Distribution and characterization of neuropeptide Y-like immunoreactivity in the brain and pituitary of the goldfish

Transgenic tools targeting the basal ganglia reveal both evolutionary conservation and specialization of neural circuits in zebrafish

The cortico-basal ganglia circuit mediates decision making. Here, we generated transgenic tools for adult zebrafish targeting specific subpopulations of the components of this circuit and utilized them to identify evolutionary homologs of the mammalian direct- and indirect-pathway striatal neurons, which respectively project to the homologs of the internal and external segment of the globus pallidus (dorsal entopeduncular nucleus [dEN] and lateral nucleus of the ventral telencephalic area [Vl]) as in mammals. Unlike in mammals, the Vl mainly projects to the dEN directly, not by way of the subthalamic nucleus. Further single-cell RNA sequencing analysis reveals two pallidal output pathways: a major shortcut pathway directly connecting the dEN with the pallium and the evolutionarily conserved closed loop by way of the thalamus. Our resources and circuit map provide the common basis for the functional study of the basal ganglia in a small and optically tractable zebrafish brain for the comprehensive mechanistic understanding of the cortico-basal ganglia circuit.

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.

mRNA expression and metabolic regulation of npy and agrp1/2 in the zebrafish brain

Neuropeptide Y (NPY) is an evolutionarily conserved neuropeptide implicated in feeding regulation in vertebrates. In mammals, NPY neurons coexpress Agouti-related protein (AgRP) in the arcuate nucleus of the hypothalamus, and NPY/AgRP neurons activate orexigenic signaling to increase food intake. Zebrafish express npy and two agrp genes, agrp1 and agrp2, in the brain. Similar to mammals, NPY and AgRP1 act as orexigenic factors in zebrafish, but the exact distribution of NPY and AgRP neurons in the zebrafish brain and the regulation of these genes by metabolic states remain unclear. In this study, we analyzed the tissue distribution of npy, agrp1, and agrp2 mRNA in the brain of larval and adult zebrafish. We detected the expression of agrp1, but not npy, in the hypothalamus of larval zebrafish. In the adult zebrafish brain, npy mRNA expression was detected in the dorsal area of the periventricular and lateral hypothalamus, but fasting induced upregulation of npy only in the lateral hypothalamus, indicating that NPY neurons in this area are implicated in feeding regulation. However, consistent with the findings in larval zebrafish, NPY neurons in the hypothalamus did not coexpress AgRP1. In contrast, fasting resulted in a dramatic increase in AgRP1 neurons in the ventral periventricular hypothalamus, which do not coexpress NPY. In addition, we found for the first time that npy- and agrp1-expressing neurons function as GABAergic inhibitory neurons in zebrafish, as they do in mammals. Taken together, our results show that the zebrafish NPY/AgRP system is involved in appetite regulation. In addition, our data suggest that although npy and agrp1 were initially expressed in distinct neurons, evolution has resulted in their coexpression in mammalian hypothalamic neurons.

Cloning, localization and differential expression of Neuropeptide-Y during early brain development and gonadal recrudescence in the catfish, Clarias gariepinus

Neuropeptide-Y (NPY) has diverse physiological functions which are extensively studied in vertebrates. However, regulatory role of NPY in relation to brain ontogeny and recrudescence with reference to reproduction is less understood in fish. Present report for the first time evaluated the significance of NPY by transient esiRNA silencing and also analyzed its expression during brain development and gonadal recrudescence in the catfish, Clarias gariepinus. As a first step, full-length cDNA of NPY was cloned from adult catfish brain, which shared high homology with its counterparts from other teleosts upon phylogenetic analysis. Tissue distribution revealed dominant expression of NPY in brain and testis. NPY expression increased during brain development wherein the levels were higher in 100 and 150days post hatch females than the respective age-matched males. Seasonal cycle analysis showed high expression of NPY in brain during pre-spawning phase in comparison with other reproductive phases. Localization studies exhibited the presence of NPY, abundantly, in the regions of preoptic area, hypothalamus and pituitary. Transient silencing of NPY-esiRNA directly into the brain significantly decreased NPY expression in both the male and female brain of catfish which further resulted in significant decrease of transcripts of tryptophan hydroxylase 2, catfish gonadotropin-releasing hormone (cfGnRH), tyrosine hydroxylase and 3β-hydroxysteroid dehydrogenase in brain and luteinizing hormone-β/gonadotropin-II (lh-β/GTH-II) in pituitary exhibiting its influence on gonadal axis. In addition, significant decrease of several ovary-related transcripts was observed in NPY-esiRNA silenced female catfish, indicating the plausible role of NPY in ovary through cfGnRH-GTH axis.

Distribution and female reproductive state differences in orexigenic and anorexigenic neurons in the brain of the mouth brooding African cichlid fish, Astatotilapia burtoni

Integration of reproduction and metabolism is necessary for species survival. While the neural circuits controlling energy homeostasis are well-characterized, the signals controlling the relay of nutritional information to the reproductive axis are less understood. The cichlid fish Astatotilapia burtoni is ideal for studying the neural regulation of feeding and reproduction because females cycle between a feeding gravid state and a period of forced starvation while they brood developing young inside their mouths. To test the hypothesis that candidate neuropeptide-containing neurons known to be involved in feeding and energy homeostasis in mammals show conserved distribution patterns, we performed immunohistochemistry and in situ hybridization to localize appetite-stimulating (neuropeptide Y, NPY; agouti-related protein, AGRP) and appetite-inhibiting (cocaine and amphetamine-regulated transcript, CART; pro-opiomelanocortin, pomc1a) neurons in the brain. NPY, AGRP, CART, and pomc1a somata showed distribution patterns similar to other teleosts, which included localization to the lateral tuberal nucleus (NLT), the putative homolog of the mammalian arcuate nucleus. Gravid females also had larger NPY and AGRP neurons in the NLT compared to brooding females, but brooding females had larger pomc1a neurons compared to gravid females. Hypothalamic agrp mRNA levels were also higher in gravid compared to brooding females. Thus, larger appetite-stimulating neurons (NPY, AGRP) likely promote feeding while females are gravid, while larger pomc1a neurons may act as a signal to inhibit food intake during mouth brooding. Collectively, our data suggest a potential role for NPY, AGRP, POMC, and CART in regulating energetic status in A. burtoni females during varying metabolic and reproductive demands.

The Ontogeny and Brain Distribution Dynamics of the Appetite Regulators NPY, CART and pOX in Larval Atlantic Cod (Gadus morhua L.)

Similar to many marine teleost species, Atlantic cod undergo remarkable physiological changes during the early life stages with concurrent and profound changes in feeding biology and ecology. In contrast to the digestive system, very little is known about the ontogeny and the localization of the centers that control appetite and feed ingestion in the developing brain of fish. We examined the expression patterns of three appetite regulating factors (orexigenic: neuropeptide Y, NPY; prepro-orexin, pOX and anorexigenic: cocaine- and amphetamine-regulated transcript, CART) in discrete brain regions of developing Atlantic cod using chromogenic and double fluorescent in situ hybridization. Differential temporal and spatial expression patterns for each appetite regulator were found from first feeding (4 days post hatch; dph) to juvenile stage (76 dph). Neurons expressing NPY mRNA were detected in the telencephalon (highest expression), diencephalon, and optic tectum from 4 dph onward. CART mRNA expression had a wider distribution along the anterior-posterior brain axis, including both telencephalon and diencephalon from 4 dph. From 46 dph, CART transcripts were also detected in the olfactory bulb, region of the nucleus of medial longitudinal fascicle, optic tectum and midbrain tegmentum. At 4 and 20 dph, pOX mRNA expression was exclusively found in the preoptic region, but extended to the hypothalamus at 46 and 76 dph. Co-expression of both CART and pOX genes were also observed in several hypothalamic neurons throughout larval development. Our results show that both orexigenic and anorexigenic factors are present in the telencephalon, diencephalon and mesencephalon in cod larvae. The telencephalon mostly contains key factors of hunger control (NPY), while the diencephalon, and particularly the hypothalamus may have a more complex role in modulating the multifunctional control of appetite in this species. As the larvae develop, the overall progression in temporal and spatial complexity of NPY, CART and pOX mRNAs expression might be correlated to the maturation of appetite control regulation. These observations suggest that teleost larvae continue to develop the regulatory networks underlying appetite control after onset of exogenous feeding.

Stimulatory effect of the secretogranin-ll derived peptide secretoneurin on food intake and locomotion in female goldfish (Carassius auratus)

Secretoneurin (SN) is a conserved peptide derived by proteolytic processing from the middle domain of the ∼600 amino acid precursor secretogranin-II (SgII). Secretoneurin is widely distributed in secretory granules of endocrine cells and neurons and has important roles in reproduction as it stimulates luteinizing hormone release from the pituitary. A potential new role of SN in goldfish feeding is the subject of this study. Firstly, we established that acute (26 h; p<0.0001) and short-term (72 h; p=0.016) fasting increased SgIIa precursor mRNA levels 1.25-fold in the telencephalon, implicating SN in the control of feeding. Secondly, we determined that intracerebroventricular injections of the type A SN (SNa; 0.2 and 1 ng/g BW) increased food intake and locomotor behavior by 60 min. Fish injected with the lower and higher doses of SNa (0.2 and 1 ng/g) respectively exhibited significant 1.77- and 2.58-fold higher food intake (p<0.0001) than the saline-injected control fish. Locomotor behavior was increased by 1.35- and 2.26-fold for 0.2 ng/g SNa (p=0.0001) and 1 ng/g SNa (p<0.0001), respectively. Injection of 1 ng/g SNa increased mRNA levels of hypothalamic neuropeptide Y 1.36-fold (p=0.038) and decreased hypothalamic cocaine-and amphetamine-regulated transcript by 33% (p=0.01) at 2h and 5h post-injection, respectively. These data suggest interactions of SNa with stimulatory and inhibitory pathways of food intake control in fish.

Interaction between dopamine and neuropeptide Y in the telencephalon of the Indian major carp, Cirrhinus cirrhosus

In teleosts, while neuropeptide Y (NPY) has emerged as one of the potent regulators of GnRH-LH axis, entopeduncular nucleus (EN) in the ventral telencephalon serves as major site for NPY synthesis/storage. Neurons of the EN innervate preoptic area and pituitary, respond to gonadal steroids, undergo reproduction phase-related changes, and are believed to convey sex steroid-borne information to GnRH neurons. In spite of the importance of EN, the neural circuitry associated with the nucleus has not been defined. Aim of the present study is to examine the possibility of the dopaminergic regulation of EN. NPY-immunoreactive cells and fibers were extensively distributed in the forebrain and pituitary of Cirrhinus cirrhosus. NPY immunoreactivity was observed in the olfactory receptor neurons, ganglion cells of terminal nerve, and in neurons of area ventralis telencephali/pars lateralis, EN, nucleus preopticus periventricularis (NPP), and nucleus lateralis tuberis. NPY-fibers were observed in the dorsal telencephalon, tuberal area and pituitary. While the area ventralis telencephali/pars intermedialis (Vi) located just above the EN contained a distinct population of tyrosine hydroxylase neurons, their axons seem to innervate NPY neurons in EN. Superfused brain slices containing EN were treated with DA D1- and D2-like receptor agonists. NPY-immunoreactivity in the EN showed significant increase (P<0.001) following DA D1-like receptor agonist, SKF-38393 treatment, but DA D2-like receptor agonist, quinpirole was ineffective. DA may regulate NPY neurons in EN via D1-like receptors. DA-NPY interaction in the EN might be important in the central regulation of reproduction in teleosts.

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.

Neuropeptide Y immunoreactivity in the cat claustrum: A light- and electron-microscopic investigation

The claustrum is a telencephalic nucleus located ventrolateral to the basal ganglia in the mammalian brain. It has an extensive reciprocal connectivity with most if not all of the cerebral cortex, in particular, primary sensory areas. However, despite renewed and growing interest amongst investigators, there remains a paucity of data concerning its peptidergic profile. The aim of the present study was to examine the presence, morphology, distribution and ultrastructure of neuropeptide Y-immunoreactive (NPY-ir) neurons and fibers in the claustrum of the cat. Ten adult healthy cats from both sexes were used. All animals received human and ethical treatment in accordance with the Principles of Laboratory Animal Care. Subjects were irreversibly anesthetized and transcardially perfused with fixative solution containing glutaraldehyde and paraformaldehyde. Brains were promptly removed, postfixed and sectioned. Slices were incubated with polyclonal anti-NPY antibodies according to the standard avidin-biotin-peroxidase complex method adopted by our Department of Anatomy, Histology and Embryology. NPY-ir neurons and fibers were found to be diffusely distributed throughout the claustrum, with no obvious topographic or functional patterning other than larger numbers in its central/broadest part (stereotaxic planes A12-A16). Neurons were generally classified by diameter into three sizes: small (under 17 μm), medium (17-25 μm) and large (over 25 μm). Staining density is varied with some neurons appearing darker than others. At the electron-microscopic level NPY immunoproduct was observed within neurons, dendrites and terminal boutons, each differing relative to their ultrastructural attributes. Two types of NPY-ir synaptic boutons were found. Lastly, it is of interest to note that gender-specific differences were not observed.

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.

Expression of kisspeptins and kiss receptors suggests a large range of functions for kisspeptin systems in the brain of the European sea bass

This study, conducted in the brain of a perciform fish, the European sea bass, aimed at raising antibodies against the precursor of the kisspeptins in order to map the kiss systems and to correlate the expression of kisspeptins, kiss1 and kiss2, with that of kisspeptin receptors (kiss-R1 and kiss-R2). Specific antibodies could be raised against the preprokiss2, but not the preoprokiss1. The data indicate that kiss2 neurons are mainly located in the hypothalamus and project widely to the subpallium and pallium, the preoptic region, the thalamus, the pretectal area, the optic tectum, the torus semicircularis, the mediobasal medial and caudal hypothalamus, and the neurohypophysis. These results were compared to the expression of kiss-R1 and kiss-R2 messengers, indicating a very good correlation between the wide distribution of Kiss2-positive fibers and that of kiss-R2 expressing cells. The expression of kiss-R1 messengers was more limited to the habenula, the ventral telencephalon and the proximal pars distalis of the pituitary. Attempts to characterize the phenotype of the numerous cells expressing kiss-R2 showed that neurons expressing tyrosine hydroxylase, neuropeptide Y and neuronal nitric oxide synthase are targets for kisspeptins, while GnRH1 neurons did not appear to express kiss-R1 or kiss-R2 messengers. In addition, a striking result was that all somatostatin-positive neurons expressed-kissR2. These data show that kisspeptins are likely to regulate a wide range of neuronal systems in the brain of teleosts.

Structural and functional characterization of neuropeptide Y in a primitive teleost, the Japanese eel (Anguilla japonica)

In the present study, the first full-length cDNA encoding Neuropeptide Y (NPY) was cloned from the brain of Japanese eel (Anguilla japonica). The open reading frame of Japanese eel NPY gene is 294 bp in length, encoding a precursor protein of 97 amino acids, which contains a 36-amino-acid mature peptide. Sequence analysis showed that the Japanese eel NPY peptide is similar to that of other species. Real-time PCR revealed that NPY in Japanese eel is mainly expressed in the brain, especially in the hypothalamus and the optic tectum thalamus. The effect of a negative energy balance on NPY gene expression was examined subsequently. The mRNA level of NPY in the hypothalamus and the optic tectum thalamus showed a pronounced increase after 4 days of food deprivation. The biological activities of Japanese eel NPY were further investigated in vivo and in vitro. Intraperitoneal injection of the NPY peptide into Japanese eel could potently elevate the expression of the mammalian gonadotropin-releasing hormone (mGnRH) in hypothalamus and the follicle-stimulating hormone beta (FSHβ), the luteinizing hormone beta (LHβ) and growth hormone (GH) in pituitary. In static incubation studies, the stimulatory effects of NPY on mGnRH expression in hypothalamic fragments and on FSHβ, LHβ and GH expression in pituitary cells were also observed. However, in vivo and in vitro studies showed that NPY exhibits an inhibitory action on the expression of thyroid-stimulating hormone beta (TSHβ) in pituitary. The results indicate that NPY is involved in the regulation of multiple physiological processes in Japanese eel.

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.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

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.

Immunohistochemical localization of glucokinase in rainbow trout brain

In mammals, glucosensing neurons reside in brain areas known to play a critical regulatory role in energy homeostasis and neuroendocrine function. In fish, although no glucosensing neurons have been characterized to date, glucokinase (GCK; the main glucosensing marker in mammals) activity and expression were found in hypothalamus and hindbrain of rainbow trout where they related to food intake regulation and glucose homeostasis. However, there are no available studies in literature regarding GCK distribution in brain areas as well as the cell types expressing that protein. In the present study we hypothesize that, as occurs in mammals, GCK would be localized where glucosensing areas have been described. In this sense, we have found GCK immunoreactivity in several areas of trout hypothalamus, of which some of them are related to glucose metabolism, energy homeostasis and food intake, including the lateral hypothalamus, anterior tuberal nucleus, posterior tuberal nucleus and lateral tuberal nucleus. On the other hand, GCKimmunoreactivity was also observed in other areas where the glucosensor system is probably functional,such as the preoptic area and the oculomotor nucleus. Therefore, in this study using immunoreactive techniques, we have demonstrated in those specific areas of the rainbow trout brain previously described as glucosensor the presence of GCK in different cell types.

Neuronal interaction between melanin-concentrating hormone- and alpha-melanocyte-stimulating hormone-containing neurons in the goldfish hypothalamus

Intracerebroventricular (ICV) administration of melanin-concentrating hormone (MCH) inhibits food intake in goldfish, unlike in rodents, suggesting that its anorexigenic action is mediated by alpha-melanocyte-stimulating hormone (alpha-MSH) but not corticotropin-releasing hormone. This led us to investigate whether MCH-containing neurons in the goldfish brain have direct inputs to alpha-MSH-containing neurons, using a confocal laser scanning microscope, and to examine whether the anorexigenic action of MCH is also mediated by other anorexigenic neuropeptides, such as cholecystokinin (CCK) and pituitary adenylate cyclase-activating polypeptide (PACAP), using their receptor antagonists. MCH- and alpha-MSH-like immunoreactivities were distributed throughout the brain, especially in the diencephalon. MCH-containing nerve fibers or endings lay in close apposition to alpha-MSH-containing neurons in the hypothalamus in the posterior part of the nucleus lateralis tuberis (NLTp). The inhibitory effect of ICV-injected MCH on food intake was not affected by treatment with a CCK A/CCK B receptor antagonist, proglumide, or a PACAP receptor (PAC(1) receptor) antagonist, PACAP((6-38)). ICV administration of MCH at a dose sufficient to inhibit food consumption also did not influence expression of the mRNAs encoding CCK and PACAP. These results strongly suggest that MCH-containing neurons provide direct input to alpha-MSH-containing neurons in the NLTp of goldfish, and that MCH plays a crucial role in the regulation of feeding behavior as an anorexigenic neuropeptide via the alpha-MSH (melanocortin 4 receptor)-signaling pathway.

Immunohistochemical Organization of the Forebrain in the White Sturgeon, Acipenser transmontanus

The distribution of substance P (SP), leucine-enkephalin (LENK), serotonin (5HT), dopamine (DA), and tyrosine hydroxylase (TH) was examined in the forebrain of the white sturgeon in order to evaluate several anatomical hypotheses based on cytoarchitectonics, and to gain a better understanding of the evolution of the forebrain in ray-finned fishes. The subpallium of the telencephalon has the highest concentration of the neuropeptides SP and LENK, allowing the pallial-subpallial border to be easily distinguished. The distribution of dopamine is similar to that of serotonin in the subpallium, fibers positive for these transmitters are particularly dense in the dorsal and ventral divisions of the subpallium. In addition, a small population of DA- and 5HT-positive cell bodies--which appear to be unique to sturgeons--was identified at the level of the anterior commissure. The internal granular layer of the olfactory bulbs had large numbers of TH-positive cell bodies and fibers, as did the rostral subpallium. The occurrence of cell bodies positive for LENK in the dorsal nucleus of the rostral subpallium supports the hypothesis that this nucleus is homologous to the striatum in other vertebrates. This is further reinforced by the apparent origin of an ascending dopaminergic pathway from cells in the posterior tubercle that are likely homologous to the ventral tegmental area/substantia nigra in land vertebrates. Finally, the differential distribution of SP and TH in the pallium supports the hypothesis that the pallium, or area dorsalis, can be divided medially into a rostral division (Dm), a caudal division (Dp) that is the main pallial target of secondary olfactory projections, and a narrow lateral division (Dd+Dl) immediately adjacent to the attachment of the tela choroidea along the entire rostrocaudal length of the telencephalic hemisphere.

Neuropeptide Y mediates ghrelin-induced feeding in the goldfish, Carassius auratus

Intracerebroventricular (ICV) and intraperitoneal (IP) administration of n-octanoic acid-modified ghrelin stimulates food intake in the goldfish. We examined the involvement of neuropeptide Y (NPY) in the orexigenic action of ghrelin using a NPY Y1-receptor antagonist, BIBP-3226. Food intake induced by ICV or IP injection of ghrelin was suppressed by ICV preinjection of BIBP-3226 for 1 h. We then examined whether ghrelin affects the expression of NPY mRNA in the goldfish brain using a real-time PCR method. ICV, but not IP, administration of ghrelin at a dose sufficient to stimulate food intake increased the expression of brain NPY mRNA obtained from 2 h after treatment. These results indicate that the orexigenic action of central ghrelin is mediated by the release of NPY in the brain with stimulating NPY synthesis, and that peripheral ghrelin also stimulates food intake via brain NPY pathway.

Cloning, expression and growth promoting action of Red tilapia (Oreochromis sp.) neuropeptide Y

Neuropeptide Y, a 36 amino acid peptide abundantly expressed in the brain, is the most potent orexigenic factor known to date in mammals. It has been shown to be one of the most conserved neuropeptides in vertebrate evolution. It seems that neuropeptide Y functions, in addition to sequence conservation, are also well conserved in fish. In the present study, we cloned and reported the cDNA sequence coding for tilapia 36 aminoacid neuropeptide Y. We express the tilapia neuropeptide Y gene in Escherichia coli driven by T7 promoter. The recombinant neuropeptide Y was purified up to 80% by affinity chromatography. We developed both, a food intake and a growth performance experiment to evaluate the effects of neuropeptide Y administration. Juvenile tilapia receiving recombinant neuropeptide Y (1 microg/g of body weight) by intraperitoneal injection increased food intake compared to controls (p < 0.05). Similarly, in the growth performance experiment, we observed an increase in body weight (p < 0.05) of tilapia fry receiving the same dose of the peptide. Neuropeptide Y treatment had no significant effect on hepatosomatic index and muscle moisture content. On the other hand, muscle protein content was increased in treated animals. These results demonstrate that administration of biologically active E. coli-derived neuropeptide Y resulted in a growth promoting action in fish.

cDNA cloning and mRNA expression of neuropeptide Y in orange spotted grouper, Epinephelus coioides

A full-length cDNA encoding the neuropeptide Y (NPY) was cloned from the hypothalamus of orange spotted grouper (Epinephelus coioides) by rapid amplification of cDNA ends approaches. The NPY cDNA sequence is 688 bp long and has an open reading frame of 300 bp encoding prepro-NPY with 99 amino acids. The deduced amino acid sequences contain a 28-amino-acids signal peptide followed by a 36-amino-acids mature NPY peptide. mRNA expression of NPY was determined using semi-quantitative RT-PCR followed by Southern blot analysis. NPY mRNA was expressed in olfactory bulb, telencephalon, pituitary, hypothalamus, optic tectum-thalamus, medulla oblongata, cerebellum and spinal cord. Low levels of NPY mRNA expression were found in retina, ovary and stomach, while much lower levels of expression were detected in liver, heart, gill, skin, anterior intestine, thymus and blood. No NPY mRNA expression was observed in unfertilized eggs, newly fertilized eggs, 16-cells stage and morula stage of the embryo and lower levels of expression were detected in the blastula, gastrula and neurula stages. It was highly expressed from lens formation stage to 52-day-old larval stage. NPY might be involved in the late embryonic and larval development of the orange spotted grouper.

The endocannabinoid system in the brain of Carassius auratus and its possible role in the control of food intake

Cannabinoid receptors and the endocannabinoids anandamide and 2-arachidonoylglycerol have been suggested to regulate food intake in several animal phyla. Orthologs of the mammalian cannabinoid CB(1) and CB(2) receptors have been identified in fish. We investigated the presence of this endocannabinoid system in the brain of the goldfish Carassius auratus and its role in food consumption. CB(1)-like immunoreactivity was distributed throughout the goldfish brain. The prosencephalon showed strong CB(1)-like immunoreactivity in the telencephalon and the inferior lobes of the posterior hypothalamus. Endocannabinoids were detected in all brain regions of C. auratus and an anandamide-hydrolysing enzymatic activity with features similar to those of mammalian fatty acid amide hydrolase was found. Food deprivation for 24 h was accompanied by a significant increase of anandamide, but not 2-arachidonoylglycerol, levels only in the telencephalon. Anandamide caused a dose-dependent effect on food intake within 2 h of intraperitoneal administration to satiated fish and significantly enhanced or reduced food intake at low (1 pg/g body weight) or intermediate (10 pg/g) doses, respectively, the highest dose tested (100 pg/g) being inactive. We suggest that endocannabinoids might variously contribute to adaptive responses to food shortage in fish.

Neuropeptide Y-immunoreactive (NPY-ir) structures in the brain of the gar Lepisosteus oculatus (Lepisosteiformes, Osteichthyes) with special regard to their anatomical relations to gonadotropin-releasing hormone (GnRH)-ir structures in the hypothalamus and the terminal nerve

The present paper describes neuropeptide Y-like-immunoreactive (NPY-ir) structures in the brain of the spotted gar, Lepisosteus oculatus, with special regard to their anatomical relations to gonadotropin-releasing hormone (GnRH)-ir structures in the hypothalamus and the terminal nerve (TN). NPY-ir cells were found in various locations including the TN, the medial zone of the area dorsalis telencephali, the ventral nucleus of the area ventralis telencephali, the habenula, the dorsal posterior nucleus, the periventricular nucleus of the hypothalamus, the posterior tubercle, the optic tectum, and the lateral part of the tegmentum. NPY-ir fibers were widely distributed throughout the brain except for the cerebellum. They were locally dense in the ventral telencephalon, in the periventricular gray matter of the thalamus and the hypothalamus, and in the ventromedial part of the brainstem, but sparse in the olfactory system. Light-microscopic double immunohistochemistry demonstrated distinct NPY-ir and GnRH-ir structures in the ventral hypothalamus: the NPY-ir system was associated mainly with the periventricular gray matter, whereas the GnRH-ir system was prominent in the external zone of the preoptico-tubero-infundibular area including the median eminence (ME). Here, NPY-ir varicose fibers occasionally abutted on GnRH-ir cells and varicosities or invested GnRH-ir cells, suggesting that NPY directly regulates the function of the hypothalamic GnRHergic neuron system. On the other hand, the TN cells and fibers in the olfactory system were doubly labeled by the antibodies against NPY and GnRH. Immuno-electron-microscopic data strongly suggested that some of the TN fibers projected to the ME.

Neuropeptide Y in the forebrain of the adult male cichlid fishOreochromis mossambicus: Distribution, effects of castration and testosterone replacement

We studied the organization of the neuropeptide Y (NPY)-immunoreactive system in the forebrain of adult male cichlid fish Oreochromis mossambicus and its response to castration and testosterone replacement by using morphometric methods. Immunoreactivity for NPY was widely distributed in the forebrain, and the pattern generally resembled that in other teleosts. Whereas immunoreactivity was conspicuous in the ganglia of nervus terminalis (NT; or nucleus olfactoretinalis), a weak reaction was detected in some granule cells in the olfactory bulb and in the cells of area ventralis telencephali pars lateralis (Vl). Moderately to intensely immunoreactive cells were distinctly seen in the nucleus entopeduncularis (NE), nucleus preopticus (NPO), nucleus lateralis tuberis (NLT), paraventricular organ (PVO), and midbrain tegmentum (MT). NPY fibers were widely distributed in the forebrain. Castration for 10/15 days resulted in a drastic loss of immunoreactivity in the cells of NE (P<0.001) and a significant decrease (P<0.01) in their cell nuclear size. However, cell nuclei of the NT neurons showed a significant increase in size. A highly significant reduction in the NPY-immunoreactive fiber density (P<0.001) was observed in several areas of the forebrain. Although testosterone replacement reversed these changes, fibers in some areas showed supranormal responses. Immunoreactive cells in Vl, NPO, NLT, PVO, and MT and fiber density in some other areas did not respond to castration. We suggest that the NPY-immunoreactive elements that respond to castration and testosterone replacement may serve as the substrate for processing the positive feedback action of the steroid hormone.

Immunohistochemical distribution of neuropeptide Y in the mesencephalon and rhombencephalon of carp, Cyprinus carpio L. (Cyprinidae: Teleostei)

The localization of neuropeptide Y (NPY)-immunoreactive elements was investigated in the mesencephalon and rhombencephalon of carp, Cyprinus carpio, by using antisera raised against porcine NPY and the immunoperoxidase technique. Concurrently, to identify the distribution of NPY-immunoreactivity, we developed an atlas of the studied areas based on Nissl-stained sections. The NPY-immunoreactive (NPY-ir) elements were located in many zones of the mesencephalon and rhombencephalon. In the mesencephalon, positive fibers were the most abundant elements while neurons were scarce. The rhombencephalon rostral part was characterized by a low to moderate fiber density, distributed in the ventro-medial and ventro-lateral region. Differently the caudal part of the rhombencephalon exhibited several NPY-ir elements. In particular, a high density of immunoreactivity was located in the gustatory area at the level of the nucleus (n.) originis nervi glossopharyngei, in the n. nervi vagi, and in the vagal lobe. The latter can be considered a valid neuroanatomical model for the study of gustatory signal processing in vertebrates. Our results regarding the primary gustatory centers give neuroanatomical support to the view that NPY may act as a neurotransmitter and/or a neuromodulator in a wide neural network for feeding behavior control.

Neuropeptide Y in the olfactory system, forebrain and pituitary of the teleost, Clarias batrachus

Distribution of neuropeptide Y (NPY)-like immunoreactivity in the forebrain of catfish Clarias batrachus was examined with immunocytochemistry. Conspicuous immunoreactivity was seen in the olfactory receptor neurons (ORNs), their projections in the olfactory nerve, fascicles of the olfactory nerve layer in the periphery of bulb and in the medial olfactory tracts as they extend to the telencephalic lobes. Ablation of the olfactory organ resulted in loss of immunoreactivity in the olfactory nerve layer of the bulb and also in the fascicles of the medial olfactory tracts. This evidence suggests that NPY may serve as a neurotransmitter in the ORNs and convey chemosensory information to the olfactory bulb, and also to the telencephalon over the extrabulbar projections. In addition, network of beaded immunoreactive fibers was noticed throughout the olfactory bulb, which did not respond to ablation experiment. These fibers may represent centrifugal innervation of the bulb. Strong immunoreactivity was encountered in some ganglion cells of nervus terminalis. Immunoreactive fibers and terminal fields were widely distributed in the telencephalon. Several neurons of nucleus entopeduncularis were moderately immunoreactive; and a small population of neurons in nucleus preopticus periventricularis was also labeled. Immunoreactive terminal fields were particularly conspicuous in the preoptic, the tuberal areas, and the periventricular zone around the third ventricle and inferior lobes. NPY immunoreactive cells and fibers were detected in all the lobes of the pituitary gland. Present results describing the localization of NPY in the forebrain of C. batrachus are in concurrence with the pattern of the immunoreactivity encountered in other teleosts. However, NPY in olfactory system of C. batrachus is a novel feature that suggests a role for the peptide in processing of chemosensory information.

Distribution of neuropeptide Y immunoreactivity in the central and peripheral nervous systems of amphioxus (Branchiostoma lanceolatum Pallas)

Immunocytochemistry techniques were employed to investigate the distribution of neuropeptide Y-like-immunoreactive (NPY-ir) cells and fibers in the central and peripheral nervous systems of adult amphioxus. NPY-ir neurons of the commissural type were abundant in the brain and present but more scarce in the spinal cord. These neurons gave rise to conspicuous NPY-ir tracts that coursed along the entire length of the nerve cord. Some fibers exhibited conspicuous Herring body-like swellings. In the peripheral nervous system, small NPY-ir neurons and a large number of thin, beaded NPY-ir fibers were observed in the atrial region, indicating the involvement of this substance in visceral regulation. A few NPY-ir fibers, possibly afferent to the spinal cord, coursed in the ventral branches of the spinal nerves of this region, whereas no NPY-ir fibers coursed in the preoral or velar nerves or in the dorsal branches of the other spinal nerves. These results indicate that NPY is widely used as a neuroregulator/neurotransmitter in the central and peripheral nervous systems of this primitive chordate. In addition, this study demonstrates the presence of tall, thin NPY-ir cells in the putative adenohypophyseal homologue, the Hatschek's pit organ, which is located in the roof of the preoral cavity (vestibule).

GnRH-LH secreting cells axis in the pituitary of the teleost Clarias batrachus responds to neuropeptide Y treatment: an immunocytochemical study

An attempt has been made to immunocytochemically visualize the effect of neuropeptide Y (NPY) on the GnRH fibers and luteinizing hormone (LH) secreting cells in the pituitary of the catfish, Clarias batrachus. Two hours following the intracranial administration of NPY at the dose of 20 ng/g body wt, a significant increase in the area occupied by the GnRH-like immunoreactive fibers, and population and size of the LH cells was observed. The treatment also resulted in considerable augmentation of immunoreactivity in the LH cells. Double immunolabeling revealed NPY fibers directly terminating on the LH cells. The results suggest that NPY may (a) stimulate some GnRH containing hypophysiotropic neuronal group in the brain, (b) promote anterograde transport of GnRH to the pituitary gland, and (c) up-regulate the LH cells.

Localization of Neuropeptide Y-like immunoreactive structures in the brain of the pejerrey, Odontesthes bonariensis (Teleostei, Atheriniformes)

The aim of this study was to determine the distribution of Neuropeptide-Y (NPY) immunoreactive neurons and fibres in the brain and pituitary of Odontesthes bonariensis by immunohistochemical methods. A wide distribution of immunoreactive NPY (ir-NPY) cells and fibres in the forebrain and midbrain was observed. A prominent ir-NPY nucleus was found in the ventral telencephalon and other ir-NPY cells groups were recognized at the dorso-medial telencephalon. The diencephalon showed ir-NPY cells in the Nucleus entopeduncularis, the Nucleus preopticus periventricularis and in the Nucleus lateralis tuberis. Ir-NPY fibres were conspicuous in the preoptic region and the hypothalamus. There were also numerous ir-NPY fibres at the epithalamic level running ventrally to the hypothalamus and the pituitary stalk. At the rhomboencephalic level, the ir-NPY neurons were observed in the Locus coeruleus. Double-labelled immunostaining showed a close association between ir-NPY fibres that reach the adenohypophysis and growth hormone (GH)- and gonadotropin (GtH)-expressing cells. Although our results exhibit some relevant differences when compared to other fish groups, they support the existence of a conserved NPY system in teleosts.

Neuropeptide tyrosine-like immunoreactive system in the brain, olfactory organ and retina of the zebrafish, Danio rerio, during development

The anatomical distribution of neuropeptide tyrosine (NPY)-like immunoreactivity was investigated in the brain, olfactory organ and retina of the zebrafish, Danio rerio, during development and in juvenile specimens, by using the indirect immunofluorescence and the peroxidase-antiperoxidase methods. In 60 h post fertilization (hpf) embryos, NPY-like immunoreactive cell bodies appeared in the hypothalamus, within the posterior periventricular nucleus. Few positive nerve fibers were found in the hypothalamus and in the tegmentum of the mesencephalon. In 72 hpf embryos, a new group of NPY-like immunoreactive cells was found in the olfactory pit. At day 4 of development, NPY-like immunoreactive cell bodies were detected between the olfactory pit and the olfactory organ. In the hypothalamus the location of positive cell bodies was similar to that reported in the previous developmental stages. A few positive nerve fibers appeared in the tegmentum of the rhombencephalon. At days 7 and 15 of development, the distribution of NPY-like immunoreactivity was very similar to that reported at day 4. However, at day 15, NPY-like immunoreactivity appeared for the first time in amacrine cells of the retina and in nerve fibers of the tectum of the mesencephalon. In 1-month/3-month-old animals, additional groups of NPY-like immunoreactive cell bodies appeared in the glomerular layer of the olfactory bulbs, the terminal nerve, the lateral nucleus of the ventral telencephalic area, the entopeduncular nucleus and in the medial region of the reticular formation of the rhombencephalon. These results show that NPY-like immunoreactive structures appear early during ontogeny of zebrafish. The distribution of the immunoreactive system increases during the ontogeny, the juvenile stages, and reaches the complete development in mature animals. The location of NPY-like immunoreactivity indicates that, during development, NPY could be involved in several neuromodulatory functions, including the processing of visual and olfactory information. In 1-month/3-month-old animals, NPY-like immunoreactive nerve fibers are present in the pituitary, suggesting that, from these stages onward, NPY may influence the secretion of pituitary hormones.

Neuropeptide Y stimulates food consumption through multiple receptors in goldfish

In this study, the acute effects of brain intracerebroventricular (icv) injections of mammalian neuropeptide Y (NPY) Y1 ([31Leu,34Pro]NPY), Y2 (NPY2-36) and Y5 ([D-32Trp]NPY) receptor subtype agonists on food intake in goldfish were examined. Icv injection of Y1 and Y5 receptor agonists in dosages of 1 and 5 ng/g exhibited dose-dependent effects on food intake; however, higher dosages of both receptor subtypes had desensitising effects on food intake, and caused a decrease in food intake in comparison to the lower dosages. At 10 and 20 ng/g, Y1 receptor agonist-treated fish exhibited feeding significantly lower than intact and saline-injected fish; fish treated with the same dosages of Y5 agonist exhibited food intake similar to intact and saline-injected fish. Y2 agonist had no effects on food intake. Co-icv administration of Y1 and Y5 agonists in dosages of 1 and 5 ng/g caused enhanced food intake that was additive of the individual doses alone. However, desensitising one receptor did not influence the responsiveness of the other. Co-icv injection of Y1 receptor agonist in desensitizing high dosages (10 and 15 ng/g) with Y5 receptor agonist in lower doses (1 and 5 ng/g, respectively) or vice versa, resulted in a food intake similar to the dosages of Y1 and Y5 receptor agonists at 1 and 5 ng/g given alone. Overall, this study demonstrates that NPY acts centrally through Y1 and Y5 receptors to stimulate food intake in goldfish. The Y1 and Y5 receptors appear to act independently in the stimulation of food intake in goldfish.

Effects of food deprivation and refeeding on neuropeptide Y (NPY) mRNA levels in goldfish

In mammals, NPY is a key factor in the regulation of feeding behavior. In the present study, the effects of refeeding for 1-3 h in 72-75-h food deprived (FD) goldfish on the levels of NPY mRNA in telencephalon-preoptic (TEL-POA), hypothalamus (HYP) and optic tectum-thalamus (OT-THAL) were examined, using Northern blot analysis. Goldfish FD for 72 h exhibited a significant increase in NPY mRNA levels in all brain regions. At 1 h after 72-h FD (73-h FD), NPY mRNA was significantly increased in TEL-POA and OT-THAL, but remained the same as 72-h FD fish in HYP. At 3 h after 72-h FD (75 h), all brain regions exhibited a significant increase in NPY mRNA levels. However, subsequent refeeding for 1-3 h rapidly and completely reversed the effects of FD in all brain regions, reaching fed levels within 1-3 h of refeeding. Serum GH levels were highest in 72-h FD fish, but decreased significantly over 1-3 h after 72-h FD; whereas, refeeding reversed the increase in serum GH levels only at 3 h after refeeding. Taken together, these results further support that NPY is a physiological brain transducer involved in the regulation of daily appetite and feeding in goldfish.

Distribution of neuropeptide Y-like immunoreactivity in the brain of the Senegalese sole (Solea senegalensis)

We present the results of an immunohistochemical study aimed at localizing the neuropeptide Y (NPY) in the brain of the Senegalese sole, Solea senegalensis, using an antiserum raised against porcine NPY and the streptavidin-biotin-peroxidase method. In this species, we have identified immunoreactive cells in the ventral and dorsal telencephalon, caudal preoptic area, ventrocaudal hypothalamus, optic tectum, torus longitudinalis, synencephalon and isthmic region. NPY-immunoreactive fibers were profusely distributed throughout the brain, also reaching the adenohypophysis. The extensive distribution of NPY suggests an important role for this neuropeptide in a variety of physiological processes, including the neuroendocrine control of adenohypophyseal functions. Our results are compared with those obtained in other teleosts and discussed in relation to putative functions of NPY in the control of metabolism and reproduction in the Senegalese sole.

Characterization and distribution of neuropeptide Y in the brain of a caecilian amphibian

Neuropeptide Y (NPY) from the brain of an amphibian from the order Gymnophiona (the caecilian, Typhlonectes natans) was characterized. We cloned a 790 base pair cDNA encoding the caecilian NPY precursor. The open reading frame consisted of 291 bases, indicating an NPY precursor of 97 amino acids. Both deduced and isolated NPY primary structures were Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu(10)-Asp-Ala-Pro-Ala-Glu-Asp-Met-Ala-Lys-Tyr(20)-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu(30)-Ile-Thr-Arg-Gln-Arg-Tyr. NH2. In caecilian brain, we observed NPY immunoreactive cells within the medial pallium, basal forebrain, preoptic area, midbrain tegmentum and trigeminal nucleus. The prevalence of preoptic and hypothalamic terminal field staining supports the hypothesis that NPY controls pituitary function in this caecilian.

The distribution of neuropeptide Y-immunoreactive neurons and nerve fibers in the forebrain of the carp Cyprinus carpio L

The present study reports the distribution of Neuropeptide Y (NPY)-immunoreactive neurons and fibers in the forebrain of the adult carp Cyprinus carpio L. Serial Nissl-stained sections were used for cytoarchitecture and identification of anatomical structures. Immunostaining of NPY-containing neurons and fibers was used as neurochemical marker and tool for comparison with other species, including the goldfish. The general outline of the cytoarchitecture of the carp forebrain is similar to that of other Cypriniformes. However, using NPY immunohistochemistry, we found several specific differences with the goldfish, especially in the diencephalon. In the hypothalamus of the carp NPY-immunoreactive (NPYir) neurons were identified in the n. dorsolateralis thalami, and in the n. ventralis lateralis thalami. In the same location, we observed the n. anterior hypothalami and the n. preglomerulosus pars lateralis, described in the goldfish, as parts of n. prerotundus. However, in the carp we were not able to identify a n. preglomerulosus pars medialis, a n. preglomerulosus pars medialis commissuralis and a n. glomerulosus. We describe a n. rotundus, in which we did not find substructures typical of the goldfish. Further differences with the goldfish, trout and salmon were also noted.

Characterization of neuropeptide Y expression in the brain of a perciform fish, the sea bass (Dicentrarchus labrax)

The distribution of neuropeptide Y (NPY) gene expression was mapped in the brain of the sea bass (Dicentrarchus labrax) by in situ hybridization with 35S-UTP labeled cRNA probes. Gene expression was mainly detected within the forebrain, although NPY mRNA transcripts were also localized in the tectum and tegmentum mesencephali and posterior brain. New NPY-expressing nuclei were found in the dorsal and ventral telencephalon, preoptic area, tuberal hypothalamus, synencephalon, tegmentum mesencephali and posterior brain. The profuse NPY gene expression within the main neuroendocrine areas of the teleost fish further supports a physiological role in the control of the pituitary secretion. In addition, NPY gene was expressed within the primary visual, olfactory and gustatory circuits of teleost which, subsequently, project to hypothalamic feeding center in teleost fish. Our results extend the NPY-expressing areas known in teleost species.

Regulation of food intake by neuropeptide Y in goldfish

In mammals, neuropeptide Y (NPY) is a potent orexigenic factor. In the present study, third brain ventricle (intracerebroventricular) injection of goldfish NPY (gNPY) caused a dose-dependent increase in food intake in goldfish, and intracerebroventricular administration of NPY Y1-receptor antagonist BIBP-3226 decreased food intake; the actions of gNPY were blocked by simultaneous injection of BIBP-3226. Goldfish maintained on a daily scheduled feeding regimen display an increase in NPY mRNA levels in the telencephalon-preoptic area and hypothalamus shortly before feeding; however, a decrease occured in optic tectum-thalamus. In both fed and unfed fish, brain NPY mRNA levels decreased after scheduled feeding. Restriction in daily food ration intake for 1 wk or food deprivation for 72 h resulted in increased brain NPY mRNA levels. Results from these studies demonstrate that NPY is a physiological brain signal involved in feeding behavior in goldfish, mediating its effects, at least in part, through Y1-like receptors in the brain.

Zebrafish genes for neuropeptide Y and peptide YY reveal origin by chromosome duplication from an ancestral gene linked to the homeobox cluster

Neuropeptide Y (NPY) and peptide YY (PYY) are related 36-amino acid peptides. NPY is widely distributed in the nervous system and has several physiological roles. PYY serves as an intestinal hormone as well as a neuropeptide. We report here cloning of the npy and pyy genes in zebrafish (Danio rerio). NPY differs at only one to four amino acid positions from NPY in other jawed vertebrates. Zebrafish PYY differs at three positions from PYY from other fishes and at 10 positions from mammals. In situ hybridization showed that neurons containing NPY mRNA have a widespread distribution in the brain, particularly in the telencephalon, optic tectum, and rhombencephalon. PYY mRNA was found mainly in brainstem neurons, as reported previously for vertebrates as divergent as the rat and the lamprey, suggesting an essential role for PYY in these neurons. PYY mRNA was observed also in the telencephalon. These results were confirmed by immunocytochemistry. As in the human, the npy gene is located adjacent to homeobox (hox) gene cluster A (copy a in zebrafish), whereas the pyy gene is located close to hoxBa. This suggests that npy and pyy arose from a common ancestral gene in a chromosomal duplication event that also involved the hox gene clusters. As zebrafish has seven hox clusters, it is possible that additional NPY family genes exist or have existed. Also, the NPY receptor system seems to be more complex in zebrafish than in mammals, with at least two receptor genes without known mammalian orthologues.

Brain regulation of feeding behavior and food intake in fish

In mammals, the orexigenic and anorexigenic neuronal systems are morphologically and functionally connected, forming an interconnected network in the hypothalamus to govern food intake and body weight. However, there are relatively few studies on the brain control of feeding behavior in fish. Recent studies using mammalian neuropeptides or fish homologs of mammalian neuropeptides indicate that brain orexigenic signal molecules include neuropeptide Y, orexins, galanin and beta-endorphin, whereas brain anorexigenic signal molecules include cholecystokinin, bombesin, corticotropin-releasing factor, cocaine- and amphetamine-regulated transcript, and serotonin. Tachykinins may also have an anorectic action in fish. The brain hypothalamic area is associated with regulation of food intake, while sites outside the hypothalamus are also involved in this function. There is correlation between short-term changes in serum growth hormone levels and feeding behavior, although possible mechanisms integrating these functions remain to be defined.

Distribution of GAD-immunoreactive neurons in the diencephalon of the african lungfish Protopterus annectens: colocalization of GAD and NPY in the preoptic area

The distribution of GABAergic neurons was investigated in the diencephalon of the African lungfish, Protopterus annectens, by using specific antibodies directed against glutamic acid decarboxylase (GAD). A dense population of immunoreactive perikarya was observed in the periventricular preoptic nucleus, whereas the caudal hypothalamus and the dorsal thalamus contained only scattered positive cell bodies. Clusters of GAD-positive cells were found in the intermediate lobe of the pituitary. The diencephalon was richly innervated by GAD-immunoreactive fibers that were particularly abundant in the hypothalamus. In the periventricular nucleus, GAD-positive fibers exhibited a radial orientation, and a few neurons extended processes toward the third ventricle. More caudally, a dense bundle of GAD-immunoreactive fibers coursing along the ventral wall of the hypothalamus terminated into the median eminence and the neural lobe of the pituitary. Double-labeling immunocytochemistry revealed that GAD and neuropeptide tyrosine (NPY)-like immunoreactivity was colocalized in a subpopulation of perikarya in the periventricular preoptic nucleus. The proportion of neurons that coexpressed GAD and NPY was higher in the caudal region of the preoptic nucleus. The distribution of GAD-immunoreactive elements in the diencephalon and pituitary of the African lungfish indicates that GABA may act as a hypophysiotropic neurohormone in Dipnoans. The coexistence of GAD and NPY in a subset of neurons of the periventricular preoptic nucleus suggests that GABA and NPY may interact at the synaptic level.