Neuropeptide ff, but not prolactin-releasing peptide, mRNA is differentially regulated in the hypothalamic and medullary neurons after salt loading

The Orexin/Hypocretin System, the Peptidergic Regulator of Vigilance, Orchestrates Adaptation to Stress

The orexin/hypocretin neuropeptide family has emerged as a focal point of neuroscientific research following the discovery that this family plays a crucial role in a variety of physiological and behavioral processes. These neuropeptides serve as powerful neuromodulators, intricately shaping autonomic, endocrine, and behavioral responses across species. Notably, they serve as master regulators of vigilance and stress responses; however, their roles in food intake, metabolism, and thermoregulation appear complementary and warrant further investigation. This narrative review provides a journey through the evolution of our understanding of the orexin system, from its initial discovery to the promising progress made in developing orexin derivatives. It goes beyond conventional boundaries, striving to synthesize the multifaceted activities of orexins. Special emphasis is placed on domains such as stress response, fear, anxiety, and learning, in which the authors have contributed to the literature with original publications. This paper also overviews the advancement of orexin pharmacology, which has already yielded some promising successes, particularly in the treatment of sleep disorders.

Central NPFF signalling is critical in the regulation of glucose homeostasis

OBJECTIVE

Neuropeptide FF (NPFF) group peptides belong to the evolutionary conserved RF-amide peptide family. While they have been assigned a role as pain modulators, their roles in other aspects of physiology have received much less attention. NPFF peptides and their receptor NPFFR2 have strong and localized expression within the dorsal vagal complex that has emerged as the key centre for regulating glucose homeostasis. Therefore, we investigated the role of the NPFF system in the control of glucose metabolism and the histochemical and molecular identities of NPFF and NPFFR2 neurons.

METHODS

We examined glucose metabolism in Npff^-/- and wild type (WT) mice using intraperitoneal (i.p.) glucose tolerance and insulin tolerance tests. Body composition and glucose tolerance was further examined in mice after 1-week and 3-week of high-fat diet (HFD). Using RNAScope double ISH, we investigated the neurochemical identity of NPFF and NPFFR2 neurons in the caudal brainstem, and the expression of receptors for peripheral factors in NPFF neurons.

RESULTS

Lack of NPFF signalling in mice leads to improved glucose tolerance without significant impact on insulin excursion after the i.p. glucose challenge. In response to an i.p. bolus of insulin, Npff^-/- mice have lower glucose excursions than WT mice, indicating an enhanced insulin action. Moreover, while HFD has rapid and potent detrimental effects on glucose tolerance, this diet-induced glucose intolerance is ameliorated in mice lacking NPFF signalling. This occurs in the absence of any significant impact of NPFF deletion on lean or fat masses, suggesting a direct effect of NPFF signalling on glucose metabolism. We further reveal that NPFF neurons in the subpostrema area (SubP) co-express receptors for peripheral factors involved in glucose homeostasis regulation such as insulin and GLP1. Furthermore, Npffr2 is expressed in the glutamatergic NPFF neurons in the SubP, and in cholinergic neurons of the dorsal motor nucleus of the vagus (DMV), indicating that central NPFF signalling is likely modulating vagal output to innervated peripheral tissues including those important for glucose metabolic control.

CONCLUSIONS

NPFF signalling plays an important role in the regulation of glucose metabolism. NPFF neurons in the SubP are likely to receive peripheral signals and mediate the control of whole-body glucose homeostasis via centrally vagal pathways. Targeting NPFF and NPFFR2 signalling may provide a new avenue for treating type 2 diabetes and obesity.

Neuropeptide FF-related gene in fish (Larimichthys polyactis): identification, characterization, and potential anti-inflammatory function

BACKGROUND

Neuropeptide FF (NPFF), an octapeptide of the RFamide-related peptides (FaRPs), is involved in regulatory function in various biological processes. The regulatory role of NPFF in the immune and inflammatory response was currently being revealed.

METHODS

Neuropeptide FF-related gene (termed LpNPFF) and its two receptors, NPFF receptor 1 (LpNPFFR1) and NPFF receptor 2 (LpNPFFR2) were identified by PCR and Semi-quantitative RT-PCR assay. Effect of LpNPFF on the production of nitric oxide (NO) in macrophage RAW264.7 cell was divided into PBS group, lipopolysaccharide (LPS) group, LPS treated with LpNPFF group, and LPS treated with LpNPFF and receptor antagonist RF9 group. Then specimens were measured by color reaction at 570 nm absorbance value.

RESULTS

Sequence analysis showed that LpNPFF cDNA consists of 835 nucleotides with a 5'- untranslated region (UTR) of 150 base pair (bp), an open reading frame (ORF) of 384 bp and a 3'-UTR of 300 bp (Accession No. MT012894). The ORF encodes 127 amino acid (aa) residues with a hydrophobic signal peptide at N-terminus and two presumptive peptides with -PQRFa structure, LpNPFF (1) and LpNPFF (2). LpNPFFR1 and LpNPFFR2 encode 427 and 444 aa residues respectively, which both have seven hydrophobic TMDs and identified as G protein coupled receptors (GPCRs). Results of tissue distribution showed that LpNPFF and receptors were highly expressed in the brain and gonad. Furtherly, in vitro assay found LpNPFF could inhibit NO production in RAW 264.7 macrophages under inflammatory stress with LPS, while its receptor antagonist RF9 caused the evoke of NO generation.

CONCLUSIONS

These results contribute to the further study of neuropeptide evolution in marine organisms, and also provide a new research idea for exploring the related functions of NPFF gene.

The distribution of Neuropeptide FF and Neuropeptide VF in central and peripheral tissues and their role in energy homeostasis control

Neuropeptide FF (NPFF) and Neuropeptide VF (NPVF) are part of the extended RFamide peptide family characterized by their common arginine (R) and amidated phenylalanine (F)-motif at the carboxyl terminus. Both peptides signal through their respective high affinity G-protein coupled receptors, NPFFR2 and NPFFR1, but also show binding affinity for the other receptor due to their sequence similarity. NPFF and NPVF are highly conserved throughout evolution and can be found across the whole animal kingdom. Both have been implicated in a variety of biological mechanisms, including nociception, locomotion, reproduction, and response to pain and stress. However, more recently a new major functional role in the control of energy homeostasis has been discovered. In this article we will summarise the current knowledge on the distribution of NPFF, NPVF, and their receptors in central and peripheral tissues, as well as how this relates to the regulation of food intake and energy balance, which will help to better understand their role in these processes and thus might help finding treatments for impaired energy homeostasis disorders, such as obesity or anorexia.

Intracerebroventricular Neuropeptide FF Diminishes the Number of Apneas and Cardiovascular Effects Produced by Opioid Receptors' Activation

The opioid-induced analgesia is associated with a number of side effects such as addiction, tolerance and respiratory depression. The involvement of neuropeptide FF (NPFF) in modulation of pain perception, opioid-induced tolerance and dependence was well documented in contrast to respiratory depression. Therefore, the aim of the present study was to examine the potency of NPFF to block post-opioid respiratory depression, one of the main adverse effects of opioid therapy. Urethane-chloralose anaesthetized Wistar rats were injected either intravenously (iv) or intracerebroventricularly (icv) with various doses of NPFF prior to iv endomorphin-1 (EM-1) administration. Iv NPFF diminished the number of EM-1-induced apneas without affecting their length and without influence on the EM-1 induced blood pressure decline. Icv pretreatment with NPFF abolished the occurrence of post-EM-1 apneas and reduced also the maximal drop in blood pressure and heart rate. These effects were completely blocked by the NPFF receptor antagonist RF9, which was given as a mixture with NPFF before systemic EM-1 administration. In conclusion, our results showed that centrally administered neuropeptide FF is effective in preventing apnea evoked by stimulation of μ-opioid receptors and the effect was due to activation of central NPFF receptors. Our finding indicates a potential target for reversal of opioid-induced respiratory depression.

Activation of NPFF2 receptor stimulates neurite outgrowth in Neuro 2A cells through activation of ERK signaling pathway

Neurite outgrowth is an important process in neural regeneration and plasticity, especially after neural injury, and recent evidence indicates that several G_αi/o protein-coupled receptors play an important role in neurite outgrowth. The neuropeptide (NP)FF system contains two G_αi/o protein-coupled receptors, NPFF₁ and NPFF₂ receptors, which are mainly distributed in the central nervous system. The aim of the present study was to determine whether the NPFF system is involved in neurite outgrowth in Neuro 2A cells. We showed that Neuro 2A cells endogenously expressed NPFF₂ receptor, and the NPFF₂ receptor agonist dNPA inhibited cyclic adenosine monophosphate (cAMP) production stimulated by forskolin in Neuro 2A cells. We also demonstrated that NPFF and dNPA dose-dependently induced neurite outgrowth in Neuro 2A cells, which was completely abolished by the NPFF receptor antagonist RF9. Pretreatment with mitogen-activated protein kinase inhibitors PD98059 and U0126 decreased dNPA-induced neurite outgrowth. In addition, dNPA increased phosphorylation of extracellular signal-regulated kinase (ERK) in Neuro 2A cells, which was completely antagonized by pretreatment with U0126. Our results suggest that activation of NPFF₂ receptor stimulates neurite outgrowth in Neuro 2A cells through activation of the ERK signaling pathway. Moreover, NPFF₂ receptor may be a potential therapeutic target for neural injury and degeneration in the future.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Development of a peptidomimetic antagonist of neuropeptide FF receptors for the prevention of opioid-induced hyperalgesia

Through the development of a new class of unnatural ornithine derivatives as bioisosteres of arginine, we have designed an orally active peptidomimetic antagonist of neuropeptide FF receptors (NPFFR). Systemic low-dose administration of this compound to rats blocked opioid-induced hyperalgesia, without any apparent side-effects. Interestingly, we also observed that this compound potentiated opioid-induced analgesia. This unnatural ornithine derivative provides a novel therapeutic approach for both improving analgesia and reducing hyperalgesia induced by opioids in patients being treated for chronic pain.

The hypothalamic neuropeptide FF network is impaired in hypertensive patients

BACKGROUND

The human hypothalamus contains the neuropeptide FF (NPFF) neurochemical network. Animal experiments demonstrated that NPFF is implicated in the central cardiovascular regulation. We therefore studied expression of this peptide in the hypothalamus of individuals who suffered from essential hypertension (n = 8) and died suddenly due to acute myocardial infarction (AMI), and compared to that of healthy individuals (controls) (n = 6) who died abruptly due to mechanical trauma of the chest.

METHODS

The frozen right part of the hypothalamus was cut coronally into serial sections of 20 μm thickness, and each tenth section was stained immunohistochemically using antibody against NPFF. The central section through each hypothalamic nucleus was characterized by the highest intensity of NPFF immunostaining and thus was chosen for quantitative densitometry.

RESULTS

In hypertensive patients, the area occupied by NPFF immunostained neuronal elements in the central sections through the suprachiasmatic nucleus (SCh), paraventricular hypothalamic nucleus (Pa), bed nucleus of the stria terminalis (BST), perinuclear zone (PNZ) of the supraoptic nucleus (SON), dorso- (DMH), ventromedial (VMH) nuclei, and perifornical nucleus (PeF) was dramatically decreased compared to controls, ranging about six times less in the VMH to 15 times less in the central part of the BST (BSTC). The NPFF innervation of both nonstained neuronal profiles and microvasculature was extremely poor in hypertensive patients compared to control.

CONCLUSIONS

The decreased NPFF expression in the hypothalamus of hypertensive patients might be a cause of impairment of its interaction with other neurochemical systems, and thereby might be involved in the pathogenesis of the disease.

The anti-inflammatory potential of neuropeptide FF in vitro and in vivo

Neuropeptide FF (NPFF) has many functions in regulating various biological processes. However, little attention has been focused on the anti-inflammatory effect of this peptide. In the present study, the in vitro anti-inflammatory activity of NPFF in both primary peritoneal macrophages and RAW 264.7 macrophages was investigated. Our data showed that NPFF suppressed the nitric oxide (NO) production of macrophages in the inflammation process. RF9, a reported antagonist of NPFF receptors, completely blocked the NPFF-induced NO suppression, suggesting a NPFF receptors-mediated pathway is mainly involved. Down-regulation of the nitric oxide synthases significantly inhibited the NPFF-induced NO reduction, indicating the involvement of nitric oxide synthases. However, the nitric oxide synthases were not the only route by which NPFF modulated the NO levels of macrophages. Pharmacological antagonists of the NF-κB signal pathway also completely suppressed the NPFF-induced NO decline. Moreover, we also observed that NPFF is capable of blocking the LPS-induced nuclear translocation of p65 in macrophages, implying the involvement of the NF-κB signal pathway. Finally, we observed that NPFF markedly attenuated the carrageenan-induced mouse paw edema, indicating that NPFF is capable of exerting anti-inflammatory potency in vivo. Collectively, our findings reveal the potential role of NPFF in the anti-inflammatory field both in vitro and in vivo, which will be helpful for the further exploitation of NPFF utility therapeutically.

Neuropeptide FF activates ERK and NF kappa B signal pathways in differentiated SH-SY5Y cells

Neuropeptide FF (NPFF) has been reported to play important roles in regulating diverse biological processes. However, little attention has been focused on the downstream signal transduction pathway of NPFF. Here, we used the differentiated neuroblastoma cell line, dSH-SY5Y, which endogenously expresses hNPFF2 receptor, to investigate the signal transduction downstream of NPFF. In particular we investigated the regulation of the extracellular signal-regulated protein kinase (ERK) and the nuclear factor kappa B (NF-κB) pathways by NPFF in these cells. NPFF rapidly and transiently stimulated ERK. H89, a selective inhibitor of cyclic AMP-dependent protein kinase A (PKA), inhibited the NPFF-activated ERK pathway, indicating the involvement of PKA in the NPFF-induced ERK activation. Down-regulation of nitric oxide synthases also attenuated NPFF-induced ERK activation, suggesting that a nitric oxide synthase-dependent pathway is involved. Moreover, the core upstream components of the NF-κB pathway were also significantly activated in response to NPFF, suggesting that the NF-κB pathway is involved in the signal transduction pathway of NPFF. Collectively, these data demonstrate that nitric oxide synthases are involved in the signal transduction pathway of NPFF, and provide the first evidence for the interaction between NPFF and the NF-κB pathway. These advances in our interpretation of the NPFF pathway mechanism will aid the comprehensive understanding of its function and provide novel molecular insight for further study of the NPFF system.

Selective mode of action of guanidine-containing non-peptides at human NPFF receptors

The binding pocket of both NPFF receptors was investigated, focusing on subtype-selective behavior. By use of four nonpeptidic compounds and the peptide mimetics RF9 and BIBP3226, agonistic and antagonistic properties were characterized. A set of Ala receptor mutants was generated. The binding pocket was narrowed down to the upper part of transmembrane helices V, VI, VII and the extracellular loop 2. Positions 5.27 and 6.59 have been shown to have a strong impact on receptor activation and were suggested to form an acidic, negatively charged binding pocket in both NPFF receptor subtypes. Additionally, position 7.35 was identified to play an important role in functional selectivity. According to docking experiments, the aryl group of AC-216 interacts with position 7.35 in the NPFF(1) but not in the NPFF(2) receptor. These results provide distinct insights into the receptor specific binding pockets, which is necessary for the development of drugs to address the NPFF system.

Characterization of novel RFamide peptides in the central nervous system of the brown hagfish: isolation, localization, and functional analysis

RFamide (RFa) peptides play various important roles in the central nervous system in both invertebrates and vertebrates. However, there is no evidence of the existence of any RFamide peptide in the brain of hagfish, one of the oldest lineages of vertebrates. In this study, we sought to identify novel RFamide peptides from the brains of hagfish (Paramyxine atami). We identified four novel RFamide peptides, which had the C-terminal Pro-Gln-Arg-Phe-NH2 structure. cDNA cloning revealed that the identified RFamide peptides are encoded in two types of cDNA. Molecular phylogenetic analysis of the two precursors indicated that the hagfish RFamide peptides belong to the PQRFamide peptide group that includes mammalian neuropeptide FF and AF. Based on immunohistochemistry and in situ hybridization, hagfish PQRFamide peptide precursor mRNA and its translated peptides were localized in the infundibular nucleus of the hypothalamus. Immunoreactive fibers were terminated on blood vessels in the infundibular nucleus. Dense immunoreactive fibers were also observed in other brain regions. We further showed that one of the hagfish PQRFamide peptides significantly stimulated the expression of gonadotropin-β mRNA in the cultured hagfish pituitary. These results indicate that the control mechanism of gonadotropin expression by a hypothalamic neuropeptide evolved in the agnathan brain. This is the first evidence describing the identification of RFamide peptides in the hagfish brain. This is also the first report showing the regulation of gonadotropin expression by a homolog of neuropeptide FF that belongs to the PQRFamide peptide group in any vertebrate.

Structure-activity studies of RFamide peptides reveal subtype-selective activation of neuropeptide FF1 and FF2 receptors

Selectivity is a major issue in closely related multiligand/multireceptor systems. In this study we investigated the RFamide systems of hNPFF₁R and hNPFF₂R that bind the endogenous peptide hormones NPFF, NPAF, NPVF, and NPSF. By use of a systematic approach, we characterized the role of the C-terminal dipeptide with respect to agonistic properties using synthesized [Xaa 7]NPFF and [Xaa 8]NPFF analogues. We were able to identify only slight differences in potency upon changing the position of Arg 7, as all modifications resulted in identical behavior at the NPFF₁R and NPFF₂R. However, the C-terminal Phe 8 was able to be replaced by Trp or His with only a minor loss in potency at the NPFF₂R relative to the NPFF₁R. Analogues with shorter side chains, such as α-amino-4-guanidino butyric acid ([Agb 7]NPFF) or phenylglycine ([Phg 8]NPFF), decreased efficacy for the NPFF₁ R to 25-31 % of the maximal response, suggesting that these agonist-receptor complexes are more susceptible to structural modifications. In contrast, mutations to the conserved Asp 6.59 residue in the third extracellular loop of both receptors revealed a higher sensitivity toward the hNPFF₂R receptor than toward hNPFF₁R. These data provide new insight into the subtype-specific agonistic activation of the NPFF₁ and NPFF(2) receptors that are necessary for the development of selective agonists.

Central locomotor and cognitive effects of a NPFF receptor agonist in mouse

NPFF receptors are expressed in several brain regions directly or indirectly involved in cognition and behavior. However, the cognitive effects of the NPFF system have been poorly studied. Therefore, the aim of our study was to analyze the effects of i.c.v. injections of 1 DMe, a stable agonist of NPFF receptors, on behavioral and cognitive performances in C57BL/6J mice. We measured locomotor activity, and an open field with objects was used to estimate the ability of mice to react to spatial changes and to measure short-term retention of information. The Morris navigation task was used to evaluate the acquisition, as well as long-term retention of a hippocampo-dependent spatial memory with a distributed training procedure. Finally, 1 DMe was tested in a contextual fear conditioning paradigm to study its effect on long-term memory of contextual information acquired in a single training session. Altogether, our results demonstrate a small but complex influence of the NPFF system on mouse behavior. 1 DMe injected i.c.v. induces a delayed hyperlocomotion and mildly impairs both short-term and long-term spatial memory processing without affecting contextual fear memory.

Multiple primary cilia modulate the fluid transcytosis in choroid plexus epithelium

Functional defects in cilia are associated with various human diseases including congenital hydrocephalus. Previous studies suggested that defects in cilia not only disrupt the flow of cerebrospinal fluid (CSF) generated by motile cilia in ependyma lining the brain ventricles, but also cause increased CSF production at the choroid plexus. However, the molecular mechanisms of CSF overproduction by ciliary dysfunction remain elusive. To dissect the molecular mechanisms, choroid plexus epithelial cells (CPECs) were isolated from porcine brain. These cells expressed clusters of primary cilia on the apical surface. Deciliation of CPECs elevated the intracellular cyclic AMP (cAMP) levels and stimulated basolateral-to-apical fluid transcytosis, without detrimental effects on other morphological and physiological features. The primary cilia possessed neuropeptide FF (NPFF) receptor 2. In deciliated cells, the responsiveness to NPFF was reduced at nanomolar concentrations. Furthermore, CPECs expressed NPFF precursor along with NPFFR2. An NPFFR antagonist, BIBP3226, increased the fluid transcytosis, suggesting the presence of autocrine NPFF signaling in CPECs for a tonic inhibition of fluid transcytosis. These results suggest that the clusters of primary cilia in CPECs act as a sensitive chemosensor to regulate CSF production.

A new key neurohormone controlling reproduction, gonadotropin-inhibitory hormone (GnIH): Biosynthesis, mode of action and functional significance

Identification of novel neurohormones that play important roles in the regulation of pituitary function is essential for the progress of neurobiology. The decapeptide gonadotropin-releasing hormone (GnRH) is the primary factor responsible for the hypothalamic control of gonadotropin secretion. Gonadal sex steroids and inhibin inhibit gonadotropin secretion via feedback from the gonads, but a neuropeptide inhibitor of gonadotropin secretion was, until recently, unknown in vertebrates. In 2000, a novel hypothalamic dodecapeptide that inhibits gonadotropin release was identified in quail and termed gonadotropin-inhibitory hormone (GnIH). This was the first demonstration of a hypothalamic neuropeptide inhibiting gonadotropin release in any vertebrate. GnIH acts on the pituitary and GnRH neurons in the hypothalamus via a novel G protein-coupled receptor for GnIH to inhibit gonadal development and maintenance by decreasing gonadotropin release and synthesis. GnIH neurons express the melatonin receptor and melatonin stimulates the expression of GnIH. Because GnIH exists and functions in several avian species, GnIH is considered to be a new key neurohormone controlling avian reproduction. From a broader perspective, subsequently the presence of GnIH homologous peptides has been demonstrated in other vertebrates. Mammalian GnIH homologous peptides also act to inhibit reproduction by decreasing gonadotropin release in several mammalian species. Thus, the discovery of GnIH has opened the door to a new research field in reproductive neurobiology. This review summarizes the advances made in our understanding of the biosynthesis, mode of action and functional significance of GnIH, a newly discovered key neurohormone, and its homologous peptides.

Modulatory role of neuropeptide FF system in nociception and opiate analgesia

The tetra-peptide FMRF-NH(2) is a cardioexcitatory peptide in the clam. Using the antibody against this peptide, FMRF-NH(2)-like immunoreactive material was detected in mammalian CNS. Subsequently, mammalian FMRF-NH(2) immunoreactive peptides were isolated from bovine brain and characterized to be FLFQPQRF-NH(2) (NPFF) and AGEGLSSPFWSLAAPQRF-NH(2) (NPAF). The genes encoding NPFF precursor proteins and NPFF receptors 1 and 2 are expressed in all vertebrate species examined to date and are highly conserved. Among many biological roles suggested for the NPFF system, the possible modulatory role of NPFF in nocicetion and opiate analgesia has been most widely investigated. Pharmacologically, NPFF-related peptides were found to exhibit analgesia and also potentiate the analgesic activity of opiates when administered intrathecally but attenuate the opiate induced analgesia when administered intracerebroventricularly. RF-NH(2) peptides including NPFF-related peptides were found to delay the rate of acid sensing ion channels (ASIC) desensitization resulting in enhancing acid gated currents, raising the possibility that NPFF also may have a pain modulatory role through ASIC. The genes for NPFF as well as NPFF-R2, preferred receptor for NPFF, are highly unevenly expressed in the rat CNS with the highest levels localized to the superficial layers of the dorsal spinal cord. These two genes are also present in the dorsal root ganglia (DRG), though at low levels in normal rats. NPFF and NPFF-R2 mRNAs were found to be coordinately up-regulated in spinal cord and DRG of rats with peripheral inflammation. In addition, NPFF-R2 immunoreactivity in the primary afferents was increased by peripheral inflammation. The findings from the early studies on the analgesic and morphine modulating activities suggested a role for NPFF in pain modulation and this possibility is further supported by the distribution of NPFF and its receptor and the regulation of the NPFF system in vivo.

Prolactin-releasing peptide, food intake, and hydromineral balance in goldfish

A potential role for prolactin-releasing peptide (PrRP) in appetite regulation and hydromineral balance in goldfish was examined. PrRP was found to be expressed in discrete regions of the goldfish brain, in particular, the hypothalamus. Intraperitoneal (IP) or intracerebroventricular administration of PrRP had dose-dependent effects to suppress food intake in goldfish. Hypothalamic PrRP mRNA expression significantly increased after feeding, as well as after 7 days of food deprivation. Refeeding fish after 7 days food deprivation did not result in a postprandial increase in PrRP mRNA expression. These data suggest an anorexigenic role for PrRP in the short term around a scheduled meal time, but not over the longer term. IP injection of PrRP significantly increased pituitary prolactin (PRL) mRNA levels, suggesting involvement in the regulation of lactotroph activity. Acclimating goldfish to an ion-poor environment decreased serum osmolality and increased PrRP and PRL mRNA levels, providing evidence for PrRP involvement in hydromineral balance through its actions on lactotrophs. Acclimation to ion-poor water diminished the anorexigenic properties of PrRP in goldfish, indicating that a role for PrRP in goldfish satiation is counterbalanced by alternate systemic needs (i.e., osmoregulatory). This was further supported by an ability to reinstate the anorexigenic actions of PrRP in fish acclimated to ion-poor water by feeding a salt-rich diet. These studies provide evidence that PrRP is involved in regulating appetite and hydromineral balance in fish, and that the degree of involvement in either process varies according to overall systemic needs in response to environmental conditions.

Microarray analysis of gene expression in the supraoptic nucleus of normoosmotic and hypoosmotic rats

1. Hypoosmolality produces a dramatic inhibition of vasopressin (VP) and oxytocin (OT) gene expression in the supraoptic nucleus (SON). This study examines the effect of sustained hypoosmolality on global gene expression in the OT and VP magnocellular neurons (MCNs) of the hypothalamo-neurohypophysial system (HNS), in order to detect novel genes in this system that might be involved in osmoregulation in the MCNs. 2. For this purpose, we used Affymetrix oligonucleotide arrays to analyze the expression of specific genes in laser microdissected rat SONs, and their changes in expression during chronic hypoosmolality. We identified over 40 genes that had three-fold or more greater expression in the SON versus total hypothalamus, and that also changed more than two fold in expression as a result of the chronic hypoosmolar treatment. These genes contained both novel as well as genes previously known to be present in the SON. All of the raw data for the genes that are expressed in the SON and altered by hypoosmolality can be found on the following NINDS website URL address: http://data.ninds.nih.gov/Gainer/Publications.

Modulatory roles of the NPFF system in pain mechanisms at the spinal level

The possible roles of the NPFF system in pain processing are summarized from the viewpoints of (1) biological activities of NPFF, (2) anatomical distribution of NPFF and its receptor(s) and (3) the regulation of NPFF and receptor(s) in animal models of pain. NPFF and NPFF analogues were found to have analgesic, pronociceptive and morphine modulating activities. Since the isolation of NPFF, several other RF-NH2 peptides have been identified and some of them were found to have nociceptive or morphine modulating activity. Depending on the pharmacological doses and locations of administration, NPFF may exhibit the biological activities of other structurally related RF-NH2 peptides thus complicating NPFF bioactivity studies and their interpretation. Acid sensing ion channels were found to respond to RF-NH2 peptides including NPFF, raising the possibility that interaction of NPFF and acid sensing ion channels can modulate nociceptive activity. NPFF and NPFF receptor mRNAs are highly expressed and localized in the superficial layers of the dorsal cord, the two genes are also in dorsal root ganglia though at much lower level. The spinal NPFF system is up-regulated by peripheral inflammation in the rat. Furthermore, immunohistochemically, NPFF receptor 2-protein was demonstrated to be increased in the primary afferents in the spinal cord of rats with peripheral inflammation. Regulation and localization of spinal NPFF systems, taken together with the analgesic bioactivity of intrathecally administered NPFF, strongly suggest involvement of spinal NPFF system in pain processing.

A new member of the hypothalamic RF-amide peptide family, LPXRF-amide peptides: structure, localization, and function

Recently, we identified a novel hypothalamic neuropeptide with a C-terminal LPLRF-amide sequence in the quail brain. This avian neuropeptide was shown to inhibit gonadotropin release from the cultured anterior pituitary. This peptide is the first hypothalamic peptide that inhibited gonadotropin release reported in vertebrates. We, therefore, termed it gonadotropin-inhibitory hormone (GnIH). After this finding, we found that GnIH-related peptides were present in the brains of other vertebrates, such as mammals, amphibians, and fish. These GnIH-related peptides possessed a LPXRF-amide (X=L or Q) motif at their C-termini in all investigated animals. Mass spectrometric analyses combined with immunoaffinity chromatography were powerful techniques for the identification of mature endogenous LPXRF-amide peptides. The identified LPXRF-amide peptides were found to be localized in the hypothalamus and brainstem areas, and to regulate pituitary hormone release. Subsequently, cDNAs that encode LPXRF-amide peptides were characterized in vertebrate brains. In this review, we summarize the identification, localization, and function of a new member of the hypothalamic RF-amide peptide family, LPXRF-amide peptides in vertebrates. Recent studies on the receptors for LPXRF-amide peptides will also be reviewed.