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[Image: see text] Anorexigenic peptides offer promise as potential therapies targeting the escalating global obesity epidemic. Prolactin-releasing peptide (PrRP), a novel member of the RFamide family secreted by the hypothalamus, shows therapeutic potential by decreasing food intake and body weight in rodent models via GPR10 activation. Here we describe the design of a long-acting PrRP using our recently developed novel multiple ethylene glycol-fatty acid (MEG-FA) stapling platform. By incorporating serum albumin binding fatty acids onto a covalent side chain staple, we have generated a series of MEG-FA stapled PrRP analogs with enhanced serum stability and in vivo half-life. Our lead compound 18-S4 exhibits good in vitro potency and selectivity against GPR10, improved serum stability, and extended in vivo half-life (7.8 h) in mouse. Furthermore, 18-S4 demonstrates a potent body weight reduction effect in a diet-induced obesity (DIO) mouse model, representing a promising long-acting PrRP analog for further evaluation in the chronic obesity setting.

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases, characterized by the accumulation of extracellular amyloid plaques and intraneuronal neurofibrillary tangles. These tangles mainly consist of hyperphosphorylated tau protein. As it induces tau hyperphosphorylation in vitro and in vivo, hypothermia is a useful tool for screening potential neuroprotective compounds that ameliorate tau pathology. In this study, we examined the effect of prolactin-releasing peptide (PrRP), its lipidized analog palm11-PrRP31 and glucagon-like-peptide-1 agonist liraglutide, substances with anorexigenic and antidiabetic properties, on tau phosphorylation and on the main kinases and phosphatases involved in AD development. Our study was conducted in a neuroblastoma cell line SH-SY5Y and rat primary neuronal cultures under normothermic and hypothermic conditions. Hypothermia induced a significant increase in tau phosphorylation at the pThr212 and pSer396/pSer404 epitopes. The palmitoylated analogs liraglutide and palm11-PrRP31 attenuated tau hyperphosphorylation, suggesting their potential use in the treatment of neurodegenerative diseases.

Background:Prolactin-releasing peptide (PrRP) is a potential drug for the treatment of obesity and associated Type 2 Diabetes Mellitus (T2DM) due to its strong anorexigenic and antidiabetic properties. In our recent study, the lipidized PrRP analog palm11-PrRP31 was proven to exert beneficial effects in APP/PS1 mice, a model of Alzheimer´s Disease (AD)-like amyloid-β (Aβ) pathology, reducing the Aβ plaque load, microgliosis and astrocytosis in the hippocampus and cortex.Objective:In this study, we focused on the neuroprotective and anti-inflammatory effects of palm11-PrRP31 and its possible impact on synaptogenesis in the cerebellum of APP/PS1 mice, because others have suggested that cerebellar Aβ plaques contribute to cognitive deficits in AD.Methods:APP/PS1 mice were treated subcutaneously with palm11-PrRP31 for 2 months, then immunoblotting and immunohistochemistry were used to quantify pathological markers connected to AD, compared to control mice.Results:In the cerebella of 8 months old APP/PS1 mice, we found widespread Aβ plaques surrounded by activated microglia detected by ionized calcium-binding adapter molecule (Iba1), but no increase in astrocytic marker Glial Fibrillary Acidic Protein (GFAP) compared to controls. Interestingly, no difference in both presynaptic markers syntaxin1A and postsynaptic marker spinophilin was registered between APP/PS1 and control mice. Palm11-PrRP31 treatment significantly reduced the Aβ plaque load and microgliosis in the cerebellum. Furthermore, palm11-PrRP31 increased synaptogenesis and attenuated neuroinflammation and apoptosis in the hippocampus of APP/PS1 mice.Conclusion:These results suggest palm11-PrRP31 is a promising agent for the treatment of neurodegenerative disorders.

Neuroendocrine, behavioural and autonomic responses to stressful stimuli are orchestrated by complex neural circuits. The caudal nucleus of the solitary tract (cNTS) in the dorsomedial hindbrain is uniquely positioned to integrate signals of both interoceptive and psychogenic stress. Within the cNTS, glucagon-like peptide-1 (GLP-1) and prolactin-releasing peptide (PrRP) neurons play crucial roles in organising neural responses to a broad range of stressors. In this review we discuss the anatomical and functional overlap between PrRP and GLP-1 neurons. We outline their co-activation in response to stressful stimuli and their importance as mediators of behavioural and physiological stress responses. Finally, we review evidence that PrRP neurons are downstream of GLP-1 neurons and outline unexplored areas of the research field. Based on the current state-of-knowledge, PrRP and GLP-1 neurons may be compelling targets in the treatment of stress-related disorders. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

Prolactin-releasing Peptide (PrRP) is a neuropeptide whose receptor is GPR10. Recently, the regulatory role of PrRP in the neuroendocrine field has attracted increasing attention. However, the influence of PrRP on macrophages, the critical housekeeper in the neuroendocrine field, has not yet been fully elucidated. Here, we investigated the effect of PrRP on the transcriptome of mouse bone marrow-derived macrophages (BMDMs) with RNA sequencing, bioinformatics, and molecular simulation. BMDMs were exposed to PrRP (18 h) and were subjected to RNA sequencing. Differentially expressed genes (DEGs) were acquired, followed by GO, KEGG, and PPI analysis. Eight qPCR-validated DEGs were chosen as hub genes. Next, the three-dimensional structures of the proteins encoded by these hub genes were modeled by Rosetta and Modeller, followed by molecular dynamics simulation by the Gromacs program. Finally, the binding modes between PrRP and hub proteins were investigated with the Rosetta program. PrRP showed no noticeable effect on the morphology of macrophages. A total of 410 DEGs were acquired, and PrRP regulated multiple BMDM-mediated functional pathways. Besides, the possible docking modes between PrRP and hub proteins were investigated. Moreover, GPR10 was expressed on the cell membrane of BMDMs, which increased after PrRP exposure. Collectively, PrRP significantly changed the transcriptome profile of BMDMs, implying that PrRP may be involved in various physiological activities mastered by macrophages.

Competing motivational drives coordinate behaviors essential for survival. For example, interoceptive feedback from the body during a state of negative energy balance serves to suppress anxiety-like behaviors and promote exploratory behaviors in rats. Results from past research suggest that this shift in motivated behavior is linked to reduced activation of specific neural populations within the caudal nucleus of the solitary tract (cNTS). However, the potential impact of metabolic state and the potential role of cNTS neurons on conditioned avoidance behaviors has not been examined. The present study investigated these questions in male and female rats, using a task in which rats learn to avoid a context (i.e., a darkened chamber) after it is paired with a single mild footshock. When rats later were tested for passive avoidance of the shock-paired chamber, male rats tested in an overnight food-deprived state and female rats (regardless of feeding status) displayed significantly less avoidance compared to male rats that were fed ad libitum prior to testing. Based on prior evidence that prolactin-releasing peptide (PrRP)-positive noradrenergic neurons and glucagon-like peptide 1 (GLP1)-positive neurons within the cNTS are particularly sensitive to metabolic state, we examined whether these neural populations are activated in conditioned rats after re-exposure to the shock-paired chamber, and whether neural activation is modulated by metabolic state. Compared to the control condition, chamber re-exposure activated PrRP+ noradrenergic neurons and also activated neurons within the anterior ventrolateral bed nucleus of the stria terminalis (vlBNST), which receives dense input from PrRP+ terminals. In parallel with sex differences in passive avoidance behavior, PrRP+ neurons were less activated in female vs. male rats after chamber exposure. GLP1+ neurons were not activated in either sex. Overnight food deprivation before chamber re-exposure reduced activation of PrRP+ neurons, and also reduced vlBNST activation. Our results support the view that PrRP+ noradrenergic neurons and their inputs to the vlBNST contribute to the expression of passive avoidance memory, and that this contribution is modulated by metabolic state.

Prolactin-releasing peptide (PrRP), an RF-amide peptide, had been originally identified as a stimulator of prolactin release from the anterior pituitary. However, further studies revealed that the prolactin-releasing effect of PrRP is inconsistent and different from ordinary hypophysiotropic hormones. However, PrRP is demonstrated to have some physiological roles, such as inhibition of feeding, and obesity, stress response, and control of release of hypothalamic hormones in mammals. On the other hand, PrRP2 (C-RFa) has been identified as a neuropeptide which originates from a common ancestral gene of PrRP. PrRP2 is found in vertebrates except for mammals. PrRP2 is a potent stimulator of prolactin in teleosts, but has a lesser effect in amphibians and chickens. As in PrRP, PrRP2 is related to energy homeostasis in teleosts and chickens. The physiological functions of PrRP and PrRP2 may have changed through evolution.

There is little information regarding effects of fasting on feeding behavior and hypothalamic physiology in young Japanese quail. The aim was thus to measure food intake and hypothalamic mRNA in response to fasting and refeeding. Five d-old quail ate little during the dark cycle. Food intake was greatest during the first 2 h of the light cycle. Six day-old quail fasted for 6 h ate the most during the first 15 min of refeeding. In 7 d-old quail, 3 h of fasting up-regulated hypothalamic neuropeptide Y (NPY), NPY receptor sub-type 2 (NPYR2), agouti-related peptide (AgRP), orexin receptor 2 (ORXR2), melanocortin receptors 3 and 4 (MC3R and MC4R, respectively), and neuropeptide S (NPS) and decreased corticotropin-releasing factor receptor sub-type 1 (CRFR1) mRNA. Quail fasted for 3 h and refed for 1 h had greater NPY, AgRP, POMC, and MC3R but less CRFR1 mRNA than fed quail. Quail fasted for 6 h expressed more NPY, NPYR1, NPYR2, and MC3R and less ORXR2, prolactin releasing peptide (PrRP), cocaine- and amphetamine-regulated transcript (CART), and calcitonin (CAL) mRNA than fed quail. Quail fasted for 6 h and refed for 1 h expressed more NPY, NPYR1, NPYR2, AgRP, MC3R, MC4R, and NPS and less galanin, ORXR2, PrRP, CART, and CAL mRNA than fed birds. Hence, fasting induced changes in hypothalamic mRNA, with the largest changes occurring in genes associated with NPY and melanocortin signaling. Most genes remained elevated or downregulated after refeeding, suggesting that there was a time lag for transcription to respond to compensatory feeding.

The molecular mechanism underlying in the onset and maintenance of incubation behavior are not fully understood, and it is still unknown the reason why White Leghorn, a layer strain, hens never display incubation behavior. Therefore, to explore specific hypothalamic genes regulating incubation behavior, cap analysis of gene expression (CAGE) were applied to comparison between incubating Silkie and laying White Leghorn hens. In addition, mRNA expression of some differentially expressed genes (DEGs) and melanocortinergic appetite genes including agouti-related peptide (AgRP) and pro-opiomelanocortin (POMC) was also analyzed on Silkie hens under natural anorexia and starvation. The CAGE identified 217 hypothalamic DEGs in incubating Silkie hens, and that of two, transthyretin (TTR) and prolactin-releasing peptide (PrRP), suggested as appetite gene, were markedly up- and down-regulated in incubating hens, respectively. In addition, AgRP and POMC expression also increased in incubating bird. mRNA expression of TTR, PrRP, and appetite genes were not differed significantly by starvation, although TTR mRNA expression was relatively high in fasting hens. Consequently, transcriptome by CAGE identified a number of hypothalamic genes differentially expressed by incubation behavior in Silkie hens. Of these, it is suggested that TTR and PrRP may, at least in part, be related to adaptation to natural anorexia in incubating Silkie chickens.

G-protein-coupled receptor GPR10 is expressed in brain areas regulating energy metabolism. In this study, the effects of GPR10 gene deficiency on energy homeostasis in mice of both sexes fed either standard chow or a high-fat diet (HFD) were studied, with a focus on neuronal activation of PrRP neurons, and adipose tissue and liver metabolism. GPR10 deficiency in males upregulated the phasic and tonic activity of PrRP neurons in the nucleus of the solitary tract. GPR10 knockout (KO) males on a standard diet displayed a higher body weight than their wild-type (WT) littermates due to an increase in adipose tissue mass; however, HFD feeding did not cause weight differences between genotypes. Expression of lipogenesis genes was suppressed in the subcutaneous adipose tissue of GPR10 KO males. In contrast, GPR10 KO females did not differ in body weight from their WT controls, but showed elevated expression of lipid metabolism genes in the liver and subcutaneous adipose tissue compared to WT controls. An attenuated non-esterified fatty acids change after glucose load compared to WT controls suggested a defect in insulin-mediated suppression of lipolysis in GPR10 KO females. Indirect calorimetry did not reveal any differences in energy expenditure among groups. In conclusion, deletion of GPR10 gene resulted in changes in lipid metabolism in mice of both sexes, however in different extent. An increase in adipose tissue mass observed in only GPR10 KO males may have been prevented in GPR10 KO females owing to a compensatory increase in the expression of metabolic genes.

Up to 80% of cancer patients are affected by the cancer anorexia-cachexia syndrome (CACS), which leads to excessive body weight loss, reduced treatment success and increased lethality. The area postrema/nucleus of the solitary tract (AP/NTS) region emerged as a central nervous key structure in this multi-factorial process. Neurons in this area are targeted by cytokines and signal to downstream sites involved in energy homeostasis. NTS neurons expressing prolactin-releasing peptide (PrRP) are implicated in the control of energy intake and hypothalamus-pituitary-adrenal (HPA) axis activation, which contributes to muscle wasting. To explore if brainstem PrRP neurons contribute to CACS, we selectively knocked down PrRP expression in the NTS of hepatoma tumor-bearing rats by an AAV/shRNA gene silencing approach. PrRP knockdown reduced body weight loss and anorexia compared to tumor-bearing controls treated with a non-silencing AAV. Gastrocnemius and total hind limb muscle weight was higher in PrPR knockdown rats. Corticosterone levels were increased in the early phase after tumor induction at day 6 in both groups but returned to baseline levels at day 21 in the PrRP knockdown group. While we did not detect significant changes in gene expression of markers for muscle protein metabolism (MuRF-1, myostatin, mTOR and REDD1), mTOR and REDD1 tended to be lower after disruption PrRP signalling. In conclusion, we identified brainstem PrRP as a possible neuropeptide mediator of CACS in hepatoma tumor-bearing rats. The central and peripheral downstream mechanisms require further investigation and might involve HPA axis activation.

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.

Numerous neuropeptide systems have been implicated to coordinately control energy homeostasis, both centrally and peripherally. However, the vertebrate neuropeptide Y (NPY) system has emerged as the best described one regarding this biological process. The protostomian ortholog of NPY is neuropeptide F, characterized by an RXRF(Y)amide carboxyterminal motif. A second neuropeptide system is short NPF, characterized by an M/T/L/FRF(W)amide carboxyterminal motif. Although both short and long NPF neuropeptide systems display carboxyterminal sequence similarities, they are evolutionary distant and likely already arose as separate signaling systems in the common ancestor of deuterostomes and protostomes, indicating the functional importance of both. Both NPF and short-NPF systems seem to have roles in the coordination of feeding across bilaterian species, but during chordate evolution, the short NPF system appears to have been lost or evolved into the prolactin releasing peptide signaling system, which regulates feeding and has been suggested to be orthologous to sNPF. Here we review the roles of both NPF and sNPF systems in the regulation of feeding and metabolism in invertebrates. ispartof: Frontiers In Endocrinology vol:10 ispartof: location:Switzerland status: published

Obesity and type 2 diabetes mellitus (T2DM) are important risk factors for Alzheimer's disease (AD). Drugs originally developed for T2DM treatment, e.g., analog of glucagon-like peptide 1 liraglutide, have shown neuroprotective effects in mouse models of AD. We previously examined the neuroprotective properties of palm11-PrRP31, an anorexigenic and glucose-lowering analog of prolactin-releasing peptide, in a mouse model of AD-like Tau pathology, THY-Tau22 mice. Here, we demonstrate the neuroprotective effects of palm11-PrRP31 in double transgenic APP/PS1 mice, a model of AD-like β-amyloid (Aβ) pathology. The 7-8-month-old APP/PS1 male mice were subcutaneously injected with liraglutide or palm11-PrRP31 for 2 months. Both the liraglutide and palm11-PrRP31 treatments reduced the Aβ plaque load in the hippocampus. Palm11-PrRP31 also significantly reduced hippocampal microgliosis, consistent with our observations of a reduced Aβ plaque load, and reduced cortical astrocytosis, similar to the treatment with liraglutide. Palm11-PrRP31 also tended to increase neurogenesis, as indicated by the number of doublecortin-positive cells in the hippocampus. After the treatment with both anorexigenic compounds, we observed a significant decrease in Tau phosphorylation at Thr231, one of the first epitopes phosphorylated in AD. This effect was probably caused by elevated activity of protein phosphatase 2A subunit C, the main Tau phosphatase. Both liraglutide and palm11-PrRP31 reduced the levels of caspase 3, which has multiple roles in the pathogenesis of AD. Palm11-PrRP31 increased protein levels of the pre-synaptic marker synaptophysin, suggesting that palm11-PrRP31 might help preserve synapses. These results indicate that palm11-PrRP31 has promising potential for the treatment of neurodegenerative diseases.

PURPOSE: Prolactin-releasing peptide (PrRP) is a neuropeptide that suppresses food intake and increases body temperature when delivered to the forebrain ventricularly or parenchymally. However, PrRP’s receptor GPR10 is widely distributed throughout the brain with particularly high levels found in the dorsomedial hindbrain. Thus, we hypothesized that hindbrain-directed PrRP administration would affect energy balance and motivated feeding behavior. METHODS: To address this hypothesis, a range of behavioral and physiologic variables were measured in Sprague-Dawley rats that received PrRP delivered to the fourth ventricle (4V) or the nucleus of the solitary tract (NTS) at the level of the area postrema (AP). RESULTS: 4V PrRP delivery decreased chow intake and body weight, in part, through decreasing meal size in ad libitum maintained rats tested at dark onset. PrRP inhibited feeding when delivered to the nucleus tractus solitarius (NTS), but not to more ventral hindbrain structures. In addition, 4V as well as direct NTS administration of PrRP increased core temperature. By contrast, 4V PrRP did not reduce ad libitum intake of highly palatable food or the motivation to work for or seek palatable foods. CONCLUSIONS: The dorsomedial hindbrain and NTS/AP, in particular, are sites of action in PrRP/GPR10-mediated control of chow intake, core temperature, and body weight.

Glutamatergic neurons that express pre‐proglucagon (PPG) and are immunopositive (+) for glucagon‐like peptide‐1 (i.e., GLP‐1+ neurons) are located within the caudal nucleus of the solitary tract (cNTS) and medullary reticular formation in rats and mice. GLP‐1 neurons give rise to an extensive central network in which GLP‐1 receptor (GLP‐1R) signaling suppresses food intake, attenuates rewarding, increases avoidance, and stimulates stress responses, partly via GLP‐1R signaling within the cNTS. In mice, noradrenergic (A2) cNTS neurons express GLP‐1R, whereas PPG neurons do not. In this study, confocal microscopy in rats confirmed that prolactin‐releasing peptide (PrRP)+ A2 neurons are closely apposed by GLP‐1+ axonal varicosities. Surprisingly, GLP‐1+ appositions were also observed on dendrites of PPG/GLP‐1+ neurons in both species, and electron microscopy in rats revealed that GLP‐1+ boutons form asymmetric synaptic contacts with GLP‐1+ dendrites. However, RNAscope confirmed that rat GLP‐1 neurons do not express GLP‐1R mRNA. Similarly, Ca2+ imaging of somatic and dendritic responses in mouse ex vivo slices confirmed that PPG neurons do not respond directly to GLP‐1, and a mouse crossbreeding strategy revealed that

Obesity is an escalating epidemic, but an effective non-invasive therapy is still scarce. For obesity treatment, anorexigenic neuropeptides are promising tools, but their delivery from the periphery to the brain is complicated by their peptide character. In order to overcome this unfavorable fact, we have applied the lipidization of neuropeptide prolactin-releasing peptide (PrRP), whose strong anorexigenic effect was demonstrated. A palmitoylated analog of human PrRP (h palm-PrRP31) was injected in free-fed Wistar rats by three routes: subcutaneous (s.c.), intraperitoneal (i.p) (both 5 mg/kg) and intravenous (i.v.) (from 0.01 to 0.5 mg/kg). We found a circulating compound in the blood after all three applications with the highest concentration after i.v. administration. This corresponds to the effect on food intake, which was also strongest after i.v. injection. Moreover, this is in agreement with the fact that the expression of c-Fos in specific brain regions involved in food intake regulation was also highest after intravenous application. Pharmacokinetic data are further supported by results obtained from dynamic light scattering and CD spectroscopy. Human palm-PrRP31 analog showed a strong tendency to micellize, and formation of aggregates suggested lower availability after i.p. or s.c. application. We have demonstrated that palm-PrRP influenced food intake even in free fed rats. Not surprisingly, the maximal effect was achieved after the intravenous application even though two orders of magnitude lower dose was used compared to both two other applications. We believe that palm-PrRP could have a potential as an antiobesity drug when its s.c. application would be improved.

Exogenous administration of prolactin-releasing peptide (PrRP) exerts anorexigenic effects in rats while causing orexigenic effects in chicks. While the central mechanism mediating PrRP's effect on food intake in rodents is somewhat understood, in chicks information is lacking. Therefore, this study was designed to elucidate the hypothalamic mechanism of PrRP induction of hunger perception in chicks. Chicks that received intracerebroventricular (ICV) injections of PrRP dose-dependently increased their food intake with no effect on water intake or whole blood glucose concentration. The threshold of food intake stimulation was as low as 3pmol, thus as compared to other neuropeptides PrRP is exceptionally potent. The mRNA abundance of several appetite-associated neuropeptide genes was quantified and hypothalamic neuropeptide Y (NPY) mRNA was increased in PrRP-injected chicks. Therefore, the orexigenic effects of PrRP may be associated with increased NPY-ergic tone. These results provide insight into the evolutionary aspects of appetite regulation during the course of divergent evolution of mammals and birds.

Energy homeostasis is the result of a balance between energy intake and expenditure, and the hypothalamus plays a key role in the regulation of these processes. The hypothalamic prolactin-releasing peptide (PrRP) is involved in food intake regulation and energy homeostasis, although only its lipidized analogs exert central anorexigenic effects after peripheral administration. The aim of the present study was to delineate the extent of the Fos expression as a marker of neuronal activation within the hypothalamic structures involved in food intake regulation after peripherally administered palmitoylated PrRP31 (palm-PrRP31) and to determine whether the anorexigenic effect of peripherally administered palm-PrRP31 influence the activity of hypocretin (HCRT) and oxytocin (OXY) neurons, i.e., the neuropeptides crucially involved in the regulation of energy homeostasis. The data confirmed an anorexigenic effect of palm-PrRP31 treatment (5mg/kg, s.c.) in mice. In the palm-PrRP31-treated animals, a significant increase in Fos expression was observed in the hypothalamic paraventricular (PVN), dorsomedial (DMN), and arcuate (Arc) nuclei and in the neurons of the nucleus of the solitary tract (NTS). Moreover, significant Fos expression was observed in the lateral hypothalamic area (LHA) HCRT neurons and PVN OXY neurons after palm-PrRP31 administration. The present findings may indicate that palm-PrRP31 may be involved in energy homeostasis via the activation of several hypothalamic structures. Fos activation of the hypothalamic OXY and HCRT neurons in the PVN and LHA emphasizes the importance of the areas mentioned in the central action of palm-PrRP31.

Background/Objectives Prolactin-releasing peptide (PrRP) has a potential to decrease food intake and ameliorate obesity, but is ineffective after peripheral administration. We have previously shown that our novel lipidized analogs PrRP enhances its stability in the circulation and enables its central effect after peripheral application. The purpose of this study was to explore if sub-chronic administration of novel PrRP analog palmitoylated in position 11 (palm11-PrRP31) to Koletsky-spontaneously hypertensive obese rats (SHROB) could lower body weight and glucose intolerance as well as other metabolic parameters. Subjects/Methods The SHROB rats (n = 16) were used for this study and age-matched hypertensive lean SHR littermates (n = 16) served as controls. Palm11-PrRP31 was administered intraperitoneally to SHR and SHROB (n = 8) at a dose of 5 mg/kg once-daily for 3 weeks. During the dosing period food intake and body weight were monitored. At the end of the experiment the oral glucose tolerance test was performed; plasma and tissue samples were collected. Thereafter, arterial blood pressure was measured. Results At the end of the experiment, vehicle-treated SHROB rats showed typical metabolic syndrome parameters, including obesity, glucose intolerance, dyslipidemia, and hypertension. Peripheral treatment with palm11-PrRP31 progressively decreased the body weight of SHR rats but not SHROB rats, though glucose tolerance was markedly improved in both strains. Moreover, in SHROB palm11-PrRP31 ameliorated the HOMA index, insulin/glucagon ratio, and increased insulin receptor substrate 1 and 2 expression in fat and insulin signaling in the hypothalamus, while it had no effect on blood pressure. Conclusions We demonstrated that our new lipidized PrRP analog is capable of improving glucose tolerance in obese SHROB rats after peripheral application, suggesting that its effect on glucose metabolism is independent of leptin signaling and body weight lowering. These data suggest that this analog has the potential to be a compound with both anti-obesity and glucose-lowering properties.

Previous studies indicate that hypothalamic prolactin-releasing peptide (PrRP), signaling via GPR10 and neuropeptide FF2 receptor, is involved in energy homeostasis, stress responses, and cardiovascular regulation. Energy homeostasis depends on the balance between food intake regulation and energy expenditure, in which the hypothalamus plays a key role. The lipidization of PrRP31 with palmitoyl acid allows it to produce its anorexigenic effect after repeated peripheral administration and to reduce body weight and improve metabolic parameters in diet-induced obese (DIO) mice. The aim of this study was to reveal the transient and long-lasting changes in neuronal activity via c-Fos and FosB immunohistochemistry in brain nuclei related to food intake regulation and energy homeostasis during the first days of treatment with a newly designed lipidized analog of PrRP31 (palm11-PrRP31) with promising antiobesity effects. The data revealed that the anorexigenic effect of repeated application of palm11-PrRP31 was associated with delayed but gradually significantly reduced cumulative food intake in mice as well as with a significant reduction in their body weight. Moreover, while the repeated application of palm11-PrRP31 was associated with a significant reduction in acute cell activity in the paraventricular hypothalamic nucleus (PVN) and nucleus of the solitary tract (NTS) compare to its acute treatment, both acute and long-lasting cell activity in the dorsomedial hypothalamic nucleus (DMN) were increased. The data indicate that DMN neurons might be tonically activated after repeated administration of lipidized PrRP analogs that may be associated with the process of long-term adaptation to modified energy homeostasis.

A potential role of the olfactory rosettes in maintaining prolactin (PRL) and prolactin-releasing peptide (PrRP) levels was examined in the euryhaline silver sea bream (Sparus sarba). The olfactory rosettes were surgically removed in silver sea bream adapted to hypo- (6 ppt) and hyper-osmotic (33 ppt) salinities and the mRNA expression of the two previously identified freshwater-adapting factors, prolactin (PRL) and prolactin-releasing peptide (PrRP), in silver sea bream was measured. The elevation of pituitary PRL and PrRP mRNA expression levels as seen in 6 ppt-adapted fish was abolished by surgical removal of the olfactory rosettes. The PRL and PrRP expression levels in fish adapted to 6 ppt were significantly lowered following olfactory rosette removal. On the other hand, hypothalamic PrRP mRNA expression in 6 ppt-adapted fish did not change. Specific signals for Na(+)-K(+)-ATPase but not CFTR mRNA expression were detected in the surface layers of olfactory epithelial cells by in situ hybridization. The mRNA abundance of CFTR and Na(+)-K(+)-ATPase α and β subunits remained unchanged in the olfactory rosette of silver sea bream adapted to 0, 6, 12, 33 and 50 ppt for 4 weeks and in fish abruptly transferred from 33 ppt to 6 ppt. Data obtained from the olfactory rosette removal experiments suggest a possible role of the olfactory system for maintaining PRL and PrRP expression during hyposmotic acclimation in sea bream.

As a preliminary step to elucidate the involvement of central neurotransmitters in the dip in voluntary feed intake during the perinatal period in cows, we investigated the effect of intracerebroventricular (ICV) administration of oxytocin, prolactin-releasing peptide (PrRP), or corticotropin-releasing hormone (CRH), the central functions of all of which undergo drastic changes during the perinatal period, on feed intake in steers. Thirty minutes before the onset of feeding, the treatment solution was injected into the third ventricle through an implanted cannula, and feeding-related behaviors were observed for 1 h after the onset of feeding. Neither ICV oxytocin (5 and 50 μg) nor PrRP (2 and 20 nmol) reduced feed intake (n=6). Twenty nanomoles of bovine CRH noticeably inhibited feeding behavior compared with vehicle treatment (n=5, p

Different neuropeptides, all containing a common carboxy-terminal RFamide sequence, have been characterized as ligands of the RFamide peptide receptor family. Currently, five subgroups have been characterized with respect to their N-terminal sequence and hence cover a wide pattern of biological functions, like important neuroendocrine, behavioral, sensory and automatic functions. The RFamide peptide receptor family represents a multiligand/multireceptor system, as many ligands are recognized by several GPCR subtypes within one family. Multireceptor systems are often susceptible to cross-reactions, as their numerous ligands are frequently closely related. In this review we focus on recent results in the field of structure-activity studies as well as mutational exploration of crucial positions within this GPCR system. The review summarizes the reported peptide analogs and recently developed small molecule ligands (agonists and antagonists) to highlight the current understanding of the pharmacophoric elements, required for affinity and activity at the receptor family. Furthermore, we address the biological functions of the ligands and give an overview on their involvement in physiological processes. We provide insights in the knowledge for the design of highly selective ligands for single receptor subtypes to minimize cross-talk and to eliminate effects from interactions within the GPCR system. This will support the drug development of members of the RFamide family.

Prolactin-releasing peptide (PrRP)-induced secretion of prolactin is not currently considered a primary function of PrRP, but the development of late-onset obesity in both PrRP and PrRP receptor knock-out mice indicates the unique anorexigenic properties of PrRP. In our recent study, we showed comparable potencies of peptides PrRP31 and PrRP20 in binding, intracellular signaling and prolactin release in pituitary RC-4B/C cells, and anorexigenic effect after central administration in fasted mice. In the present study, eight analogs of PrRP20 with C-terminal Phe amide modified with a bulky side chain or a halogenated aromatic ring revealed high binding potency, activation of mitogen-activated protein kinase/extracellular-regulated kinase (MAPK/ERK1/2) and cAMP response element-binding protein (CREB) and prolactin release in RC-4B/C cells. In particular, [PheNO(2)(31)]PrRP20, [1-Nal(31)]PrRP20, [2-Nal(31)]PrRP20 and [Tyr(31)]PrRP20 showed not only in vitro effects comparable or higher than those of PrRP20, but also a very significant and long-lasting anorexigenic effect after central administration in fasted mice. The design of potent and long-lasting PrRP analogs with selective anorexigenic properties promises to contribute to the study of food intake disorders.

We compared levels of prolactin-releasing peptide (PrRP) mRNA expression in mouse medulla at different stages of pregnancy and lactation. Mouse medulla samples were collected on days 6, 12 and 18 of pregnancy and lactation, respectively (six per group), for mRNA. Expression levels of PrRP mRNA in the medulla were measured by semi-quantitative RT-PCR, with glyceraldehyde 3-phosphate dehydrogenase as a control. PrRP mRNA was highly expressed in mouse medulla oblongata on day 6 of pregnancy (0.53), followed by 0.43 at lactation day 6, and 0.42 at lactation day 12. The expression level of PrRP mRNA on days 12 and 18 of pregnancy and day 18 of lactation shared the same value of 0.36. PrRP mRNA levels during lactation decreased slightly compared with that during pregnancy, but the differences between them were not significant. In summary, PrRP mRNA levels in the medulla oblongata remain relatively stable during pregnancy and lactation. This is evidence that medulla PrRP is not involved in the regulation of prolactin secretion.

Prolactin (PRL)-releasing peptides (PrRP) have been identified in mammals, amphibians and fishes, and these animals have several PrRPs that consist of different numbers of amino acids such as 20, 31 and 37. In the present study, we identified the cDNA encoding chicken prepro-PrRP, which can generate putative PrRPs, and cloned and sequenced it. Sequences for the coding region suggested the occurrence of putative PrRPs of 20, 31 and 32 amino acid residues. The amino acid sequence of chicken PrRP20 showed 100%, 95% and 70% identity with those of PrRP20s from teleosts, Xenopus laevis and mammals, respectively. On the other hand, chicken PrRP31 showed approximately 90% and 52-55% homology to PrRP31s of X. laevis and mammals, respectively. Native chicken PrRPs were purified from an acid extract of chick brain by a Sep-Pak C18 cartridge (Waters Corp., Milford, MA, USA), affinity chromatography using anti-salmon PrRP serum, and reverse phase high-performance liquid chromatography (HPLC) on an ODS-120T column (TOSOH, Tokyo, Japan). The existence of chicken PrRP20 and PrRP31 in the brain was demonstrated by comparing them with the synthetic peptides using HPLC and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. Chicken PrRP31 increased plasma PRL concentration when administered peripherally, whereas central administration decreased the concentration, suggesting that chicken PrRP31 has a distinct effect on PRL secretion between tissues in chicks. On the other hand, plasma growth hormone concentration decreased with both peripheral and central administrations of chicken PrRP31. Furthermore, central administration of chicken PrRP31 increased food intake in chicks compared to those observed in mammals and fishes. Taken together with the results indicating that chicken PrRP20 did not show endocrine and behavioural effects, we showed that chicken PrRP has a similar amino acid sequence to teleosts, Xenopus laevis and mammals, although the actions were variable among vertebrates.

Subsequent to the isolation of the first recognized RFamide neuropeptide, FMRFamide, from the clam, a large number of these peptides have been identified. There are now five groups of RFamide peptides identified in mammals. RFamide peptides show diversity with respect to their N-terminal sequence and biological activity. RFamide peptides have been implicated in a variety of roles, including energy metabolism, stress and pain modulation, as well as effects in the neuroendocrine and cardiovascular systems. In the present minireview, we focus on prolactin-releasing peptide (PrRP) and RFamide related peptide (RFRP) with respect to their roles in the control of energy metabolism and stress responses. Both food intake and stressful stimuli activate PrRP neurons. The administration of PrRP affects energy metabolism and neuroendocrine systems. PrRP-deficient or PrRP receptor-deficient mice show abnormal energy metabolism and/or stress responses. On the other hand, RFRP neurons are activated by stressful stimuli and the administration of RFRP induces neuroendocrine and behavioral stress responses. Taken together, these data suggests that PrRP and RFRP neurons play a role in the control of energy metabolism and/or stress responses.

In the modern world, improvements in human health can be offset by unhealthy lifestyle factors, including the deleterious consequences of stress and obesity. For energy homeostasis, humoral factors and neural afferents from the gastrointestinal tract, in combination with long-term nutritional signals, communicate information to the brain to regulate energy intake and expenditure. Energy homeostasis and stress interact with each other, and stress affects both food intake and energy expenditure. Prolactin-releasing peptide, synthesized in discrete neuronal populations in the hypothalamus and brainstem, plays an important role in integrating these responses. This review describes how prolactin-releasing peptide neurons receive information concerning both internal metabolic states and environmental conditions, and play a key role in energy homeostasis and stress responses.

Prolactin-releasing peptide (PrRP) is known to have functions in prolactin secretion, stress responses, cardiovascular regulation and food intake suppression. In addition, PrRP-knockout (KO) male mice show obesity from the age of 22 weeks and increase their food intake. The plasma concentrations of insulin, leptin, cholesterol and triglyceride are also increased in obese PrRP-KO mice. Fatty liver, hypertrophied white adipose tissue, decreased uncoupling protein 1 mRNA expression in brown adipose tissue and glucose intolerance were observed in obese PrRP-KO mice. As we reported previously, PrRP stimulates corticotrophin-releasing factor and regulates the hypothalamic-pituitary-adrenal axis. Therefore, it is speculated that PrRP regulates both food intake and metabolism as a stress responses. In the present study, we compared blood glucose and plasma glucocorticoid concentrations in PrRP-KO mice, and found that PrRP-KO mice showed higher concentrations of blood glucose and corticosterone compared to wild-type mice after restraint stress. By contrast, there were no difference in c-Fos expression in the paraventricular hypothalamic nucleus and plasma adrenocorticotrophic hormone concentrations between the two groups. These results suggest that the different stress responses as to glucocorticoid secretion may be induced by different responses of the adrenal glands between wild-type and PrRP-KO mice. Thus, we conclude that PrRP-KO mice become obese as a result of increased food intake, a change in metabolism, and abnormal stress responses as to glucose concentration and glucocorticoid secretion.

We report that satiation evokes neuronal activity in the ventral subdivision of the hypothalamic dorsomedial nucleus (DMH) as indicated by increased c-fos expression in response to refeeding in fasted rats. The absence of significant Fos activation following food presentation without consumption suggests that satiation but not craving for food elicits the activation of ventral DMH neurons. The distribution pattern of the prolactin-releasing peptide (PrRP)-immunoreactive (ir) network showed remarkable correlations with the distribution of activated neurons within the DMH. The PrRP-ir fibers and terminals were immunolabeled with tyrosine hydroxylase, suggesting their origin in lower brainstem instead of local, hypothalamic PrRP cells. PrRP-ir fibers arising from neurons of the nucleus of the solitary tract could be followed to the hypothalamus. Unilateral transections of these fibers at pontine and caudal hypothalamic levels resulted in a disappearance of the dense PrRP-ir network in the ventral DMH while PrRP immunoreactivity was increased in transected fibers caudal to the knife cuts as well as in perikarya of the nucleus of the solitary tract ipsilateral to the transections. In accord with these changes, the number of Fos-expressing neurons following refeeding declined in the ipsilateral but remained high in the contralateral DMH. However, the Fos response in the ventral DMH was not attenuated following chemical lesion (neonatal monosodium glutamate treatment) of the hypothalamic arcuate nucleus, another possible source of DMH inputs. These findings suggest that PrRP projections from the nucleus of the solitary tract contribute to the activation of ventral DMH neurons during refeeding, possibly by transferring information on cholecystokinin-mediated satiation.

Prolactin-releasing peptide (PrRP)-producing neurones are known to be localised mainly in the medulla oblongata and to act as a stress mediator in the central nervous system. In addition, central administration of PrRP elevates the arterial pressure and heart rate. However, the neuronal pathway of the cardiovascular effects of PrRP has not been revealed. In the present study, we demonstrate that PrRP-immunoreactive neurones projected to the locus coeruleus (LC) and the paraventricular nucleus (PVN) of the hypothalamus. The c-fos positive neurones among the noradrenaline cells in the LC, and the parvo- and magnocellular neurones in the PVN, were increased after central administration of PrRP. The arterial pressure and heart rate were both elevated after i.c.v. administration of PrRP. Previous studies have demonstrated that PrRP stimulated the neurones in the PVN [i.e. oxytocin-, vasopressin- and corticotrophin-releasing hormone (CRH)-producing neurones], which suggests that PrRP may induce its cardiovascular effect via arginine vasopressin (AVP) or CRH. Although the elevation of blood pressure and heart rate elicited by PrRP administration were not inhibited by an AVP antagonist, they were completely suppressed by treatment with a CRH antagonist. Thus, we conclude that PrRP stimulated CRH neurones in the PVN and that CRH might regulate the cardiovascular system via the sympathetic nervous system.

PRL and PrRP cDNAs have been isolated from euryhaline silver sea bream (Sparus sarba). The PRL cDNA consists of 1360bp encoding 212 amino acids whereas the PrRP cDNA contains 631bp encoding preproPrRP with 122 amino acids. The mature PrRP sequence within the preprohormone is identical to the PrRPs isolated from other fish species. PRL mRNA was uniquely expressed in sea bream pituitary but PrRP mRNA was expressed in a variety of organs and tissues including the intestines, olfactory rosette and various brain regions such as hypothalamus and pituitary. Expression levels of PRL and PrRP mRNA have been examined in sea bream adapted to different salinities (0, 6, 12, 33 and 50ppt). In the pituitary, both PRL and PrRP mRNA were significantly higher in fish adapted to low salinities (0 and 6ppt) and the expression profiles of both hormones closely paralleled each other. However, expression of hypothalamic PrRP was significantly higher in fish adapted to iso-osmotic salinity (12ppt) when pituitary PRL expression was low. The present study demonstrates, for the first time, a synchronized mRNA expression pattern between PRL and PrRP in fish pituitary but a disparity of mRNA expression levels between hypothalamic PrRP and pituitary PRL during salinity adaptation. These data suggest that PrRP may possibly act as a local modulator in pituitary rather than a hypothalamic factor for regulation of pituitary PRL expression in silver sea bream.

Two neuropeptides, neuropeptide B (NPB) and prolactin-releasing peptide (PrRP), have been suggested to play important roles in control of the hypothalamic-pituitary-adrenal (HPA) axis in rodents. The aim of the present study was to clarify the central actions of NPB or PrRP in sheep. Ovariectomized ewes were surgically implanted with a cannula directed to the lateral ventricle. They received intracerebroventricular (icv) administration of 400 mul of artificial cerebrospinal fluid, NPB (0.05, 0.5 or 5 nmol), PrRP (0.5, 5 or 50 nmol) or corticotropin-releasing hormone (CRH, 0.5 or 5 nmol) through the cannula, and blood samples were taken 30 and 0 min prior to and 15, 30, 60 and 90 min after the injection. Cortisol concentrations in plasma were determined by enzyme immunoassay. Administration of 0.5 nmol NPB resulted in a significant increase in the cortisol concentration compared with the vehicle control, whereas the cortisol concentration after lower or higher doses of NPB did not differ from the control value. Thus, an icv injection of NPB produced a bell-shaped dose-response of cortisol concentration. Administration of PrRP had no significant effect on the cortisol concentrations at any dose examined. Icv injection of CRH dose-dependently increased plasma cortisol concentrations. These results demonstrate that central NPB stimulates cortisol secretion, suggesting that this neuropeptide plays some roles in control of the HPA axis in sheep. On the other hand, unlike its role in rodents, PrRP is unlikely to be involved in control of the HPA axis in this species.

Domestic chickens are precocial and therefore have relatively well-developed processes at hatch. As a result, neonatal chicks grow well at hatch with no parental care. The regulation of food intake in animals, including domestic birds, is complicated. Just after hatching, neonatal chicks find their food by themselves and they can control their food intake. Recently, prolactin releasing peptide and gonadotropin-inhibitory hormone were confirmed as central orexigenic factors in the neonatal chick. Both peptides have a common structure as RFamide peptides. On the other hand, vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide, both belonging to the glucagon superfamily, were recognized as inhibitory. Broiler chicks have either a greater capability to acclimatize to novel environments, or a blunted hypothalamus-pituitary-adrenal axis compared with layer chicks. These differences are explained by higher melatonin concentrations in the pineal gland and other parts of the brain of broiler chicks since melatonin attenuates the stress response. Stressful behavior in chicks can be attenuated by neurotransmitters or by nutrients such as creatine, phosphatidylserine, L-serine and (-)-epigallocatechin gallate. It is suggested that the regulation of behavior is somewhat specific and can be attenuated by some manipulation in neonatal chicks.

The Prolactin-releasing Peptide (PrRP) is a 31-aminoacid peptide produced and secreted from the hypothalamus, and postulated to promote the prolactin release from the pituitary. However, the action of PrRP remain controversial, since it was described to have potency comparable enough to TRH, although there are many evidences that PrRP is less potent than TRH. Here we have studied the effects of PrRP alone or in combination with TRH in the prolactin levels of rat pituitary primary cell cultures in vitro and also in vivo prolactin responses in randomly cycling and estrogens-treated female rats. PrRP itself increased prolactin levels in vitro and in vivo, although in a magnitude several times lower than TRH. In vivo PrRP promotes an atypical non-peaking progressive and maintained prolactin increase. On the other hand, PrRP markedly increased the prolactin responses to TRH in vitro (10-30 fold increase) and in vivo (up to three-fold increase). In addition, FGF-2 and EGF, two important growth factors present in the pituitary, reduced the PrRP-induced prolactin increase in vitro. Taken together our results suggest that PrRP released from the hypothalamus may be relevant to modulate the circulating prolactin levels in the rat. © Humana Press Inc. 2007.

Immunohistochemical localization and ontogenic development of prolactin-releasing peptide (PrRP) in the brain of the ovoviviparous fish species Poecilia reticulata (guppy) were examined to gain a better understanding of this hormone in teleost fish. In adult guppies, PrRP-immunoreactive (ir) cell bodies were detected in the posterior part of the hypothalamus. In the pituitary, a small number of PrRP-ir fibers were observed adjacent to the prolactin cells, whereas numerous PrRP-ir fibers were detected not only in the hypothalamus but also widely throughout the brain. PrRP-ir cell bodies and prolactin cells were already detected on the birth day in the hypothalamus and pituitary, respectively. The number of PrRP-ir fibers in the brain increased as the fish developed. These results suggest that PrRP is involved in neuromodulation in the brain and that PrRP plays some physiological roles in the early development of the guppy.

Electroacupuncture (EA) in reproductive medicine has become established in Western medicine as a therapy over the last decade. EA performs a variety of neuromodulatory functions in the central nervous system (CNS). Prolactin-releasing peptide (PrRP) is a neuropeptide identified as an endogenous ligand for the orphan G protein-coupled receptor hGR3. PrRP can affect the function of hypothalamus-pituitary-ovary axis (HPOA) and hypothalamus-pituitary-adrenal axis (HPAA). The present study was undertaken to characterize the effect of EA on the expression of PrRP in the medulla oblongata in ovariectomized (OVX) rats by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). In addition, estrogen (E 2 ) levels were detected by radioimmunoassay (RIA). The results suggest that EA significantly increase the blood level of E 2 and the expression of PrRP in the medulla oblongata of OVX rats. The number of PrRP immunoreactive (ir) neurons was higher in the group ovariectomized with EA than that in the OVX group. The numbers of PrRP-ir neurons in intact (INT) and intact with EA (INT + EA) were not significantly different between the two groups. The expression of PrRP mRNA was increased in the OVX + EA group than that in the OVX group. These results suggest that the mechanism that EA improved reproductive disorders induced by ovariectomy in rats is related to the modulation of the blood E 2 level and the expression of PrRP in the medulla oblongata.

Immediately after hatching, neonatal chicks can find their food and control food intake, but the mechanisms for feeding are not completely understood. Food intake regulation in the brain involves neuropeptides. While some neuropeptides have effects similar to that observed in mammals, others have an opposite effect. Since the neonatal chick is precocial, the ability to obtain food is very important. However, the orexigenic factors are limited to neuropeptide Y, opioid, prolactin releasing peptide and gonadotropin-inhibitory hormone. The effects of anorexigenic peptides were well conserved in the neonatal chick. The higher food intake observed in broiler chicks can be explained by the lower expression of anorexigenic neuropeptides rather than the higher expression of orexigenic neuropeptides.

Amino acid sequences for identified prolactin (PRL)-releasing peptides (PrRPs) were conserved in mammals (90%) or teleost fishes (100%), but there were considerable differences between these classes in the sequence (65%) as well as in the role of PrRP. In species other than fishes and mammals, we have identified frog PrRP. The cDNA encoding Xenopus laevis prepro-PrRP, which can generate putative PrRPs, was cloned and sequenced. Sequences for the coding region showed higher identity with teleost PrRPs than mammalian homologues, but suggested the occurrence of putative PrRPs of 20 and 31 residues as in mammals. The amino acid sequence of PrRP20 was only one residue different from teleost PrRP20, but shared 70% identity with mammalian PrRP20s. In primary cultures of bullfrog (Rana catesbeiana) pituitary cells, Xenopus PrRPs increased prolactin concentrations in culture medium to 130-160% of the control, but PrRPs was much less potent than thyrotropin-releasing hormone (TRH) causing a three- to four-fold increase in prolactin concentrations. PrRP mRNA levels in the developing Xenopus brain peak in early prometamorphosis, different from prolactin levels. PrRP may not be a major prolactin-releasing factor (PRF), at least in adult frogs, as in mammals.

We have shown previously that prolactin-releasing peptide (PrRP) plays a role in the regulation of feeding and energy expenditure in rats. We hypothesize that PrRP may have a physiological action through its putative receptor, GPR10, to mediate the central anorexigenic effects of peripheral satiety factors. Here we examine the effects of PrRP and cholecystokinin (CCK) on feeding in mice, including PrRP receptor gene knockout animals (GPR10(-/-)). Intracerebroventricular administration of PrRP (1-4 nmol) inhibited feeding in C57B6/J mice under both fast-induced and nocturnal feeding conditions. In contrast to the observations made in wild-type mice, neither PrRP nor CCK reduced food intake in GRP10(-/-) mice. The reduction in feeding and the release of corticosterone induced by systemic injection of the stressor lipopolysaccharide was similar in both GPR10(+/+) and GPR10(-/-) mice. These findings suggest that PrRP, acting through GPR10, is involved in regulating food intake and may be a key intermediary in the central satiating actions of CCK.

Prolactin releasing peptide (PrRP) was originally reported to act in the anterior lobe of the pituitary gland to stimulate prolactin (PRL) release; however, numerous other pharmacologic actions of PrRP have been described. In the central nervous system PrRP inhibits food intake, stimulates sympathetic tone, and activates stress hormone secretion. Here, we confirm the presence of immunoreactive PrRP in a pheochromocytoma-derived cell line (PC-12) and the ability of exogenous PrRP to stimulate adenylyl cyclase activity in these cultures. Our novel findings are that PrRP stimulated PC-12 cell growth. Furthermore, a role for endogenous PrRP in PC-12 cell growth is suggested by our observations that antisense oligonucleotides and small interfering RNA molecules, which decrease peptide content in these cells, also decrease thymidine incorporation, suggesting an autocrine action of the peptide.

Prolactin-releasing peptide (PrRP) was named for its originally reported effects as a prolactin (PRL) secretagogue in mammals. Carassius RFamide (C-RFa) is an orthologous PRL secretagogue in fishes and a gene encoding a 20-amino acid peptide of identical sequence is present in the chicken. These facts suggest that C-RFa is a putative chicken PrRP. However, no information is available for the physiological effects of C-RFa in chickens. Therefore, in the present study, we compared the effect of intracerebroventricular (ICV) injection of C-RFa and mammalian PrRP (mPrRP) on feeding behavior and plasma PRL, growth hormone (GH), and corticosterone (CORT) concentrations. ICV injection of C-RFa did not affect feeding behavior of chicks while mPrRP was stimulatory. The injection of C-RFa also did not significantly affect plasma PRL, GH, and CORT concentrations. In contrast, ICV injection of mPrRP exerted similar effects to those reported in mammals by increasing plasma CORT and decreasing GH concentrations. Additionally, the peptide induced an unexpected inhibitory effect on plasma PRL concentrations. Overall, these data suggest that an as yet unidentified peptide that shares some functional similarities with mPrRP is present in birds, but that the physiological role of the avian 20-amino acid C-RFa peptide remains to be determined.

Prolactin (PRL)-releasing peptide (PrRP) is a strong candidate stimulator of pituitary PRL transcription and secretion in teleosts. However, the role in control of extrapituitary PRL expression is unclear even in mammals. To study the possible presence of PrRP–PRL axes not only in the brain-pituitary but also in peripheral organs, the expression patterns of PrRP, PRL and growth hormone (GH) were characterized in amphibious euryhaline mudskippers (Periophthalmus modestus). PrRP mRNA is abundantly expressed not only in the brain but also in the liver, gut and ovary, while less abundant expression was also detected in the skin and kidney. Corresponding to the distribution of PrRP mRNA, PRL mRNA was also detectable in these organs. During adaptation to different environments, the changes in mRNA levels of PrRP paralleled those in PRL in the brain-pituitary, liver and gut in an organ-specific manner. Brain PrRP mRNA and the pituitary PRL mRNA increased under freshwater and terrestrial conditions (PP

Although the G-protein coupled receptor GPR10 is highly expressed in the anterior pituitary, the action of its ligand prolactin-releasing peptide-31 (PrRP) in this tissue is controversial. The present study examined the acute effect of this peptide on prolactin secretion in perifused rat pituitary reaggregate cell cultures from adult male rats. PrRP readily and dose-dependently stimulated prolactin release at concentrations of 10 and 100 nM, although with a magnitude several times lower than that of thyrotropin-releasing hormone. Surprisingly, PrRP inhibited prolactin release at 0.1 and 1 nm in a pertussis toxin-sensitive manner. Inhibition was markedly favoured by long-term culture. Stimulation and inhibition were differentially affected by the presence of hormones during culture: dexamethasone favoured the inhibitory effect and decreased the magnitude of the stimulatory effect, while oestradiol and triiodothyronine strongly reduced stimulation, as well as inhibition. PrRP, even at 1 nm, counteracted the inhibition of prolactin release by dopamine. There was no effect of PrRP on growth hormone release in aggregates cultured either in the absence or presence of hormones. The present results confirm the prolactin-releasing capacity of PrRP at nanomolar doses and reveal a hitherto unrecognized inhibitory activity of this peptide. Furthermore, dopamine inhibition of prolactin release is antagonized by PrRP, irrespective of the PrRP dose.

SUMMARY 1. We have confirmed the Diabetes Mellitus OLETF type I (Dmo1) effect on hyperphagia, dyslipidaemia and obesity in the Otsuka Long-Evans Tokushima Fatty (OLETF) strain. The critical interval was narrowed down to 570 kb between D1Got258 to p162CA1 by segregation analyses using congenic lines. 2. Within the critical 570 kb region of the Dmo1 locus, we identified the G-protein-coupled receptor gene GPR10 as the causative gene mutated in the OLETF strain. The ATG translation initiation codon of GPR10 is changed into ATA in this strain and, so, is unavailable for the initiation of translation. 3. The GPR10 protein has a cognate ligand, namely prolactin-releasing peptide (PrRP). Centrally administered PrRP suppressed the food intake of congenic rats that have a Brown Norway derived Dmo1 region (i.e. with wild-type GPR10), but did not suppress that of the OLETF strain, indicating that GPR10 is without function and could explain hyperphagia in the OLETF strain. 4. Moreover, when restricted in food volume to the same level consumed by the congenic strain, OLETF rats showed few differences in the parameters of dyslipidaemia and obesity compared with congenic strains. 5. Taken together, these results demonstrate that the mutated GPR10 receptor is responsible for the hyperphagia leading to obesity and dyslipidaemia in the obese diabetic strain rat.

Prolactin (PRL) is an important regulator of multiple biological functions, and the control of PRL expression integrates a wide spectrum of molecules throughout vertebrates. PRL-releasing peptide (PrRP) seems to be an essential stimulator of PRL transcription and secretion in teleost pituitary and peripheral organs. In the amphibious euryhaline mudskipper, the localization of mRNA levels of PrRP and PRL as well as their regulation during acclimation to different environments are closely related. The presence of PrRP-PRL axes in the peripheral organs might suggest an ancient history of this axis prior to the evolution of the hypothalamus-pituitary, and it is possible that the PrRP is an original and primary regulator of PRL. In the euryhaline fishes, the permeability of gut of seawater-acclimated fish is generally greater than that of the freshwater (FW)-acclimated fish. The modification in the epithelial cell renewal system may play an important role in regulation of the permeability. PRL induces the cell proliferation during FW acclimation, whereas cortisol stimulates both cell proliferation and apoptosis. Indeed, a large proportion of the various actions of PRL seem to be associated directly or indirectly with cell proliferation and/or apoptosis, which might be a primary function of PRL.

Prolactin-releasing peptide (PrRP) is a novel peptide found in bovine hypothalamus as an endogenous ligand of an orphan G-protein-coupled receptor (hGR3). It is known that PrRP is widely distributed and plays roles in the central nervous system (CNS). In particular, PrRP acts as a neurotransmitter that mediates stress and activates the hypothalamo-pituitary-adrenal axis. On the other hand, only a few studies have so far been performed on PrRP in peripheral tissues. Among peripheral tissues, appreciable levels of PrRP are found only in the adrenal gland; however, the PrRP-producing cells in the adrenal gland have not been identified. In this study, we detected PrRP mRNA in the rat adrenal medulla. So, we tried to identify the PrRP-producing cells in primary culture cells of the adrenal medulla. We found immunopositive PrRP cells among the cultured cells from the adrenal gland, but not in the adrenal gland tissue, by means of immunocytochemistry. The PrRP immunopositive cells were double positive for tyrosine hydroxylase (TH) and for phenylethanolamine N-methyltransferase (PNMT), which indicates that PrRP may be produced in a part of the adrenaline cells in the adrenal gland. This is the first report that PrRP is produced in the adrenaline-containing cells of the adrenal gland.

Prolactin-releasing peptide (PrRP) is a recently discovered neuropeptide implicated in the central control of feeding behaviour and autonomic homeostasis. PrRP-containing neurones and PrRP receptor mRNA are found in abundance in the caudal portion of the nucleus tractus solitarius (NTS), an area which together with the dorsal motor nucleus of the vagus (DMV) comprises an integrated structure, the dorsal vagal complex (DVC) that processes visceral afferent signals from and provides parasympathetic motor innervation to the gastrointestinal tract. In this study, microinjection experiments were conducted in vivo in combination with whole-cell recording from neurones in rat medullary slices to test the hypothesis that PrRP plays a role in the central control of gastric motor function, acting within the DVC to modulate the activity of preganglionic vagal motor neurones that supply the stomach. Microinjection of PrRP (0.2 pmol (20 nl)(-1)) into the DMV at the level of the area postrema (+0.2 to +0.6 mm from the calamus scriptorius, CS) markedly stimulated gastric contractions and increased intragastric pressure (IGP). Conversely, administration of peptide into the DMV at sites caudal to the obex (0.0 to -0.3 mm from the CS) decreased IGP and reduced phasic contractions. These effects occurred without change in mean arterial pressure and were abolished by ipsilateral vagotomy, indicating mediation via a vagal-dependent mechanism(s). The pattern of gastric motor responses evoked by PrRP mimicked that produced by administration of L-glutamate at the same sites, and both the effects of L-glutamate and PrRP were abolished following local administration of NMDA and non-NMDA-type glutamate receptor antagonists. On the other hand, microinjection of PrRP into the medial or comissural nucleus of the solitary tract (mNTS and comNTS, respectively) resulted in less robust changes in IGP in a smaller percentage of animals, accompanied by marked alterations in arterial pressure. Superfusion of brain slices with PrRP (100-300 nm) produced a small depolarization and increased spontaneous firing in 10 of 30 retrogradely labelled gastric-projecting DMV neurones. The excitatory effects were blocked by administration of TTX (2 mum) or specific glutamate receptor antagonists, indicating that they resulted from interactions of PrRP at a presynaptic site. Congruent with this, PrRP increased the amplitude of excitatory postsynaptic currents (EPSCs, 154 +/- 33%, 12 of 25 neurones) evoked by electrical stimulation in mNTS or comNTS. In addition, administration of PrRP decreased the paired-pulse ratio of EPSCs evoked by two identical stimuli delivered 100 ms apart (from 0.95 +/- 0.08 to 0.71 +/- 0.11, P < 0.05), whereas it did not affect the amplitude of inward currents evoked by exogenous application of L-glutamate to the slice. The frequency, but not amplitude of spontaneous EPSCs and action potential-independent miniature EPSCs was also increased by administration of PrRP, suggesting that the peptide was acting at least in part at receptors on presynaptic nerve terminals to enhance glutamatergic transmission. In recordings obtained from a separate group of slices, we did not observe any direct effects of PrRP on spontaneous discharge or postsynaptic excitability in either mNTS or comNTS neurones (n = 31). These data indicate that PrRP may act within the DVC to regulate gastric motor function by modulating the efficacy of conventional excitatory synaptic inputs from the NTS onto gastric-projecting vagal motor neurones.

Prolactin (PRL)-releasing peptide (PrRP) is a new peptide present in the hypothalamus and in the circulation that may be involved in the regulation of feeding behavior. In the present experiment, we measured it in a well-known model of obesity, the Zucker rat. We also measured the reactivity of this animal in terms of food intake after the intraperitoneal (I.P.) or central injection of PrRP-13, a potent PrRP agonist. Plasma PrRP levels were 35% lower in obese fa/fa than in the lean rats (p