Effects of fibroblast growth factors and platelet-derived growth factor on food intake in rats

Metabolic Messengers: fibroblast growth factor 1

While fibroblast growth factor (FGF) 1 is expressed in multiple tissues, only adipose-derived and brain FGF1 have been implicated in the regulation of metabolism. Adipose FGF1 production is upregulated in response to dietary stress and is essential for adipose tissue plasticity in these conditions. Similarly, in the brain, FGF1 secretion into the ventricular space and the adjacent parenchyma is increased after a hypercaloric challenge induced by either feeding or glucose infusion. Potent anorexigenic properties have been ascribed to both peripheral and centrally injected FGF1. The ability of recombinant FGF1 and variants with reduced mitogenicity to lower glucose, suppress adipose lipolysis and promote insulin sensitization elevates their potential as candidates in the treatment of type 2 diabetes mellitus and associated comorbidities. Here, we provide an overview of the known metabolic functions of endogenous FGF1 and discuss its therapeutic potential, distinguishing between peripherally or centrally administered FGF1.

Effects of high fat diet and perinatal dioxin exposure on development of body size and expression of platelet-derived growth factor receptor β in the rat brain

Environmental exposure to dioxins, consumption of a high fat diet, and platelet-derived growth factor receptor β signaling in the brain affect feeding behavior, which is an important determinant of body growth. In the present study, we investigated the effects of prenatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin and high fact diet after weaning on body growth and expression of platelet-derived growth factor receptor β in the brain in rat pups. Subjects from the control and dioxin exposure groups were assigned to 1 of 3 different diet groups: standard diet, high fat diet in the juvenile period, or high fat diet in adulthood. Body weight gain rate in the juvenile high fat diet group and the length gain rate in the adult high fat diet group were greater than the corresponding values in the standard diet group only in male offspring, although the effects of dioxin exposure on growth were not significant. Consumption of a high fat diet decreased platelet-derived growth factor receptor β levels in the amygdala and hippocampus in both sexes compared to control groups, while 2,3,7,8-tetrachlorodibenzo-p-dioxin decreased platelet-derived growth factor receptor platelet-derived growth factor receptor β levels in the amygdala and striatum only in females receiving an high fat diet. Furthermore, platelet-derived growth factor receptor β levels in the hippocampus and platelet-derived growth factor receptor β striatum were inversely correlated with increases in body length, while changes in platelet-derived growth factor receptor β in the amygdala and nucleus accumbens were significantly correlated to body weight gain or body mass index. In conclusion, these findings suggest that these 2,3,7,8-tetrachlorodibenzo-p-dioxin and high fat diet-induced changes in body growth and feeding behaviors might be partially mediated by changes in brain platelet-derived growth factor receptor β levels.

FGF1 - a new weapon to control type 2 diabetes mellitus

A hypercaloric diet combined with a sedentary lifestyle is a major risk factor for the development of insulin resistance, type 2 diabetes mellitus (T2DM) and associated comorbidities. Standard treatment for T2DM begins with lifestyle modification, and includes oral medications and insulin therapy to compensate for progressive β-cell failure. However, current pharmaceutical options for T2DM are limited in that they do not maintain stable, durable glucose control without the need for treatment intensification. Furthermore, each medication is associated with adverse effects, which range from hypoglycaemia to weight gain or bone loss. Unexpectedly, fibroblast growth factor 1 (FGF1) and its low mitogenic variants have emerged as potentially safe candidates for restoring euglycaemia, without causing overt adverse effects. In particular, a single peripheral injection of FGF1 can lower glucose to normal levels within hours, without the risk of hypoglycaemia. Similarly, a single intracerebroventricular injection of FGF1 can induce long-lasting remission of the diabetic phenotype. This Review discusses potential mechanisms by which centrally administered FGF1 improves central glucose-sensing and peripheral glucose uptake in a sustained manner. Specifically, we explore the potential crosstalk between FGF1 and glucose-sensing neuronal circuits, hypothalamic neural stem cells and synaptic plasticity. Finally, we highlight therapeutic considerations of FGF1 and compare its metabolic actions with FGF15 (rodents), FGF19 (humans) and FGF21.

Cell type-specific transcriptomics of hypothalamic energy-sensing neuron responses to weight-loss

Molecular and cellular processes in neurons are critical for sensing and responding to energy deficit states, such as during weight-loss. Agouti related protein (AGRP)-expressing neurons are a key hypothalamic population that is activated during energy deficit and increases appetite and weight-gain. Cell type-specific transcriptomics can be used to identify pathways that counteract weight-loss, and here we report high-quality gene expression profiles of AGRP neurons from well-fed and food-deprived young adult mice. For comparison, we also analyzed Proopiomelanocortin (POMC)-expressing neurons, an intermingled population that suppresses appetite and body weight. We find that AGRP neurons are considerably more sensitive to energy deficit than POMC neurons. Furthermore, we identify cell type-specific pathways involving endoplasmic reticulum-stress, circadian signaling, ion channels, neuropeptides, and receptors. Combined with methods to validate and manipulate these pathways, this resource greatly expands molecular insight into neuronal regulation of body weight, and may be useful for devising therapeutic strategies for obesity and eating disorders.

DOI:http://dx.doi.org/10.7554/eLife.09800.001

Humans and other animals must get adequate nutrition in order to survive. As a result, the body has several systems that work side by side to maintain a healthy body weight and ensure that enough food gets eaten to provide the energy that the body needs. Problems with these systems can contribute towards obesity and other eating disorders.

Certain types of cells in the brain play important roles in controlling weight and appetite, although the genes and cellular mechanisms that underlie these abilities are not well understood. When an animal is deprived of food, so-called AGRP neurons produce molecules that increase appetite and make it easier to gain weight. These neurons also go through structural changes and increase their electrical activity during weight loss. Another group of cells, called the POMC neurons, becomes less active when an animal is deprived of energy.

Using a technique called cell type-specific transcriptomics, Henry, Sugino et al. have now revealed that the expression of hundreds of genes in AGRP and POMC neurons changes depending on whether mice are well fed or food deprived. Food deprivation also affects more genes in AGRP neurons than has been seen in other types of brain cell, and the AGRP neurons are also more sensitive to a change in food intake than POMC neurons.

In the future, this gene expression data and knowledge of the pathways affected by the genes could help researchers to develop new treatments for obesity and other disorders that affect appetite. Henry, Sugino et al. then mapped how these changes in gene expression trigger molecular “pathways” in the neurons that alter how the cells work. These affect many parts of the cells, including ion channels, transcription factors, receptors, and secreted proteins. In addition, food deprivation activated pathways in AGRP neurons that protect the cells from damage and death caused by elevated neuron activity and also triggered signaling pathways that increase body weight.

In the future, this gene expression data and knowledge of the pathways affected by the genes could help researchers to develop new treatments for obesity and other disorders that affect appetite.

DOI:http://dx.doi.org/10.7554/eLife.09800.002

Glucose intolerance induced by blockade of central FGF receptors is linked to an acute stress response

Objective

Central administration of ligands for fibroblast growth factor receptors (FGFRs) such as fibroblast growth factor-19 (FGF19) and FGF21 exert glucose-lowering effects in rodent models of obesity and type 2 diabetes (T2D). Conversely, intracerebroventricular (icv) administration of the non-selective FGFR inhibitor (FGFRi) PD173074 causes glucose intolerance, implying a physiological role for neuronal FGFR signaling in glucose homeostasis. The current studies were undertaken to identify neuroendocrine mechanisms underlying the glucose intolerance induced by pharmacological blockade of central FGFRs.

Methods

Overnight fasted, lean, male, Long-Evans rats received icv injections of either PD173074 or vehicle (Veh) followed 30 min later by performance of a frequently sampled intravenous glucose tolerance test (FSIGT). Minimal model analysis of glucose and insulin data from the FSIGT was performed to estimate insulin-dependent and insulin-independent components of glucose disposal. Plasma levels of lactate, glucagon, corticosterone, non-esterified free fatty acids (NEFA) and catecholamines were measured before and after intravenous (iv) glucose injection.

Results

Within 20 min of icv PD173074 injection (prior to the FSIGT), plasma levels of lactate, norepinephrine and epinephrine increased markedly, and each returned to baseline rapidly (within 8 min) following the iv glucose bolus. In contrast, plasma glucagon levels were not altered by icv FGFRi at either time point. Consistent with a previous report, glucose tolerance was impaired following icv PD173074 compared to Veh injection and, based on minimal model analysis of FSIGT data, this effect was attributable to reductions of both insulin secretion and the basal insulin effect (BIE), consistent with the inhibitory effect of catecholamines on pancreatic β-cell secretion. By comparison, there were no changes in glucose effectiveness at zero insulin (GEZI) or the insulin sensitivity index (S_I). To determine if iv glucose (given during the FSIGT) contributed to the rapid resolution of the sympathoadrenal response induced by icv FGFRi, we performed an additional study comparing groups that received iv saline or iv glucose 30 min after icv FGFRi. Our finding that elevated plasma catecholamine levels returned rapidly to baseline irrespective of whether rats subsequently received an iv bolus of saline or glucose indicates that the rapid reversal of sympathoadrenal activation following icv FGFRi was unrelated to the subsequent glucose bolus.

Conclusions

The effect of acute inhibition of central FGFR signaling to impair glucose tolerance likely involves a stress response associated with pronounced, but transient, sympathoadrenal activation and an associated reduction of insulin secretion. Whether this effect is a true consequence of FGFR blockade or involves an off-target effect of the FGFR inhibitor requires additional study.

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icv FGFR antagonist causes glucose intolerance in rats.

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This effect is associated with robust sympathoadrenal activation.

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The sympathoadrenal response is rapid in onset, but clears rapidly.

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Reduced insulin secretion contributes to FGFR inhibitor-induced glucose intolerance.

Fibroblast Growth Factor Signaling in Metabolic Regulation

The prevalence of obesity is a growing health problem. Obesity is strongly associated with several comorbidities, such as non-alcoholic fatty liver disease, certain cancers, insulin resistance, and type 2 diabetes, which all reduce life expectancy and life quality. Several drugs have been put forward in order to treat these diseases, but many of them have detrimental side effects. The unexpected role of the family of fibroblast growth factors in the regulation of energy metabolism provides new approaches to the treatment of metabolic diseases and offers a valuable tool to gain more insight into metabolic regulation. The known beneficial effects of FGF19 and FGF21 on metabolism, together with recently discovered similar effects of FGF1 suggest that FGFs and their derivatives carry great potential as novel therapeutics to treat metabolic conditions. To facilitate the development of new therapies with improved targeting and minimal side effects, a better understanding of the molecular mechanism of action of FGFs is needed. In this review, we will discuss what is currently known about the physiological roles of FGF signaling in tissues important for metabolic homeostasis. In addition, we will discuss current concepts regarding their pharmacological properties and effector tissues in the context of metabolic disease. Also, the recent progress in the development of FGF variants will be reviewed. Our goal is to provide a comprehensive overview of the current concepts and consensuses regarding FGF signaling in metabolic health and disease and to provide starting points for the development of FGF-based therapies against metabolic conditions.

Human FGF1 promoter is active in ependymal cells and dopaminergic neurons in the brains of F1B-GFP transgenic mice

FGF1 is involved in multiple biological functions and exhibits the importance in neuroprotective effects. Our previous studies indicated that, in human brain and retina, the FGF1B promoter controlled the expression of FGF1. However, the exact function and regulation of FGF1 in brain is still unclear. Here, we generated F1B-GFP transgenic mice that expressed the GFP reporter gene under the control of human FGF1B promoter (-540 to +31). Using the fresh brain sections of F1B-GFP transgenic mice, we found that the F1B-GFP cells expressed strong fluorescent signals in the ventricular system throughout the brain. The results of immunohistochemistry further showed that two distinct populations of F1B-GFP(+) cells existed in the brains of F1B-GFP transgenic mice. We demonstrated that one population of F1B-GFP(+) cells was ependymal cells, which distributed along the entire ventricles, and the second population of F1B-GFP(+) cells was neuronal cells that projected their long processes into multiple directions in specific areas of the brain. The double labeling of F1B-GFP(+) cells and tyrosine hydroxylase indicated that a subpopulation of F1B-GFP(+) -neuronal cells was dopaminergic neurons. Importantly, these F1B-GFP(+) /TH(+) cells were distributed in the main dopaminergic neuronal groups including hypothalamus, ventral tegmental area, and raphe nuclei. These results suggested that human FGF1B promoter was active in ependymal cells, neurons, and a portion of dopaminergic neurons. Thus, the F1B-GFP transgenic mice provide an animal model not only for studying FGF1 gene expression in vivo but also for understanding the role of FGF1 contribution in neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease.

In silico molecular comparisons of C. elegans and mammalian pharmacology identify distinct targets that regulate feeding

This paper takes advantage of similarities between the C. elegans and human pharmacopeia to identify and validate pharmacological targets that regulate C. elegans feeding rates.

Phenotypic screens can identify molecules that are at once penetrant and active on the integrated circuitry of a whole cell or organism. These advantages are offset by the need to identify the targets underlying the phenotypes. Additionally, logistical considerations limit screening for certain physiological and behavioral phenotypes to organisms such as zebrafish and C. elegans. This further raises the challenge of elucidating whether compound-target relationships found in model organisms are preserved in humans. To address these challenges we searched for compounds that affect feeding behavior in C. elegans and sought to identify their molecular mechanisms of action. Here, we applied predictive chemoinformatics to small molecules previously identified in a C. elegans phenotypic screen likely to be enriched for feeding regulatory compounds. Based on the predictions, 16 of these compounds were tested in vitro against 20 mammalian targets. Of these, nine were active, with affinities ranging from 9 nM to 10 µM. Four of these nine compounds were found to alter feeding. We then verified the in vitro findings in vivo through genetic knockdowns, the use of previously characterized compounds with high affinity for the four targets, and chemical genetic epistasis, which is the effect of combined chemical and genetic perturbations on a phenotype relative to that of each perturbation in isolation. Our findings reveal four previously unrecognized pathways that regulate feeding in C. elegans with strong parallels in mammals. Together, our study addresses three inherent challenges in phenotypic screening: the identification of the molecular targets from a phenotypic screen, the confirmation of the in vivo relevance of these targets, and the evolutionary conservation and relevance of these targets to their human orthologs.

Many beneficial pharmacological interventions were first discovered by observing the effects of perturbation of intact biological systems by small organic molecules without a priori knowledge of their targets. This forward pharmacological approach has the advantage of directly identifying new pharmacological agents that are active on complex biological processes. However, because of experimental feasibility, systematic application of this approach is generally limited to small animals such as the roundworm C. elegans and zebrafish, raising the question of whether use of these animals could identify compounds that act on ortholgous mammalian targets. A significant challenge in addressing this question is the determination of the molecular identities of the compounds' targets responsible for the desired phenotypic outcomes. Here we describe a computational approach for target identification based on structural similarities of newly identified compounds to known ligand interactions with mostly mammalian targets. For several of the compounds emerging from a C. elegans phenotypic screen, we predict and confirm mammalian targets using in vitro binding assays. Using genetic and pharmacological assays, we then demonstrate that a subset of these compounds alter C. elegans feeding rates through the C. elegans counterparts of the predicted mammalian targets.

Fibroblast growth factor-19 action in the brain reduces food intake and body weight and improves glucose tolerance in male rats

Fibroblast growth factor-19 (FGF19) and its rodent ortholog, FGF15, are hormones produced in the distal small intestine and secreted into the circulation after a meal. In addition to controlling the enterohepatic circulation of bile acids, FGF15/19 also regulates systemic lipid and glucose metabolism. In these experiments we investigated the hypothesis that, like other gut-derived postprandial hormones, FGF15/19 can act in the central nervous system to elicit its metabolic effects. We found that FGF-receptors 1 and 4 are present in rat hypothalamus, and that their expression was reduced by up to 60% in high-fat fed rats relative to lean controls. Consistent with a potential role for brain FGF15/19 signaling to regulate energy and glucose homeostasis, and with a previous report that intracerebroventricular (i.c.v.) administration of FGF19 increases energy expenditure, we report that acute i.c.v. FGF19 reduces 24-h food intake and body weight, and acutely improves glucose tolerance. Conversely, i.c.v. administration of an FGF-receptor inhibitor increases food intake and impairs glucose tolerance, suggesting a physiological role for brain FGF receptor signaling. Together, these findings identify the central nervous system as a potentially important target for the beneficial effects of FGF19 in the treatment of obesity and diabetes.

Monoclonal antibody antagonists of hypothalamic FGFR1 cause potent but reversible hypophagia and weight loss in rodents and monkeys

We generated three fully human monoclonal antibody antagonists against fibroblast growth factor receptor-1 (FGFR1) that potently block FGF signaling. We found that antibodies targeting the c-splice form of the receptor (FGFR1c) were anorexigenic when administered intraperitoneally three times weekly to mice, resulting in rapid, dose-dependent weight loss that plateaued (for doses>4 mg/kg) at 35-40% in 2 wk. Animals appeared healthy during treatment and regained their normal body weights and growth trajectories upon clearance of the antibodies from the bloodstream. Measurements of food consumption and energy expenditure indicated that the rapid weight loss was induced primarily by decreased energy intake and not by increased energy expenditure or cachexia and was accompanied by a greater reduction in fat than lean body mass. Hypophagia was not caused through malaise or illness, as indicated by absence of conditioned taste aversion, pica behavior, and decreased need-induced salt intake in rats. In support of a hypothalamic site of action, we found that, after intraperitoneal injections, anti-FGFR1c (IMC-A1), but not a control antibody, accumulated in the median eminence and adjacent mediobasal hypothalamus and that FGFR1c is enriched in the hypothalamus of mice. Furthermore, a single intracerebroventricular administration of 3 microg of IMC-A1 via the 3rd ventricle to mice caused an approximately 36% reduction in food intake and an approximately 6% weight loss within the ensuing 24 h. Our data suggest that FGF signaling through FGFR1c may play a physiological role in hypothalamic feeding circuit and that blocking it leads to hypophagia and weight loss.

Different mechanisms influencing permeation of PDGF-AA and PDGF-BB across the blood-brain barrier

Platelet-derived growth factor (PDGF) exerts neurotrophic and neuromodulatory effects on the CNS. To determine the permeability of the blood-brain barrier (BBB) to PDGF, we examined the blood-to-brain influx of radioactively labeled PDGF isoforms (PDGF-AA and PDGF-BB) by multiple-time regression analysis after intravenous (i.v.) injection and by in-situ perfusion, and also determined the physicochemical characteristics which affect their permeation across the BBB, including lipophilicity (measured by octanol:buffer partition coefficient), hydrogen bonding (measured by differences in octanol : buffer and isooctane : buffer partition coefficients), serum protein binding (measured by capillary electrophoresis), and stability of PDGF in blood 10 min after i.v. injection (measured by HPLC). After i.v. bolus injection, neither 125I-PDGF-AA nor 125I-PDGF-BB crossed the BBB, their influx rates being similar to that of the vascular marker 99mTc-albumin. 125I-PDGF-AA degraded significantly faster in blood than 125I-PDGF-BB. PDGF-BB, however, was completely bound to a large protein in serum whereas PDGF-AA showed no binding. Thus, degradation might explain the poor blood-to-brain influx of PDGF-AA, whereas protein binding could explain the poor influx of circulating PDGF-BB. Despite their lack of permeation in the intact mouse, both 125I-PDGF-AA and 125I-PDGF-BB entered the brain by perfusion in blood-free buffer, and the significantly faster rate of 125I-PDGF-AA than 125I-PDGF-BB may be explained by the lower hydrogen bonding potential of 125I-PDGF-AA. Thus, the lack of significant distribution of PDGF from blood to brain is not because of the intrinsic barrier function of the BBB but probably because of degradation and protein binding. Information from these studies could be useful in the design of analogues for delivery of PDGF as a therapeutic agent.

Impulse activity of individual sensorimotor cortex neurons in rabbits after microiontophoretic administration of antibodies against acid fibroblast growth factor

We studied the sensitivity of sensorimotor cortex neurons in rabbits to microiontophoretic administration of antibodies against acid fibroblast growth factor (anti-aFGF). Spontaneous activity and reaction of neurons to electrical stimulation of 'feeding centers' in the lateral hypothalamic area (LHA) were recorded. We analyzed impulse activity of 52 neurons in the sensorimotor cortex. It was shown that 14 neurons (25%) reacted to microiontophoresis of anti-aFGF (excitation and inhibition in 9 and 5 neurons, respectively). Microiontophoretic administration of anti-aFGF did not change the reaction (excitation or inhibition) of 27 neurons to electrical stimulation of LHA. Initially, 14 neurons did not response to LHA stimulation. After microiontophoretic administration of anti-aFGF, 6 of 14 neurons displayed pronounced reactions to electrical stimulation of LHA (excitation and inhibition in 2 and 4 neurons, respectively). These data suggest that aFGF plays an important physiological role in feeding motivations.

Expression of tenascin-C long isoforms is induced in the hypothalamus by FGF-1

Fibroblast growth factor (FGF)-1 modulates various brain functions, such as the hypothalamic control of feeding. In the rat, we examined the effect of intracerebroventricularly infused FGF-1 on the hypothalamic expression of tenascin-C, a selective mediator of neuron-glial interaction. In situ hybridization revealed little tenascin-C mRNA expression in control brains, but greatly increased expression in ependymal cells around the third ventricle in the FGF-1-infused rats. Reverse transcription-linked PCR analysis of hypothalamic mRNA revealed an FGF-1-induced expression not of the shortest isoform of tenascin-C, but of the long isoforms (with additional fibronectin type III-domain insertions). Quantitative analysis by real time PCR revealed that this induction was transient and dose-dependent. Specific modulation of hypothalamic neuron-glial interactions by tenascin-C may mediate FGF-1-induced feeding suppression.

Feeding suppression by fibroblast growth factor-1 is accompanied by selective induction of heat shock protein 27 in hypothalamic astrocytes

It has been suggested that fibroblast growth factor (FGF)-1 serves as a physiological satiety factor in the hypothalamus, although the molecular mechanism underlying such a function is poorly understood. To gain additional insight into this issue, we used a Sendai virus (SeV) gene expression system in rats to explore genes differentially expressed subsequent to expression of FGF-1. Using cDNA arrays, we determined that infusion of FGF-1/SeV into one lateral ventricle induced selective expression of heat shock protein (HSP) 27 in the hypothalamus. Whereas FGF-1 expression was restricted to the ependymal cell layer of the cerebral ventricles, HSP27 was more widely expressed in astrocytes residing in the surrounding periventricular region. Similarly, infusion of FGF-1 polypeptide into a lateral ventricle induced dose-dependent HSP27 expression in periventricular astrocytes surrounding the third ventricle, with maximum mRNA levels being attained 6 h after infusion. This induction of HSP27 was accompanied by a significant suppression of feeding behaviour. Interestingly, suppression of feeding caused by intracerebro ventricular infusion of ciliary neurotrophic factor was also accompanied by induction of HSP27 in periventricular astrocytes, but suppression of feeding caused by infusion of leptin was not. It therefore appears that suppression of feeding by FGF-1 is accompanied by selective induction of HSP27 expression in hypothalamic astrocytes surrounding the third ventricle, and that this response may be a key component of the mechanism by which appetite is regulated by FGF-1.

Fibroblast growth factor inhibits locomotor activity as well as feeding behavior of rats

The effects of acute and chronic intracerebroventricular (i.c.v.) administration of basic fibroblast growth factor (bFGF) on behavior were examined in free-feeding rats. An i.c.v. injection of bFGF induced behavioral changes, such as an increase in resting and decreases in grooming, moving, and food intake at a dose of 20 or 50 ng. These effects appeared at 4-5 h and lasted at least 11 h after the injection. These changes, as well as inhibition of body weight gain, were also found during a 6-day period of chronic i.c.v. infusion of bFGF at a dose of 20 ng/h. These results indicate that bFGF as both bolus i.c.v. injection and chronic i.c.v. infusion inhibits not only feeding behavior but also locomotor activity in rats. It is suggested that the inhibitory effect of bFGF on food intake may be in part ascribed to the suppression of behavior by bFGF.

Evidence that platelet-derived growth factor may be a novel endogenous pyrogen in the central nervous system

Platelet-derived growth factor (PDGF) exerts neurotrophic and neuromodulatory actions in the mammalian central nervous system (CNS). Like the cytokines, PDGF primarily signals through tyrosine phosphorylation-dependent pathways that activate multiple intracellular molecules including Janus family kinases. We previously showed that microinjection of PDGF-BB into the lateral ventricle induced a febrile response in rats that was reduced by pretreatment with Win 41662, a potent inhibitor of PDGF receptors (Pelá IR, Ferreira MES, Melo MCC, Silva CAA, and Valenzuela CF. Ann NY Acad Sci 856: 289-293, 1998). In this study, we further characterized the role of PDGF-BB in the febrile response in rats. Microinjection of PDGF-BB into the third ventricle produced a dose-dependent increase in colonic temperature that peaked 3-4 h postinjection. Win 41662 attenuated fever induced by intraperitoneal injection of bacterial lipopolysaccharide, suggesting that endogenous PDGF participates in the febrile response to this exogenous pyrogen. Importantly, febrile responses induced by tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 were unchanged by Win 41662. Both indomethacin and dexamethasone blocked the PDGF-BB-induced increase in colonic temperature, and, therefore, we postulate that PDGF-BB may act via prostaglandin- and/or inducible enzyme-dependent pathways. Thus our findings suggest that PDGF-BB is an endogenous CNS mediator of the febrile response in rats.

Localization of glucokinase-like immunoreactivity in the rat lower brain stem: for possible location of brain glucose-sensing mechanisms

Pancreatic glucokinase (GK) is considered an important element of the glucose-sensing unit in pancreatic beta-cells. It is possible that the brain uses similar glucose-sensing units, and we employed GK immunohistochemistry and confocal microscopy to examine the anatomical distribution of GK-like immunoreactivities in the rat brain. We found strong GK-like immunoreactivities in the ependymocytes, endothelial cells, and many serotonergic neurons. In the ependymocytes, the GK-like immunoreactivity was located in the cytoplasmic area, but not in the nucleus. The GK-positive ependymocytes were found to have glucose transporter-2 (GLUT2)-like immunoreactivities on the cilia. In addition, the ependymocytes had GLUT1-like immunoreactivity on the cilia and GLUT4-like immunoreactivity densely in the cytoplasmic area and slightly in the plasma membrane. In serotonergic neurons, GK-like immunoreactivity was found in the cytoplasm and their processes. The present results raise the possibility that these GK-like immunopositive cells comprise a part of a vast glucose-sensing mechanism in the brain.

Acidic fibroblast growth factor activates adrenomedullary secretion and sympathetic outflow in rats

Effects of exogenous acidic fibroblast growth factor (aFGF), which is increased in the brain by food intake, on the plasma levels of catecholamines and on sympathetic efferent outflow were examined in anesthetized rats. A guide cannula was inserted into the cerebral third ventricle, and a vascular indwelling catheter was inserted into the right atrium from the jugular vein. Plasma epinephrine (Epi) and norepinephrine (NE) increased markedly in a dose-dependent manner for up to 120 min after intracerebroventricular or intravenous administration of aFGF (6-667 fmol/rat). Concomitant increases occurred in the efferent activity in the sympathetic nerves supplying the adrenal, spleen, and interscapular brown adipose tissue after the above administrations of aFGF. Both intravenous and intracerebroventricular administration of 10 ng basic FGF (bFGF) also increased sympathetic adrenal efferent activity and plasma Epi and NE concentrations. However, the increases induced by 10 ng bFGF were smaller than those induced by 10 ng aFGF. Bilateral splanchnicotomy completely prevented the increases in Epi induced by intracerebroventricular or intravenous aFGF but had less effect on the increases in NE. Pretreatment with an antibody against corticotropin-releasing factor (CRF), given via the intracerebroventricular route, significantly attenuated the increases in Epi and NE evoked by intracerebroventricular or intravenous administration of aFGF. Hepatic vagotomy also greatly reduced the increases in both catecholamines and the increases in sympathetic efferent firing rates evoked by intravenous administration of aFGF. These findings indicate that 1) aFGF administered intracerebroventricularly activates adrenomedullary secretion and sympathetic outflow via CRF release and 2) aFGF injected intravenously also induces sympathoadrenomedullary activation via centrally released CRF. The idea is discussed that sympathetic activation induced either by endogenous aFGF after feeding or by exogenously administered aFGF may play roles both in energy expenditure after overeating and in the modulation of immune functions.

Acidic fibroblast growth factor activates hypothalamic-pituitary-adrenocortical axis in rats

Effects of acidic fibroblast growth factor (aFGF), an endogenous satiety substance, on the hypothalamic-pituitary-adrenocortical axis were examined under pentobarbital sodium anesthesia in rats. A guide cannula was inserted into the cerebral third ventricle and a vascular indwelling catheter was inserted into the right atrium from the jugular vein 2 wk and 3 days, respectively, before the experiment. A marked dose-dependent increase in plasma corticosterone was detected from 20 min to 2 h after intracerebroventricular administration of aFGF (1-10 ng). Significant increases in plasma adrenocorticotropic hormone (ACTH) were observed from 5 to 150 min after the intracerebroventricular administration of 10 ng aFGF. Significant dose-dependent increases in plasma corticosterone were also observed after intravenous injections of aFGF (1, 10, and 100 ng), together with increases in the plasma ACTH level. Pretreatment with antibody to corticotropin-releasing factor via the intracerebroventricular route abolished the increases in corticosterone induced by intracerebroventricularly administered aFGF, but not those induced by intravenous injection of aFGF. In adrenal glands perfused in situ with artificial medium, the corticosterone secretion rate increased slightly in response to 10(-9) M aFGF. These findings suggest that intracerebroventricular administration of aFGF activates the hypothalamic-pituitary-adrenal axis via corticotropin-releasing factor release in the brain, whereas peripheral administration of aFGF activates adrenocortical secretion mainly via a direct action on ACTH release.

Roles of platelet-derived growth factor in the developing and mature nervous systems

In spite of its association by history and name to platelets, platelet-derived growth factor (PDGF) exerts important actions in a myriad of tissues, including the nervous system. PDGF and PDGF receptors are widely expressed in neuronal and glial cells of many regions of both the central and peripheral nervous systems. In this topical review, the roles played by PDGF in the development and maintenance of the nervous system are discussed. We also discuss the modulatory effects of PDGF on synaptic transmission, its role in neoplastic and non-neoplastic conditions of the central nervous system, and the neuroprotective effects of this growth factor.

Regulation of aldose reductase expression in rat astrocytes in culture

Aldose reductase (AR) is known to be responsible for many side effects of diabetes. In the present work, we studied the effects of various extracellular signals on the regulation of the expression of AR in astrocytes in culture, by determining its enzymatic activity or its mRNA level. We found that basic fibroblast growth factor (bFGF), acidic fibroblast growth factor (aFGF), epidermal growth factor (EGF), and hypertonic NaCl were able to increase the expression of AR in astrocytes. A superinduction was found when bFGF was combined with hypertonicity. We also observed that AR activity was independent of glucose concentration in the culture medium. However, when the concentration of glucose in the culture medium was under 1 g/l, bFGF did not increase the activity of AR. Thus, when glucose is depleted, the regulation of AR expression by bFGF does not operate. In addition, AR does not seem to be involved in control of astrocyte proliferation, in contrast to the effects reported on other cell types. These results indicate that AR is expressed in astrocytes and that its expression is upregulated by hypertonicity but also by FGFs and EGF. This suggests that in these cells, AR elicits some regulatory functions.

Fibroblast growth factor decreases locomotor activity in rats

The spontaneous locomotor behavior of rats receiving subcutaneous administration of either acidic or basic fibroblast growth factors was recorded in an activity cage. We report that doses between 1 and 100 micrograms/kg significantly decreased the horizontal and vertical activity, as well as the exploratory and stereotypy behavior of the rats. These effects of fibroblast growth factors seem to be specific since (i) they were cancelled by protein hydrolysis and anti-fibroblast growth factor antibodies, (ii) they were unrelated to their hypotensive activity and (iii) they were not attributable to their high structural similarity with the cytokine interleukin-1. Thus fibroblast growth factors did not show any thermogenic activity, did not affect the hypothalamic output of corticotropin-releasing factor and did not change the plasma levels of corticosterone. Pretreatment of the rats with a specific inhibitor of brain nitric oxide synthase prevented the effects of fibroblast growth factors, suggesting the involvement of nitric oxide in these behavioral modifications. Our results contribute to the accumulating evidence describing non-mitogenic activities of fibroblast growth factors.

Immunohistochemical localization of glucose transporters (GLUT1 and GLUT3) in the rat hypothalamus

Immunohistochemical localization of the glucose transporters was studied in the rat hypothalamus by using a specific rabbit antiserum raised against either the isoform 1 (GLUT1) or the isoform 3 (GLUT3). Immunoreactive staining for GLUT1 was found in glia cells and capillaries, whereas positive staining for GLUT3 occurred mainly in neurons and partly in ependymal cells. Double immunostaining indicated that a small population of GLUT1-positive cells were reactive for glial fibrillary acidic protein, a marker for astrocytes. Another doubly stained section showed that GLUT1-positive glia cells were never stained with an OX42 antibody, a marker for microglia cells. Neurons staining positively for GLUT3, often large in cell size, were confined mainly in the lateral hypothalamic area and partly in the dorsomedial and periventricular hypothalamic nuclei. Possible significance of these two glucose transporters in the hypothalamus is briefly discussed.

Actions of acidic fibroblast growth factor fragments on food intake in rats

Acidic fibroblast growth factor (aFGF) has suppressive effects on food intake. In the present study, the effect of aFGF fragments on food intake were investigated in rats. Infusion of a carboxyl-terminal fragment of aFGF, aFGF-(114-140), did not affect food intake, whereas an amino-terminal fragment of aFGF, aFGF-(1-15), was significantly inhibitory. Other amino-terminal fragments, aFGF-(1-20), aFGF-(1-29) and aFGF-(9-29), did not affect food intake. However, [Ala16]aFGF-(1-29) and [Ser16]aFGF-(1-29) in which the cysteine residue at position 16 was replaced with alanine and serine, respectively, had significant suppressive effects on food intake. Infusion of a functional antagonist for FGF receptor, anti-FGFR-1 antibody, into the lateral hypothalamus (LHA) significantly increased food intake. The results suggest that: the amino-terminal portion of aFGF is active in food intake suppression; the replacement of cysteine residue by alanine or serine is important in some amino-terminal aFGF fragments; and the LHA is involved in feeding suppression actions by aFGF and some fragments.

Central action of basic fibroblast growth factor on ingestive behaviour in mice

Intracerebroventricular (ICV) infusion of basic fibroblast growth factor (FGF-2) at 50 ng/h for 5 days in male BALB/c mice suppressed the daily intakes of water and food (n = 4). Intakes were reduced on the second day, and were suppressed until the second day after stopping the infusion. The same infusion for 4 days had little effect on the high intakes of 0.3 M NaCl solution and water induced by prolonged ICV infusion of angiotensin II, or the daily food intake in these experiments (n = 7). However, the same infusion for 3-4 days reduced the increased intake of NaCl solution in Na-depleted mice (n = 8), reduced the increased water intake of water-restricted mice (n = 6 or n = 7), and reduced daily food intake in both experiments. Ventricular enlargement was noted in mice at the end of these experiments but, for reasons advanced, did not appear to account for the responses. The results indicate that FGF-2 may have an inhibitory role in these ingestive behaviours.

An amino-terminal fragment peptide of acidic fibroblast growth factor modulates synaptic transmission in rat hippocampal slices

Effects of acidic fibroblast growth factor (aFGF) fragments such as aminoterminal aFGF (1-15) and carboxyl-terminal aFGF (114-140) on synaptic transmission were investigated in rat hippocampal slices. Stimulation was applied to Schaffer collateral/commissural afferents, and evoked population spikes were recorded in the CA1 pyramidal cell layer. Continuous perfusion of slices with aFGF (1-15) slightly decreased the basal amplitude of population spikes and significantly increased the paired-pulse facilitation. When brief tetanic stimulation (7 pulses at 100 Hz) was applied 30 min after the perfusion of aFGF (1-15), aFGF (1-15)-treated slices enhanced the magnitude of short-term potentiation after the tetanus and facilitated a generation of long-term potentiation. These effects of aFGF (1-15) were dose-dependent. Perfusion of slices with aFGF (114-140) had no effect on the basal spike amplitude, paired-pulse facilitation, and short-term potentiation. Both aFGF (1-15) and aFGF (114-140) had no effect on the DNA synthesis-stimulating activity in BALB/c 3T3-L1 cells. The results suggest that aFGF (1-15), which is not involved in mitogenic activity, is implicated in a modulatory mechanism of synaptic plasticity.

Effects of fibroblast growth factors and related peptides on food intake by rats

The effects of acidic fibroblast growth factor (aFGF), basic FGF (bFGF), and related peptides, such as aFGF fragments, on food and water intake were investigated. Infusion of aFGF and bFGF into the third cerebral ventricle significantly suppressed food intake. The potency of aFGF was 1.5 that of bFGF in food intake inhibition. Both FGFs also suppressed water intake. Infusion of a carboxyl-terminal fragment of aFGF, aFGF-(114-140), did not affect food intake, whereas an amino-terminal fragment of aFGF, aFGF-(1-15), was significantly inhibitory. Other amino-terminal fragments, aFGF-(1-20) and aFGF-(1-29), did not affect food intake. However, [Ala16]aFGF-(1-29), in which the cysteine residue at position 16 was replaced with alanine, significantly suppressed food intake. Infusions of functional antagonists for FGFs, anti-aFGF, anti-bFGF, and anti-aFGF-(1-15) IgGs, into the lateral hypothalamus significantly increased food intake. The results suggest that: aFGF, bFGF, and some amino-terminal peptides of aFGF participate in the central regulation of food intake; the lateral hypothalamus is involved in their feeding suppression actions; and these peptides may function as physiologically relevant substances in the adult central nervous system, other than as neurotrophic factors.

Acidic fibroblast growth factor facilitates generation of long-term potentiation in rat hippocampal slices

In the present study, effects of acidic fibroblast growth factor (aFGF, 0.5-2.5 ng/ml) on synaptic transmission were investigated in rat hippocampal slices. Stimulation was applied to Schaffer collateral/commissural afferents and evoked spikes were recorded in CA1 pyramidal cell layer. Continuous perfusion of slices with aFGF slightly decreased the basal amplitude of the spikes and significantly increased the paired-pulse facilitation. When brief tetanic stimulation (7 impulses at 100 Hz) was applied 30 min after the perfusion of aFGF, aFGF-treated slices enhanced the magnitude of short-term potentiation after the tetanus and facilitated the generation of long-term potentiation. aFGF also enhanced post-tetanic potentiation directly after the tetanus. These effects of aFGF were dose-dependent. The enhancement of short-term potentiation and facilitation of the generation of long-term potentiation were not evident when aFGF was applied with or 10 min after the tetanus. The results suggest that aFGF is implicated in modulation of synaptic efficacy and can activate some mechanisms related to the generation of long-term potentiation.

Memory facilitation educed by food intake

Acidic fibroblast growth factor (aFGF) in rat CSF increased 1000 times in the 2-h period after food intake, or IP, or ICV glucose infusion. The ICV application of aFGF dose dependently depresses and anti-aFGF antibody facilitates food intake. aFGF is produced in the ependymal cells and released into the CSF in response to increased glucose in the CSF caused by food intake. Released aFGF diffused into the brain parenchyma and was taken up into neurons in the hypothalamus, hippocampus, amygdala, etc. IP injection of glucose 2 h before a task that combined acquisition with passive avoidance significantly increased retention of avoidance by mice tested 24 h later. In a Morris water maze task, IP glucose injection 2 h before a first trial block reduced time to find and climb onto a platform hidden just below the water surface. The glucose facilitation of these affective and spatial memory were abolished by pretreatment with anti-aFGF antibody applied ICV. Continuous ICV infusion of aFGF into rats also significantly increased the reliability of passive avoidance for several days. After food intake, centrally released aFGF reaches the hippocampus and facilitates memory; peripherally released cholecystokinin reaches the endings of the afferent vagal nerves in the portal vein and changes their activity, which modulates hippocampal activity, to lead to memory facilitation. This, however, is blocked by vagotomy below the diaphragm. The results indicate the importance of food intake, not only to maintain homeostasis, but also to prepare a readiness state for memory facilitation.