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

Intraperitoneal administration of arginine vasotocin (AVT) induces anorexigenic and anxiogenic actions via the brain V1a receptor-signaling pathway in the tiger puffer, Takifugu rubripes

Arginine vasotocin (AVT) is produced mainly in the hypothalamus and as a neurohypophyseal hormone peripherally regulates water-mineral balance in sub-mammals. In addition, AVT-containing neurons innervate several areas of the brain, and AVT also acts centrally as both an anorexigenic and anxiogenic factor in goldfish. However, it is unclear whether these central effects operate in fish in general. In the present study, therefore, we investigated AVT-like immunoreactivity in the brain of the tiger puffer, a cultured fish with a high market value in Japan and also a representative marine teleost species, focusing particularly on whether AVT affects food intake and psychomotor activity. AVT-like immunoreactivity was distributed higher in the ventral region of the telencephalon, the hypothalamus and midbrain. Intraperitoneal (IP) administration of AVT at 100 pmol g-1 body weight (BW) increased the immunoreactivity of phosphorylated ribosomal proteinS6 (RPS6), a neuronal activation marker, in the telencephalon and diencephalon, decreased food consumption and enhanced thigmotaxis. AVT-induced anorexigenic and anxiogenic actions were blocked by IP co-injection of a V1a receptor (V1aR) antagonist, Manning compound (MC) at 300 pmol g-1 BW. These results suggest that AVT acts as an anorexigenic and anxiogenic factor via the V1aR-signaling pathway in the tiger puffer brain.

Neuropeptide Y receptor Y8b (npy8br) regulates feeding and digestion in Japanese medaka (Oryzias latipes) larvae: evidence from gene knockout

Neuropeptide Y receptor Y8 (NPY8R) is a fish-specific receptor with two subtypes, NPY8AR and NPY8BR. Changes in expression levels during physiological processes or in vivo regulation after ventricular injection suggest that NPY8BR plays an important role in feeding regulation; this has been found in only a few fish, at present. In order to better understand the physiological function of npy8br, especially in digestion, we used clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) technology to generate npy8br-/- Japanese medaka (Oryzias latipes). We found that the deletion of npy8br in medaka larvae affected their feeding and digestion ability, ultimately affecting their growth. Specifically, npy8br deficiency in medaka larvae resulted in decreased feed intake and decreased expression levels of orexigenic genes (npy and agrp). npy8br-/- medaka larvae fed for 10 d (10th day of feeding) still had incompletely digested brine shrimp (Artemia nauplii) in the digestive tract 8 h after feeding, the messenger RNA (mRNA) expression levels of digestion-related genes (amy, lpl, ctra, and ctrb) were significantly decreased, and the activity of amylase, trypsin, and lipase also significantly decreased. The deletion of npy8br in medaka larvae inhibited the growth and significantly decreased the expression of growth-related genes (gh and igf1). Hematoxylin and eosin (H&E) sections of intestinal tissue showed that npy8br-/- medaka larvae had damaged intestine, thinned intestinal wall, and shortened intestinal villi. So far, this is the first npy8br gene knockout model established in fish and the first demonstration that npy8br plays an important role in digestion.

The effect of environmental stressors on growth in fish and its endocrine control

Fish body growth is a trait of major importance for individual survival and reproduction. It has implications in population, ecology, and evolution. Somatic growth is controlled by the GH/IGF endocrine axis and is influenced by nutrition, feeding, and reproductive-regulating hormones as well as abiotic factors such as temperature, oxygen levels, and salinity. Global climate change and anthropogenic pollutants will modify environmental conditions affecting directly or indirectly fish growth performance. In the present review, we offer an overview of somatic growth and its interplay with the feeding regulatory axis and summarize the effects of global warming and the main anthropogenic pollutants on these endocrine axes.

Mapping key neuropeptides involved in the melanocortin system in Atlantic salmon (Salmo salar) brain

The melanocortin system is a key regulator of appetite and food intake in vertebrates. This system includes the neuropeptides neuropeptide y (NPY), agouti-related peptide (AGRP), cocaine- and amphetamine-regulated transcript (CART), and pro-opiomelanocortin (POMC). An important center for appetite control in mammals is the hypothalamic arcuate nucleus, with neurons that coexpress either the orexigenic NPY/AGRP or the anorexigenic CART/POMC neuropeptides. In ray-finned fishes, such a center is less characterized. The Atlantic salmon (Salmo salar) has multiple genes of these neuropeptides due to whole-genome duplication events. To better understand the potential involvement of the melanocortin system in appetite and food intake control, we have mapped the mRNA expression of npy, agrp, cart, and pomc in the brain of Atlantic salmon parr using in situ hybridization. After identifying hypothalamic mRNA expression, we investigated the possible intracellular coexpression of npy/agrp and cart/pomc in the tuberal hypothalamus by fluorescent in situ hybridization. The results showed that the neuropeptides were widely distributed, especially in sensory and neuroendocrine brain regions. In the hypothalamic lateral tuberal nucleus, the putative homolog to the mammalian arcuate nucleus, npya, agrp1, cart2b, and pomca were predominantly localized in distinct neurons; however, some neurons coexpressed cart2b/pomca. This is the first demonstration of coexpression of cart2b/pomca in the tuberal hypothalamus of a teleost. Collectively, our data suggest that the lateral tuberal nucleus is the center for appetite control in salmon, similar to that of mammals. Extrahypothalamic brain regions might also be involved in regulating food intake, including the olfactory bulb, telencephalon, midbrain, and hindbrain.

Neuropeptide Y in Spotted Scat (Scatophagus Argus), Characterization and Functional Analysis towards Feed Intake Regulation

Neuropeptide Y (Npy) is an intricate neuropeptide regulating numerous physiological processes. It is a highly conserved peptide known to improve feed intake in many vertebrates, including fishes. To enlighten the mechanism of Npy in spotted scat feed intake control, we cloned and identified the Npy cDNA sequence. We further examined its expression in some tissues and explored its expression effects at different time frames (hours and days). Here, we discovered that spotted scat Npy comprised a 300 bp open reading frame (ORF) and a 99 amino acid sequence. Npy was identified to be expressed in all tissues examined. Using in situ hybridization examination, we proved that npy has a wide expression in the brain of the spotted scat. Furthermore, the expression of npy in the hypothalamus significantly increased one hour after feeding (p < 0.05). Further, it was revealed that npy expression significantly increased in fish that were fasted for up to 5 days and significantly increased after refeeding from the 8th to the 10th day. This suggests that Npy is an orexigenic peptide, and hence, it increases food intake and growth in the spotted scat. Additionally, results from in vitro and in vivo experiments revealed that Npy locally interacts with other appetite-regulating peptides in the spotted scat hypothalamus. This research aimed to set a fundamental study in developing the feed intake regulation, improving growth and reproduction, which is significant to the aquaculture industry of the spotted scat.

Recent advances in neuropeptide-related omics and gene editing: Spotlight on NPY and somatostatin and their roles in growth and food intake of fish

Feeding and growth are two closely related and important physiological processes in living organisms. Studies in mammals have provided us with a series of characterizations of neuropeptides and their receptors as well as their roles in appetite control and growth. The central nervous system, especially the hypothalamus, plays an important role in the regulation of appetite. Based on their role in the regulation of feeding, neuropeptides can be classified as orexigenic peptide and anorexigenic peptide. To date, the regulation mechanism of neuropeptide on feeding and growth has been explored mainly from mammalian models, however, as a lower and diverse vertebrate, little is known in fish regarding the knowledge of regulatory roles of neuropeptides and their receptors. In recent years, the development of omics and gene editing technology has accelerated the speed and depth of research on neuropeptides and their receptors. These powerful techniques and tools allow a more precise and comprehensive perspective to explore the functional mechanisms of neuropeptides. This paper reviews the recent advance of omics and gene editing technologies in neuropeptides and receptors and their progresses in the regulation of feeding and growth of fish. The purpose of this review is to contribute to a comparative understanding of the functional mechanisms of neuropeptides in non-mammalians, especially fish.

Regional Expression of npy mRNA Paralogs in the Brain of Atlantic Salmon (Salmo salar, L.) and Response to Fasting

Neuropeptide Y (NPY) is known as a potent orexigenic signal in vertebrates, but its role in Atlantic salmon has not yet been fully established. In this study, we identified three npy paralogs, named npya1, npya2, and npyb, in the Atlantic salmon genome. In silico analysis revealed that these genes are well conserved across the vertebrate’s lineage and the mature peptide sequences shared at least 77% of identity with the human homolog. We analyzed mRNA expression of npy paralogs in eight brain regions of Atlantic salmon post-smolt, and the effect of 4 days of fasting on the npy expression level. Results show that npya1 was the most abundant paralog, and was predominantly expressed in the telencephalon, followed by the midbrain and olfactory bulb. npya2 mRNA was highly abundant in hypothalamus and midbrain, while npyb was found to be highest expressed in the telencephalon, with low mRNA expression levels detected in all the other brain regions. 4 days of fasting resulted in a significant (p < 0.05) decrease of npya1 mRNA expression in the olfactory bulb, increased npya2 mRNA expression in the midbrain and decreased npyb mRNA expression in the pituitary. In the hypothalamus, the vertebrate appetite center, expression of the npy paralogs was not significantly affected by feeding status. However, we observed a trend of increased npya2 mRNA expression (p = 0.099) following 4 days of fasting. Altogether, our findings provide a solid basis for further research on appetite and energy metabolism in Atlantic salmon.

The Roles of Neuropeptide Y (Npy) and Peptide YY (Pyy) in Teleost Food Intake: A Mini Review

Neuropeptide Y family (NPY) is a potent orexigenic peptide and pancreatic polypeptide family comprising neuropeptide Y (Npy), peptide YYa (Pyya), and peptide YYb (Pyyb), which was previously known as peptide Y (PY), and tetrapod pancreatic polypeptide (PP), but has not been exhaustively documented in fish. Nonetheless, Npy and Pyy to date have been the key focus of countless research studies categorizing their copious characteristics in the body, which, among other things, include the mechanism of feeding behavior, cortical neural activity, heart activity, and the regulation of emotions in teleost. In this review, we focused on the role of neuropeptide Y gene (Npy) and peptide YY gene (Pyy) in teleost food intake. Feeding is essential in fish to ensure growth and perpetuation, being indispensable in the aquaculture settings where growth is prioritized. Therefore, a better understanding of the roles of these genes in food intake in teleost could help determine their feeding regime, regulation, growth, and development, which will possibly be fundamental in fish culture.

Nutrient regulation of somatic growth in teleost fish. The interaction between somatic growth, feeding and metabolism

This review covers the current knowledge on the regulation of the somatic growth axis and its interaction with metabolism and feeding regulation. The main endocrine and neuroendocrine factors regulating both the growth axis and feeding behavior will be briefly summarized. Recently discovered neuropeptides and peptide hormones will be mentioned in relation to feeding control as well as growth hormone regulation. In addition, the influence of nutrient and nutrient sensing mechanisms on growth axis will be highlighted. We expect that in this process gaps of knowledge will be exposed, stimulating future research in those areas.

Growth and Metabolic Response of Chinese Perch to Different Dietary Protein-to-Energy Ratios in Artificial Diets

The effect of dietary nutrients on novel farm species has always garnered wide research and economic interest. Chinese perch, an economically important carnivorous fish, accepts an artificial diet after taming, so it is essential to evaluate and optimize the nutritional and metabolic demands of this species. However, little is known about the effect of an artificial diet on the growth and metabolism of Chinese perch. Therefore, the present study evaluated the growth and metabolic responses of Chinese perch to experimental diets with different dietary protein/energy (P/E) ratios. Five isoenergetic diets (18 kJ/g) with graded levels of P/E ratios of 30.58, 33.22, 35.90, 38.6, and 41.35 mg/kJ (named A, B, C, D, and E) were formulated. A total of 225 Chinese perch (64.89 ± 0.28 g) were divided into five groups (triplicate tanks for each group), distributed into 15 (350 L) fiberglass tanks, and fed twice a day at 4% of fish wet body weight with the respective P/E ratio diets for 10 weeks. Compared with the other groups, Chinese perch in Group C showed significantly improved growth performance, weight gain (WG), specific growth rate (SGR), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat (IPF), feed utilization, feed intake (FI), feed conversion ratio (FCR), protein efficiency ratio (PER), protein retention efficiency (PRE), energy retention efficiency (ERE), and feed efficiency (FE) as well as whole-body, muscle, and liver composition. Chinese perch in Group A, on the other hand, had the lowest growth performance, feed utilization, and body composition compared with the other groups. The activities of nitrogen metabolism-related enzymes (alanine aminotransferase (ALT), aspartate aminotransferase (AST) glutamate dehydrogenase (GDH), and adenosine 5′-monophosphate deaminase (AMPD)) as well as the mRNA expression of the GDH and AMPD genes were significantly lower than those in the other groups. Similarly, the expression of NPY and AgRp were significantly higher in Group C compared with the other groups. However, the gene expression of CART and POMC was not affected by the dietary P/E ratios. In Group A, the expression of mTOR, S6K, and 4EBP1 was significantly lower and that of AMPK, LKB1, and eEF2 was significantly higher when compared with the other groups. Biochemical analysis of blood showed that ALT, AST, total protein (TP), alkaline phosphatase (ALP), glucose (GLU), blood urea nitrogen (BUN), and triglyceride (TG) levels were also affected by the dietary P/E ratio. From our results, we concluded that Chinese perch growth performance and nutrient metabolism were significantly affected by the P/E ratio of the artificial diet. Second-order polynomial regression analysis revealed that Chinese perch growth performance was optimal at a P/E ratio of 37.98 in the artificial diet.

Metabolic hormones and the regulation of spermatogenesis in fishes

Metabolic hormones play essential regulatory roles in many biological processes, including morphogenesis, growth, and reproduction through the maintenance of energy balance. Various metabolic hormones originally discovered in mammals, including ghrelin, leptin, and nesfatin-1 have been identified and characterized in fish. However, physiological roles of these metabolic hormones in regulating reproduction are largely unknown in fishes, especially in males. While the information available is restricted, this review attempts to summarize the main findings on the roles of metabolic peptides on the reproductive system in male fishes with an emphasis on testicular development and spermatogenesis. Specifically, the primary goal is to review the physiological interactions between hormones that regulate reproduction and hormones that regulate metabolism as a critical determinant of testicular function. A brief introduction to the localization of metabolic hormones in fish testis is also provided. Besides, the consequences of fasting and food deprivation on testicular development and sperm quality will be discussed with a focus on interactions between metabolic and reproductive hormones.

Nutrient Regulation of Endocrine Factors Influencing Feeding and Growth in Fish

Endocrine factors regulate food intake and growth, two interlinked physiological processes critical for the proper development of organisms. Somatic growth is mainly regulated by growth hormone (GH) and insulin-like growth factors I and II (IGF-I and IGF-II) that act on target tissues, including muscle, and bones. Peptidyl hormones produced from the brain and peripheral tissues regulate feeding to meet metabolic demands. The GH-IGF system and hormones regulating appetite are regulated by both internal (indicating the metabolic status of the organism) and external (environmental) signals. Among the external signals, the most notable are diet availability and diet composition. Macronutrients and micronutrients act on several hormone-producing tissues to regulate the synthesis and secretion of appetite-regulating hormones and hormones of the GH-IGF system, eventually modulating growth and food intake. A comprehensive understanding of how nutrients regulate hormones is essential to design diet formulations that better modulate endogenous factors for the benefit of aquaculture to increase yield. This review will discuss the current knowledge on nutritional regulation of hormones modulating growth and food intake in fish.

Appetite-Controlling Endocrine Systems in Teleosts

Mammalian studies have shaped our understanding of the endocrine control of appetite and body weight in vertebrates and provided the basic vertebrate model that involves central (brain) and peripheral signaling pathways as well as environmental cues. The hypothalamus has a crucial function in the control of food intake, but other parts of the brain are also involved. The description of a range of key neuropeptides and hormones as well as more details of their specific roles in appetite control continues to be in progress. Endocrine signals are based on hormones that can be divided into two groups: those that induce (orexigenic), and those that inhibit (anorexigenic) appetite and food consumption. Peripheral signals originate in the gastrointestinal tract, liver, adipose tissue, and other tissues and reach the hypothalamus through both endocrine and neuroendocrine actions. While many mammalian-like endocrine appetite-controlling networks and mechanisms have been described for some key model teleosts, mainly zebrafish and goldfish, very little knowledge exists on these systems in fishes as a group. Fishes represent over 30,000 species, and there is a large variability in their ecological niches and habitats as well as life history adaptations, transitions between life stages and feeding behaviors. In the context of food intake and appetite control, common adaptations to extended periods of starvation or periods of abundant food availability are of particular interest. This review summarizes the recent findings on endocrine appetite-controlling systems in fish, highlights their impact on growth and survival, and discusses the perspectives in this research field to shed light on the intriguing adaptations that exist in fish and their underlying mechanisms.

Modulation of appetite, lipid and glucose metabolism of juvenile grass carp (Ctenopharyngodon idellus) by different dietary protein levels

This study was undertaken to explore the systemic metabolic strategies of juvenile grass carp (Ctenopharyngodon idellus) to maintain growth when fed with different dietary protein levels. The optimal growth group and two growing discomfort groups were selected through the basic data, to explain the growth difference from appetite regulation and lipid and glucose metabolism perspective. Three experimental diets were formulated with three dietary protein levels at 200.3, 296.1 and 442.9 g kg^-1, named P1, P2 and P3, respectively. Juvenile grass carp (initial body weight 12.28 ± 0.14 g) were fed with three diets with 3 replications per dietary treatment in an indoor recirculation system for an 8-week feeding trial. Fish fed with diet P2 dietary group showed significantly higher WG, SGR, FI and PER than other groups. Compared with other groups, mRNA expressions of NPY, Y8a and Y8b in fish fed with P2 significantly down-regulated, while the expressions of CCK and CART in fish fed with P3 significantly down-regulated (P < 0.05). With increasing dietary protein levels, G6Pase, GK, PK and PEPCK were all significantly inhibited (P < 0.05). For lipid metabolism, the mRNA expression of ACC in P1 dietary group was significantly higher than P3 dietary group; besides, LPL expression in P3 group was significantly higher than other two groups (P < 0.05). PPARα expression in P2 was significantly lower than other groups (P < 0.05). These results suggested that grass carp fed with P2 (296.1 g kg^-1 protein level) showed highest weight gain, contributed to more balanced nutrient metabolism and appetite regulation. Too high dietary protein (442.9 g kg^-1) should be avoided because it induced lowest PER, body lipid and liver lipid, and inhibited glucose and lipid metabolism in juvenile grass carp.

The Neuroendocrine Regulation of Food Intake in Fish: A Review of Current Knowledge

Fish are the most diversified group of vertebrates and, although progress has been made in the past years, only relatively few fish species have been examined to date, with regards to the endocrine regulation of feeding in fish. In fish, as in mammals, feeding behavior is ultimately regulated by central effectors within feeding centers of the brain, which receive and process information from endocrine signals from both brain and peripheral tissues. Although basic endocrine mechanisms regulating feeding appear to be conserved among vertebrates, major physiological differences between fish and mammals and the diversity of fish, in particular in regard to feeding habits, digestive tract anatomy and physiology, suggest the existence of fish- and species-specific regulating mechanisms. This review provides an overview of hormones known to regulate food intake in fish, emphasizing on major hormones and the main fish groups studied to date.

Effects of postprandial starvation on mRNA expression of endocrine-, amino acid and peptide transporter-, and metabolic enzyme-related genes in zebrafish (Danio rerio)

The goal of this study was to systematically evaluate the molecular activities of endocrine-, amino acid and peptide transporters-, and metabolic enzyme-related genes in 35-day-old mixed-sex zebrafish (Danio rerio) after feeding . Zebrafish with initial body weights ranging from 9 to 11 mg were fasted for 384 h in a controlled indoor environment. Fish were sampled at 0, 3, 6, 12, 24, 48, 96, 192, and 384 h after fed. Overall, the present study results show that the regulatory mechanism that insulin-like growth factor I negative feedback regulated growth hormone is conserved in zebrafish, as it is in mammals, but that regulation of growth hormone receptors is highly intricate. Leptin and cholecystokinin are time-dependent negative feedback signals, and neuropeptide Y may be an important positive neuropeptide for food intake in zebrafish. The amino acid/carnitine transporters B(0,+) (ATB(0,+)) and broad neutral (0) amino acid transporter 1(B(0)AT1) mRNA levels measured in our study suggest that protein may be utilized during 24-96 h of fasting in zebrafish. Glutamine synthetase mRNA levels were downregulated, and glutamate dehydrogenase, alanine aminotransferase, aspartate transaminase, and trypsin mRNA levels were upregulated after longtime fasting in this study. The mRNA expression levels of fatty acid synthetase decreased significantly (P < 0.05), whereas those of lipoprotein lipase rapidly increased after 96 h of fasting. Fasting activated the expression of glucose synthesis genes when fasting for short periods of time; when fasting is prolonged, the mRNA levels of glucose breakdown enzymes and pentose phosphate shunt genes decreased.

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.

Characterization and expression analysis of two distinct neuropeptide Ya paralogues in Jian carp (Cyprinus carpio var. Jian)

Two distinct neuropeptide Ya paralogues (jlNPYa1 and jlNPYa2) were cloned and characterized in Jian carp (Cyprinus carpio var. Jian), with a highly conserved organization encoded by four exons and three introns. The cDNAs for jlNPYa1 and jlNPYa2 were 693 and 730 bp in size, respectively. jlNPYa1 and jlNPYa2 both encoded a 96-amino acid protein, which shared 97.9 % identity. Phylogenetic tree showed that it has two NPYa genes, called jlNPYa1 and jlNPYa2, that presumably resulted from the tetraploidization event in the carp lineage. Analysis of expression profiles of jlNPYa1 and jlNPYa2 showed that the two NPY genes had a broad tissue distribution but expressed primarily in the forebrain, hypothalamus, testis and liver. The expression pattern was different in juvenile and adult (female and male) Jian carp. In juvenile, the highest expression level of jlNPYa1 and jlNPYa2 was detected in the testis. In adult, it was detected in the forebrain. In female hypothalamus, the expression level of jlNPYa1 was significantly higher than that of jlNPYa2. However, the opposite was true in male hypothalamus. The differing distribution patterns of the two NPY genes suggested that jlNPYa1 and jlNPYa2 might play different roles in Jian carp.

An investigation of appetite-related peptide transcript expression in Atlantic cod (Gadus morhua) brain following a Camelina sativa meal-supplemented feeding trial

Camelina sativa is a hardy oilseed crop with seeds that contain high levels of ω3 polyunsaturated fatty acids and protein, which are critical components of fish feed. Camelina might thus be used as a cheaper and more sustainable supplement to fish-based products in aquaculture. Atlantic cod, Gadus morhua, is a species of interest in the aquaculture industry due to a decrease in wild populations and subsequent collapse of some cod fisheries. As cod are carnivorous fish, it is necessary to determine how this species physiologically tolerates plant-based diets. In this study, juvenile Atlantic cod were subjected to 13 weeks of either 15 or 30% camelina meal (CM)-supplemented diets or a control fish meal feed. Growth and food intake were evaluated and the mRNA expression of appetite-related hormones [pro-melanin-concentrating hormone (pmch), hypocretin (synonym: orexin, hcrt), neuropeptide Y (npy) and cocaine- and amphetamine-regulated transcript (cart)] was assessed using quantitative real-time PCR in brain regions related to food intake regulation (telencephalon/preoptic area, optic tectum/thalamus and hypothalamus). CM inclusion diets caused decreases in both growth and food intake in Atlantic cod. Optic tectum pmch transcript expression was significantly higher in fish fed the 30% CM diet compared to fish fed the 15% CM diet. In the hypothalamus, compared to fish fed the control diet, hcrt expression was significantly higher in fish fed the 30% CM diet, while npy transcript expression was significantly higher in fish fed the 15% CM diet. cart mRNA expression was not affected by diet in any brain region. Further studies are needed to determine which factors (e.g. anti-nutritional factors, palatability and nutritional deficits) contribute to reduced feed intake and growth, as well as the maximum CM inclusion level that does not negatively influence feed intake, growth rate and the transcript expression of appetite-related factors in Atlantic cod.

Central pathways integrating metabolism and reproduction in teleosts

Energy balance plays an important role in the control of reproduction. However, the cellular and molecular mechanisms connecting the two systems are not well understood especially in teleosts. The hypothalamus plays a crucial role in the regulation of both energy balance and reproduction, and contains a number of neuropeptides, including gonadotropin-releasing hormone (GnRH), orexin, neuropeptide-Y, ghrelin, pituitary adenylate cyclase-activating polypeptide, α-melanocyte stimulating hormone, melanin-concentrating hormone, cholecystokinin, 26RFamide, nesfatin, kisspeptin, and gonadotropin-inhibitory hormone. These neuropeptides are involved in the control of energy balance and reproduction either directly or indirectly. On the other hand, synthesis and release of these hypothalamic neuropeptides are regulated by metabolic signals from the gut and the adipose tissue. Furthermore, neurons producing these neuropeptides interact with each other, providing neuronal basis of the link between energy balance and reproduction. This review summarizes the advances made in our understanding of the physiological roles of the hypothalamic neuropeptides in energy balance and reproduction in teleosts, and discusses how they interact with GnRH, kisspeptin, and pituitary gonadotropins to control reproduction in teleosts.

Orexin and neuropeptide Y: tissue specific expression and immunoreactivity in the hypothalamus and preoptic area of the cichlid fish Cichlasoma dimerus

Neuropeptide Y (NPY) and orexin are neuropeptides involved in the regulation of feeding in vertebrates. In this study we determined the NPY and orexin mRNA tissue expression and their immunoreactivity distribution in both preoptic area and hypothalamus, regions involved in the regulation of feeding behavior. Both peptides presented a wide expression in all tissues examined. The NPY-immunoreactive (ir) cells were localized in the ventral nucleus posterioris periventricularis (NPPv) and numerous ir-NPY fibers were found in the nucleus lateralis tuberis (NLT), the nucleus recess lateralis (NRL) and the neurohypophysis. Ir-orexin cells were observed in the NPPv, dorsal NLT, ventral NLT, lateral NLT (NLTl) and the lateral NRL. Ir-orexin fibers were widespread distributed along all the hypothalamus, especially in the NLTl. Additionally, we observed the presence of ir-orexin immunostaining in adenohypophyseal cells, especially in somatotroph cells and the presence of a few ir-orexin-A fibers in the neurohypophysis. In conclusion, both peptides have an ubiquitous mRNA tissue expression and are similarly distributed in the hypothalamus and preoptic area of Cichlasoma dimerus. The presence of ir-orexin in adenohypohyseal cells and the presence of ir-orexin and NPY fibers in the neurohypophysis suggest that both peptides may play an important neuroendocrine role in anterior pituitary.

Neuropeptide Y gene expression around meal time in the Brazilian flounder Paralichthys orbignyanus

Neuropeptide Y (NPY) is considered the major stimulant for food intake in mammals and fish. Previous results indicate that NPY is involved in the feeding behaviour of the Brazilian flounder, Paralichthys orbignyanus. In this study, we evaluated hypothalamic NPY expression before (-2 h), during (0 h) and after feeding (+2 h) in two independent experiments: (1) during a normal feeding schedule and (2) in fish fasted for 2 weeks. During normal feeding, changes in the levels of NPY mRNA were periprandial, with expression levels being significantly elevated at meal time (P less than 0.05) and significantly reduced 2 h later (P less than 0.05). Comparing the fasting and unfasted groups, NPY mRNA levels were significantly higher (P less than 0.05) at -2 h and +2 h in the fasting group, but there was no difference at 0 h. In addition, the higher NPY mRNA levels that were observed in the fasting group were maintained throughout the sampling period. In summary, our results show that NPY expression was associated with meal time (0 h) in food intake regulation.

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.

Characterization of neuropeptide Y in snakeskin gourami and the change in its expression due to feeding status and melanocortin 4 receptor expression

In this study, we characterized the neuropeptide Y (NPY) mRNA in snakeskin gourami (Trichogaster pectoralis) (TpNPY). TpNPY displayed characteristics typical of previously reported NPYs, and it exhibited a high degree of homology with the NPY proteins of other vertebrates. A phylogenetic analysis demonstrated that TpNPY was closely related to the NPYs found in the acanthomorpha and salmoniformes fish species. TpNPY was found to be ubiquitously expressed in all brain regions when assessed by real-time RT-PCR and in situ hybridization. In addition, a graded expression level of TpNPY was observed in peripheral tissues; for example, a moderate level of TpNPY was found in the gills, liver, kidney, stomach, intestine, spleen and gonads, while a low level of TpNPY was found in the muscle. The change in expression of TpNPY with respect to daily feeding habits was investigated in distinct brain regions, including the telencephalon, mesencephalon, metencephalon, and diencephalon. Fluctuations in the expression level of TpNPY were observed for a 24h post-prandial period. Except for the telencephalon, a reduction in TpNPY expression was found after a meal, while a peak level of TpNPY was observed 1h before the scheduled breakfast. Furthermore, there was a positive correlation between TpNPY and TpMC4R in the telencephalon and diencephalon throughout the circadian feeding cycle, which suggests that there is a connection between the function of NPY and the melanocortin system for the regulation of daily feeding. Fish brains were incubated with an MC4R antagonist (i.e., HS024), and the expression of TpNPY and TpMC4R was measured. Interestingly, there was a significant relationship between the expression of TpNPY and TpMC4R under the effects of HS024, which demonstrates that there are interactions between MC4R and NPY, particularly in a hyperphagic state.

Neuropeptide Y stimulates food intake in the Zebrafish, Danio rerio

Neuropeptide Y (NPY) is a potent orexigenic neuropeptide implicated in feeding regulation in mammals. However, except for the case of the goldfish, the involvement of NPY in the feeding behaviour of teleost fish has not well been studied. Therefore, we investigated the role of NPY in food intake using a zebrafish (Danio rerio) model because the molecular bases of NPY and its receptor have been well studied in this species. We examined the effect of feeding status on NPY-like immunoreactivity and the expression level of the NPY transcript in the brain. The number of neuronal cells showing NPY-like immunoreactivity in the hypothalamic regions, including the periventricular nucleus of posterior tuberculum and the posterior tuberal nucleus, was significantly increased in fish fasted for 7 days. NPY mRNA levels in the hypothalamus, but not the telencephalon, obtained from fish fasted for 7 days were higher than those in fish that had been fed normally. We then investigated the effect of i.c.v. administration of NPY on food intake. Cumulative food intake was significantly increased by i.c.v. administration of NPY (at 1 and 10 pmol/g body weight; BW) during a 60-min observation period. The NPY-induced orexigenic action (at 10 pmol/g BW) was blocked by treatment with a NPY Y1 receptor antagonist, BIBP-3226, at 100 pmol/g BW. These results indicate that NPY acts as an orexigenic factor in the zebrafish.