Stimulation of feeding behavior and food consumption in the goldfish, Carassius auratus, by orexin-A and orexin-B

The neuropeptides, orexin-A and orexin-B, have been demonstrated to have a physiological role in the regulation of food intake in mammals. The effects of human orexin-A and orexin-B intracerebroventricular (i.c.v.) injection on the feeding behavior of goldfish (Carassius auratus) were investigated. I.c.v. injection of orexin-A and orexin-B both caused a significant increase in appetite, as indicated by an increased number of feeding acts. Orexin-A and orexin-B both significantly stimulated food consumption, as indicated by increased total food intake during a 60-min observation period; the actions of orexin-A were dose dependent. Orexin-A was more potent than orexin-B in stimulation of both feeding behavior and food intake. These results indicate that orexin peptides are involved in the hypothalamic regulatory pathways of feeding behavior in goldfish.     

Interactions of neuropeptide Y,hypocretin-I (orexin A) and melanin-concentrating hormone on feeding in rats

Amongst various neuropeptidergic systems, neuropeptide Y (NPY), hypocretin-1 and melanin-concentrating hormone (MCH) producing neurons have been shown to play an important role in the regulation of food intake and body weight. All of these neuropeptides are orexigenic signals and recent evidence suggests the existence of morphological connections between these neuronal systems in the hypothalamus. However, the functional interactions between these neuronal systems are not clearly understood. Therefore, in the present study, we examined whether there is a cooperative action on food intake between these neuropeptides after third intracerebroventricular (icv) injection in the rat. The icv administration of NPY (0.118, 0.588, 1.176 nmol), hypocretin-1 (1, 3 nmol) and MCH (0.42, 1.048, 2.096 nmol) stimulated food intake in a dose dependent manner. Coinjection with 0.118 nmol of NPY and hypocretin-1 (1, 3 nmol) or MCH (0.42, 1.048, 2.096 nmol) had no additive effect on food intake as compared to that of NPY alone. However, coinjection with lower dose of NPY (0.023 nmol) and hypocretin-1 (0.25 nmol), that did not have any effect alone, significantly induced food intake. In contrast, combination of a lower dose of NPY (0.023 nmol) or hypocretin-1 (0.25 nmol) with lower stimulatory dose (0.21, 0.42 nmol) of MCH did not result in further increase in food intake as compared to that of MCH alone. Also, combination of 0.25 nmol hypocretin-1 and a non-stimulatory dose of MCH (0.105 nmol) was ineffective in stimulating food intake. Finally, coinjection with of 0.023 nmol NPY and 0.105 nmol MCH significantly induced food intake as compared to saline control group but not as compared to NPY or MCH treated groups. In total, these results show (1) a synergistic action between NPY and hypocretin-1, (2) no interaction between hypocretin-1 and MCH and (3) very little interaction, if any, between NPY and MCH in inducing food intake. In conclusion, these results provide a physiological concomitant to the previous demonstration of morphological contacts between NPY and hypocretin producing neurons by suggesting an interaction between these two orexigenic signals in control of food intake, and further suggest that MCH's action on feeding may be independent of NPY and hypocretin-1 action.     

Role of leptin in the control of feeding of goldfish Carassius auratus: interactions with cholecystokinin,neuropeptide Y and orexin A,and modulation by fasting

To assess the role of leptin on food intake regulation in goldfish, we examined the effects of central (intracerebroventricular, ICV) and peripheral (intraperitoneal, IP) injections of recombinant murine leptin on feeding behavior. Centrally (100 ng/g) and peripherally (300 ng/g) injected leptin both caused a significant decrease in food intake, compared to the saline-treated controls. To test the hypothesis that leptin influenced orexigenic neuropeptide systems in goldfish, fish were co-injected with neuropeptide Y (NPY) or orexin A and leptin. Both NPY (5 ng/g) and orexin A (10 ng/g) significantly increased food intake. Fish co-injected ICV with NPY (5 ng/g) or orexin A (10 ng/g) and leptin (1 or 10 ng/g) had a food intake lower than that of fish treated with NPY or orexin A alone. NPY mRNA expression in goldfish brain was reduced 2 and 6 h following central injection of leptin. To test the hypothesis that the cholecystokinin (CCK) mediates the effects of leptin in goldfish, fish were simultaneously injected ICV with an ineffective dose of leptin (10 ng/g) and either ICV or IP with an ineffective doses of CCK (1 ng/g ICV or 25 ng/g IP). These fish had a food intake lower than vehicle-treated fish, suggesting that leptin potentiates the satiety actions of CCK. CCK hypothalamic mRNA expression was increased 2 h following central treatment with leptin. The CCK receptor antagonist proglumide blocked both central and peripheral CCK satiety effects. Blockade of CCK brain receptors by proglumide resulted in an inhibition of the leptin-induced decrease in food intake and an attenuation of the inhibiting action of leptin on both NPY- and orexin A-induced feeding. These data suggests that CCK has a role in mediating the effects of leptin on food intake. Fasting potentiated the actions of leptin and attenuated the effects of CCK. Whereas fasting had no effects on the brain mRNA expression of CCK, it increased the brain mRNA expression of NPY and decreased the expression of CART. These changes in neuropeptide expression were partially reversed when fish were treated ICV with leptin. These results provide strong evidence that, in goldfish, leptin influences food intake, in part by modulating the orexigenic effects of NPY and orexin and that its actions are mediated, at least in part, by CCK.     

Effect of lateral cerebroventricular injection of the appetite-stimulating neuropeptide, orexin and neuropeptide Y, on the various behavioral activities of rats

The effect of lateral cerebroventricular injection of the appetite-stimulating neuropeptide, orexin and neuropeptide Y (NPY), on the behavior of rats was investigated. An immediate increase in face washing activity was observed after injection of orexin A or orexin B, but not NPY. Orexin A had a more potent effect on face washing behavior than orexin B. Grooming and burrowing activities also increased significantly after injection of orexin A, whereas, orexin B significantly increased burrowing and searching behavior. Feeding behavior and food consumption increased dramatically within 10 min of injection of NPY. Although the significant increase in feeding behavior was also observed after injection of orexin A, total food intake did not change significantly. These results suggest that orexin may be involved in the regulation of several other behavioral activities in rats, besides feeding.     

The effects of exogenous neuropeptide Y on feeding and sexual behavior in the red-sided garter snake (Thamnophis sirtalis parietalis)

Actively courting adult male red-sided garter snakes were injected with one of two dosages of neuropeptide Y (NPY) or saline into the third cerebral ventricle. Courtship and feeding responses were assessed prior to surgery, 4–5 h and 24 h post-surgery. Feeding behavior was tested by the presentation of a favored food, an earthworm. NPY significantly reduced courtship behavior scores at both low (0.16 nmol) and high (0.77 nmol) doses 4–5 h after surgery. Snakes also took much longer to reach the criterion courtship score at the high dose. Feeding occurred only in snakes treated with NPY. At the low dose 29% ate at 4–5 h and 24 h after surgery; 43% of the snakes treated with the high dose ate 4–5 h post-surgery. When tested the day following injection, animals were courting at levels comparable to presurgery levels and refused food.     

c-fos expression in the rat brain following central administration of neuropeptide Y and effects of food consumption

Administration of neuropeptide Y (NPY) intracerebroventricularly (i.c.v.) results in the release of a number of hypothalamic and pituitary hormones and stimulation of feeding and suppression of sexual behavior. In this study, we sought to identify cellular sites of NPY action by evaluating perikaryal Fos-like immunoreactivity (FLI), a marker of cellular activation, in those hypothalamic and extrahypothalamic sites previously implicated in the control of neuroendocrine function and feeding behavior. Additionally, we compared the topography of FLI in these brain sites when food was either available ad libitum or withheld after NPY injection (1 nmol/3 μl, i.c.v.). The results showed that one hour after NPY injection a large number of cells in the parvocellular region of the paraventricular nucleus (PVN) were FLI-positive in the absence of food consumption. However, in association with food intake, a significant number of cells were intensely stained in the magnocellular region of the PVN. An analogous increase in FLI in association with feeding was apparent in the supraotic nucleus (SON), the dorsomedial nucleus and the bed nucleus of the stria terminalis in the hypothalamus. Anong the extrahypothalamic sites, feeding facilitated FLI in a large number of cells located in the lateral subdivision of the central amygdaloid nucleus and the lateral subdivision of the solitary tract. FLI was observed in a moderate number of cells in the hypothalamic arcuate nucleus (ARC) and ventromedial nucleus, and this response was not changed by feeding. Cumulatively, these results show that neurons in a number of discrete hypothalamic and extrahypothalamic sites, previously implicated in the control of neuroendocrine function and feeding behavior, are activated by NPY and further, a divergent pattern of c-fos expression emerged in some of these sites if feeding occurs after NPY injection. Stimulation of FLI in cells of the PVN, SON and ARC by NPY imply the presence of NPY target cells that play a role in the neuroendocrine control of pituitary function. The finding that NPY induced FLI in cells located in the parvocellular subdivision of the PVN even in the absence of feeding, imply that cells involved in initiation of food intake by NPY may reside in this subdivision of the PVN. On the other hand, the appearance of Fos-cells in the magnocellular subdivision of the PVN in response to feeding, suggests neural mechanisms that operate during the post-ingestion period, including those associated with termination of NPY-induced feeding, may impinge upon this subdivision of the PVN.     

Influence of fasting and neuropeptide Y on the suppressive food intake induced by intracerebroventricular injection of glucagon-like peptide-1 in the neonatal chick

Recently, we have reported that central administration of glucagon-like peptide-1 (GLP-1) strongly decreased food intake of chicks. The aim of the present study was to elucidate whether suppressed food intake by central injection of GLP-1 would be modified by an appetite stimulant such as fasting and neuropeptide Y (NPY). Birds (2 days old) were starved for 3 or 6 h and then GLP-1 (0.03 μg/10 μl) or saline was injected by the intracerebroventricular (i.c.v.) route. Birds starved for 6 h ate significantly more food than those starved for 3 h, while irrespective of the time for fasting GLP-1 strongly inhibited food intake as rapidly as 10 min after i.c.v injection. The suppressive effect on food intake continued until 4 h after injection. Central administration of NPY (2.5 μg/10 μl) greatly enhanced food intake, but co-injection of GLP-1 (0.01, 0.02 or 0.03 μg/10 μl) decreased food intake in a dose-dependent fashion. Under GLP-1 (0.03 μg/10 μl) treatment, whether NPY modifies food intake of chicks in a dose-dependent manner was investigated by co-injection of graded levels of NPY (0.4, 1.0 and 2.5 μg/10 μl). GLP-1 completely inhibited the effect of NPY on food intake without a dose response. These results suggest that central GLP-1 may interact with NPY and may be the most potent inhibitor of food intake in the chicken.     

Identification of visual pallial telencephalon in the goldfish, Carassius auratus: a combined cytochrome oxidase and electrophysiological study

A strategy based upon a comparative decrease in bilateral symmetry of cytochrome oxidase (COX) histochemistry following unilateral eye enucleation was used to identify the primary visual area in the area dorsalis of the telencephalon of the goldfish, Carassius auratus. The lateral zone of area dorsalis (Dl) at about the level of the anterior commissure exhibits such a bilateral difference. A parallel decline in the symmetry COX reactivity was observed in the associated part of the central zone (Dc). Electrophysiological activity using extracellular techniques confirmed the visually-driven activity of neurons in these areas. Lesions confirmed the loci in the lateral zone of area dorsalis, including both its dorsal and ventral parts. Single- and multi-unit recordings exhibited a variety of responses to different light stimuli. Single unit latency measures proved not to be a reliable measure of target areas. Responses habituated to stimuli repeated within 5 s and were only reliably evoked with intervals greater than several seconds.     

Neuropeptide Y, epinephrine and norepinephrine in the paraventricular nucleus: Stimulation of feeding and the release of corticosterone, vasopressin and glucose

The paraventricular nucleus (PVN) is known to have an important function in mediating a variety of behavioral and endocrine responses. In the present study, the responsiveness of the PVN to the effects of the coexisting neurotransmitters, neuropeptide Y (NPY), epinephrine (EPI) and norepinephrine (NE), was examined. Albino rats were each chronically implanted with a swivel brain-cannula that permits chemicals to be infused without disturbing the animals' ongoing behavior. When infused into the PVN, each of these neurotransmitters elicited a reliable feeding response during the first hour after injection. The response to EPI was significantly stronger than that of NE and NPY, while the latency to eat after injection was considerably longer for NPY as compared to the catecholamines. In tests with food absent, each of these substances also increased blood levels of corticosterone (EPI greater than NE = NPY) and vasopressin (NPY greater than EPI greater than NE) and revealed a significant positive correlation between circulating levels of these two hormones. In addition, EPI and NE, in contrast to NPY, caused a simultaneous rise in blood glucose, producing levels that were positively correlated with the hormones. No relationship, however, was detected between these endocrine changes and the rats' feeding-stimulatory responses. Together with other evidence, these results suggest that adrenergic as well as noradrenergic innervation to the PVN has a key role in the behavioral and endocrine systems of this nucleus and, moreover, that NPY generally mimics the effects of these catecholamines in the PVN.     

Effects of gender on the central actions of neuropeptide Y and norepinephrine on vasopressin and blood pressure in the rat

Neuropeptide Y (NPY) and norepinephrine are co-localized in the noradrenergic projection from the A₁ nucleus of the medulla to the vasopressinergic magnocellular neurons of the supraoptic and paraventricular nuclei. Because this pathway is involved in the control of vasopressin release, we have examined the possibility that NPY and norepinephrine interact in this control. Because the stimulation of vasopressin release by the intracerebroventricular (i.c.v.) administration of norepinephrine is greater in male than in female rats, the experiments were carried out in conscious male rats and in female rats in the proestrous and non-proestrous phases of the estrous cycle. NPY (940 pmol i.c.v.) caused small sustained increases in plasma vasopressin concentrations that were greater in proestrous than in non-proestrous females and males. Norepinephrine i.c.v. increased plasma vasopressin levels transiently and to a greater extent in females than males. When NPY and norepinephrine were given together, the pattern of the vasopressin response was similar to that of norepinephrine alone. The magnitude of this response in males and proestrous females did not differ from that to norepinephrine alone; in non-proestrous females the response was twice that to norepinephrine alone. In non-proestrous rats, NPY also enhanced the pressor response to norepinephrine. Thus, NPY interacts centrally with norepinephrine in vasopressin release and cardiovascular function and this effect is dependent upon gender and phase of the estrous cycle.     

Effects of chronic alcohol consumption,withdrawal and nerve growth factor on neuropeptide Y expression and cholinergic innervation of the rat dentate hilus

Several studies have demonstrated the vulnerability of the hippocampal formation (HF) to chronic alcohol consumption and withdrawal. Among the brain systems that appear to be particularly vulnerable to the effects of these conditions are the neuropeptide Y (NPY)-ergic and the cholinergic systems. Because these two systems seem to closely interact in the HF, we sought to study the effects of chronic alcohol consumption (6 months) and subsequent withdrawal (2 months) on the expression of NPY and on the cholinergic innervation of the rat dentate hilus. As such, we have estimated the areal density and the somatic volume of NPY-immunoreactive neurons, and the density of the cholinergic varicosities. In addition, because alcohol consumption and withdrawal are associated with impaired nerve growth factor (NGF) trophic support and the administration of exogenous NGF alters the effects of those conditions on various cholinergic markers, we have also estimated the same morphological parameters in withdrawn rats infused intracerebroventricularly with NGF. NPY expression increased after withdrawal and returned to control values after NGF treatment. Conversely, the somatic volume of these neurons did not differ among all groups. On other hand, the expression of vesicular acetylcholine transporter (VAChT) was reduced by 24% in ethanol-treated rats and by 46% in withdrawn rats. The administration of NGF to withdrawn rats increased the VAChT expression to values above control levels. These results show that the effects of prolonged alcohol intake and protracted withdrawal on the hilar NPY expression differ from those induced by shorter exposures to ethanol and by abrupt withdrawal. They also suggest that the normalizing effect of NGF on NPY expression might rely on the NGF-induced improvement of cholinergic neurotransmission in the dentate hilus.     

Unilateral cortical spreading depression in the rat: Effects on feeding, drinking and other behaviors

The effects of unilateral cortical spreading depression (CSD) on feeding, drinking and other behaviors were studied in rats. CSD waves were elicited by a microinjection of KC1 solution through an implanted cannula. The animal's behavior and slow potential changes (SPC) accompanying CSD were then simultaneously monitored for 20 min. Intensive face grooming was observed while the CSD wave-front propagated across the sensorimotor cortex. Animals commenced their first feeding or drinking shortly after the invasion of the negative SPC into the frontal cortex of Krieg's area 6 and 10 [14]had reached its maximum height. A two-way switching effect between the first feeding or drinking and quiescence (freezing) and a close relationship between their onsets were observed. The results are discussed specifically in relation to cortico-hypothalamic pathways.     

The origin of the centrifugal fibers to the olfactory bulb in the goldfish,Carassius auratus: An experimental study using the fluorescent dye primuline as a retrograde tracer

The origin of the centrifugal fibers to the olfactory bulb in the goldfish was examined by injecting a fluorescent dye, primuline, into the olfactory bulb by means of hydraulic pressure. Three to five days after the primuline injection, which was confined to the unilateral olfactory bulb, a large number of primuline-labeled perikarya appeared in two telencephalic areas on the ipsilateral side: the area ventralis telencephali pars dorsalis (Vd) and the ventral part of the area dorsalis telencephali pars lateralis (Dlv). No labeled cells were observed in the other olfactory bulb or in the contralateral telencephalic hemisphere or more posterior part of the brain. A combination of the primuline injection and the transection of either the medial or lateral olfactory tract showed that the main course of the centrifugal fibers was through the medial olfactory tract. These results may support Sheldon's opinion that the so-called tractus olfactorius ascendens, which corresponds to the medial part of the medial olfactory tract, is a centrifugal bundle originating from the cells in the nucleus medianus. The areas of the telencephalic hemisphere into which the olfactory bulbar fibers projected were also examined and compared with the originating areas of the centrifugal fibers. There was a considerable overlap between these two areas. This suggests a reciprocal connection between the olfactory bulb and the telencephalon.     

Retinal ganglion cell response to axotomy and nerve growth factor antiserum treatment in the regenerating visual system of the goldfish (Carassius auratus): An in vivo and in vitro analysis

In vitro nerve growth factor (NGF) antiserum (anti-NGF) treatment was found to significantly depress retinal ganglion cell neurite outgrowth in goldfish explant culture. Goldfish retinas, conditioned by a 14-day prior optic nerve crush, demonstrated a significant dose response inhibition of neurite outgrowth if incubated with various concentrations of the antiserum (i.e. concentrations from full strength to 1:100) before explanation for tissue culture. NGF added to the incubation medium containing antiserum partially eliminated the inhibition of neurite outgrowth during the first 4 days of explant culture. Antiserum treatment at the higher concentrations (i.e. full strength and 1:1.5 dilution) caused a cessation of nerve growth from explants between culture days 3 and 4. However, controls at this time still exhibited vigorous neurite outgrowth.In vivo treatment with anti-NGF administered intraocularly at 7 days after optic nerve crush (i.e. 7 DPA) was found to significantly reduce the size and complexity of retinal ganglion cell nucleoli when analyzed morphometrically at 14 DPA. No other cell parameters measured (i.e. cell size, nuclear size, cell/nuclear ratios and mitochondrial, Golgi and RER densities) were found to be affected by the single antiserum treatment.     

Effects of intracerebroventricularly infused histamine and selective H1, H2 and H3 agonists on food and water intake and urine flow in Wistar rats

The actions of intracerebroventricularly infused histamine and selective histamine H₁, H₂ and H₃ receptor agonists on food and water intake and urine flow were studied in rats. It was found that 100–800 nmoles of histamine significantly suppressed feeding. The H₁ agonist 2-(3-trifluoromethylphenyl)histamine (FMPH) decreased food intake, whereas the H₂ agonist dimaprit was without effect. Histamine- and FMPH-induced suppressions of feeding were attenuated by blockade of H₁ but not by H₂ receptors. The results clearly demonstrate that activation of brain H₁ receptors decreases food intake. In subsequent studies, we found that both metoprine and thioperamide, which increase histaminergic activity through different mechanisms, also reduced food intake. This finding indicates that the brain histaminergic system is associated with feeding behavior. The same is true with body water homeostasis. Histamine caused a long-lasting diuresis. Also dimaprit and metoprine increased urine flow and the blockade of H₂ receptors abolished the diuretic responses to histamine and dimaprit. On the other hand, the H₃ agonist (R)-α-methylhistamine elicited drinking and this effect could be prevented by thioperamide pretreatment. The results imply that activation of H₃ receptors predominantly provokes drinking, whereas central H₂ receptors mediate the diuretic effect of histamine.