Pufferfish and zebrafish have five distinct NPY receptor subtypes, but have lost appetite receptors Y1 and Y5

The neuropeptide Y receptor gene repository, phylogeny and comparative expression in allotetraploid common carp

NPY-family receptors belong to G protein-coupled receptors (GPCR), which lays a physiological foundation for the transmembrane transport of an endogenous appetite-stimulating factor neuropeptide Y and related peptides. In this study, we investigated the npyr genes in ten representative species, and twelve npyr genes were identified from allotetraploid C. carpio, the npyr gene number of C. carpio was twice the number of its subgenome B progenitor-like diploid Poropuntius huangchuchieni. Phylogenetic analysis showed that all npyr genes were divided into three subgroups, and they underwent strong purifying selection according to selection pressure analysis. Subsequently, synteny analysis showed that most npyr genes were evenly distributed on the homologous chromosomes of two subgenomes in allotetraploid C. carpio, in which npy1r and npy2r were tandem duplicated, respectively. In addition, the global expression of npyr genes during embryonic development in allotetraploid C. carpio suggested the potential function of npyr genes in immunity and reproduction. In adult tissues, npyr genes were mainly distributed in the brain, gonad, and skin, which displayed a similar expression pattern between the C. carpio B subgenome and P. huangchuchieni. In general, our research could provide reference information for future exploration of the NPY receptors and neuroendocrine system of allotetraploid C. carpio and vertebrates.

Neuropeptide Y and melanocortin receptors in fish: regulators of energy homeostasis

Energy homeostasis, which refers to the physiological processes that the energy intake is exquisitely coordinated with energy expenditure, is critical for survival. Therefore, multiple and complex mechanisms have been involved in the regulation of energy homeostasis. The central melanocortin system plays an important role in modulating energy homeostasis. This system includes the orexigenic neurons, expressing neuropeptide Y/Agouti-related protein (NPY/AgRP), and the anorexigenic neurons expressing proopiomelanocortin (POMC). The downstream receptors of NPY, AgRP and post-translational products of POMC are G protein-coupled receptors (GPCRs). This review summarizes the compelling evidence demonstrating that NPY and melanocortin receptors are involved in energy homeostasis. Subsequently, the comparative studies on physiology and pharmacology of NPY and melanocortin receptors in humans, rodents and teleosts are summarized. Also, we provide a strategy demonstrating the potential application of the new ligands and/or specific variants of melanocortin system in aquaculture.

Identification of reproduction-related genes and pathways in the Culter alburnus H-P-G axis and characterization of their expression differences in malformed and normal gynogenetic ovaries

This study applied RNA-seq technology to discover reproduction-related genes and pathways in female topmouth culter brain (including pituitary) and ovarian tissues. In functional analysis, 2479 and 2605 unigenes in the brain and ovary tissue were assigned to the "reproductive process" subcategory in addition to the 2660 and 2845 unigenes assigned to the "reproduction" subcategory. Twenty-three complete cDNA sequences were identified through the different gene expression (DGE) approach from five reproduction-related pathways (MAPK signaling pathway, neuroactive ligand-receptor interaction pathway, gonadotropin-releasing hormone signaling pathway, oocyte meiosis pathway, and steroid biosynthesis pathway). The expression levels of 16 candidate genes using qPCR in this study were in accordance with the results of transcriptome analysis. In addition, the expression levels of the FSH, 3β-HSD, PGR, and NPYR genes in malformed gynogenetic ovaries were considerably low, which was consistent with the progress of oocytogenesis in the ovaries of topmouth culter. The high expression of these four genes in the ovaries of normal topmouth culter suggested they might involve in the preparation for the shift of oogenesis to ovulation. Hence, our work identified a set of annotated gene products that are candidate factors affecting reproduction in the topmouth culter H-P-G axis. These results could be essential for further research in functional genomics and genetic editing for topmouth culter reproduction.

Pharmacological characterization, cellular localization and expression profile of NPY receptor subtypes Y2 and Y7 in large yellow croaker, Larimichthys crocea

Neuropeptide Y (NPY) receptors are suggested to mediate the multi-physiological functions of NPY family peptides, such as food intake, in teleost fish. However, the structure and signaling of fish NPY receptors are yet to be fully elucidated. In this study, we report the cloning and characterization of two neuropeptide Y receptor subtypes, Y2 (NPY2R) and Y7 (NPY7R), in yellow croaker Larimichthys crocea (L. crocea) (LcNPY2R, LcNPY7R). The gene structure, pharmacological characterization, cell location, and tissue expression of these two receptors were explored. The phylogenetic results showed that LcNPY2R and LcNPY7R had typical G protein-coupled receptor profiles, associated with the Y2 subfamily, with coding sequences that are highly conserved in vertebrates. The expression of both LcNPY2R and LcNPY7R could be activated by LcNPY in HEK293 cells. However, truncated LcNPY_18-36 was only able to activate LcNPY2R at the same level as full length LcNPY. Expression analysis revealed that LcNPY2R mRNA was predominantly expressed in the intestine and liver, whereas LcNPY7R was expressed in the stomach, which indicated that both receptors were related to the digestive system. Overall, our data establishes a molecular basis to determine the actions of LcNPY2R and LcNPY7R, which could be used to elucidate the conserved roles of these receptor-ligand pairs in vertebrates.

Cloning, expression, and ligand-binding characterization of two neuropeptide Y receptor subtypes in orange-spotted grouper, Epinephelus coioides

As one of the most important multifunctional peptides, neuropeptide Y (NPY) performs its physiological functions through different subtype receptors. In this study, full-length cDNAs of two NPY receptors (YRs) in orange-spotted grouper (Epinephelus coioides) were cloned and named npy8br (y8b) and npy2r (y2). Phylogenetic analysis indicated that the Y8b receptor is an ortholog of the teleostean Y8b receptor, which belongs to the Y1 subfamily, and the Y2 receptor is an ortholog of the teleostean Y2 receptor, which belongs to the Y2 subfamily. Both of the YRs have G protein-coupled receptor family profiles. Multiple alignments demonstrate that the extracellular loop regions of YRs have distinctive residues of each species. Expression profile analysis revealed that the grouper Y8b receptor mRNA is primarily expressed in the brain, stomach and intestine, while the grouper Y2 receptor mRNA is primarily expressed in the brain, ovary, liver and heart. Double immunofluorescence analysis determined that the grouper YRs interact with the grouper NPY around the human embryonic kidney 293T cell surface. Furthermore, site-directed mutagenesis in a phage display system revealed that Asp(6.59) might be a common NPY-binding site, while Asp(2.68) of the Y8b receptor and Glu(5.24) of the Y2 receptor could be likely involved in subtype-specific binding. Combining the expression profile and ligand-binding feature, the grouper Y8b receptor could be involved in regulating food intake via the brain-gut axis and the grouper Y2 receptor might play a role in balancing the regulatory activity of the Y8b receptor and participate in metabolism in the liver and ovary.

Molecular and physiological evidences for the role in appetite regulation of apelin and its receptor APJ in Ya-fish (Schizothorax prenanti)

Apelin is a recently discovered peptide produced by several tissues with diverse physiological actions mediated by its receptor APJ. In order to better understand the role of apelin in the regulation of appetite in fish, we cloned the cDNAs encoding apelin and APJ, and investigated their mRNA distributions in Ya-fish (Schizothorax prenanti) tissues. We also assessed the effects of different nutritional status on apelin and APJ mRNAs abundance. Apelin and APJ mRNAs were ubiquitously expressed in all tissues tested, relatively high expression levels were detected in the heart, spleen, hypothalamus and kidney. Short-term fasting significant increased APJ mRNA expression, but no significant difference between fasted fish and fed control on 5- and 7-day. Meanwhile, apelin mRNA expression consistently increased during the 7-day food deprivation. In order to further characterize apelin in fish, we performed intraperitoneal (i.p.) injection of apelin-13 and examined food intake of the injected fish. Apelin injected at a dose of 100 ng/g body weight induced a significant increase in food intake compared to saline injected fish. Our results suggest that apelin acts as an orexigenic factor in Ya-fish. Their widespread distributions also suggest that apelin and APJ might play multiple physiological regulating roles in fish.

Cloning, phylogeny, and regional expression of a Y5 receptor mRNA in the brain of the sea lamprey (Petromyzon marinus)

The NPY receptors known as Y receptors are classified into three subfamilies, Y1, Y2, and Y5, and are involved in different physiological functions. The Y5 receptor is the only member of the Y5 subfamily, and it is present in all vertebrate groups, except for teleosts. Both molecular and pharmacological studies show that Y5 receptor is highly conserved during vertebrate evolution. Furthermore, this receptor is widely expressed in the mammalian brain, including the hypothalamus, where it is thought to take part in feeding and homeostasis regulation. Lampreys belong to the agnathan lineage, and they are thought to have branched out between the two whole-genome duplications that occurred in vertebrates. Therefore, they are in a key position for studies on the evolution of gene families in vertebrates. Here we report the cloning, phylogeny, and brain expression pattern of the sea lamprey Y5 receptor. In phylogenetic studies, the lamprey Y5 receptor clusters in a basal position, together with Y5 receptors of other vertebrates. The mRNA of this receptor is broadly expressed in the lamprey brain, being especially abundant in hypothalamic areas. Its expression pattern is roughly similar to that reported for other vertebrates and parallels the expression pattern of the Y1 receptor subtype previously described by our group, as it occurs in mammals. Altogether, these results confirm that a Y5 receptor is present in lampreys, thus being highly conserved during the evolution of vertebrates, and suggest that it is involved in many brain functions, the only known exception being teleosts.

New advances in models and strategies for developing anti-obesity drugs

INTRODUCTION

Obesity is a worldwide pandemic. Obesity-related health and economic costs are staggering. Existing strategies to combat obesity through lifestyle improvements and medical intervention have had limited success. Pharmacotherapy, in combination with lifestyle modification, may play a vital role in reversing the disease burden. However, past and current weight-loss medications have had serious safety risks, notably cardiovascular and psychiatric events.

AREAS COVERED

The authors review the strategies for designing new anti-obesity drugs by describing those currently in development. They describe their target, mechanism of action and developmental or regulatory status. Furthermore, they discuss the problem of weight regain following weight loss, and its relevance to the long-term success of anti-obesity pharmacotherapy.

EXPERT OPINION

For weight management drugs to achieve the safety and efficacy required to be impactful, current studies are uncovering and characterizing new targets, including new signaling circuits and hormones regulating appetite and metabolism, and re-evaluating the role of pharmacotherapy in weight management. To avoid the safety failures of many past weight-loss drugs, the models and strategies covered in this article incorporate recent advances in knowledge and technology. We discuss the emergence of cGMP signaling as a potentially transformative target in weight management. Modulating cGMP signaling may represent an ideal goal for an anti-obesity pharmacotherapy, reflecting some of the major themes described in the present review: targeting pathways that are newly realized as relevant for weight management; promoting safety by re-purposing drugs that are safe, proven, and approved for clinical use; and having a synergistic effect on multiple, reinforcing pathways.

Neuroendocrine control of feeding behavior and psychomotor activity by neuropeptideY in fish

Neuropeptide Y (NPY) is a neuropeptide distributed widely among vertebrates. In mammals, NPY and its related peptides such as pancreatic polypeptide and peptide YY (PYY) are distributed throughout the brain and gastrointestinal tissues, and are centrally involved in many physiological functions such as the regulation of food intake, locomotion and psychomotor activities through their receptors. With regard to non-mammalian vertebrates, there has also been intensive study aimed at the identification and functional characterization of NPY, PYY and their receptors, and recent investigations of the role of NPY have revealed that it exerts several behavioral effects in goldfish and zebrafish. Both of these species are excellent teleost fish models, in which it has been demonstrated that NPY increases food consumption as an orexigenic factor and reduces locomotor activity, as is the case in mammals. This paper reviews current knowledge of NPY derived from studies of teleost fish, as representative non-mammals, focusing particularly on the role of the NPY system, and examines its significance from a comparative viewpoint.

Neuropeptide Y in tiger puffer (Takifugu rubripes): distribution, cloning, characterization, and mRNA expression responses to prandial condition

Neuropeptide tyrosine (NPY) is a potent orexigenic neuropeptide implicated in feeding regulation in rodents. However, the involvement of NPY in feeding behavior has not well been studied in fish. Therefore, we investigated the role of NPY in food intake using a tiger puffer (Takifugu rubripes) model. We observed the distribution of NPY-like immunoreactivity in the brain. Neuronal cell bodies containing NPY were located in the telencephalon, hypothalamus, mesencephalon, and medulla oblongata, and their nerve fibers were also found throughout the brain. We cloned two cDNAs, encoding NPYa and NPYb orthologs, respectively, from the brain, and also confirmed two genes encoding these NPYs in the Takifugu genome database. We examined the distribution of these transcripts in the brain using real-time PCR. Levels of NPYa mRNA in the telencephalon, mesencephalon and hypothalamus were much higher than in the medulla oblongata and cerebellum, whereas levels of NPYb mRNA in the medulla oblongata were higher than in other regions. We also examined prandial effects on the expression level of these transcripts in the telencephalon and hypothalamus. NPYa mRNA levels in the hypothalamus, but not in the telencephalon, obtained from fish fasted for one week were higher than those in fish that had been fed normally. The level was decreased at 2 h after feeding. Levels of NPYb mRNA were not affected by prandial conditions. These results suggest that NPY is present throughout the brain, and that NPYa, but not NPYb, in the hypothalamus is involved in the feeding regulation in the tiger puffer.

Relationship between alpha-melanocyte-stimulating hormone- and neuropeptide Y-containing neurons in the goldfish hypothalamus

Intracerebroventricular (ICV) injection of alpha-melanocyte-stimulating hormone (alpha-MSH) inhibits, whereas ICV injection of neuropeptide Y (NPY) stimulates food intake in the goldfish. However, there is little information about the functional relationship between alpha-MSH-induced anorexigenic and NPY-induced orexigenic actions in the goldfish. In this study we examined the relationship between alpha-MSH- and NPY-containing neurons in the goldfish hypothalamus to investigate whether these alpha-MSH- and NPY-containing neurons have direct mutual inputs. alpha-MSH- and NPY-like immunoreactivities were distributed throughout the brain, especially in the diencephalon. In particular, alpha-MSH-containing nerve fibers or endings lay in close apposition to NPY-containing neurons in a specific region of the hypothalamus, the nucleus posterioris periventricularis (NPPv). NPY-containing nerve fibers or endings also lay in close apposition to alpha-MSH-containing neurons specifically in the interior part of the nucleus lateralis tuberis (NLTi). We also investigated the effect of ICV injection of melanocortin 4 receptor agonist (melanotan II) at 100 pmol/g body weight (BW), which is enough to suppress food intake, or NPY at 10 pmol/g BW, which is enough to enhance food intake, on expression levels of mRNA for NPY or proopiomelanocortin (POMC) in the hypothalamus. ICV injection of melanotan II and NPY induced a significant decrease in the expression levels for NPY and POMC mRNA, respectively. These observations suggest that alpha-MSH- and NPY-containing neurons share direct mutual inputs in the NPPv and the NLTi of the hypothalamus, and that alpha-MSH and NPY functionally interact or exhibit mutual inhibition to regulate feeding behavior in the goldfish.

Transmembrane protein topology prediction using support vector machines

Background

Alpha-helical transmembrane (TM) proteins are involved in a wide range of important biological processes such as cell signaling, transport of membrane-impermeable molecules, cell-cell communication, cell recognition and cell adhesion. Many are also prime drug targets, and it has been estimated that more than half of all drugs currently on the market target membrane proteins. However, due to the experimental difficulties involved in obtaining high quality crystals, this class of protein is severely under-represented in structural databases. In the absence of structural data, sequence-based prediction methods allow TM protein topology to be investigated.

Results

We present a support vector machine-based (SVM) TM protein topology predictor that integrates both signal peptide and re-entrant helix prediction, benchmarked with full cross-validation on a novel data set of 131 sequences with known crystal structures. The method achieves topology prediction accuracy of 89%, while signal peptides and re-entrant helices are predicted with 93% and 44% accuracy respectively. An additional SVM trained to discriminate between globular and TM proteins detected zero false positives, with a low false negative rate of 0.4%. We present the results of applying these tools to a number of complete genomes. Source code, data sets and a web server are freely available from .

Conclusion

The high accuracy of TM topology prediction which includes detection of both signal peptides and re-entrant helices, combined with the ability to effectively discriminate between TM and globular proteins, make this method ideally suited to whole genome annotation of alpha-helical transmembrane proteins.

Neuronal relationship between orexin-A- and neuropeptide Y-induced orexigenic actions in goldfish

Orexin-induced orexigenic action is mediated by neuropeptide Y (NPY) in goldfish and rodents. A previous study indicated that NPY-induced orexigenic action may also be mediated by orexin-A in goldfish. However, there is little information about the mutual actions of orexin-A and NPY in the goldfish. Therefore, using their specific receptor antagonists, we examined whether the orexigenic actions of orexin-A and NPY mutually interact in the goldfish. The stimulatory effect of intracerebroventricular injection of NPY at 1 pmol/g body weight (BW) on food intake was abolished by treatment with the orexin receptor-1 antagonist, SB334867, at 10 pmol/g BW whereas the NPY Y1-receptor antagonist, BIBP3226, at 100 pmol/g BW attenuated orexin-A (at 2.8 pmol/g BW)-stimulated feeding. This led us, using a double-immunostaining method and confocal laser scanning microscopy, to investigate whether orexin-A- and NPY-containing neurons in the goldfish brain have direct mutual inputs. Orexin-A- and NPY-like immunoreactivities were distributed throughout the brain, especially in the diencephalon. Orexin-A- and NPY-containing neurons were located in a region of the hypothalamus, the nucleus posterioris periventricularis (NPPv), in close proximity to each other: NPY-containing nerve fibers or endings lay in close apposition to orexin-A-containing neurons in the NPPv, and orexin-A-containing nerve fibers or endings also lay in close apposition to NPY-containing neurons in the same region. These results indicate that, in goldfish, orexin-A- and NPY-induced orexigenic actions are mediated by mutual signaling pathways.

Phylogenetic and chromosomal analyses of multiple gene families syntenic with vertebrate Hox clusters

Background

Ever since the theory about two rounds of genome duplication (2R) in the vertebrate lineage was proposed, the Hox gene clusters have served as the prime example of quadruplicate paralogy in mammalian genomes. In teleost fishes, the observation of additional Hox clusters absent in other vertebrate lineages suggested a third tetraploidization (3R). Because the Hox clusters occupy a quite limited part of each chromosome, and are special in having position-dependent regulation within the multi-gene cluster, studies of syntenic gene families are needed to determine the extent of the duplicated chromosome segments. We have analyzed in detail 14 gene families that are syntenic with the Hox clusters to see if their phylogenies are compatible with the Hox duplications and the 2R/3R scenario. Our starting point was the gene family for the NPY family of peptides located near the Hox clusters in the pufferfish Takifugu rubripes, the zebrafish Danio rerio, and human.

Results

Seven of the gene families have members on at least three of the human Hox chromosomes and two families are present on all four. Using both neighbor-joining and quartet-puzzling maximum likelihood methods we found that 13 families have a phylogeny that supports duplications coinciding with the Hox cluster duplications. One additional family also has a topology consistent with 2R but due to lack of urochordate or cephalocordate sequences the time window when these duplications could have occurred is wider. All but two gene families also show teleost-specific duplicates.

Conclusion

Based on this analysis we conclude that the Hox cluster duplications involved a large number of adjacent gene families, supporting expansion of these families in the 2R, as well as in the teleost 3R tetraploidization. The gene duplicates presumably provided raw material in early vertebrate evolution for neofunctionalization and subfunctionalization.

Molecular characterization of neuropeptide Y gene in Chinese perch, an acanthomorph fish

The full-length neuropeptide Y (NPY) cDNA of Chinese perch Siniperca chuatsi was 704 bp in length, and contained a 300 bp open reading frame encoding a prepro-NPY with 99 amino acids. The predicted prepro-NPY peptide contained a putative signal peptide of 28 amino acids and a mature NPY of 36 amino acids, followed by the proteolytic processing site Gly-Lys-Arg and 35 amino acids that comprise the C-terminal peptide of NPY. Amino acid alignment and phylogenetic analysis indicate that the predicted Chinese perch prepro-NPY (composed of 99 amino acids) had high identities to the prepro-NPY of acanthomorph fishes (93-95%), whereas it had much lower identities to the prepro-NPY (composed of 96 or 97 amino acids) of cyprinid fishes (59-60%) or mammals (57-63%). Chinese perch NPY gene consists of four exons and three introns. The ratio of intron 2 to intron 3 was over 14 in Chinese perch NPY gene, whereas this ratio was below 4 in zebrafish and mammalian NPY gene. The total size of the Chinese perch NPY gene was 2223 bp, which was only about 28% of the size of NPY gene in higher vertebrate. Analysis of a 1622 bp promoter region of Chinese perch NPY gene, revealed a typical TATA box, a GC box and an untypical CAAT box, located at 84 bp, 101 bp and 303 bp upstream of the start codon respectively. Three STAT binding site-like elements (TCCAGTA) which were necessary for the leptin-induced transcriptional control of rat NPY gene were identified. In consistence to the effect of cortisol on fish brain NPY mRNA expression, four glucocorticoid-responsive elements were detected. Besides the highest expression in brain, substantial level of Chinese perch NPY mRNA expression was detected in the spleen and liver, and trace level of NPY mRNA expression was also detected in the adipose tissue, intestine and muscle. These results indicated that Chinese perch NPY might be involved in the food intake control by leptin and cortisol system, and diversification of NPY signaling should exist between acanthomorph fishes and cyprinid fishes as well as mammals.

Cloning and characterization of neuropeptide Y (NPY) and cocaine and amphetamine regulated transcript (CART) in Atlantic cod (Gadus morhua)

Neuropeptide Y (NPY) and cocaine and amphetamine regulated transcript (CART) are two neuropeptides involved in the regulation of feeding in both mammals and fish. NPY stimulates feeding whereas CART inhibits feeding. In this study, we have cloned the full-length cDNA and complete genomic DNA sequences for NPY and CART in Atlantic cod. Atlantic cod preproNPY share a 45-85% identity with preproNPY from other fish whereas preproCART shows a 70% identity to CART peptides from zebrafish and goldfish. RT-PCR revealed that NPY mRNA is expressed in brain, in particular the forebrain, and in peripheral tissues, including intestine and kidney. CART mRNA is expressed throughout the brain and in ovaries. In order to assess the role of these peptides in the regulation of feeding, we examined changes in mRNA expression in the forebrain before, during and after a meal. NPY and CART mRNA both undergo peri-prandial changes in expression, with NPY levels being elevated around meal time and CART showing a decline 2 h after a meal. Food deprivation for 7 days induced a decrease in CART mRNA expression in the brain but did not affect NPY mRNA expression. Overall, our results suggest that NPY and CART are conserved peptides that might be involved in the regulation of feeding and other physiological functions in Atlantic cod.

Cloning and sequence analysis of the neuropeptide Y receptors Y5 and Y6 in the coelacanth Latimeria chalumnae

Two coelacanth species, Latimeria chalumnae and Latimeria menadoensis, the recently discovered second species, have a key evolutionary position at the divergence of bony fishes and tetrapods. Together with lungfishes, they are the only living species separating the species-rich tetrapods from the other major group of vertebrates, the ray-finned fishes. The coelacanth is therefore of great importance for comparisons of gene families that differ between these two groups, such as the neuropeptide Y (NPY) receptor family. In this work we have sequenced the full-length genes for two NPY receptors in Latimeria chalumnae. Phylogenetic analysis indicated that the two sequences are orthologs of the mammalian Y5 and Y6 receptors. The Y5 gene has been implicated in appetite stimulation in mammals but is absent from teleost fishes. The presence of the Y5 receptor in Latimeria together with phylogenetic analysis shows that Y5 existed before the separation of bony fishes and tetrapods. The Latimeria receptor has about 62% identity to tetrapod Y5 sequences and contains the extended third intracellular loop with several highly conserved motifs that may be involved in signal transduction. The Latimeria Y6 receptor has about 60% identity to tetrapod Y6 sequences. The functional role of Y6 is unclear as the gene is seemingly functional in some mammals but is non-functional in others. The Y6 receptor is also missing in teleost fishes. Our results confirm an early vertebrate origin for all NPY receptor subtypes presently found in mammals followed by differential gene loss in the different classes of vertebrates.

The role of neuropeptide Y, orexins, cocaine and amphetamine-related transcript, cholecystokinin, amylin and leptin in the regulation of feeding in fish

In fish, as in all vertebrates, the brain is the primary center of regulation of food intake. Afferent signals continuously inform the central nervous system about changes in energy homeostasis. The brain interprets and integrates these signals and responds with efferent signals that help maintain a constant energy balance. Neuropeptides that originate from the hypothalamus regulate food intake either by stimulating (orexigenic factors) or inhibiting (anorexigenic factors) appetite. Studies using brain or peripheral peptide injections have shown that neuropeptide Y (NPY) and orexins are potent orexigenic factors in fish, whereas cocaine and amphetamine-related transcript (CART) peptides decrease food intake. Complex interactions exist between these central neuropeptide systems. For example, NPY and orexins have synergistic effects on food intake and they are both modulated by CART peptides. These systems are also influenced by endocrine factors from the periphery, including hormones from the gut, such as cholecystokinin (CCK), the pancreatic hormone amylin and the adipocyte hormone leptin. Fasting or ingestion of a meal induces changes in the mRNA expression of NPY, orexins and CART, suggesting that nutritional status modulates the action of these systems. This brief review will focus on our current knowledge on the structure and role of these six appetite-regulating peptides in fish.