under ad libitum conditions. The present study suggests that GnIH and its related peptides act as endogenous orexigenic factors in the brain of chicks.

Intracerebroventricular injection of agouti-related protein attenuates the anorexigenic effect of alpha-melanocyte stimulating hormone in neonatal chicks

It is well known that alpha-melanocyte stimulating hormone (alpha-MSH) inhibits feeding via melanocortin receptor-4 (MC4R) in the mammalian brain. The anorexigenic effect of alpha-MSH is attenuated by agouti-related protein (AGRP), an antagonist for MC4R. Present studies were carried out to clarify whether human AGRP (86-132) antagonizes the anorexigenic effect of alpha-MSH in broiler chicks. Intracerebroventricular injection of AGRP attenuated the anorexigenic effect of alpha-MSH. Furthermore, AGRP stimulated food intake of layer-type chicks under an ad libitum feeding condition but not broiler chicks, suggesting that the orexigenic effect of AGRP is different between two breeds. These also imply that the extent of the anorexigenic effect of endogenous alpha-MSH is different among two breeds. This may be a part of the difference in food intake between two breeds.

Intracerebroventricular injection of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibits feeding in chicks

Previous research has indicated an involvement of glucagon superfamily peptides in the regulation of feeding in the domestic chick brain. However the possible roles of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide-38 (PACAP) have not yet been investigated. We therefore examined the effect of intracerebroventricular (ICV) injections of VIP or PACAP on food intake in chicks. ICV injection of both VIP and PACAP significantly inhibited food intake over 4 h at doses ranging from 12 to 188 pmol. Subsequently, we compared the anorexic effect the glucagon superfamily peptides VIP, PACAP, growth hormone-releasing factor (GRF) and glucagon-like peptide-1 (GLP-1) after ICV injection at an equimolar dose (12 pmol). All four peptides significantly inhibited food intake, although the anorexic effects of VIP and PACAP were weaker than those of GRF and GLP-1. These findings support the hypothesis that glucagon superfamily peptides play an important role in the regulation of appetite in the chick brain.

Intracerebroventricular injection of l-serine analogs and derivatives induces sedative and hypnotic effects under an acute stressful condition in neonatal chicks

Four experiments were conducted to clarify the central functions of L-serine and its analogs on an acute stressful condition. Intracerebroventricular (i.c.v.) injection of L-serine (0.21, 0.42 and 0.84 micromol) attenuated stress responses in a dose-dependent fashion, as well as induced sleep, in Experiment 1. The effects of L- and D-serine in Experiment 2, those of L-serine, phosphoserine, acetylserine and L-cysteine in Experiment 3 and those of L-serine, glycine and lysophosphatidylserine in Experiment 4 were compared at an equimolar basis (0.84 micromol). D-Serine, proposed as an endogenous agonist of N-methyl-D-aspatate (NMDA) receptor, did not have sedative and hypnotic effects as observed with L-serine. In contrast, all the analogs and derivatives of L-serine had a sedative effect, although with a different manner in several behavioral markers of stress such as spontaneous activity and distress vocalizations. No significant changes in plasma corticosterone concentration were observed in any experiment. Taken together, the i.c.v. injection of L-serine analogs and its derivatives have sedative and hypnotic effects under an acute stressful condition, which does not involve the hypothalamic-pituitary-adrenal axis. In conclusion, L-serine may be effective in improving anxiety or sleep disorders induced by psychological stressor.

Identification, Localization, and Function of a Novel Avian Hypothalamic Neuropeptide, 26RFa, and Its Cognate Receptor, G Protein-Coupled Receptor-103

Several neuropeptides with the C-terminal RFamide sequence have been identified in the hypothalamus of a variety of vertebrates. Among the RFamide peptide groups, however, only LPXRFamide peptides, including gonadotropin-inhibitory hormone, have been characterized in the avian brain. In the present study, we sought for the presence of other RFamide peptides in the avian hypothalamus. We identified a cDNA encoding an RFamide peptide orthologous to 26RFa (also referred to as QRFP) in the hypothalamus of the Japanese quail. The deduced quail 26RFa precursor consisted of 120-amino-acid residues, encoding one RFamide peptide with 27 amino acids. This RFamide peptide was flanked at the N terminus by a dibasic amino acid cleavage site and at the C terminus by a glycine amidation signal. Quantitative RT-PCR analysis demonstrated specific expression of quail 26RFa mRNA in the diencephalon including the hypothalamus. Furthermore, mass spectrometry analysis revealed the presence of a peptide exhibiting the mass of mature 26RFa, indicating that the peptide is actually produced from the precursor in the diencephalon. 26RFa-producing cell bodies were localized in the anterior hypothalamic nucleus in the brain. Synthetic 26RFa increased intracellular Ca(2+) concentration in HEK293T cells transfected with the chicken G protein-coupled receptor GPR103. Intracerebroventricular injection of 26RFa in broiler chicks stimulated feeding behavior. These data provide the first evidence for the occurrence of the peptide 26RFa in the avian hypothalamus and indicate that this peptide exerts orexigenic activity.

Comparison of brain arginine-vasotocin and corticotrophin-releasing factor for physiological responses in chicks

Arginine-vasotocin (AVT), a non-mammalian homologue of mammalian arginine-vasopressin, is a stress-related peptide in the brain of birds. The aim of the present study was to determine the effects of intracerebroventricular (ICV) injection of AVT on feeding behavior, body temperature, corticosterone release and several behavioral parameters in chicks. These effects were compared with those of corticotrophin-releasing factor (CRF), another stress-related peptide. The ICV injection of AVT inhibited feeding behavior, increased rectal temperature, and increased plasma corticosterone concentrations, but these effects were weaker than those of CRF. AVT induced hypoactivity as evidenced by decreased vocalization and stepping while CRF induced hyperactivity. The present results demonstrate that some functions of brain AVT are similar to those of CRF, although these effects are weaker than those induced by CRF. However, some AVT-induced behaviors were different from CRF, indicating that the physiological roles of AVT in the regulation of stress behavior are different from those of CRF in chicks.

Effect of central administration of carnosine and its constituents on behaviors in chicks

Even though their contents in the brain are high, the function of brain carnosine and its constituents has not been clarified. Both carnosine and anserine inhibited food intake in a dose dependent fashion when injected intracerebroventricularly. The constituents of carnosine, beta-alanine (beta-Ala) and l-histidine (His), also inhibited food intake, but their effects were weaker than carnosine itself. Co-administration with beta-Ala and His inhibited food intake similar to carnosine, but also altered other behaviors. Injection of carnosine induced hyperactivity and increased plasma corticosterone level, whereas beta-Ala plus His induced hypoactivity manifested as sleep-like behavior. This later effect seemed to be derived from beta-Ala, not His. These results suggest that central carnosine may act in the brain of chicks to regulate brain function and/or behavior in a manner different from its constituents.

Central administration of cocaine- and amphetamine-regulated transcript inhibits food intake in chicks.

The present study was done to clarify whether intracerebroventricular (ICV) injection of cocaine- and amphetamine-regulated transcript (CART) affects feeding in chicks. ICV injection of CART significantly inhibited fasting-induced feeding of broiler chicks. In layer chicks, on the other hand, CART inhibited food intake in birds with ad libitum access to feed but only weakly affected intake of fasted birds. In addition, the ICV injection of CART attenuated neuropeptide Y (NPY)-induced feeding in both broiler and layer chicks. These results indicate that CART is one of the important regulators of feeding in chicks, but the suppressive effect on feeding is somewhat different between strains. Furthermore, the present study also demonstrates that CART interacts with NPY in the central nervous system to regulate feeding in chicks.