Intracerebroventricular injection of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibits feeding in chicks

PACAP and VIP Neuropeptides' and Receptors' Effects on Appetite, Satiety and Metabolism

The overwhelming increase in the prevalence of obesity and related disorders in recent years is one of the greatest threats to the global healthcare system since it generates immense healthcare costs. As the prevalence of obesity approaches epidemic proportions, the importance of elucidating the mechanisms regulating appetite, satiety, body metabolism, energy balance and adiposity has garnered significant attention. Currently, gastrointestinal (GI) bariatric surgery remains the only approach capable of achieving successful weight loss. Appetite, satiety, feeding behavior, energy intake and expenditure are regulated by central and peripheral neurohormonal mechanisms that have not been fully elucidated yet. Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and Vasoactive Intestinal Polypeptide (VIP) are members of a family of regulatory peptides that are widely distributed in parallel with their specific receptors, VPAC1R, VPAC2R and PAC1R, in the central nervous system (CNS) and in the periphery, such as in the gastrointestinal tract and its associated organs and immune cells. PACAP and VIP have been reported to play an important role in the regulation of body phenotype, metabolism and homeostatic functions. The purpose of this review is to present recent data on the effects of PACAP, VIP, VPAC1R, VPAC2R and PAC1R on the modulation of appetite, satiety, metabolism, calorie intake and fat accumulation, to evaluate their potential use as therapeutic targets for the treatment of obesity and metabolic syndrome.

Vasoactive intestinal peptide promotes hypophagia and metabolic changes: role of paraventricular hypothalamic nucleus and nitric oxide

Vasoactive intestinal peptide (VIP), a neuromodulator present in the hypothalamus, plays an important role in the regulation of food intake. Paraventricular nucleus of the hypothalamus (PVN) is involved in ingestive responses and regulates the nitric oxide (NO) pathway. The main objectives of this study were to investigate metabolic changes established after different doses and times of VIP microinjection on the PVN, and the effect of VIP microinjection on the PVN on food intake and the role of NO in this control. In anesthetized rats, increased blood plasma glucose and insulin levels were observed following the doses of 40 and 80ng/g of body weight. At the dose of 40ng/g, VIP promoted hyperglycemia and hyperinsulinemia 5, 10, and 30min after microinjection, and increased free fatty acids and total lipids plasma levels after 5min, and triglycerides after 10min. In awake animals, once again, VIP administration increased plasmatic levels of glucose, free fatty acids, corticosterone, and insulin 10min after the microinjection. Moreover, VIP promoted hypophagia in the morning and night periods, and L-arginine (L-Arg) and monosodium glutamate (MSG) or a combination of both attenuated VIP-induced reduction on food intake. In addition, nitrate concentration in the PVN was decreased after VIP microinjection. Our data show that the PVN participates in the anorexigenic and metabolic effects of VIP, and that VIP-induced hypophagia is likely mediated by reduction of NO.

The PACAP/PAC1 Receptor System and Feeding

Pituitary adenylyl cyclase activating polypeptide (PACAP) belongs to the vasoactive intestinal polypeptide (VIP)/secretin/glucagon superfamily. PACAP is present in two forms (PACAP-38 and PACAP-27) and binds to three guanine-regulatory (G) protein-coupled receptors (PAC1, VPAC1, and VPAC2). PACAP is expressed in the central and peripheral nervous systems, with high PACAP levels found in the hypothalamus, a brain region involved in feeding and energy homeostasis. PAC1 receptors are high-affinity and PACAP-selective receptors, while VPAC1 and VPAC2 receptors show a comparable affinity to PACAP and VIP. PACAP and its receptors are expressed in the central and peripheral nervous systems with moderate to high expression in the hypothalamus, amygdala, and other limbic structures. Consistent with their expression, PACAP is involved in several physiological responses and pathological states. A growing body of literature suggests that PACAP regulates food intake in laboratory animals. However, there is no comprehensive review of the literature on this topic. Thus, the purpose of this article is to review the literature regarding the role of PACAP and its receptors in food intake regulation and to synthesize how PACAP exerts its anorexic effects in different brain regions. To achieve this goal, we searched PubMed and reviewed 68 articles regarding the regulatory action of PACAP on food intake. Here, we present the literature regarding the effect of exogenous PACAP on feeding and the role of endogenous PACAP in this process. We also provide evidence regarding the effect of PACAP on the homeostatic and hedonic aspects of food intake, the neuroanatomical sites where PACAP exerts its regulatory action, which PACAP receptors may be involved, and the role of various signaling pathways and neurotransmitters in hypophagic effects of PACAP.

Metformin Treatment Attenuates Brain Inflammation and Rescues PACAP/VIP Neuropeptide Alterations in Mice Fed a High-Fat Diet

High-fat diet (HFD)-induced comorbid cognitive and behavioural impairments are thought to be the result of persistent low-grade neuroinflammation. Metformin, a first-line medication for the treatment of type-2 diabetes, seems to ameliorate these comorbidities, but the underlying mechanism(s) are not clear. Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) are neuroprotective peptides endowed with anti-inflammatory properties. Alterations to the PACAP/VIP system could be pivotal during the development of HFD-induced neuroinflammation. To unveil the pathogenic mechanisms underlying HFD-induced neuroinflammation and assess metformin’s therapeutic activities, (1) we determined if HFD-induced proinflammatory activity was present in vulnerable brain regions associated with the development of comorbid behaviors, (2) investigated if the PACAP/VIP system is altered by HFD, and (3) assessed if metformin rescues such diet-induced neurochemical alterations. C57BL/6J male mice were divided into two groups to receive either standard chow (SC) or HFD for 16 weeks. A further HFD group received metformin (HFD + M) (300 mg/kg BW daily for 5 weeks) via oral gavage. Body weight, fasting glucose, and insulin levels were measured. After 16 weeks, the proinflammatory profile, glial activation markers, and changes within the PI3K/AKT intracellular pathway and the PACAP/VIP system were evaluated by real-time qPCR and/or Western blot in the hypothalamus, hippocampus, prefrontal cortex, and amygdala. Our data showed that HFD causes widespread low-grade neuroinflammation and gliosis, with regional-specific differences across brain regions. HFD also diminished phospho-AKT^(Ser473) expression and caused significant disruptions to the PACAP/VIP system. Treatment with metformin attenuated these neuroinflammatory signatures and reversed PI3K/AKT and PACAP/VIP alterations caused by HFD. Altogether, our findings demonstrate that metformin treatment rescues HFD-induced neuroinflammation in vulnerable brain regions, most likely by a mechanism involving the reinstatement of PACAP/VIP system homeostasis. Data also suggests that the PI3K/AKT pathway, at least in part, mediates some of metformin’s beneficial effects.

The anorexigenic effect of vasoactive intestinal polypeptide in Japanese quail is associated with molecular changes in the arcuate and dorsomedial hypothalamic nuclei

Vasoactive intestinal polypeptide (VIP) is involved in gastric smooth muscle relaxation, vasodilation, and gastric secretions. It is also associated with appetite regulation, eliciting an anorexigenic response in mammals, birds, and fish; however, the molecular mechanism mediating this response is not well understood. The aim of the present study was thus to investigate hypothalamic mechanisms mediating VIP-induced satiety in 7-d old Japanese quail. In experiment 1, chicks that received intracerebroventricular (ICV) injection of VIP had reduced food intake for up to 180 min after injection and reduced water intake for 90 min. In experiment 2, VIP-treated chicks that were food restricted did not reduce water intake. In experiment 3, there was increased c-Fos immunoreactivity in the arcuate (ARC) and dorsomedial (DMN) nuclei of the hypothalamus in VIP-injected quail. In experiment 4, ICV VIP was associated with decreased neuropeptide Y mRNA in the ARC and DMN and an increase in corticotropin releasing factor mRNA in the DMN. In experiment 5, VIP-treated chicks displayed fewer feed pecks and locomotor behaviors. These results demonstrate that central VIP causes anorexigenic effects that are likely associated with reductions in orexigenic tone involving the ARC and DMN.

Prolactin-releasing peptide increases food intake and affects hypothalamic physiology in Japanese quail (Coturnix japonica)

Prolactin-releasing peptide (PrRP) increases food intake in birds, whereas it is a potent satiety factor in rodents and fish. The aim of this study was to determine the effects of central injection of PrRP on feeding behaviors and hypothalamic physiology in juvenile Japanese quail (Coturnix japonica). Intracerebroventricular injection of 1,692 pmol of PrRP increased food intake for the first 90 min after injection but did not affect water intake. Quail treated with PrRP displayed more food and drink pecks, less time standing but more perching, and decreased defecations. Prolactin-releasing peptide-injected quail had increased c-Fos immunoreactivity in the dorsomedial nucleus (DMN) and arcuate nucleus (ARC) of the hypothalamus. Hypothalamic neuropeptide Y receptor subtypes 2 and 5 and melanocortin receptor 4 mRNAs were greater in PrRP- than vehicle-injected quail. In the DMN, there was less corticotropin-releasing factor (CRF) mRNA and in the ARC, more CRF mRNA in PrRP- than vehicle-injected chicks. Thus, PrRP increases food intake in quail, which is associated with changes in hypothalamic CRF and neuropeptide Y receptor gene expression and c-Fos-immunolabeled cells in the ARC and DMN.

Pleiotropic pituitary adenylate cyclase-activating polypeptide (PACAP): Novel insights into the role of PACAP in eating and drug intake

Pituitary adenylate cyclase-activating polypeptide (PACAP) was discovered thirty years ago, but its role in eating and drug use disorders has only recently begun to be investigated. The present review develops the hypothesis that, although PACAP normally functions to tightly regulate intake, inhibiting it through negative feedback, this relationship can become dysregulated with the development of dependence, such that PACAP instead acts through positive feedback to promote excessive intake. We propose that repeated exposure to palatable food and drugs of abuse can alter the downstream responses of specific populations of neurons to stimulation by PACAP, leading to the perpetuation of the addiction cycle. Thus, this review will first describe published literature on homeostatic food intake, which shows that PACAP suppresses food intake, while its levels are themselves increased by overfeeding. Next, it will present literature on palatable food, cocaine, alcohol, and nicotine, which overall demonstrates that PACAP in specific limbic brain regions can promote their seeking and intake and itself is stimulated by their intake. Then, it will present literature on affective behavior, which shows that chronic stress increases levels of PACAP, which then promotes anxiety and depression, factors that can trigger substance seeking. Finally, the review will address mechanisms through which chronic substance exposure may dysregulate the PACAP system, proposing that it alters expression of PACAP receptor splice variants. While many questions remain to be addressed, the current evidence suggests that PACAP could be a viable medication target for the treatment of binge eating and drug and alcohol use disorders.

The role of endogenous pituitary adenylyl cyclase activating polypeptide (PACAP) in nicotine self-administration, reward and aversion

Pituitary adenylyl cyclase activating polypeptide (PACAP) and its receptors (PAC1, VPAC1, and VPAC2) are localized in brain regions implicated in stress response, reward seeking and aversive responses, raising the possibility that PACAP may be involved in motivational effects of nicotine. To test this hypothesis, we used two-bottle choice (TBC) and place conditioning paradigms and assessed if nicotine preference or conditioned place preference (CPP) or aversion (CPA) induced by nicotine would be altered in mice lacking PACAP compared to their wild-type controls. In the TBC paradigm, mice had access to two water bottles during the first week and then one of the water bottles was switched to nicotine solution (20, 40 and then 80 μg/mL). The volume of water and nicotine consumed was measured every day. In the place conditioning paradigm, mice were tested for baseline place preference on day 1, received conditioning with saline versus a low (0.25) or high (1 mg/kg) dose nicotine and, respectively, tested for CPP or CPA 24 h following the last conditioning. We discovered that mice lacking PACAP compared to their wild-type controls exhibited more preference for nicotine over water in the TBC paradigm, particularly at the two higher concentrations of nicotine. While the rewarding action of the low dose nicotine was not altered in mice lacking PACAP, the aversive effect of the high dose nicotine was blunted in these mice compared to their wild-type controls. The present results suggest that endogenous PACAP may play a functional role in nicotine preference and its aversive effect.

Expression Patterns of PACAP and PAC1R Genes and Anorexigenic Action of PACAP1 and PACAP2 in Zebrafish

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with potent suppressive effects on feeding behavior in rodents, chicken, and goldfish. Teleost fish express two PACAPs (PACAP1, encoded by the adcyap1a gene, and PACAP2, encoded by the adcyap1b gene) and two PACAP receptors (PAC1Rs; PAC1Ra, encoded by the adcyap1r1a gene, and PAC1Rb, encoded by the adcyap1r1b gene). However, the mRNA expression patterns of the two PACAPs and PAC1Rs, and the influence and relationship of the two PACAPs on feeding behavior in teleost fish remains unclear. Therefore, we first examined mRNA expression patterns of PACAP and PAC1R in tissue and brain. All PACAP and PAC1Rs mRNAs were dominantly expressed in the zebrafish brain. However, adcyap1a mRNA was also detected in the gut and testis. In the brain, adcyap1b and adcyap1r1a mRNA levels were greater than that of adcyap1a and adcyap1r1b, respectively. Moreover, adcyap1b and adcyap1r1a mRNA were dominantly expressed in telencephalon and diencephalon. The highest adcyap1a mRNA levels were detected in the brain stem and diencephalon, while the highest levels of adcyap1r1b were detected in the cerebellum. To clarify the relationship between PACAP and feeding behavior in the zebrafish, the effects of zebrafish (zf) PACAP1 or zfPACAP2 intracerebroventricular (ICV) injection were examined on food intake, and changes in PACAP mRNA levels were assessed against feeding status. Food intake was significantly decreased by ICV injection of zfPACAP1 (2 pmol/g body weight), zfPACAP2 (2 or 20 pmol/g body weight), or mammalian PACAP (2 or 20 pmol/g). Meanwhile, the PACAP injection group did not change locomotor activity. Real-time PCR showed adcyap1 mRNA levels were significantly increased at 2 and 3 h after feeding compared with the pre-feeding level, but adcyap1b, adcyap1r1a, and adcyap1r1b mRNA levels did not change after feeding. These results suggest that the expression levels and distribution of duplicated PACAP and PAC1R genes are different in zebrafish, but the anorexigenic effects of PACAP are similar to those seen in other vertebrates.

Neuronal Signal Transduction-Involved Genes in Pig Hypothalamus Affect Feed Efficiency as Revealed by Transcriptome Analysis

Feed efficiency (FE) is an important trait affecting costs in swine industry. Investigation on FE-related genes in different tissues is valuable for molecular breeding. Hypothalamus is a convergent and integrated centre for multiple nutrient-related signals. The present study identified 363 differentially expressed (DE) genes and 14 DE lincRNAs in the hypothalamus of high- and low-FE Yorkshire pigs. Furthermore, 983 significantly correlated DE gene-lincRNA pairs were identified through weighted correlation network analysis (WGCNA) and Pearson correlation analysis. These DE genes were primarily enriched in the neuronal signal transduction process containing the upregulated genes of VIPR1, CCR1, CCR5, LEPR, INSR, ADRA1A, CCKAR, and ADORA3 and the downregulated genes of GRM1, GRM4, GRM5, and VIPR2, which were located in the cell membrane. These signal receptors were mainly connected to downstream Jak-STAT signaling that involved the increased genes (JAK2, STAT3, and POMC) and mTOR signaling pathway, including the decreased genes (CAMKK2, AMPK, and MTOR). STAT3 and AMPK genes also played a role in two major hypothalamic neurons of POMC and NPY/AGRP. A total of eight DE lincRNAs also participated in the potential network. In conclusion, neuronal signaling transduction-involved genes and lincRNAs were related to FE variation in pig hypothalamus.

Corticotrophin-releasing factor mediates vasoactive intestinal peptide-induced hypophagia and changes in plasma parameters

Vasoactive intestinal peptide (VIP) and corticotrophin-releasing factor (CRF) are anorexigenic neuropeptides that act in the hypothalamus to regulate food intake. Intracerebroventricular (ICV) microinjection of VIP promotes increased plasma adrenocorticotrophic hormone (ACTH) and corticosterone, indicating that VIP activates hypothalamic-pituitary-adrenal axis. The aim of this study was to evaluate the interaction between VIP and CRF, by verifying the effects of ICV administration of VIP on the activity of neurons and CRF mRNA expression in paraventricular nucleus of hypothalamus (PVN). In addition, it was evaluated the effects of pretreatment with CRF type 1 receptor (CRFR1) antagonist (Antalarmin, ANT) or CRF type 2 receptor (CRFR2) antagonist (Antisauvagine-30, AS30) on VIP-induced changes on food intake and plasma parameters of male rats. Compared to Saline group, VIP increased not only the number of Fos-related antigens (FRA)-immunoreactive neurons in the PVN but also CRF mRNA levels in this nucleus. Both ANT and AS30 treatment attenuated the inhibition of food intake promoted by VIP, ANT showing a more pronounced effect. Both antagonists also attenuated VIP-induced reduction and enhancement of free fatty acids and corticosterone plasma levels, respectively, and only AS30 was able to attenuate the hyperglycemia. These results suggest that CRF is an important mediador of VIP effects on energy balance, and CRFR1 and CRFR2 are involved in these responses.

Quantitative Mass Spectrometry Reveals Food Intake-Induced Neuropeptide Level Changes in Rat Brain: Functional Assessment of Selected Neuropeptides as Feeding Regulators

Endogenous neuropeptides are important signaling molecules that function as regulators of food intake and body weight. Previous work has shown that neuropeptide gene expression levels in a forebrain reward site, the nucleus accumbens (NAc), were changed by feeding. To directly monitor feeding-induced changes in neuropeptide expression levels within the NAc, we employed a combination of cryostat dissection, heat stabilization, neuropeptide extraction and label-free quantitative neuropeptidomics via a liquid chromatography-high resolution mass spectrometry platform. Using this methodology, we described the first neuropeptidome in NAc and discovered that feeding caused the expression level changes of multiple neuropeptides derived from different precursors, especially proSAAS-derived peptides such as Big LEN, PEN and little SAAS. We further investigated the regulatory functions of these neuropeptides derived from the ProSAAS family by performing an intra-NAc microinjection experiment using the identified ProSAAS neuropeptides, 'Big-LEN' and 'PEN'. Big LEN significantly increased rats' food and water intake, whereas both big LEN and PEN affected other behaviors including locomotion, drinking and grooming. In addition, we quantified the feeding-induced changes of peptides from hippocampus, hypothalamus and striatum to reveal the neuropeptide interplay among different anatomical regions. In summary, our study demonstrated neuropeptidomic changes in response to food intake in the rat NAc and other key brain regions. Importantly, the microinfusion of ProSAAS peptides into NAc revealed that they are behaviorally active in this brain site, suggesting the potential use of these peptides as therapeutics for eating disorders.

Central Control of Feeding Behavior by the Secretin, PACAP, and Glucagon Family of Peptides

Constituting a group of structurally related brain-gut peptides, secretin (SCT), pituitary adenylate cyclase-activating peptide (PACAP), and glucagon (GCG) family of peptide hormones exert their functions via interactions with the class B1 G protein-coupled receptors. In recent years, the roles of these peptides in neuroendocrine control of feeding behavior have been a specific area of research focus for development of potential therapeutic drug targets to combat obesity and metabolic disorders. As a result, some members in the family and their analogs have already been utilized as therapeutic agents in clinical application. This review aims to provide an overview of the current understanding on the important role of SCT, PACAP, and GCG family of peptides in central control of feeding behavior.

Neuropeptide Control of Feeding Behavior in Birds and Its Difference with Mammals

Feeding is an essential behavior for animals to sustain their lives. Over the past several decades, many neuropeptides that regulate feeding behavior have been identified in vertebrates. These neuropeptides are called “feeding regulatory neuropeptides.” There have been numerous studies on the role of feeding regulatory neuropeptides in vertebrates including birds. Some feeding regulatory neuropeptides show different effects on feeding behavior between birds and other vertebrates, particularly mammals. The difference is marked with orexigenic neuropeptides. For example, melanin-concentrating hormone, orexin, and motilin, which are regarded as orexigenic neuropeptides in mammals, have no effect on feeding behavior in birds. Furthermore, ghrelin and growth hormone-releasing hormone, which are also known as orexigenic neuropeptides in mammals, suppress feeding behavior in birds. Thus, it is likely that the feeding regulatory mechanism has changed during the evolution of vertebrates. This review summarizes the recent knowledge of peptidergic feeding regulatory factors in birds and discusses the difference in their action between birds and other vertebrates.

Adcyap1 polymorphism covaries with breeding latitude in a Nearctic migratory songbird, the Wilson's warbler (Cardellina pusilla)

Understanding the genetic background of complex behavioral traits, showing multigenic control and extensive environmental effects, is a challenging task. Among such traits, migration is known to show a large additive genetic component. Yet, the identification of specific genes or gene regions explaining phenotypic variance in migratory behavior has received less attention. Migration ultimately depends on seasonal cycles, and polymorphism at phenological candidate genes may underlie variation in timing of migration or other aspects of migratory behavior. In this study of a Nearctic–Neotropical migratory songbird, the Wilson's warbler (Cardellina pusilla), we investigated the association between polymorphism at two phenological candidate genes, Clock and Adcyap1, and two aspects of the migratory phenotype, timing of spring migration through a stopover site and inferred latitude of the breeding destination. The breeding destination of migrating individuals was identified using feather deuterium ratio (δ²H), which reliably reflects breeding latitude throughout the species' western breeding range. Ninety‐eight percent of the individuals were homozygous at Clock, and the rare heterozygotes did not deviate from homozygous migration phenology. Adcyap1 was highly polymorphic, and allele size was not significantly associated with migration date. However, Adcyap1 allele size significantly positively predicted the inferred breeding latitude of males but not of females. Moreover, we found a strong positive association between inferred breeding latitude and Adcyap1 allele size in long‐distance migrating birds from the northern sector of the breeding range (western Canada), while this was not the case in short‐distance migrating birds from the southern sector of the breeding range (coastal California). Our findings support previous evidence for a role of Adcyap1 in shaping the avian migratory phenotype, while highlighting that patterns of phenological candidate gene–phenotype associations may be complex, significantly varying between geographically distinct populations and even between the sexes.

PACAP intraperitoneal treatment suppresses appetite and food intake via PAC1 receptor in mice by inhibiting ghrelin and increasing GLP-1 and leptin

Pituitary adenylate cyclase-activating peptide (PACAP) is expressed within the gastroenteric system, where it has profound physiological effects. PACAP was shown to regulate food intake and thermogenesis centrally; however, PACAP peripheral regulation of appetite and feeding behavior is unknown. Therefore, we studied PACAP's effect on appetite and food intake control by analyzing feeding behavior and metabolic hormones in PAC1-deficient (PAC1-/-) and age-matched wild-type (WT) mice intraperitoneally injected with PACAP1-38 or PACAP1-27 before the dark phase of feeding. Food intake and feeding behavior were analyzed using the BioDAQ system. Active ghrelin, glucagon-like peptide-1 (GLP-1), leptin, peptide YY, pancreatic polypeptide, and insulin were measured following PACAP1-38 administration in fasted WT mice. PACAP1-38/PACAP1-27 injected into WT mice significantly decreased in a dose-dependent manner cumulative food intake and reduced bout and meal feeding parameters. Conversely, PACAP1-38 injected into PAC1-/- mice failed to significantly change food intake. Importantly, PACAP1-38 reduced plasma levels of active ghrelin compared with vehicle in WT mice. In PAC1-/- mice, fasting levels of active ghrelin, GLP-1, insulin, and leptin and postprandial levels of active ghrelin and insulin were significantly altered compared with levels in WT mice. Therefore, PAC1 is a novel regulator of appetite/satiety. PACAP1-38/PACAP1-27 significantly reduced appetite and food intake through PAC1. In PAC1-/- mice, the regulation of anorexigenic/orexigenic hormones was abolished, whereas active ghrelin remained elevated even postprandially. PACAP significantly reduced active ghrelin in fasting conditions. These results establish a role for PACAP via PAC1 in the peripheral regulation of appetite/satiety and suggest future studies to explore a therapeutic use of PACAP or PAC1 agonists for obesity treatment.

Hypothalamic Agouti-Related Peptide mRNA is Elevated During Natural and Stress-Induced Anorexia

As part of their natural lives, animals can undergo periods of voluntarily reduced food intake and body weight (i.e. animal anorexias) that are beneficial for survival or breeding, such as during territorial behaviour, hibernation, migration and incubation of eggs. For incubation, a change in the defended level of body weight or 'sliding set point' appears to be involved, although the neural mechanisms reponsible for this are unknown. We investigated how neuropeptide gene expression in the arcuate nucleus of the domestic chicken responded to a 60-70% voluntary reduction in food intake measured both after incubation and after an environmental stressor involving transfer to unfamiliar housing. We hypothesised that gene expression would not change in these circumstances because the reduced food intake and body weight represented a defended level in birds with free access to food. Unexpectedly, we observed increased gene expression of the orexigenic peptide agouti-related peptide (AgRP) in both incubating and transferred animals compared to controls. Also pro-opiomelanocortin (POMC) mRNA was higher in incubating hens and significantly increased 6 days after exposure to the stressor. Conversely expression of neuropeptide Y and cocaine- and amphetamine-regulated transcript gene was unchanged in both experimental situations. We conclude that AgRP expression remains sensitive to the level of energy stores during natural anorexias, which is of adaptive advantage, although its normal orexigenic effects are over-ridden by inhibitory signals. In the case of stress-induced anorexia, increased POMC may contribute to this inhibitory role, whereas, for incubation, reduced feeding may also be associated with increased expression in the hypothalamus of the anorexigenic peptide vasoactive intestinal peptide.

Pituitary adenylate cyclase activating polypeptide in stress-related disorders: data convergence from animal and human studies

The maladaptive expression and function of several stress-associated hormones have been implicated in pathological stress and anxiety-related disorders. Among these, recent evidence has suggested that pituitary adenylate cyclase activating polypeptide (PACAP) has critical roles in central neurocircuits mediating stress-related emotional behaviors. We describe the PACAPergic systems, the data implicating PACAP in stress biology, and how altered PACAP expression and signaling may result in psychopathologies. We include our work implicating PACAP signaling within the bed nucleus of the stria terminalis in mediating the consequences of stressor exposure and relatedly, describe more recent studies suggesting that PACAP in the central nucleus of the amygdala may impact the emotional aspects of chronic pain states. In aggregate, these results are consistent with data suggesting that PACAP dysregulation is associated with posttraumatic stress disorder in humans.

Regulation of Appetite, Body Composition, and Metabolic Hormones by Vasoactive Intestinal Polypeptide (VIP)

Vasoactive intestinal peptide (VIP) is a 28-amino acid neuropeptide that belongs to the secretin-glucagon superfamily of peptides and has 68 % homology with PACAP. VIP is abundantly expressed in the central and peripheral nervous system and in the gastrointestinal tract, where it exercises several physiological functions. Previously, it has been reported that VIP regulates feeding behavior centrally in different species of vertebrates such as goldfishes, chicken and rodents. Additional studies are necessary to analyze the role of endogenous VIP on the regulation of appetite/satiety, feeding behavior, metabolic hormones, body mass composition and energy balance. The aim of the study was to elucidate the physiological pathways by which VIP regulates appetite/satiety, feeding behavior, metabolic hormones, and body mass composition. VIP deficient (VIP -/-) and age-matched wild-type (WT) littermates were weekly monitored from 5 to 22 weeks of age using a whole body composition EchoMRI analyzer. Food intake and feeding behavior were analyzed using the BioDAQ automated monitoring system. Plasma levels of metabolic hormones including active-ghrelin, GLP-1, leptin, PYY, pancreatic polypeptide (PP), adiponectin, and insulin were measured in fasting as well as in postprandial conditions. The genetic lack of VIP led to a significant reduction of body weight and fat mass and to an increase of lean mass as the mice aged. Additionally, VIP-/- mice had a disrupted pattern of circadian feeding behavior resulting in an abolished regular nocturnal/diurnal feeding. These changes were associated with an altered secretion of adiponectin, GLP-1, leptin, PYY and insulin in VIP-/- mice. Our data demonstrates that endogenous VIP is involved in the control of appetite/satiety, feeding behavior, body mass composition and in the secretion of six different key regulatory metabolic hormones. VIP plays a key role in the regulation of body phenotype by significantly enhancing body weight and fat mass accumulation. Therefore, VIP signaling is critical for the modulation of appetite/satiety and body mass phenotype and is a potential target for future treatment of obesity.

PAC1 receptor antagonism in the bed nucleus of the stria terminalis (BNST) attenuates the endocrine and behavioral consequences of chronic stress

Chronic or repeated stressor exposure can induce a number of maladaptive behavioral and physiological consequences and among limbic structures, the bed nucleus of the stria terminalis (BNST) has been implicated in the integration and interpretation of stress responses. Previous work has demonstrated that chronic variate stress (CVS) exposure in rodents increases BNST pituitary adenylate cyclase activating polypeptide (PACAP, Adcyap1) and PAC1 receptor (Adcyap1r1) transcript expression, and that acute BNST PACAP injections can stimulate anxiety-like behavior. Here we show that chronic stress increases PACAP expression selectively in the oval nucleus of the dorsolateral BNST in patterns distinct from those for corticotropin releasing hormone (CRH). Among receptor subtypes, BNST PACAP signaling through PAC1 receptors not only heightened anxiety responses as measured by different behavioral parameters but also induced anorexic-like behavior to mimic the consequences of stress. Conversely, chronic inhibition of BNST PACAP signaling by continuous infusion with the PAC1 receptor antagonist PACAP(6-38) during the week of CVS attenuated these stress-induced behavioral responses and changes in weight gain. BNST PACAP signaling stimulated the hypothalamic-pituitary-adrenal (HPA) axis and heightened corticosterone release; further, BNST PACAP(6-38) administration blocked corticosterone release in a sensitized stress model. In aggregate with recent associations of PACAP/PAC1 receptor dysregulation with altered stress responses including post-traumatic stress disorder, these data suggest that BNST PACAP/PAC1 receptor signaling mechanisms may coordinate the behavioral and endocrine consequences of stress.

PACAP in the BNST produces anorexia and weight loss in male and female rats

Recent gene association studies have implicated pituitary adenylate cyclase-activating peptide (PACAP) systems in several psychiatric disorders associated with stressor exposure, and we have argued that many of the behavioral consequences of repeated stressor exposure may depend on the expression of PACAP in the bed nucleus of the stria terminalis (BNST). One behavioral consequence of the activation of stress systems can be anorexia and subsequent weight loss, and both the activation of central PACAP systems as well as neuronal activity in the BNST have also been associated with anorexic states in rodents. Hence, we investigated the regulation of food and water intake and weight loss following BNST PACAP infusion. BNST PACAP38 dose-dependently decreased body weight, as well as food and water intake in the first 24 h following infusion. Because different BNST subregions differentially regulate stress responding, we further examined the effects of PACAP38 in either the anterior or posterior BNST. Anterior BNST PACAP38 infusion did not alter weight gain, whereas posterior PACAP38 infusion resulted in weight loss. PACAP38 infused into the lateral ventricles did not alter weight, suggesting that the effects of BNST-infused PACAP were not mediated by leakage into the ventricular system. These data suggest that PACAP receptor activation in posterior BNST subregions can produce anorexia and weight loss, and corroborate growing data implicating central PACAP activation in mediating the consequences of stressor exposure.

Central pathways integrating metabolism and reproduction in teleosts

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

CRF mediates the anxiogenic and anti-rewarding, but not the anorectic effects of PACAP

Anxiety disorders represent the most common mental disturbances in the world, and they are characterized by an abnormal response to stress. Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor PAC1 have been proposed to have a key role in mediating the responses to stress as well as the regulation of food intake and body weight. Corticotropin-releasing factor (CRF), the major stress peptide in the brain, has been hypothesized to be involved in PACAP effects, but the reports are conflicting so far. The present study was aimed at further characterizing the behavioral effects of PACAP in rats and at determining the role of central CRF receptors. We found that intracerebroventricular PACAP treatment induced anxiety-like behavior in the elevated plus maze test and elevated intracranial self-stimulation thresholds; both of these effects were fully blocked by concurrent treatment with the CRF receptor antagonist D-Phe-CRF(12-41). Interestingly, the CRF antagonist had no effect on PACAP-induced increased plasma corticosterone, reduction of food intake, and body weight loss. Finally, we found that PACAP increased CRF levels in the paraventricular nucleus of the hypothalamus and, importantly, in the central nucleus of the amygdala, as measured by solid phase radioimmunoassay and quantitative real-time PCR. Our results strengthen the notion that PACAP is a strong mediator of the behavioral response to stress and prove for the first time that this neuropeptide has anti-rewarding (ie, pro-depressant) effects. In addition, we identified the mechanism by which PACAP exerts its anxiogenic and pro-depressant effects, via the recruitment of the central CRF system and independently from HPA axis activation.

Contributions of endocrinology to the migration life history of birds

Migration is a key life cycle stage in nearly 2000 species of birds and is a greatly appreciated phenomenon in both cultural and academic arenas. Despite a long research tradition concerning many aspects of migration, investigations of hormonal contributions to migratory physiology and behavior are more limited and represent a comparatively young research field. We review advances in our understanding of the hormonal mechanisms of migration with particular emphasis on the sub-stages of the migration life history: development, departure, flight and arrival. These sub-stages vary widely in their behavioral, ecological and physiological contexts and, as such, should be given appropriate individual consideration.

Feeding response following central administration of chicken vasoactive intestinal peptide in chicks

Vasoactive intestinal peptide (VIP) is expressed in central nervous systems and peripheral tissues across lower and higher vertebrates and is involved in many physiological functions. One of these functions is appetite regulation; however the mechanisms mediating this response are poorly understood. Therefore, the purpose of this study was to investigate central mechanisms of VIP induction of satiety using chicks as models. Intracerebroventricular (ICV) injection of VIP (0.1 and 0.5 nmol) significantly decreased food intake under both ad libitum and food deprivation conditions and chicken VIP (cVIP) was more potent than mammalian VIP. The mechanisms involved with the VIP-induced anorexigenic effect were investigated by studying the involvement of the central corticotrophin-releasing hormone (CRH) systems. ICV injection of cVIP caused increased plasma corticosterone concentration and decreased diencephalic mRNA expression of CRH, CRH receptor-2 (CRH-R2) and urocortin 3 (UCN-3, which has high affinity for CRH-R2). This simultaneous decrease in the expression of ligands and their receptor, with the increase in plasma corticosterone concentration suggests that the anorexigenic effect of cVIP might be related to CRH systems. The cVIP-induced anorexigenic effect was partly attenuated by co-injection of astressin, a CRH-R2 antagonist, supporting this thesis. The present study demonstrated that VIP inhibits feeding behavior via CRH systems in the brain of chicks.

Identification of a gene associated with avian migratory behaviour

Bird migration is one of the most spectacular and best-studied phenomena in behavioural biology. Yet, while the patterns of variation in migratory behaviour and its ecological causes have been intensively studied, its genetic, physiological and neurological control remains poorly understood. The lack of knowledge of the molecular basis of migration is currently not only limiting our insight into the proximate control of migration, but also into its evolution. We investigated polymorphisms in the exons of six candidate genes for key behavioural traits potentially linked to migration, which had previously been identified in several bird species, and eight control loci in 14 populations of blackcaps (Sylvia atricapilla), representing the whole range of geographical variation in migration patterns found in this species, with the aim of identifying genes controlling variation in migration. We found a consistent association between a microsatellite polymorphism and migratory behaviour only at one candidate locus: the ADCYAP1 gene. This polymorphism explained about 2.6 per cent of the variation in migratory tendency among populations, and 2.7–3.5% of variation in migratory restlessness among individuals within two independent populations. In all tests, longer alleles were associated with higher migratory activity. The consistency of results among different populations and levels of analysis suggests that ADCYAP1 is one of the genes controlling the expression of migratory behaviour. Moreover, the multiple described functions of the gene product indicate that this gene might act at multiple levels modifying the shift between migratory and non-migratory states.

The biological role of pituitary adenylate cyclase-activating polypeptide (PACAP) in growth and feeding behavior in juvenile fish

To date, many technologies have been developed to increase efficiency in aquaculture, but very few successful biotechnology molecules have arrived on the market. In this context, marine biotechnology has an opportunity to develop products to improve the output of fish in aquaculture. Published in vivo studies on the action of the pituitary adenylate cyclase-activating polypeptide (PACAP) in fish are scarce. Recently, our group, for the first time, demonstrated the biological role of this neuropeptide administrated by immersion baths in the growth and development of larval fish. In this work, we have evaluated the effects of recombinant Clarias gariepinus PACAP administration by intraperitoneal injection on growth performance and feeding behavior in juvenile fish. Our results showed the physiological role of this peptide for growth control in fish, including the juvenile stage, and confirm that its biological functions are well conserved in fish, since C. gariepinus PACAP stimulated growth in juvenile tilapia Oreochromis niloticus. In addition, we have observed that the growth-promoting effect of PACAP in juvenile tilapia was correlated with higher GH concentration in serum. With regard to the neuroendocrine regulation of growth control by PACAP, it was demonstrated that PACAP stimulates food intake in juvenile tilapia. In general, PACAP appears to act in the regulation of the growth control in juvenile fish. These findings propose that PACAP is a prominent target with the potential to stimulate fish growth in aquaculture.

Feeding and drinking response following central administration of neuromedin S in chicks

Neuromedin S (NMS) is recognized as an anorexigenic peptide in the brain of mammals. In chicks (Gallus gallus), however, the effect of NMS has not been investigated. Therefore, the purpose of the present study was to investigate whether intracerebroventricular (ICV) injection of NMS affected feeding and drinking behavior in chicks. The injection of NMS (0.01-1 nmol) significantly decreased food intake under both ad libitum and food deprivation-induced feeding conditions. However, NMS did not affect water deprivation-induced drinking behavior. ICV injection of NMS stimulated voluntary locomotion and wing-flapping behavior. In addition, we found that those effects of NMS might be related to the hypothalamus-pituitary-adrenal axis because ICV injection of NMS stimulated corticosterone release. The present study suggests that central NMS functions an anorexigenic factor in chicks.

PACAP neurons in the hypothalamic ventromedial nucleus are targets of central leptin signaling

The adipose-derived hormone, leptin, was discovered over 10 years ago, but only now are we unmasking its downstream pathways which lead to reduced energy intake (feeding) and increased energy expenditure (thermogenesis). Recent transgenic models have challenged the long-standing supposition that the hypothalamic arcuate nucleus (Arc) is omnipotent in the central response to leptin, and research focus is beginning to shift to examine roles of extra-arcuate sites. Dhillon et al. (2006) demonstrated that targeted knock out of the signaling form of the leptin receptor (lepr-B) in steroidogenic factor 1 (SF-1) cells of the hypothalamic ventromedial nucleus (VMN) produces obesity of a similar magnitude to the pro-opiomelanocortin (POMC)-driven lepr-B deleted mouse, via a functionally distinct mechanism. These findings reveal that SF-1 cells of the VMN could be equally as important as POMC cells in mediating leptin's anti-obesity effects. However, the identification of molecular and cellular correlates of this relationship remains tantalizingly unknown. Here, we have shown that mRNA expression of the VMN-expressed neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is regulated according to energy status and that it exerts catabolic effects when administered centrally to mice. Furthermore, we have shown that SF-1 and PACAP mRNAs are colocalized in the VMN, and that leptin signaling via lepr-B is required for normal PACAP expression in these cells. Finally, blocking endogenous central PACAP signaling with the antagonist PACAP(6-38) markedly attenuates leptin-induced hypophagia and hyperthermia in vivo. Thus, it appears that PACAP is an important mediator of central leptin effects on energy balance.

Cloning, tissue distribution and effects of food deprivation on pituitary adenylate cyclase activating polypeptide (PACAP)/PACAP-related peptide (PRP) and preprosomatostatin 1 (PPSS 1) in Atlantic cod (Gadus morhua)

Full-length complementary deoxyribonucleic acid sequences encoding pituitary adenylate cyclase activating polypeptide (PACAP)/PACAP-related peptide (PRP) and preprosomatostatin 1 (PPSS 1) were cloned from Atlantic cod (Gadus morhua) hypothalamus using reverse transcription and rapid amplification of complementary deoxyribonucleic acid ends. Semi-quantitative reverse transcriptase polymerase chain reaction shows that PRP/PACAP mRNA and PPSS 1 mRNA are widely distributed throughout cod brain. During development, PRP/PACAP and PPSS 1 were detected at the 30-somite stage and pre-hatching stage, respectively, and expression levels gradually increased up to the hatched larvae. PPSS 1, but not PRP/PACAP, appeared to be affected by food availability during early development. In juvenile cod, PPSS 1 expression levels increased and remained significantly higher than that of control fed fish throughout 30 days of starvation and during a subsequent 10 days refeeding period. In contrast, PRP/PACAP expression levels were not affected by 30 days of food deprivation, but a significant increase in expression levels was observed during the 10 days refeeding period in the experimental food-deprived group as compared to the control fed group. Our results suggest that PRP/PACAP and PPSS 1 may be involved in the complex regulation of growth, feeding and metabolism during food deprivation and refeeding in Atlantic cod.

Long-term administration of maxadilan improves glucose tolerance and insulin sensitivity in mice

Maxadilan and its truncated variant, M65, are agonist and antagonist specific, respectively, for the PAC1 receptor. PAC1 is the specific receptor for the pituitary adenylate cyclase-activating peptide (PACAP), which is not shared by vasoactive intestinal peptide (VIP). PACAP is a ubiquitous peptide of the glucagon superfamily that is involved in glucose homeostasis and regulation of insulin secretion. This study employed the recombinant maxadilan and M65 to evaluate the PAC1 receptor-mediated effects on energy metabolism using NIH mice. First, the acute effect of maxadilan-induced hyperglycemia was blocked by M65. In long-term studies, NIH mice were given daily intraperitoneal injections with maxadilan, M65, or vehicle for 21 days. Maxadilan suppressed feeding and enhanced water intake significantly for the first several days. After that period, maxadilan treatment continued to promote food and water intake. Long-term administration of maxadilan led to an increase in body weight (P<0.01), decrease in body fat (P<0.01), down-regulation of basal plasma glucose (P<0.01), upregulation of basal plasma insulin (P<0.01) and improved glucose tolerance (P<0.01) and insulin sensitivity (P<0.01). An elevation in plasma LDL (P<0.01) was also observed in the maxadilan group. However, M65 displayed no significant adverse effects on the aforementioned parameters except basal plasma glucose (P<0.05). The significant changes induced by maxadilan indicate that the PAC1 receptor plays multiple key roles in carbohydrate metabolism, lipid metabolism and energy homeostasis in mice.

Feeding and metabolism in mice lacking pituitary adenylate cyclase-activating polypeptide

Disruption of the pituitary adenylate cyclase-activating polypeptide (PACAP) gene in mice has demonstrated a role for this highly conserved neuropeptide in the regulation of metabolism and temperature control. Localization of PACAP neurons within hypothalamic nuclei that regulate appetite suggest PACAP may affect feeding and thus energy balance. We used PACAP-null mice to address this question, examining both food intake and energy expenditure. PACAP-null mice were leaner than wild-type littermates due to decreased adiposity and displayed increased insulin sensitivity. The lean phenotype in the PACAP-null mice was completely eliminated if animals were fed a high-fat diet or housed near thermoneutrality (28 C). Further metabolic analyses of PACAP-null mice housed at 21 C indicated that the reduced body weight could not be explained by decreased food intake, increased metabolic rate, or increased locomotor activity. The thyroid hormone axis of PACAP-null mice was affected, because mRNA levels of hypothalamic TRH and brown adipose tissue type 2 deiodinase were reduced in PACAP-null mice housed at room temperature, and brain deiodinase activity was lower in PACAP-null mice after an acute cold challenge compared with wild-type controls. These results demonstrate that PACAP is not required for the regulation of food intake yet is necessary to maintain normal energy homeostasis, likely playing a role in central cold-sensing mechanisms.

Regulation of feeding behavior by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) in vertebrates

The hypothalamic region of the brain in vertebrates is a center that plays an important role in feeding regulation. Many kinds of hypothalamic neuropeptides or peripheral transmitters, such as orexin, neuropeptide Y, Agouti-related peptide, melanin-concentrating hormone, proopiomelanocortin-derived peptides, galanin, galanin-like peptide, ghrelin, corticotropin releasing hormone, cholecystokinin, cocaine amphetamine-related transcript peptides and leptin, have been implicated in the regulation of feeding behavior, psychomotor activity and energy homeostasis in rodents. Recent studies have also examined the effects of these neuropeptides or factors on food intake in non-mammalian vertebrates, especially chick and goldfish, and the role of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) in feeding behavior, locomotor activity or psychomotor activity in vertebrates. This article gives an overview of the regulation of feeding behavior and related physiology by PACAP and VIP in vertebrates in order to clarify the appetite-regulating system mediated by the two peptides.

Changes of PACAP levels in the brain show gender differences following short-term water and food deprivation

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide exerting diverse actions in the central and peripheral nervous systems. A few studies indicate that PACAP is involved in the regulation of feeding and water homeostasis. The aim of the present study was to investigate changes in PACAP38 concentrations in different brain areas following food or water deprivation in male and female rats. Rats were sacrificed 12, 36 and 84h after water or food removal. PACAP levels were determined by radioimmunoassay. Our results show that levels of PACAP decreased in the hypothalamus in both sexes after water deprivation, with a more marked, significant decrease in females at 12h. A decrease was observed also in the telencephalon, with a similar pattern in both genders: levels were lowest after 12h, and showed a gradual increase at the other two time-points. PACAP levels increased in the brainstem of male rats, while females had a decrease 12h after water deprivation. The pattern of changes in PACAP levels was very different after food deprivation. In male rats, PACAP levels showed a significant increase in the hypothalamus, telencephalon and brainstem 12h after the beginning of starvation. In females, a less marked increase was observed only in the hypothalamus while no changes were found in the other brain areas. Our results show a sensitive reaction in changes of endogenous PACAP levels to water and food deprivation in most brain areas, but they are differentially regulated in male and female rats.

Central administration of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide differentially regulates energy metabolism in chicks

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the members of the glucagon superfamily and bind to common receptors while PACAP also acts via the PACAP-specific receptor, PAC1. The aim of the present study was to investigate whether intracerebroventricular (i.c.v.) injection of VIP and PACAP acts in a similar or different manner to affect body temperature and energy expenditure in the domestic chick. I.c.v. injection of VIP did not significantly affect rectal temperature, but decreased energy expenditure. On the other hand, i.c.v. injection of PACAP significantly increased both body temperature and energy expenditure. These specific actions of PACAP could be explained by an interaction with the PAC1 receptor, since they were partly, but not entirely, attenuated by PACAP (6-38), a PAC1 receptor antagonist. In addition, it was observed that central administration of both VIP and PACAP induced a reduction in respiratory quotient and increased plasma non-esterified fatty acid concentrations. This suggests that both peptides act centrally to regulate a catabolic response. In summary, brain VIP and PACAP both appear to exert generally catabolic effects on energy metabolism in the chick, but their influence on body temperature and glucose metabolism differs and their central effects do not appear to be mediated by the same receptors.

Comparative aspects of GH and metabolic regulation in lower vertebrates

In all vertebrates, the regulations of growth and energy balance are complex phenomena which involve elaborate interactions between the brain and peripheral signals. Most vertebrates adopt and maintain a life style after birth, but lower vertebrates may have complex life histories involving metamorphoses, migrations and long periods of fasting. In order to achieve the complex developmental programs associated with these changes, coordinated regulation of all aspects of energy metabolism is required. Somatotropic axis (somatostatin (SRIH) growth hormone (GH) and insulin-like growth factor 1 (IGF1), is known to be involved in the regulation of growth and energy balance. Interestingly, recent studies showed that additional factors such as pituitary adenylate cyclase-activated polypeptide (PACAP), corticotropin-releasing hormone (CRH), ghrelin and leptin could also have major roles in the control of growth and metabolism in lower vertebrates (fish, amphibians and reptiles). This mini-review will survey the function of GH and metabolic regulation in lower vertebrates.

Long-term administration of PACAP receptor antagonist, PACAP(6-27), impairs glucose tolerance and insulin sensitivity in obese diabetic ob/ob mice

Pituitary adenylate cyclase-activating peptide (PACAP) is a ubiquitous peptide of the glucagon superfamily that is involved in glucose homeostasis and regulation of insulin secretion. This study employed the PACAP receptor antagonist, PACAP(6-27) to evaluate the role of endogenous PACAP in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob mice. Acute in vivo antagonistic potency of PACAP(6-27) was confirmed in ob/ob mice by blockade of the insulin-releasing action but not hyperglycaemia. In longer-term studies, ob/ob mice were given once daily injections of PACAP(6-27) or vehicle for 14 days. Feeding activity, body weight, basal plasma glucose and plasma insulin concentrations were not significantly affected by chronic PACAP(6-27) treatment. However, PACAP(6-27) treatment impaired glucose tolerance, insulin sensitivity and the glycaemic response to feeding. Plasma glucagon and lipids were unchanged. These observations indicate a role of endogenous PACAP for normal glucose homeostasis, but indicate a minor involvement in the regulation of insulin secretion in ob/ob mice.

Relationship between anorexigenic action of pituitary adenylate cyclase-activating polypeptide (PACAP) and that of corticotropin-releasing hormone (CRH) in the goldfish, Carassius auratus

Our recent research has indicated that intracerebroventricular (ICV) injection of pituitary adenylate cyclase-activating polypeptide (PACAP) suppresses food intake and locomotor activity in the goldfish. However, the anorexigenic mechanism of PACAP has not yet been clarified. The aim of this study was to investigate the relationship between the anorexigenic action of PACAP and that of corticotropin-releasing hormone (CRH), which is implicated in the regulation of energy homeostasis as a powerful anorexigenic peptide in the goldfish brain. We first examined feeding-induced changes in the expression of CRH mRNA, and the effect of ICV administration of PACAP on the expression of CRH mRNA in the goldfish brain. Semiquantitative analysis revealed that the expression of CRH mRNA was significantly increased by excessive feeding for 7 days. ICV administration of PACAP at a dose sufficient to suppress food intake induced a significant increase in the expression of CRH mRNA. We also examined the effect of alpha-helical CRH(9-41), a CRH antagonist, on the anorexigenic action of PACAP in the goldfish. The inhibitory effect of PACAP was completely suppressed by treatment with alpha-helical CRH(9-41). We finally investigated the effect of ICV-administered CRH on locomotor activity in the goldfish. CRH at a dose sufficient to suppress food intake induced a significant increase in locomotor activity, unlike ICV-injected PACAP. These results suggest that, in the goldfish, the anorexigenic action of PACAP is related to the CRH neuronal pathway, but that the modulation of locomotor activity by PACAP is independent of modulation by CRH.

Involvement of CRF on the anorexic effect of GLP-1 in layer chicks

Glucagon-like peptide-1 (GLP-1) is recognized as an anorexic peptide in the brain of chicks. However, the mechanism underlying the inhibition of feeding has not been well studied. It is reported that GLP-1 activates neurons containing corticotrophin-releasing factor (CRF) in the brain of mammals. Since CRF is also an anorexic peptide, it is possible that the anorexic effect of GLP-1 is mediated by CRF in chicks. The present study was carried out to test this. First, we determined plasma corticosterone (CORT) concentrations after intracerebroventricular (ICV) injection of GLP-1 and found that this treatment increased CORT release in layer chicks. The CORT-releasing effect was partly attenuated by co-injection of astressin, a CRF receptor antagonist, demonstrating that GLP-1 stimulated CORT secretion by activation of CRF neurons. CRF neurons also appear to be involved in mediating the inhibition of food intake by GLP-1 because this effect was also partly attenuated by astressin. Furthermore, we demonstrated that the anorexic effect of GLP-1 was weaker in broiler than layer chicks. The present results suggest that the anorexic effect of GLP-1 might be mediated by CRF neurons in the chick brain and that the sensitivity of the inhibitory response to GLP-1 differs between chick strains.