Changes in the microstructure of feeding after administration of enterostatin into the paraventricular nucleus and the amygdala

Effects of dietary fat and enterostatin on dopamine and 5-hydroxytrytamine release from rat striatal slices

Studies have demonstrated defects of DA and 5HT neurotransmission in dietary fat induced obese animals. In the present study, we used a perfusion system to assay the release of DA and 5HT from striatal slices preloaded with [(3)H]-DA or [(3)H]-5HT. The release of both DA and 5HT from striatal slices of rats fed a high fat diet for 10 days, but not 3 days, was reduced when compared to striatal slices taken from rats fed a low fat diet. Enterostatin, an endogenous pentapeptide inhibits dietary fat intake when administered peripherally and centrally in animals. The central mechanism for the action of enterostatin is not yet determined even though several mechanisms have been suggested. We have shown that enterostatin enhanced [(3)H]-DA release, but not [(3)H]-5HT release from striatal slices of rats that had been adapted to high fat diet for 10 days. The enterostatin-induced increase in [(3)H]-DA release was blocked by nomifensine. Enterostatin did not alter [(3)H]-DA or [(3)H]-5HT release from striatal slices of rats adapted to high fat or low fat diet feeding for 3 days. These findings suggest that enterostatin may inhibit dietary fat intake by blocking dopamine reuptake transport to increase central striatal DA release from rats that have acquired diminished dopamine signal after an adaptive period of fat consumption.

Neuropeptide Y administration into the amygdala alters high fat food intake

The orexigenic effects of neuropeptide Y (NPY) are mediated through the hypothalamus, while the anxiolytic effects of NPY appear to be mediated through the amygdala. We hypothesized that intra-amygdalar administration of NPY might alter food preference without changing total food intake. Neuropeptide Y was administered into the central nucleus of the amygdala in both satiated and overnight-fasted rats, and intake and preference for a high fat diet (56%)/low carbohydrate (20%) diet or a low fat (10%)/high carbohydrate (66%) diet were measured. Intra-amygdalar NPY administration in satiated rats did not change total caloric intake, but it did produce a dose-dependent decrease in intake of and preference for high fat diet relative to low fat diet over 24 h. In overnight-fasted rats, intra-amygdalar NPY also decreased the intake and preference for a high fat diet relative to low fat diet over 24 h, without altering total caloric intake. Intra-amygdalar NPY administration did not produce conditioned taste aversions to a novel saccharin solution. These results suggest that amygdalar NPY may have a role in macronutrient selection, without altering total caloric intake.

Different metabolic responses to central and peripheral injection of enterostatin

Enterostatin, a pentapeptide cleaved from procolipase, suppresses fat intake after peripheral and central administration. Chronic treatment of rats with enterostatin decreases body weight and body fat. The effect was greater than could be accounted by the reduction in food intake alone. Hence, we have investigated the effect of enterostatin on energy metabolism. Male Sprague-Dawley rats adapted to a high-fat diet were implanted with lateral cerebral ventricular or amygdala cannulas. The metabolic effects were determined by indirect calorimetry. After habituation to the test cages, fasted rats were injected with either saline vehicle or enterostatin given either intraperitoneally (100 nmol) or intracerebroventricularly (1 nmol) or into specific brain regions [amygdala (0.01 nmol) or paraventricular nucleus (PVN) (0.1 nmol)]. Respiratory quotient (RQ) and energy expenditure were monitored over 2 h. Intraperitoneal enterostatin reduced RQ (saline: 0.81 +/- 0.02 vs. enterostatin: 0.76 +/- 0.01) and increased energy expenditure by 44%. Intracerebroventricular enterostatin increased the energy expenditure without any effects on RQ, whereas PVN enterostatin increased metabolic rate, while preventing the increase in RQ observed in the control animals. In contrast, neither RQ nor energy expenditure was altered after enterostatin was injected into the amygdala. Enterostatin activated AMP-activated protein kinase in primary cultures of human myocytes in a dose- and time-dependent manner and increased the rate of fatty acid beta-oxidation. These findings suggest that enterostatin regulates energy expenditure and substrate partitioning through both peripheral and central effects.

5-HT1B receptors modulate the feeding inhibitory effects of enterostatin

Serotonin (5-HT) is considered to play an important role in control of appetite. Enterostatin has been shown to alter 5-HT release in the brain, and non-specific 5-HT antagonists blocked the anorectic response to icv enterostatin. The aim of this study was to further identify which 5-HT receptor subtype mediates the enterostatin feeding behavior and whether this effect occurs due to action in the PVN. Wild-type and 5-HT2C receptor-/- (KO) mice and normal Sprague-Dawley rats were used in these experiments. All animals were fed a high fat diet. Enterostatin (120 nmol, i.p.) reduced the intake of high fat diet in 5-HT2C receptor mutant mice (saline 4.54 +/- 0.47 kcal vs. Ent 2.53 +/- 0.76 kcal) 1 h after injection. A selective 5-HT1B antagonist (GR55526, 40 mg/kg body weight, i.p.) blocked the enterostatin hypophagic effects in these KO mice. Rats were implanted with cannulas into the amygdala and the ipsilateral PVN. The 5-HT receptor antagonists metergoline (non-specific receptor subtypes 1 and 2), or ritanserin (selective 2C), or GR55562 (selective l B) was injected into the PVN prior to enterostatin (0.01 nmol) injection into the amygdala. Enterostatin reduced food intake (saline: 5.80 +/- 0.59 g vs. enterostatin 3.47 +/- 0.56 g, P < 0.05 at l h). Pretreatment with either metergoline (10 nmol) or GR55526 (10 nmol) but not ritanserin (10 nmol) into the PVN attenuated the anorectic response to amygdala enterostatin. The data imply that the enterostatin anorectic response may be modulated by 5-HT1B receptors and that a neuronal pathway from the amygdala to the PVN regulates the enterostatin response through activation of 5-HTlB receptors in PVN.

Amygdala enterostatin induces c-Fos expression in regions of hypothalamus that innervate the PVN

Enterostatin selectively inhibits the intake of the dietary fat after both central and peripheral administration. Our previous studies have shown that a central site of action is the central nucleus of amygdala. Serotonergic agonists administered into the paraventricular nucleus (PVN) inhibit fat intake and serotonergic antagonists block the feeding suppression induced by amygdala enterostatin, suggesting that there are functional connections between the PVN and amygdala that affect the feeding response to enterostatin. Our purpose was to identify the anatomic and functional projections from the amygdala to the PVN and hypothalamic area that are responsive to enterostatin, by using a retrograde tracer fluorogold (FG) and c-Fos expression. Rats were injected with fluorogold unilaterally into the PVN and a chronic amygdala cannula was implanted ipsilaterally. After 10 days recovery, rats were injected with either enterostatin (0.1 nmol) or saline vehicle (0.1 microl) into the amygdala and sacrificed 2 h later by cardiac perfusion under anesthesia. The brains were subjected to dual immunohistochemistry to visualize both FG and c-Fos-positive cells. FG/c-Fos double-labeled cells were found in forebrain regions including the PVN, amygdala, lateral hypothalamus (LH), ventral medial hypothalamus (VMH) and arcuate nucleus (ARC). The data provides the first anatomical evidence that enterostatin activates amygdala neurons that have functional and anatomic projections directly to the PVN and also activates neurons in the arcuate, LH and VMH, which innervate the PVN.

The F1-ATPase beta-subunit is the putative enterostatin receptor

It has been suggested that the F1-ATPase beta-subunit is the enterostatin receptor. We investigated the binding activity of the purified protein with a labeled antagonist, beta-casomorphin1-7, in the absence and presence of cold enterostatin. 125I-beta-casomorphin1-7 weakly binds to the rat F1-ATPase beta-subunit. Binding was promoted by low concentrations of cold enterostatin but displaced by higher concentrations. To study the relationship between binding activity and feeding behavior, we examined the ability of a number of enterostatin analogs to affect beta-casomorphin1-7 binding to the F1-ATPase beta-subunit. Peptides that suppressed food intake promoted beta-casomorphin1-7 binding whereas peptides that stimulated food intake or did not affect the food intake displaced beta-casomorphin1-7 binding. Surface plasmon resonance measurements show that the beta-subunit of F1-ATPase binds immobilized enterostatin with a dissociation constant of 150 nM, where no binding could be detected for the assembled F1-ATPase complex. Western blot analysis showed the F1-ATPase beta-subunit was present on plasma and mitochondrial membranes of rat liver and amygdala. The data provides evidence that the F1-ATPase beta-subunit is the enterostatin receptor and suggests that enterostatin and beta-casomorphin1-7 bind to distinct sites on the protein.

c-Kit mutant mouse behavioral phenotype: altered meal patterns and CCK sensitivity but normal daily food intake and body weight

The mouse W/Wv mutation of the c-Kit receptor causes extensive loss of gastrointestinal interstitial cells of Cajal and vagal intramuscular arrays (IMAs; one of the two putative mechanoreceptors in gastrointestinal smooth muscle). To characterize the behavioral phenotype of the c-Kit mouse and to evaluate the roles of these mechanoreceptors in controlling food intake, meal patterns and daily intakes of W/Wv mice and controls were examined using solid (20-mg pellets) and liquid (Isocal) maintenance diets. After the meal pattern experiments, CCK (0.5, 1, 2, 4, 8, and 16 microg/kg ip) was administered to examine the role of the interstitial cells and vagal IMA mechanoreceptors in relaying peripheral signals of satiety activated by CCK-A receptors, whereas the specificity of the response was assessed with the antagonist devazepide (300 microg/kg ip). On both diets, the W/Wv mice ate smaller meals for shorter durations, with a compensatory increase in meal number, resulting in daily intakes and body weights similar to the controls. After CCK injections, the mutant mice consistently suppressed intake more ( approximately 2x) in 30-min tests, regardless of the test diet (12.5% glucose, chow, pellets, and Isocal). The increased sensitivity of W/Wv mice to CCK reflected an increased potency of the hormone (c-Kit mouse ED50 = 2.4 microg/kg; control ED50 = 6.4 microg/kg) and a shift of the dose-response curve to the left. Devazepide blocked the CCK suppression of ingestion. These results indicate that the selective loss of the interstitial cells and IMAs disrupts short-term feeding of the W/Wv mice by inducing an earlier satiety, possibly by altering gastric accommodation and/or emptying, without affecting the long-term mechanisms controlling overall intake or body weight. The results also suggest that the reduction of interstitial cells and IMAs augments the sensitivity to or increases the efficiency of exogenous CCK.

Enterostatin inhibition of dietary fat intake is dependent on CCK-A receptors

Enterostatin, a pentapeptide released from the exocrine pancreas and gastrointestinal tract, selectively inhibits fat intake through activation of an afferent vagal signaling pathway. This study investigated if the effects of enterostatin were mediated through a CCK-dependent pathway. The series of in vivo and in vitro experiments included studies of 1) the feeding effect of peripheral enterostatin on Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors, 2) the effect of CCK-8S on the intake of a two-choice high-fat (HF)/low-fat (LF) diet, 3) the effects of peripheral or central injection of the CCK-A receptor antagonist lorglumide on the feeding inhibition induced by either central or peripheral enterostatin, and 4) the ability of enterostatin to displace CCK binding in a 3T3 cell line expressing CCK-A receptor gene and in rat brain sections. The results showed that OLTEF rats did not respond to enterostatin (300 microg/kg ip) in contrast to the 23% reduction in intake of HF diet in Long Evans Tokushima Otsuka (LETO) control rats. CCK (1 microg/kg ip) decreased the intake of the HF diet in a two-choice diet regime with a compensatory increase in intake of the LF diet. Peripheral injection of lorglumide (300 microg/kg) blocked the feeding inhibition induced by either near-celiac arterial or intracerebroventricular enterostatin, whereas intracerebroventricular lorglumide (5 nmol icv) only blocked the response to intracerebroventricular enterostatin but not to arterial enterostatin. Enterostatin did not bind on CCK-A receptors because neither enterostatin nor its analogs VPDPR and beta-casomorphin displaced [3H]L-364,718 from CCK-A receptors expressed in 3T3 cells or the binding of 125I-CCK-8S from rat brain sections. The data suggest that both the peripheral and central responses to enterostatin are mediated through or dependent on peripheral and central CCK-A receptors.

Uptake across the blood-brain barrier and tissue distribution of enterostatin after peripheral administration in rats

Enterostatin, the N-terminal activation pentapeptide of procolipase that is produced by the pancreas, reduces food intake from high-fat diet when injected either peripherally or centrally to rats. We investigated uptake across the blood-brain barrier (BBB) and tissue distribution of enterostatin by giving radioactive-labeled enterostatin (3H-VPDPR) intravenously. Low levels of 3H-VPDPR were detected in many areas of the brain, with greatest radioactivity in the frontal cortex, hippocampus and cerebellum. Radioactivity was found in the plasma and all tissues, with the highest amount detected in the pancreas.

Plasma enterostatin: identification and release in rats in response to a meal

OBJECTIVE

To discover a possible absorption and/or secretion of enterostatin into the circulating blood, as well as to compare the levels of circulating enterostatin after high-fat feeding and low-fat feeding.

RESEARCH METHODS AND PROCEDURES

Using a specific enzyme-linked immunosorbent assay, plasma enterostatin levels were determined after feeding a high-fat, a high-fat/-sucrose, or a low-fat meal to Sprague-Dawley rats deprived of food overnight.

RESULTS

The enterostatin levels were increased by all diets; the response to the high-fat and the high-fat/-sucrose meals was greater in magnitude and duration than that to the low-fat meal. In addition, enterostatin levels correlated with the intake of dietary fat. Plasma enterostatin levels after high-fat feeding were found to be similar to those after intravenous administration of exogenous enterostatin known to inhibit high-fat food intake. Gel chromatography of pooled postprandial plasma extracts followed by high-performance liquid chromatography analysis showed that plasma enterostatin was identical to synthetic enterostatin. Affinity cross-linking of plasma proteins with 125I-enterostatin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by autoradiography, revealed a single band with a molecular weight of about 66 kDa, indicating the presence of a potential enterostatin-binding protein in plasma.

DISCUSSION

The measurements of plasma enterostatin may be a sensitive indicator for the measurement of fat intake.

Comparative study of enterostatin sequence in five rat strains and enterostatin binding proteins in rat and chicken serum

Enterostatin, a pentapeptide derived from the precursor protein procolipase has been shown to inhibit dietary fat intake and to reduce body fat after chronic administration in rats. We repeat that the enterostatin amino acid sequence from the genomic DNA of 5 different rat strains is APGPR. 125I-APGPR bound to three proteins (300, 205 and 60 kDa) in rat serum and one 60 kDa protein in chicken serum. These serum binding proteins were also eluted by APGPR affinity chromatography. Western blot analysis of serum protein identified enterostatin-like immunoreactivity associated with the same molecular weight bands. Our results demonstrate the enterostatin sequence in rat is APGPR and suggest the presence of enterostatin binding proteins in rat and chicken serum.

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

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

Obesity: an epidemic in need of therapeutics

Recent developments in the quest for control of human obesity include the discovery of hormones, neuropeptides, receptors and transcription factors involved in feeding behavior, metabolic rate and adipocyte development. As a result, obesity research is quickly developing a level of sophistication that is expected to yield new treatment approaches. Even though newly approved clinical interventions are being tested in the market place, the obesity epidemic continues to face numerous unmet clinical needs and awaits the development and implementation of safe and highly effective pharmacotherapy.

Pharmacology of appetite suppression

Despite a rising worldwide epidemic of obesity there is currently only a very small number of anti-obesity drugs available to manage the problem. Large numbers of differing pharmacological agents reliably produce a reduction in food intake when administered acutely to animals, and when administered chronically they result in a significant decrease in body mass. Behavioural analysis of drug-induced anorexia in animals demonstrates that various compounds profoundly effect feeding behaviour in differing ways. This indicates the variety of mechanisms by which pharmacological agents can induce changes in food intake, body weight and eventually body composition. Some of the same drugs produce decreases in food intake and weight loss in humans. Some of these drugs do so by modifying the functioning of the appetite system as measured by subjective changes in feelings of hunger and fullness (indices of satiety). Such drugs can be considered as "appetite suppressants" with clinical potential as anti-obesity agents. Other drugs induce changes in food intake and body weight through various physiological mechanisms inducing feelings of nausea or even by side effect related malaise. Of the drugs considered suitable candidates for appetite suppressants are agents which act via peripherally satiety peptide systems (such as CCK, Bombesin/GRP, Enterostatin and GLP-1), or alter the CNS levels of various hypothalamic neuropeptides (NPY, Galanin, Orexin and Melanocortins) or levels of the key CNS appetite monoamine neurotransmitters such as serotonin (5-HT) and noradrenaline (NA). Recently, the hormone leptin has been regarded as a hormonal signal linking adipose tissue status with a number of key central nervous system circuits. The peptide itself stimulates leptin receptors and it links with POMC and MC-4 receptors. These receptors may also provide drug targets for the control of appetite. Any changes induced by a potential appetite suppressant should be considered in terms of the (i) psychological experience and behavioural expression of appetite, (ii) metabolism and peripheral physiology, and (iii) functioning of CNS neural pathways. In humans, modulation of appetite may involve changes in total caloric consumption, subjective changes in feelings of hunger and fullness, preferences for specific food items, and general macronutrient preferences. These may be expressed behaviourally as changes in meal patterns, snacking behaviour and food choice. Within the next 20 years it is certain that clinicians will have a new range of anti-obesity compounds available to choose from. Such novel compounds may act on a single component of the appetite system or target a combination of these components detailed in this review. Such compounds used in combination with lifestyle changes and dietary intervention may be useful in dealing with the rising world epidemic of obesity.

Centrally administered MTII affects feeding, drinking, temperature, and activity in the Sprague-Dawley rat

MTII, an agonist of melanocortinergic receptors, is a well-documented anorexigenic agent in rats. Many investigators have reported its effects on feeding without considering concurrent alterations in other behaviors. Accordingly, we performed studies to simultaneously measure nocturnal feeding, drinking, activity, and temperature of rats after intracerebroventricular (third ventricle) administration of a wide dose range of MTII (0.05-500 ng). We observed that MTII modulates these physiological parameters in a dose-dependent manner. Low doses of MTII (0.05 ng) caused reductions in feeding without alterations in body temperature, drinking, or activity. In contrast, hyperthermia and disrupted drinking patterns, along with food intake reductions, were evident at doses exceeding 50 ng. The fact that low doses altered only feeding, whereas higher doses affected a range of parameters, suggests that certain melanocortin-induced behavioral changes may be mediated by distinct populations of melanocortin receptors with varying affinities or that those changes seen at higher doses may be nonspecific in nature.

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

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