Dissociated feeding and hypothermic effects of neuropeptide Y in the paraventricular and perifornical hypothalamus

Neuropeptide S increases motor activity and thermogenesis in the rat through sympathetic activation

The central role of neuropeptide S (NPS), identified as the endogenous ligand for GPR154, now named neuropeptide S receptor (NPSR), has not yet been fully clarified. We examined the central role of NPS for body temperature, energy expenditure, locomotor activity and adrenal hormone secretion in rats. Intracerebroventricular (icv) injection of NPS increased body temperature in a dose-dependent manner. Energy consumption and locomotor activity were also significantly increased by icv injection of NPS. In addition, icv injection of NPS increased the peripheral blood concentration of adrenalin and corticosterone. Pretreatment with the β1- and β2-adrenergic receptor blocker timolol inhibited the NPS-induced increase of body temperature. The expression of both NPS mRNA in the brainstem and NPSR mRNA in the hypothalamus showed a nocturnal rhythm with a peak occurring during the first half of the dark period. To examine whether the endogenous NPS is involved in regulation of body temperature, NPSR antagonist SHA68 was administered one hour after darkness. SHA68 attenuated the nocturnal rise of body temperature. These results suggest that NPS contributes to the regulation of the sympathetic nervous system.

Neuropeptide-Y modulates eating patterns and masticatory muscle activity in rats

Neuropeptide Y (NPY) is a powerful orexigenic peptide secreted by hypothalamic neurons. The present study investigates how NPY injection into the lateral ventricle modulates masticatory movements and eating behavior. Behavioral experiments showed that cumulative food intake over a 4-h period and latency to eating were increased and decreased, respectively, in NPY-injected rats compared to saline-injected control rats. The feeding time for 2 g pellets was shorter in NPY-injected rats and resulted in an increased feeding rate, with more potent effects observed at 1 μg compared to 10 μg NPY. After injection of 10 μg NPY, a greater number of bouts with shorter average bout duration for eating 2g, compared to 1 μg NPY, were observed. Furthermore, 10 μg NPY injection resulted in prolonged periods of moving and shortened sleep and grooming. Electromyography recordings from the digastric and masseter muscles showed two distinct patterns of bursts corresponding to the gnawing and chewing phases. After the injection of 1 μg NPY, the burst magnitude of masseter muscle during the gnawing phase increased, reflecting strong jaw-closing muscle activity. The relative integrated EMG of masseter muscle in both phases was smaller following injection of 10 μg NPY in comparison with that of 1 μg NPY. The present study indicates that 1 μg NPY administration promotes feeding behavior together with increased feeding rate and powerful jaw-closing muscle activity; whereas 10 μg NPY administration lowers jaw-closing muscle activity during biting and produces mastication with shorter and more frequent feeding bouts than 1 μg NPY.

Efferent projections of neuropeptide Y-expressing neurons of the dorsomedial hypothalamus in chronic hyperphagic models

The dorsomedial hypothalamus (DMH) has long been implicated in feeding behavior and thermogenesis. The DMH contains orexigenic neuropeptide Y (NPY) neurons, but the role of these neurons in the control of energy homeostasis is not well understood. NPY expression in the DMH is low under normal conditions in adult rodents but is significantly increased during chronic hyperphagic conditions such as lactation and diet-induced obesity (DIO). To understand better the role of DMH-NPY neurons, we characterized the efferent projections of DMH-NPY neurons using the anterograde tracer biotinylated dextran amine (BDA) in lactating rats and DIO mice. In both models, BDA- and NPY-colabeled fibers were limited mainly to the hypothalamus, including the paraventricular nucleus of the hypothalamus (PVH), lateral hypothalamus/perifornical area (LH/PFA), and anteroventral periventricular nucleus (AVPV). Specifically in lactating rats, BDA-and NPY-colabeled axonal swellings were in close apposition to cocaine- and amphetamine-regulated transcript (CART)-expressing neurons in the PVH and AVPV. Although the DMH neurons project to the rostral raphe pallidus (rRPa), these projections did not contain NPY immunoreactivity in either the lactating rat or the DIO mouse. Instead, the majority of BDA-labeled fibers in the rRPa were orexin positive. Furthermore, DMH-NPY projections were not observed within the nucleus of the solitary tract (NTS), another brainstem site critical for the regulation of sympathetic outflow. The present data suggest that NPY expression in the DMH during chronic hyperphagic conditions plays important roles in feeding behavior and thermogenesis by modulating neuronal functions within the hypothalamus, but not in the brainstem.

Molecules affecting hypothalamic control of core body temperature in response to calorie intake

Core body temperature (CBT) and calorie intake are main components of energy homeostasis and two important regulators of health, longevity, and aging. In homeotherms, CBT can be influenced by calorie intake as food deprivation or calorie restriction (CR) lowers CBT whereas feeding has hyperthermic effects. The finding that in mice CBT prolonged lifespan independently of CR, suggested that the mechanisms modulating CBT may represent important regulators of aging. Here we summarize the current knowledge on the signaling molecules and their receptors that participate in the regulation of CBT responses to calorie intake. These include hypothalamic neuropeptides regulating feeding but also energy expenditure via modulation of thermogenesis. We also report studies indicating that nutrient signals can contribute to regulation of CBT by direct action on hypothalamic preoptic warm-sensitive neurons that in turn regulate adaptive thermogenesis and hence CBT. Finally, we show the role played by two orphans G protein-coupled receptor: GPR50 and GPR83, that were recently demonstrated to regulate temperature-dependent energy expenditure.

Urocortin I inhibits the effects of ghrelin and neuropeptide Y on feeding and energy substrate utilization

The corticotropin releasing hormone-related ligand, urocortin-I (UcnI), suppresses food intake when injected into multiple hypothalamic and extrahypothalamic areas. UcnI also alters energy substrate utilization, specifically via enhanced fat oxidation as reflected in reductions in respiratory quotient (RQ). In the present study we compared the feeding and metabolic effects of ghrelin and NPY following pretreatment with UcnI. Direct PVN injections of NPY (50 pmol) and ghrelin (50 pmol) were orexigenic while UcnI (10-40 pmol) reliably suppressed food intake. Both ghrelin and NPY increased RQ, indicating enhanced utilization of carbohydrates and the preservation of fat stores. UcnI alone suppressed RQ responses. PVN UcnI attenuated the effects of both ghrelin and NPY on food intake and energy substrate utilization. While ghrelin (5 pmol) potentiated the effect of NPY (25 pmol) on RQ and food intake, these responses were inhibited by pretreatment with UcnI (10 pmol). In conclusion, PVN NPY and ghrelin stimulate eating and promote carbohydrate oxidation while inhibiting fat utilization. These effects are blocked by UcnI which alone suppresses appetite and promotes fat oxidation. Overall these findings are consistent with a possible interactive role of PVN NPY, ghrelin and urocortin in the modulation of appetite and energy metabolism.

Central and peripheral mechanisms of the NPY system in the regulation of bone and adipose tissue

Skeletal research is currently undergoing a period of marked expansion. The boundaries of "bone" research are being re-evaluated and with this, a growing recognition of a more complex and interconnected biology than previously considered. One aspect that has become the focus of particular attention is the relationship between bone and fat homeostasis. Evidence from a number of avenues indicates that bone and adipose regulation are both related and interdependent. This review examines the neuropeptide Y (NPY) system, known to exert powerful control over both bone and fat tissue. The actions of this system are characterized by signaling both within specific nuclei of the hypothalamus and also the target tissues, mediated predominantly through two G-protein coupled receptors (Y1 and Y2). In bone tissue, elevated NPY levels act consistently to repress osteoblast activity. Moreover, both central Y2 receptor and osteoblastic Y1 receptor signaling act similarly to repress bone formation. Conversely, loss of NPY expression or receptor signaling induces increased osteoblast activity and bone mass in both cortical and cancellous envelopes. In fat tissue, NPY action is more complex. Energy homeostasis is powerfully altered by elevations in hypothalamic NPY, resulting in increases in fat accretion and body-wide energy conservation, through the action of locally expressed Y1 receptors, while local Y2 receptors act to inhibit NPY-ergic tone. Loss of central NPY expression has a markedly reduced effect, consistent with a physiological drive to promote fat accretion. In fat tissue, NPY and Y1 receptors act to promote lipogenesis, consistent with their roles in the brain. Y2 receptors expressed in adipocytes also act in this manner, showing an opposing action to their role in the hypothalamus. While direct investigation of these processes has yet to be completed, these responses appear to be interrelated to some degree. The starvation-based signal of elevated central NPY inducing marked inhibition of osteoblast activity, whilst promoting fat accretion, indicating skeletal tissue is a component of the energy conservation system. Moreover, when NPY expression is reduced, consistent with high calorie intake and weight gain, bone formation is stimulated, strengthening the skeleton. In conclusion, NPY acts to regulate both bone and fat tissue in a coordinated manner, and remains a strong candidate for mediating interactions between these two tissues.

Fasting and postprandial conditions affect both fatty acids and lipid compositions in the hypothalamus and fat-soluble vitamins in the serum of male rats

The purpose of this study was to examine the effects of fasting and re-feeding on lipid derivative patterns in the hypothalamus, and on vitamin, cholesterol and malondialdehyde (MDA) levels in serum. Adult male Wistar albino rats were assigned (n = 6/group) as follows: normally-fed controls (CON), fasted for 24 h (24F), fasted for 48 h (48F), and fed normally for 2 d after fasting for 48 h (FAF). Biochemical measures were analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC). Our results demonstrate that hypothalamic saturated fatty acid (C16:0, C18:0) levels were lower, and unsaturated fatty acid (C22:6 n-3, C22:4 n-6, C20:4 n-6) levels were higher, in the 48F and FAF groups than in CON (). In addition, hypothalamic monounsaturated fatty acid (MUFA) levels were lower, and polyunsaturated fatty acids (PUFA) levels were higher, in 24F than in CON. Total hypothalamic lipids in both 24F and 48F were higher than CON, and cholesterol was elevated in the hypothalami of all experimental groups as compared to CON. Serum malondialdehyde was higher in fasted and FAF groups; 24F and 48F also had higher serum cholesterol levels, than CON (, ). Serum α-tocoferol, retinol and vitamin C values were lower in 48F than CON (). In conclusion, we demonstrate that feeding state can significantly alter brain fatty acid and lipid derivative levels, and serum concentrations of cholesterol and vitamins. These changes may consequently influence lipid peroxidation, fatty acid synthase or desaturase system in hypothalamic fields.

Role of the arcuate nucleus of the hypothalamus in regulation of body weight during energy deficit

Acute or long-term energy deficit in lean or obese rodents or humans stimulates food intake or appetite and reduces metabolic rate or energy expenditure. These changes contribute to weight regain in post-obese animals and humans. Some studies show that the reduction in metabolic rate with energy deficit in overweight people is transient. Energy restriction has been shown in some but not all studies to reduce physical activity, and this may represent an additional energy-conserving adaptation. Energy restriction up-regulates expression of the orexigenic neuropeptide Y, agouti related peptide and opioids and down-regulates that of the anorexigenic alpha-melanocyte stimulating hormone or its precursor pro-opioomelanocortin and the co-expressed cocaine and amphetamine-regulated transcript in the arcuate nucleus of the hypothalamus. Recapitulating these hypothalamic changes in sated animals mimics the effects of energy deficit, namely increased food intake, reduced physical activity and reduced metabolic rate, suggesting that these energy-conserving adaptations are at least partially mediated by the hypothalamus.

Peripheral neuropeptide Y Y1 receptors regulate lipid oxidation and fat accretion

OBJECTIVE

Neuropeptide Y and its Y receptors are important players in the regulation of energy homeostasis. However, while their functions in feeding regulation are well recognized, functions in other critical aspects of energy homeostasis are largely unknown. To investigate the function of Y1 receptors in the regulation of energy homeostasis, we examined energy expenditure, physical activity, body composition, oxidative fuel selection and mitochondrial oxidative capacity in germline Y1(-/-) mice as well as in a conditional Y1-receptor-knockdown model in which Y1 receptors were knocked down in peripheral tissues of adult mice.

RESULTS

Germline Y1(-/-) mice of both genders not only exhibit a decreased respiratory exchange ratio, indicative of increased lipid oxidation, but interestingly also develop late-onset obesity. However, the increased lipid oxidation is a primary effect of Y1 deletion rather than secondary to increased adiposity, as young Y1(-/-) mice are lean and show the same effect. The mechanism behind this is likely because of increased liver and muscle protein levels of carnitine palmitoyltransferase-1 (CPT-1) and maximal activity of key enzymes involved in beta-oxidation; beta-hydroxyacyl CoA dehydrogenase (betaHAD) and medium-chain acyl-CoA dehydrogenase (MCAD), leading to increased mitochondrial capacity for fatty acid transport and oxidation. These effects are controlled by peripheral Y1-receptor signalling, as adult-onset conditional Y1 knockdown in peripheral tissues also leads to increased lipid oxidation, liver CPT-1 levels and betaHAD activity. Importantly, these mice are resistant to diet-induced obesity.

CONCLUSIONS

This work shows the primary function of peripheral Y1 receptors in the regulation of oxidative fuel selection and adiposity, opening up new avenues for anti-obesity treatments by targeting energy utilization in peripheral tissues rather than suppressing appetite by central effects.

Appetitive and consummatory ingestive behaviors stimulated by PVH and perifornical area NPY injections

Food is acquired (obtained by foraging) and frequently stored (hoarded) across animal taxa, including humans, but the physiological mechanisms underlying these behaviors are virtually unknown. We found that peptides that stimulate food intake in rats stimulate food foraging and/or hoarding more than intake in Siberian hamsters. Neuropeptide Y (NPY) is a potent orexigenic peptide that increases food foraging and hoarding (appetitive behavior) and food intake (consummatory behavior). Given that NPY injections into the hypothalamic paraventricular nucleus (PVH) or perifornical area (PFA) increase food intake by rats, it is possible that these injections may stimulate food foraging or hoarding by Siberian hamsters. We also tested whether antagonism of the NPY Y1 receptor (Y1-R), the agonism of which stimulates hoarding, would inhibit post-food-deprivation increases in foraging and hoarding. We injected one of three doses of NPY or vehicle into the PVH or PFA of animals housed in a simulated foraging-hoarding housing system and measured these behaviors at 1, 2, 4, and 24 h. A subset of animals was subsequently food deprived and then given PVH or PFA Y1-R antagonist microinjections before they were refed. NPY PVH microinjections decreased foraging but increased hoarding and food intake, whereas NPY PFA microinjections increased all three behaviors, but the greatest increase was in hoarding. Y1-R antagonist inhibited post-food-deprivation increases in hoarding when injected into the PVH and PFA and inhibited foraging when injected into the PFA. These results support the view that NPY is involved in appetitive and consummatory ingestive behaviors, but each may be controlled by different brain areas and/or NPY receptor subtypes.

Neuropeptide Y and alpha-melanocyte-stimulating hormone: interaction in obesity and possible role in the development of hypertension

AIM

Obesity and hypertension frequently coexist and both represent important risk factors for cardiovascular disease. The mechanisms implicated in the regulation of food intake have not been completely elucidated. Recent data suggests that peripheral and central neuropeptides play an important role in the maintenance of energy balance. More specifically, leptin, neuropeptide Y (NPY) and alpha-melanocyte-stimulating hormone (a-MSH) appear to be implicated in the pathogenesis of obesity and also contribute to the development of hypertension in obesity.

METHODS

Analysis of the pertinent bibliography published in PubMed database.

RESULTS

Leptin is produced in the adipose tissue directly correlated with fat tissue mass. Leptin acts on two distinct neural populations in the hypothalamus: the first expresses the orexigenic peptides NPY and agouti-related protein (AgRP), the second pro-opiomelanocortin (POMC). The activation of POMC neurons increases the production of the anorexigenic hormone a-MSH and inhibits the release of NPY and AgRP. In addition, the hypothalamus integrates the neuroendocrine systems with the autonomic nervous system and controls the activity of the latter. Stimulation of hypothalamic nuclei elicits sympathetic responses including blood pressure elevation. Both NPY and a-MSH appears to be implicated in the hypothalamic regulation of sympathetic nervous system (SNS) activity.

CONCLUSION

Alterations in leptin, NPY and a-MSH are frequently observed in obesity and might stimulate SNS activity, contributing to the development of hypertension in obese patients. These neuropeptides might provide a pathophysiologic link between excess weight and hypertension. However, more research is needed before the pharmacologic manipulation of these complex neuroendocrine systems can be applied in the treatment of obesity and hypertension.

Neuropeptide Y in the amygdala induces long-term resilience to stress-induced reductions in social responses but not hypothalamic-adrenal-pituitary axis activity or hyperthermia

Resilience to mental and physical stress is a key determinant for the survival and functioning of mammals. Although the importance of stress resilience has been recognized, the underlying neural mediators have not yet been identified. Neuropeptide Y (NPY) is a peptide known for its anti-anxiety-like effects mediated via the amygdala. The results of our current study demonstrate, for the first time that repeated administration of NPY directly into the basolateral nucleus of the amygdala (BLA) produces selective stress-resilient behavioral responses to an acute restraint challenge as measured in the social interaction test, but has no effect on hypothalamic-adrenal-pituitary axis activity or stress-induced hyperthermia. More importantly, the resilient behaviors observed in the NPY-treated animals were present for up to 8 weeks. Antagonizing the activity of calcineurin, a protein phosphatase involved in neuronal remodeling and present in NPY receptor containing neurons within the BLA, blocked the development of long-term, but not the acute increases in social interaction responses induced by NPY administration. This suggests that the NPY-induced long-term behavioral resilience to restraint stress may occur via mechanisms involving neuronal plasticity. These studies suggest one putative physiologic mechanism underlying stress resilience and could identify novel targets for development of therapies that can augment the ability to cope with stress.

Differential effects of recombinant adeno-associated virus-mediated neuropeptide Y overexpression in the hypothalamic paraventricular nucleus and lateral hypothalamus on feeding behavior

It is well known that neuropeptide Y (NPY) increases food intake. The hypothalamic paraventricular nucleus (PVN) and the lateral hypothalamus (LH) are both involved in the acute, hyperphagic effects of NPY. Although it is obvious that increased energy intake may lead to obesity, it is less understood which aspects of feeding behavior are affected and whether one or multiple neural sites mediate the effects of long-term increased NPY signaling. By long-term overexpressing NPY in either the PVN or the LH, we uncovered brain site-specific effects of NPY on meal frequency, meal size, and diurnal feeding patterns. In rats injected with adeno-associated virus-NPY in the PVN, increased food intake resulted from an increase in the amount of meals consumed, whereas in rats injected in the LH, increased food intake was attributable to increased meal size. Interestingly, food intake and body weight gain were only temporarily increased in PVN-injected rats, whereas in LH-injected rats hyperphagia and body weight gain remained for the entire 50 d. Moreover, in LH-NPY rats, but not in PVN-NPY rats, diurnal rhythmicity with regard to food intake and body core temperature was lost. These data clearly show that the NPY system differentially regulates energy intake and energy expenditure in the PVN and LH, which together adjust energy balance.

Viral mediated neuropeptide Y expression in the rat paraventricular nucleus results in obesity

OBJECTIVE

Chronic central administration of neuropeptide Y (NPY) has dramatic effects on energy balance; however, the exact role of the hypothalamic paraventricular nucleus (PVN) in this is unknown. The aim of this study was to further unravel the contribution of NPY signaling in the PVN to energy balance.

RESEARCH METHODS AND PROCEDURES

Recombinant adeno-associated viral particles containing NPY (rAAV-NPY) were injected in the rat brain with coordinates targeted at the PVN. For three weeks, body weight, food intake, endocrine parameters, body temperature, and locomotor activity were measured. Furthermore, effects on insulin sensitivity and expression of NPY, agouti-related protein (AgRP), and pro-opiomelanocortin in the arcuate nucleus were studied.

RESULTS

Food intake was increased specifically in the light period, and dark phase body temperature and locomotor activity were reduced. This resulted in obesity characterized by increased fat mass; elevated plasma insulin, leptin, and adiponectin; decreased AgRP expression in the arcuate nucleus; and decreased insulin sensitivity; whereas plasma corticosterone was unaffected.

DISCUSSION

These data suggest that increased NPY expression targeted at the PVN is sufficient to induce obesity. Interestingly, plasma concentrations of leptin and insulin were elevated before a rise in food intake, which suggests that NPY in the PVN influences leptin and insulin secretion independently from food intake. This strengthens the role of the PVN in regulation of energy balance by NPY.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

Chronic PYY3-36 treatment promotes fat oxidation and ameliorates insulin resistance in C57BL6 mice

PYY(3-36) is a gut-derived hormone acting on hypothalamic nuclei to inhibit food intake. We recently showed that PYY(3-36) acutely reinforces insulin action on glucose disposal in mice. We aimed to evaluate effects of PYY(3-36) on energy metabolism and the impact of chronic PYY(3-36) treatment on insulin sensitivity. Mice received a single injection of PYY(3-36) or were injected once daily for 7 days, and energy metabolism was subsequently measured in a metabolic cage. Furthermore, the effects of chronic PYY(3-36) administration (continuous and intermittent) on glucose turnover were determined during a hyperinsulinemic-euglycemic clamp. PYY(3-36) inhibited cumulative food intake for 30 min of refeeding after an overnight fast (0.29 +/- 0.04 vs. 0.56 +/- 0.12 g, P = 0.036) in an acute setting, but not after 7 days of daily dosing. Body weight, total energy expenditure, and physical activity were not affected by PYY(3-36). However, it significantly decreased the respiratory quotient. Both continuous and intermittent PYY(3-36) treatment significantly enhanced insulin-mediated whole body glucose disposal compared with vehicle treatment (81.2 +/- 6.2 vs. 77.1 +/- 5.2 vs. 63.4 +/- 5.5 micromol.min(-1).kg(-1), respectively). In particular, PYY(3-36) treatment increased glucose uptake in adipose tissue, whereas its impact on glucose disposal in muscle did not attain statistical significance. PYY(3-36) treatment shifts the balance of fuel use in favor of fatty acids and enhances insulin sensitivity in mice, where it particularly promotes insulin-mediated glucose disposal. Notably, these metabolic effects of PYY(3-36) remain unabated after chronic administration, in contrast to its anorexic effects.

Mediation of the behavioral, endocrine and thermoregulatory actions of ghrelin

The action of ghrelin on telemetrically recorded motor activity and the transmission of the effects of this neuropeptide on spontaneous and exploratory motor activity and some related endocrine and homeostatic parameters were investigated. Different doses (0.5-5 microg) of ghrelin administered intracerebroventricularly caused significant increases in both square crossing and rearing activity in the "open-field" apparatus, while only the dose of 5 microg evoked a significant increase in the spontaneous locomotor activity recorded by telemetry. Ghrelin also induced significant increases in corticosterone release and core temperature. To determine the transmission of these neuroendocrine actions, the rats were pretreated with different antagonists, such as a corticotropin-releasing hormone (CRH) antagonist (alpha-helical CRH(9-41)), the nitric oxide synthase inhibitor Nomega-nitro-L-arginine-methyl ester (L-NAME), haloperidol, cyproheptadine or the cyclooxygenase inhibitor noraminophenazone (NAP). The open-field and biotelemetric observations revealed that the motor responses were diminished by pretreatment with the CRH antagonist and haloperidol. In the case of HPA (hypothalamic pituitary adrenal) activation, only cyproheptadine pretreatment proved effective; haloperidol and L-NAME did not modify the corticosterone response. NAP had only a transient, while cyproheptadine elicited a more permanent impact on the hyperthermic response evoked by ghrelin; the other antagonists proved to be ineffective. The present data suggest that both CRH release and dopaminergic transmission may be involved in the ghrelin-evoked behavioral responses. On the other hand, ghrelin appears to have an impact on the HPA response via a serotonergic pathway and on the hyperthermic response via a cyclooxygenase and a serotonergic pathway.

Distribution of urocortin 3 neurons innervating the ventral premammillary nucleus in the rat brain

Urocortin 3 (Ucn 3) is a recently described peptide of the corticotropin-releasing factor family. Neurons expressing Ucn 3 mRNA and peptide are distributed in specific brain areas, including the median preoptic nucleus, the perifornical area (PFx), and the medial nucleus of the amygdala (MEA). Fibers immunoreactive to Ucn 3 are confined to certain brain nuclei, being particularly dense in the ventral premammillary nucleus (PMV). In studies involving electrolytic lesions and analysis of Fos distribution according to behavioral paradigms, the PMV has been potentially implicated in conspecific aggression and sexual behavior. However, the role that Ucn 3 plays in this pathway has not been explored. Therefore, we investigated the origins of the urocortinergic innervation of the PMV of Wistar rat in an attempt to map the brain circuitry and identify likely related functions. We injected the retrograde tracer cholera toxin b subunit into the PMV and found that 88% of the Ucn 3-immunoreactive fibers in the PMV originate in the dorsal MEA, and that few originate in the PFx. As a control, we injected the anterograde tracer biotin dextran amine into both regions. We observed that the PMV is densely innervated by the MEA, and scarcely innervated by the PFx. The MEA is a secondary relay of the vomeronasal system and projects amply to hypothalamic nuclei related to hormonal and behavioral adjustments, including the PMV. Although physiological studies should also be performed, we hypothesize that Ucn 3 participates in such pathways, conveying sensory information to the PMV, which in turn modulates behavioral and neuroendocrine responses.

Hypothalamic and zona incerta neurons expressing hypocretin, but not melanin concentrating hormone, project to the hamster intergeniculate leaflet

The hypocretins (Hcrt; also known as orexins) and melanin-concentrating hormone comprise distinct families of neuropeptides synthesized in cells located in the lateral hypothalamus and adjacent areas. The Hcrts are thought to modulate food intake and sleep/wake patterns in mammals. Melanin-concentrating hormone has a well-documented role in energy metabolism. A moderate plexus of Hcrt immunoreactive terminals has been described in the hamster intergeniculate leaflet, part of the circadian rhythm system. This study investigated the origin of Hcrt-immunoreactive terminals in the intergeniculate leaflet and determined whether melanin-concentrating hormone neurons also project to the intergeniculate leaflet. The tracer, cholera toxin beta-subunit, was injected into the intergeniculate leaflet of the golden hamster. Double-label fluorescent immunohistochemistry for cholera toxin beta-subunit and Hcrt or melanin-concentrating hormone was then performed to identify retrogradely labeled cells also containing immunoreactive peptide. Most cholera toxin beta-subunit-labeled cells were detected in the medial zona incerta and sub-incertal zone, with few observed in the lateral hypothalamus. Hcrt-immunoreactive cells were abundant and found largely in the lateral hypothalamus and adjacent nuclei. Melanin-concentrating hormone cells were also abundant in the medial zona incerta, in close proximity to cholera toxin beta-subunit-labeled cells, but ventral to them. Cells containing both cholera toxin beta-subunit and Hcrt-immunoreactive, were present in the dorsal aspect of the lateral hypothalamus. The number observed was small, < or = 1% of the total number of Hcrt cells counted in the hamster. No cholera toxin beta-subunit-immunoreactive cells also contained melanin-concentrating hormone and no melanin-concentrating hormone-immunoreactive processes were evident in the intergeniculate leaflet. The results show that a small number of lateral hypothalamus cells containing Hcrt-immunoreactivity project to the intergeniculate leaflet, but they are scattered rather than collected into a discrete group. At the present time there is no information regarding the function of these cells, although they may contribute to the regulation of sleep/arousal, circadian rhythmicity, or vestibulo-oculomotor function.

Neuropeptide Y induces torpor-like hypothermia in Siberian hamsters

Intracerebroventricular (ICV) injections of neuropeptide Y (NPY) are known to decrease body temperature (Tb) of laboratory rats by 1-3 degrees C. Several NPY pathways in the brain terminate in hypothalamic structures involved in energy balance and thermoregulation. Laboratory rats are homeothermic, maintaining Tb within a narrow range. We examined the effect of ICV injected NPY on Tb in the heterothermic Siberian hamster (Phodopus sungorus), a species that naturally undergoes daily torpor in which Tb decreases by as much as 15-20 degrees C. Minimum effective dose was determined in preliminary testing then various doses of NPY were tested in cold-acclimated Siberian hamsters while food was withheld. NPY markedly reduced Tb in the heterothermic Siberian hamster. In addition, the reduction in Tb in 63% of the observations was sufficient to reach the criterion for daily torpor (Tb < 32 degrees C for at least 30 min). Neither the incidence of torpor nor its depth or duration was related to NPY dose. Both likelihood and magnitude of response varied within animals on different test days. NPY decreased 24-h food intake and this was exaggerated in the animals reaching criterion for torpor; the decrease in food intake was positively correlated with the magnitude of the decrease in Tb. The mild hypothermia seen in homeothermic laboratory rats after NPY injected ICV is exaggerated, often greatly, in the heterothermic Siberian hamster. NPY treatment may be activating hypothalamic systems that normally integrate endogenous torpor-producing signals and initiate torpor.

Neuropeptide Y, alpha-melanocyte-stimulating hormone, and monoamines in food intake regulation

Obesity is increasing in severity and prevalence in the United States and represents a major public health issue. No effective pharmacologic treatment leading to sustained weight loss currently exists. The growing interest in the regulation of food intake stems from the current drug treatments for obesity, almost all of which interfere with the monoamine system. Our knowledge of potential interactions between the orexigenic and anorexigenic pathways is limited and fragmented, making the development of targeted drug therapy for obesity difficult. The present review of the interaction of neuropeptides and monoamines emphasizes the complexity of the central mechanisms that regulate feeding behavior. Two main systems are implicated in food intake regulation: neuropeptide Y (NPY) and pro-opiomelanocortin. alpha-Melanocyte-stimulating hormone is a tridecapeptide cleaved from pro-opiomelanocortin that acts to inhibit food intake. The predominant NPY orexigenic receptors are NPY-Y1 and NPY-Y5, and the two anorexigenic melanocortin receptors involved in hypothalamic food intake control are MC3-R and MC4-R. Both neuropeptides interact with monoamines in the hypothalamus to control physiologic states such as hunger, satiation, and satiety. Serotonin suppresses food intake and body weight, acting mainly through the serotonin 1B receptor. Dopamine regulates hunger and satiety by acting in specific hypothalamic areas, through the D1 and D2 receptors. Noradrenaline activation of alpha1- and beta2-adrenoceptors decreases food intake, and stimulation of the alpha2-adrenoceptor increases food intake. A better understanding of the detailed mechanisms underlying the pathogenesis of hyperphagia and hypophagia is needed to develop new therapeutic approaches to obesity.

Acute, subacute and chronic effects of central neuropeptide Y on energy balance in rats

Central neuropeptide Y (NPY) injection has been reported to cause hyperphagia and in some cases also hypometabolism or hypothermia. Chronic central administration induced a moderate rise of short duration in body weight, without consistent metabolic/thermal changes. In the present studies the acute and subsequent subacute ingestive and metabolic/thermal changes were studied following intracerebroventricular (i.c.v.) injections of NPY in cold-adapted and non-adapted rats, or the corresponding chronic changes following i.c.v. NPY infusion. Besides confirming basic earlier data, we demonstrated novel findings: a temporal relationship for the orexigenic and metabolic/thermal effects, and differences of coordination in acute/subacute/chronic phases or states. The acute phase (30-60 min after injection) was anabolic: coordinated hyperphagia and hypometabolism/hypothermia. NPY evoked a hypothermia by suppressing any (hyper)metabolism in excess of basal metabolic rate, without enhancing heat loss. Thus, acute hypothermia was observed in sub-thermoneutral but not thermoneutral environments. The subsequent subacute catabolic phase exhibited opposite effects: slight increase in metabolic rate, rise in body temperature, reaching a plateau within 3-4 h after injection -- this was maintained for at least 24 h; meanwhile the food intake decreased and the normal daily weight gain stopped. This rebound is only indirectly related to NPY. Chronic (7-day long) i.c.v. NPY infusion induced an anabolic phase for 2-3 days, followed by a catabolic phase and fever, despite continued infusion. In cold-adaptation environment the primary metabolic effect of the infusion induced a moderate hypothermia with lower daytime nadirs and nocturnal peaks of the circadian temperature rhythm, while at near-thermoneutral environments in non-adapted rats the infusion attenuated only the nocturnal temperature rise by suppressing night-time hypermetabolism. Further finding is that in cold-adapted animals, the early feeding effect of NPY-infusion was enhanced, whereas the early hypothermic effect in cold was limited by interference with competing thermoregulatory mechanisms.

Ontogeny of the hypothalamic neuropeptide Y system

Early onset obesity and type II diabetes is rapidly becoming an epidemic, especially within the United States. This dramatic increase is likely due to many factors including both prenatal and postnatal environmental cues. The purpose of this review is to highlight some of the recent advances in our knowledge of the development of the hypothalamic circuits involved in the regulation of energy balance, with a focus on the neuropeptide Y (NPY) system. Unlike the adult rat, during the postnatal period NPY is transiently expressed in several hypothalamic regions, along with the expected expression within the arcuate nucleus (ARH). These transient populations of NPY neurons during the postnatal period may provide local NPY production to sustain the necessary energy intake during this critical growth phase. This may be physiologically important since ARH-NPY projections do not fully develop until the 3rd postnatal week. The significance of this ontogeny is that many peripheral metabolic signals have little effect of feeding prior to the development of the ARH projections. The essential questions now are whether prenatal and/or postnatal exposure to high levels of insulin or leptin during development can cause permanent changes in the function of hypothalamic circuits. It is vital to understand not only the natural development of the hypothalamic circuits that regulate energy homeostasis, but also their abnormal development caused by maternal and postnatal environmental cues. This will be pivotal for designing intervention and therapeutics to treat early onset obesity/type II diabetes, which may very well need to be different from those designed to prevent/treat adult onset obesity/type II diabetes.

Fasting activates neuropeptide Y neurons in the arcuate nucleus and the paraventricular nucleus in the rhesus macaque

It is well accepted that neuropeptide Y (NPY) plays a pivotal role in the regulation of food intake and energy homeostasis in the rodent, with NPY neurons in the arcuate nucleus (ARH) being thought of as the major contributor to the complex central feeding circuitry. Recent data from our group also indicate that NPY is important in the regulation of energy homeostasis in the nonhuman primate (NHP); exogenous NPY administration into the 3rd ventricle is a potent stimulator of food intake in the male rhesus macaque. The purpose of this study was to determine if NPY neurons in the rhesus macaque respond to a metabolic challenge, induced by 48 h of fasting, in a manner similar to that seen in the rodent. NPY mRNA was detected in hypothalamic sections from 48-h fasted or fed rhesus monkeys by in situ hybridization, using a [35S]UTP-labeled riboprobe specific for human NPY. Not surprisingly, NPY mRNA was abundant in the ARH of the NHP; however, of great interest was the expression of NPY mRNA in neurons within the paraventricular nucleus of the hypothalamus (PVH) and the supraoptic nucleus (SON). This raised the question as to whether all of these populations of NPY neurons are sensitive to changes in energy availability. Indeed, NPY expression in the ARH and PVH was significantly elevated in response to fasting; however, no significant change was detected in the SON. These data indicate that the NPY neurocircuitry involved in the regulation of food intake is more complex in the NHP than in rodents.

Orexin neurons express a functional pancreatic polypeptide Y4 receptor

The receptor subtypes that mediate the effects of neuropeptide Y (NPY) on food intake have not been clearly defined. The NPY Y4 receptor has been identified recently as a potential mediator of the regulation of food intake. The purpose of the present study was to characterize the central site of action of the Y4 receptor using a combination of neuroanatomical and physiological approaches. Using immunocytochemistry, Y4-like immunoreactivity was found to be colocalized with orexin cell bodies in the lateral hypothalamic area (LHA) and orexin fibers throughout the brain. In situ hybridization confirmed the expression of Y4 mRNA in orexin neurons. To determine the functional interaction between Y4 receptors and orexin neurons, we examined the effects of rat pancreatic polypeptide (rPP), a Y4-selective ligand, or NPY, a nonselective ligand, administered directly into the LHA on the stimulation of food and water intake and c-Fos expression. Both rPP and NPY significantly increased food and water intake when they were administered into the LHA, although NPY was a more potent stimulator of food intake. Furthermore, both NPY and rPP significantly stimulated c-Fos expression in the LHA. However, whereas rPP stimulated c-Fos expression in orexin neurons, NPY did not. Neither rPP nor NPY stimulated c-Fos in melanin-concentrating hormone neurons, but both activated neurons of an unknown phenotype in the LHA. These results suggest that a functional Y4 receptor is expressed on orexin neurons and that these neurons are activated in response to a ligand with high affinity for the Y4 receptor (rPP). Although these data suggest a role for central Y4 receptors, the endogenous ligand for this receptor has yet to be clearly established.

Hypothalamic regulation of energy homeostasis

The co-ordinated regulation of food intake and energy expenditure takes place in the hypothalamic regions of the brain. Current understanding of the systems involved in this regulation suggests that, in the hypothalamus, there are two major groups of neuropeptides involved in orexigenic and anorexic processes. The orexigenic neuropeptides are neuropeptide Y (NPY) and agouti-related peptide (AgRP) and the anorexic neuropeptides are alpha-melanocyte-stimulating hormone (alpha-MSH) and cocaine and amphetamine-related transcript (CART). Theneurons expressing these neuropeptides interact with each other and with signals from the periphery (such as leptin, insulin, ghrelin and glucocorticoids) to regulate feeding behaviour, energy expenditure and various endocrine axes. Although direct evidence is limited, there are examples of genetic obesity in humans which suggest that the balance between orexigenic and anorexic pathways in the hypothalamus is also pivotally important in the maintenance of energy homeostasis in humans.

Hypothalamic paraventricular 5-hydroxytryptamine: receptor-specific inhibition of NPY-stimulated eating and energy metabolism

The feeding effects of 5-hydroxytryptamine (5-HT)(1) and 5-HT(2) receptor agonists injected into the hypothalamic paraventricular nucleus (PVN) immediately prior to PVN administration of neuropeptide Y (NPY) were examined. The impact of these same compounds on NPY-induced alterations in energy metabolism was also assessed in an attempt to characterize further the potential interactive relationship of PVN NPY and 5-HT on feeding and whole body calorimetry. Specifically, several experiments examined the effect of various 5-HT receptor agonists on NPY-stimulated eating and alterations in energy substrate utilization [respiratory quotient (RQ)]. This included the 5-HT(1A) receptor agonist 8-OH-DPAT, the 5-HT(1B/1A) agonist RU 24969, the 5-HT(1D) agonist L-694,247, the 5-HT(2A/2C) agonist DOI, the 5-HT(2B) agonist BW 723C86 and the 5-HT(2C) agonist mCPP. In feeding tests conducted at the onset of the dark cycle, drugs were administered 5 min prior to PVN injection of NPY and food intake was measured 2 h postinjection. The metabolic effects of NPY following a similar pretreatment were monitored using an open-circuit calorimeter measuring the volume of oxygen consumed (VO(2)), carbon dioxide produced (VCO(2)) and RQ (VCO(2)/VO(2)). PVN injection of NPY (100 pmol) potentiated feeding and evoked reliable increases in RQ. Only DOI (2.5--5 nmol) pretreatment antagonized NPY-induced eating and blocked the peptide's effect on energy substrate utilization. Direct PVN pretreatment with spiperone (SPRN), a 5-HT(2A) receptor antagonist, and ketanserin (KTSN), a 5-HT(2A/2C) antagonist, but not SDZ SER 082, a 5-HT(2B/2C) antagonist, or the 5-HT(2C) antagonist RS 102221, blocked the effect of DOI in both feeding and metabolic tests providing additional evidence that activation of PVN 5-HT(2A) receptors inhibits NPY's action on feeding and substrate utilization.

The role of NPY in the mediation of orexin-induced hypothermia

The mediation of orexin-A-induced hypothermia was investigated. Different doses of orexin-A (140-560 pmol) were administered intracerebroventricularly (i.c.v.) to adult male rats, and the colon temperature was used as an index of the thermoregulatory action. Orexin-A decreased both the basal colon temperature and the lipopolysaccharide-induced fever and exhibited a bell-shaped dose-response curve. I.c.v. pretreatment with neuropeptide Y (NPY) antiserum 24 h before orexin administration significantly decreased the hypothermic effect of orexin-A. These data strengthen the hypothesis that this appetite-regulating peptide might also play a role in thermoregulation, and its hypothermic effect seems to be mediated at least partially by NPY.

Chronic central melanocortin-4 receptor antagonism and central neuropeptide-Y infusion in rats produce increased adiposity by divergent pathways

Increased hypothalamic neuropeptide-Y (NPY) action and disruption of the melanocortin (MC)-4 receptor both result in hyperphagia and obesity. To determine whether similar hormonal and metabolic mechanisms are involved in these two obesity syndromes, we investigated the time course of effects induced by 6-day intracerebroventricular (ICV) infusion of NPY (3.5 nmol/day) or the MC4 receptor antagonist HS014 (4.8 nmol/day) in rats pair-fed with vehicle-infused controls. The weight of white adipose tissue (WAT) deposits was increased after 6-day NPY and HS014 infusion compared with controls, and the increase was significantly greater in HS014- than in NPY-infused rats (retroperitoneal WAT: NPY 0.57 +/- 0.05; HS014 0.80 +/- 0.05; control 0.43 +/- 0.03% body wt, n = 8-13, P < 0.05). Plasma leptin was also increased in both experimental groups (NPY 10.6 +/- 1.9; HS014 4.4 +/- 0.9; control 2.0 +/- 0.1 ng/ml, n = 8-13, P < 0.05 for all comparisons). Basal plasma corticosterone and insulin levels were increased by ICV NPY infusion, whereas HS014-infused rats showed no significant increase in these parameters on any of 1-6 days of infusion. Both NPY and HS014 infusion potentiated intravenous glucose-induced (300 mg/kg) plasma insulin levels, and there was no difference in glycemia among groups. In NPY-infused rats, the plasma free fatty acid levels were decreased and triglyceridemia was increased compared with controls, but these parameters were unchanged in HS014-infused rats. Hepatic triglyceride content was significantly increased by HS014 but not by NPY infusion. Levels of uncoupling protein-1 mRNA in brown adipose tissue were significantly decreased after 6 days of HS014 infusion, similar to the effect of central NPY. Because ICV HS014 induced at least as great an increase in fat mass as ICV NPY and yet had divergent hormonal and metabolic effects, we conclude that MC4 receptor antagonism does not induce obesity solely by regulation of the endogenous NPY-ergic system.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

Hypothalamic and vagal neuropeptide circuitries regulating food intake

It has been recognized for some time that a number of different neuropeptides exert powerful effects on food intake. During the last few years, the neurocircuitry within which these peptides operate has also begun to be elucidated. Peptidergic feeding-regulatory neurones are found both in the hypothalamus and the brainstem, where they act as input stations for hormonal and gastrointestinal information, respectively. These cell populations both project to several other brain regions and interconnect extensively. The present review summarizes the neuroanatomy and connectivity of some prominent peptides involved in food intake control, including neuropeptide Y, melanocortin peptides, agouti gene-related protein, cocaine- and amphetamine-regulated transcript, orexin/hypocretin, melanin-concentrating hormone and cholecystokinin. Disturbances in the hypothalamic neuropeptide systems have been implicated in the phenotype of a genetic model of fatal hypophagia, the mouse anorexia (anx) mutation, which is also discussed.

Hypothalamic paraventricular nucleus injections of urocortin alter food intake and respiratory quotient

Corticotropin releasing hormone (CRH) acts on the central nervous system to alter energy balance and influence both food intake and sympathetically-mediated thermogenesis. CRH is also reported to inhibit food intake in several models of hyperphagia including neuropeptide Y (NPY)-induced eating. The recently identified CRH-related peptide, urocortin (UCN), also binds with high affinity to CRH receptor subtypes and decreases food intake in food-deprived and non-deprived rats. The present experiment characterized further the feeding and metabolic effects of UCN by examining its impact after direct injections into the paraventricular nucleus (PVN) of the hypothalamus. In feeding tests (n=8), UCN (50-200 pmol) was injected into the PVN at the onset of the dark cycle and food intake was measured 1, 2 and 4 h postinjection. In separate rats (n=8), the metabolic effects of UCN were monitored using an open circuit calorimeter which measured oxygen consumption (V(O2)) and carbon dioxide production (V(CO2)). Respiratory quotient (RQ) was calculated as V(CO2)/V(O2). UCN suppressed feeding at all times studied and reliably decreased RQ within 30 min of infusion. Additional work examined the effect of UCN (50-100 pmol) pretreatment on the feeding and metabolic effects of NPY. NPY, injected at the start of the dark period, reliably increased 2 h food intake. This effect was blocked by PVN UCN administration. Similarly, UCN blocked the increase in RQ elicited by NPY alone. These results suggest that UCN-sensitive mechanisms within the PVN may modulate food intake and energy substrate utilization, possibly through an interaction with hypothalamic NPY.

The rewarding properties of neuropeptide Y in perifornical hypothalamus vs. nucleus accumbens

There is a high coexistence of substance abuse in humans with eating disorders. One theory offered to account for this fact is that a common biochemical substrate may exist that mediates both processes. Brain neuropeptide Y (NPY) is one neurochemical system that might contribute to these separate, yet related, problems. To clarify the role of NPY in mediating reward processes and the possible interaction between reward and feeding, the present study examined the effects of injecting NPY bilaterally into the perifornical hypothalamus (PFH) vs. the nucleus accumbens (NAC) on intake of preferred vs. non-preferred food types, as well as on conditioned place preference (CPP) learning. NPY (24, 78, 156 and 235 pmol/side) stimulated intake of both regular powdered chow and sucrose when injected into the PFH, but not the NAC. A CPP that was negatively correlated with food intake occurred with the low (24 pmol/side) dose of NPY in the PFH, while a CPP that was not correlated with food intake was produced with the same dose in the NAC. The extent of the CPPs produced by NPY injection in both brain sites mirrored that produced by peripheral injection of amphetamine (2.5 mg/kg). These results indicate that NPY elicits reward-related behavior, but not feeding, from the NAC, and both behaviors from the PFH. However, the feeding effect derived from the PFH appears to overshadow a rewarding effect derived from this site. Considered together, these findings suggest that altered NPY functioning in both brain regions may contribute to some of the pathophysiological processes observed in eating disordered patients who have additional proclivities for substance abuse.

Effects of three neurochemical stimuli on delayed feeding and energy metabolism

Infusions of norepinephrine (NE), the gamma-aminobutyric acid agonist, muscimol (MUS), or neuropeptide Y (NPY) into the paraventricular nucleus (PVN) of the hypothalamus all increase food intake. Such feeding may be due to direct activation of behavioral processes driving ingestion and/or to alterations in nutrient metabolism that feeding serves to normalize. To examine these possibilities, male Sprague-Dawley rats received PVN infusions of vehicle, 20 nmol NE, 1 nmol MUS or 100 pmol NPY at dark onset, then food intake was measured under three feeding conditions: (1) 1 and 2 h immediately after injections, (2) 1 h after a 1 h delay between injections and access to food, and (3) 1 h after a 1 h feeding delay, but with injections occurring just before presenting food. Measures of energy expenditure (EE) and respiratory quotients (RQs) in the absence of food were made over 2 h in parallel experiments. Results confirmed that NE, MUS and NPY all increased dark-onset feeding, but only NPY increased intake above control levels after a 1 h feeding delay. No neurochemically-induced changes in EE were observed, nor were there changes in RQs after NE or MUS. However, NPY reliably enhanced RQs from 30 to 120 min of testing. Our findings imply that NE and MUS initiate relatively immediate, short-term feeding that is not associated with changes in nutrient metabolism and does not summate with cues stimulated by delayed access to food. NPY initiates more protracted feeding temporally linked to enhanced carbohydrate metabolism. This may indicate that part of NPY's feeding stimulatory effects are secondary to physiological processes driving ingestion.

Paraventricular nucleus injections of naloxone methiodide inhibit NPY's effects on energy substrate utilization

Microinjection of neuropeptide Y (NPY) into the paraventricular nucleus (PVN) of the hypothalamus stimulates eating and increases respiratory quotient. In contrast, administration of opioid receptor antagonists reduces food intake and suppresses NPY-induced feeding. The present study examined whether naloxone methiodide, an opioid antagonist, would suppress the potentiation of NPY on energy substrate utilization, when injected into the PVN. Naloxone methiodide was injected at doses of 0.1 and 1.0 g, 10 min prior to NPY treatment. NPY was administered immediately prior to the start of the nocturnal period and RQ was determined using an open-circuit calorimeter. Doses of 50 and 100 pmol NPY alone evoked reliable increases in RQ within 30min of treatment. Following naloxone methiodide pretreatment, the stimulatory action of NPY was significantly attenuated. These data indicate that opioid receptors in the PVN influence the action of NPY on energy substrate utilization.

Differences in the skin peptides of the male and female Australian tree frog Litoria splendida. The discovery of the aquatic male sex pheromone splendipherin, together with phe8 caerulein and a new antibiotic peptide caerin 1.10

The skin secretions of female and male Litoria splendida have been monitored monthly over a three-year period using HPLC and electrospray mass spectrometry. Two minor peptides are present only in the skin secretion of the male. The first of these is the female-attracting aquatic male sex pheromone that we have named splendipherin, a 25 amino acid peptide (GLVSSIGKALGGLLADVVKSKGQPA-OH). This pheromone constitutes about 1% of the total skin peptides during the breeding season (January to March), dropping to about 0.1% during the period June to November. Splendipherin attracts the female in water at a concentration of 10-11-10-9 M, and is species specific. The second peptide is a wide-spectrum antibiotic of the caerin 1 group, a 25 residue peptide (GLLSVLGSVAKHVLPHVVPVIAEKL-NH2) named caerin 1.10. The neuropeptides of L. splendida are also seasonally variable, the change identical for both the female and male. During the period October to March, the sole neuropeptide present in skin secretions is caerulein [pEQDY(SO3)TGWMDF-NH2]; this is active on smooth muscle and is also an analgaesic. During the southern winter (June to September), more than half of the caerulein is hydrolysed to [pEQDYTGWMDF-NH2], a peptide that shows no smooth muscle activity. In place of caerulein, a new peptide, Phe8 caerulein [pEQDY(SO3)TGWFDF-NH2], becomes a major component of the skin secretion. Perhaps this seasonal change is involved in thermoregulation, that is, with the initiation and maintenance of the inactive (hibernation) phase of the animal.

Activation of the NPY Y5 receptor regulates both feeding and energy expenditure

Intracerebroventricular (ICV) administration of neuropeptide Y (NPY) has been shown to decrease energy expenditure, induce hypothermia, and stimulate food intake. Recent evidence has suggested that the Y5 receptor may be a significant mediator of NPY-stimulated feeding. The present study attempts to further characterize the role of NPY Y5-receptor subtypes in feeding and energy expenditure regulation. Satiated Long-Evans rats with temperature transponders implanted in the interscapular brown adipose tissue (BAT) displayed a dose-dependent decrease in BAT temperature and an increase in food intake after ICV infusion of NPY. Similar effects were induced by ICV administration of peptide analogs of NPY that activate the Y5 receptor, but not by analogs that activate Y1, Y2, or Y4 receptors. Furthermore, ICV infusion of the Y5 selective agonist D-[Trp(32)]-NPY significantly reduced oxygen consumption and energy expenditure of rats as measured by indirect calorimetry. These data suggest that the NPY Y5-receptor subtype not only mediates the feeding response of NPY but also contributes to brown fat temperature and energy expenditure regulation.

5-HT(2A/2C) receptor antagonists in the paraventricular nucleus attenuate the action of DOI on NPY-stimulated eating

Hypothalamic neuropeptide Y (NPY) and serotonin (5-HT)-containing neurons are believed to exert an interactive effect on ingestive behavior. The present study examined the ability of two serotonergic antagonists, spiperone (SPIP), a 5-HT2A antagonist, and mianserin (MIAN), a 5-HT(2A/2C) antagonist, to block the inhibitory action of the 5-HT(2A/2C) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on NPY-stimulated eating. Drugs were injected directly into the paraventricular nucleus (PVN), the perifornical (PFH) or the ventromedial hypothalamus (VMH) at the onset of the dark cycle. PVN, PFH and VMH injections of NPY potentiated food intake although only PVN pretreatment with DOI (5-20 nmol) suppressed NPY-induced eating. SPIP or MIAN, injected immediately prior to PVN DOI, reversed the suppressive effect of DOI on NPY feeding. These findings are consistent with other recent data showing that 5-HT2A receptors within the PVN modulate NPY's effect on food intake at the start of the nocturnal period.

Regulation of neuropeptide Y release by neuropeptide Y receptor ligands and calcium channel antagonists in hypothalamic slices

Neuropeptide Y (NPY) is an important regulator of energy balance in mammals through its orexigenic, antithermogenic, and insulin secretagogue actions. We investigated the regulation of endogenous NPY release from rat hypothalamic slices by NPY receptor ligands and calcium channel antagonists. High-potassium stimulation (60 mM) of the slices produced a calcium-dependent threefold increase in NPY release above basal release. The Y2 receptor agonists NPY(13-36) and N-acetyl[Leu28,Leu31]NPY(24-36), the Y4 agonist rat pancreatic polypeptide (rPP), and the Y4/Y5 agonist human pancreatic polypeptide (hPP) significantly reduced both basal and stimulated NPY release. NPY(13-36)-induced reduction of NPY release could be partially prevented in the presence of the weak Y2 antagonist T4-[NPY(33-36)]4, whereas the hPP- and rPP-induced inhibition of release was not affected by the Y5 antagonist CGP71683A or the Y1 antagonist BIBP3226. The selective Y1, Y2, and Y5 antagonists had no effect on either basal or potassium-stimulated release when administered alone. The calcium channel inhibitors omega-conotoxin GVIA (N-type), omega-agatoxin TK (P/Q-type), and omega-conotoxin MVIIC (Q-type) all significantly inhibited potassium-stimulated NPY release, without any effect on basal release, whereas nifedipine had no effect on either basal or stimulated release. Addition of both omega-conotoxin GVIA and omega-agatoxin TK together completely inhibited the potassium-stimulated release. In conclusion, we have demonstrated that NPY release from hypothalamic slices is calcium-dependent, involving N-, P-, and Q-type calcium channels. NPY release is also inhibited by Y2 agonists and rPP/hPP, suggesting that Y2 and Y4 receptors may act as autoreceptors on NPY-containing nerve terminals.

Leptin differentially regulates NPY and POMC neurons projecting to the lateral hypothalamic area

Recent studies have reinforced the view that the lateral hypothalamic area (LHA) regulates food intake and body weight. We identified leptin-sensitive neurons in the arcuate nucleus of the hypothalamus (Arc) that innervate the LHA using retrograde tracing with leptin administration. We found that retrogradely labeled cells in the Arc contained neuropeptide Y (NPY) mRNA or proopiomelanocortin (POMC) mRNA. Following leptin administration, NPY cells in the Arc did not express Fos but expressed suppressor of cytokine signaling-3 (SOCS-3) mRNA. In contrast, leptin induced both Fos and SOCS-3 expression in POMC neurons, many of which also innervated the LHA. These findings suggest that leptin directly and differentially engages NPY and POMC neurons that project to the LHA, linking circulating leptin and neurons that regulate feeding behavior and body weight homeostasis.

Neuropeptide Y receptor alterations in the hypothalamus of lactating rats

Hypothalamic neuropeptide Y (NPY) neurons are influenced by circulating levels of insulin and leptin and are thought to be involved in mediating hunger following underfeeding. We have investigated hypothalamic NPY receptor subtypes in lactating rats, which are markedly hyperphagic throughout the day and night. NPY receptors were measured by using [125I] peptide YY, a high-affinity ligand, and Y1 receptors were masked by using the highly specific antagonist BIBP 3226. Freely fed lactating rats showed no changes in the densities of Y1, or non-Y1, NPY binding sites in whole hypothalamic homogenates or in individual hypothalamic regions (measured by quantitative autoradiography) examined during the day or night (P > 0.05; n = 10/group, and n = 6/group, respectively). However, reducing food intake by 35% had a more profound effect on NPY receptor density in lactating than in control rats, producing down-regulation of non-Y1 receptors in the ventromedial, dorsomedial, and perifornical lateral areas (all P < 0.05; n = 7/group) and reduction of plasma insulin and leptin levels (both P < 0.01). Thus, although the NPY system may not have a major role in the hyperphagia of freely fed lactating rats, it appears to have an important function in the response to undernutrition in such animals.

Effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides from 1994 through 1998

Effects of peptides on the central nervous system are presented in two ways so as to provide a cross-listing. In the first table, the peptides are listed alphabetically. In the second table, the central nervous system effects are arranged alphabetically. No longer can there be any doubt that peptides affect the central nervous system, sometimes in several ways.

Hypothalamic NPY status during positive energy balance and the effects of the NPY antagonist, BW 1229U91, on the consumption of highly palatable energy-rich diet

We have studied the hypothalamic activity of the neuropeptide Y (NPY) system in dietary-induced obese male Wistar rats and examined whether the NPY antagonist, BW1229U91, can inhibit the hyperphagia during positive energy balance associated with feeding rats an energy-rich, highly palatable diet. Rats given a highly palatable, high-fat diet became obese after 8 weeks and exhibited hyperinsulinemia and hyperleptinemia, as compared to lean rats fed on standard pellet laboratory diet. Hypothalamic NPY mRNA concentrations were significantly reduced by approximately 70% in dietary-obese rats compared with lean controls, and the former were hypersensitive to intracerebroventricular injections of NPY, possibly as a result of NPY receptor up-regulation. Intracerebroventricular injections of BW 1229U91, that inhibits food intake in starved rats, did not alter food intake in either control or obese rats fed either standard pellet diet or the highly palatable diet, respectively. We conclude that dietary-obese rats have underactive hypothalamic NPYergic neurons compared to lean controls, possibly as a result of increased plasma concentrations of leptin and/or insulin that directly inhibit the NPY neuronal activity. The lack of effect of BW1229U91 on the increased caloric intake of dietary-obese rats suggests that the hyperphagia is not NPY-driven and supports the data indicating reduced synaptic activity of the hypothalamic NPY system.

Is there appetite after GLP-1 and PACAP?

Anitobesity drugs must increase the sensitivity of the hypothalamic satiety center towards leptin and antagonize the synthesis and action of NPY. The array of pharmacologic tools available is vast and presently ineffective. Among peptide analogs considered for evaluation [NPY-5 antagonists and CCK-A, bombesin, amylin and melanocyte-stimulating hormone-4 (or melanin-concentrating hormone?) agonists], is there a place for GLP-1 and PACAP? GLP-1 receptors present in ARC, PVN, VMN, and SON are the target for both central and blood-borne GLP-1 in those hypothalamic neurons endowed with GLUT-2 and glucokinase. GLP-1, hypersecreted by L-cells after a meal, is a potent insulinotropic agent and, together with glucose, reduces food intake and induces c-fos in the ARC. PACAP is present in the ARC, PVN, and SCH, and its hypothalamic type I receptor elevates cAMP and inositol triphosphate in the PVN, where it may perhaps antagonize NPY-induced food intake and hyperinsulinemia. However, irrelevant neuroendocrine, autonomic, and circadian functions are also activated by this peptide, making it a less than ideal base on which to build an obesity treatment.

5-Hydroxytryptaminergic receptor agonists: effects on neuropeptide Y potentiation of feeding and respiratory quotient

The objective of the present report was to characterize further the potential interactive effects of NPY and 5-HT on feeding and whole-body calorimetry. Specifically, several experiments examined the impact of various 5-HT receptor agonists on NPY stimulated eating and alterations in respiratory quotient (RQ). This included the 5-HT1A/1B receptor agonist RU 24969, the 5-HT1B/2C agonist TFMPP and the 5-HT2A/2C agonist DOI. In feeding tests conducted at the onset of the dark cycle, RU 24969, TFMPP and DOI were administered 5 min prior to PVN injection of NPY and food intake was measured 1 h postinjection. The metabolic effects of NPY following similar pretreatment were monitored using an open-circuit calorimeter measuring the volume of oxygen consumed (VO2), carbon dioxide produced (VCO2) and RQ (VCO2/VO2). PVN injection of NPY (50-100 pmol) potentiated feeding and evoked reliable increases in RQ. DOI (5-20 nmol), but not RU 24969 (5-20 nmol) or TFMPP (10-40 nmol), antagonized NPY induced eating and blocked the peptide's effects on RQ. These findings suggest that 5-HT2A receptors within the PVN modulate NPY's effect on feeding and energy substrate utilization at the start of the nocturnal period.

Galanin in the hypothalamus raises dopamine and lowers acetylcholine release in the nucleus accumbens: a possible mechanism for hypothalamic initiation of feeding behavior

Rats were prepared with two implanted guide shafts, one for microdialysis to measure extracellular dopamine (DA) and acetylcholine (ACh) in the posterior, medial nucleus accumbens (NAc), and the other for microinjection of galanin, neuropeptide Y or saline in the hypothalamic paraventricular nucleus (PVN). There was an increase in DA release and a decrease in ACh in the NAc following microinjections of galanin into the PVN. The effect was observed only in rats for which identical galanin injections induced feeding in separate tests. Ringer injections had no effects. Unlike galanin, neuropeptide Y in the PVN induced eating without altering DA/ACh; whereas earlier results showed that norepinephrine in the PVN works like galanin. These results suggest that galanin initiates feeding, in part, by activating the mesolimbic DA system and suppressing intrinsic cholinergic activity in the NAc. This may prime instrumental behavior with DA while disinhibiting behavior by lowering ACh.

Lipopolysaccharide (LPS)- and muramyl dipeptide (MDP)-induced anorexia during refeeding following acute fasting: characterization of brain cytokine and neuropeptide systems mRNAs

We investigated the effectiveness of lipopolysaccharide (LPS) and muramyl dipeptide (MDP) administered into the brain to induce anorexia in acutely fasted Wistar rats allowed to refeed. We also assayed for changes in mRNA levels of IL-1 system components, TNF-alpha, TGF-beta1, glycoprotein 130 (gp 130), leptin receptor (OB-R), pro-opiomelanocortin (POMC), neuropeptide Y (NPY), glucocorticoid receptor (GR), and CRF receptor (CRF-R) in selected brain regions. The data show that LPS and MDP induced anorexia differentially during refeeding. LPS-induced anorexia was of a stronger magnitude and duration than that of MDP. RNase protection assays showed that LPS and MDP significantly increased the expression of IL-1beta, IL-1 receptor type I, and TNF-alpha mRNAs in the cerebellum, hippocampus, and hypothalamus; LPS was more potent in all cases. MDP treatment, on the other hand, induced a stronger increase in hypothalamic levels of IL-1 receptor antagonist (IL-1Ra) and TGF-beta1 mRNAs relative to LPS. In addition, competitive RT-PCR analysis showed that LPS induced an eleven-fold increase in IL-1alpha mRNA in the hypothalamus relative to vehicle. These findings suggest that LPS and MDP mediate anorexia through different cytokine mechanisms. A stronger up-regulation of anti-inflammatory cytokines (IL-1Ra and TGF-beta1) mRNA expression by MDP may be involved in the weaker MDP-induced anorexia relative to LPS. No significant changes were observed in the peptide components examined except for an up-regulation in cerebellar gp 130 mRNA and down-regulation of hypothalamic GR mRNA expression in response to LPS or MDP. This study shows that LPS and MDP induce anorexia in fasted rats allowed to refeed, and suggests an important role for endogenous cytokine-cytokine interactions.