Ondansetron, a selective 5-HT3 receptor antagonist, reduces palatable food consumption in the nondeprived rat

Dietary Tryptophan Supplementation Alters Fat and Glucose Metabolism in a Low-Birthweight Piglet Model

Low birthweight (LBW) is associated with metabolic complications, such as glucose and lipid metabolism disturbances in early life. The objective of this study was to assess: (1) the effect of dietary tryptophan (Trp) on glucose and fat metabolism in an LBW piglet model, and (2) the role peripheral 5-hydroxytryptamine type 3 (5HT3) receptors in regulating the feeding behavior in LBW piglets fed with Trp-supplemented diets. Seven-day-old piglets were assigned to 4 treatments: normal birthweight-0%Trp (NBW-T0), LBW-0%Trp (LBW-T0), LBW-0.4%Trp (LBW-T0.4), and LBW-0.8%Trp (LBW-T0.8) for 3 weeks. Compared to LBW-T0, the blood glucose was decreased in LBW-T0.8 at 60 min following the meal test, and the triglycerides were lower in LBW-T0.4 and LBW-T0.8. Relative to LBW-T0, LBW-T0.8 had a lower transcript and protein abundance of hepatic glucose transporter-2, a higher mRNA abundance of glucokinase, and a lower transcript of phosphoenolpyruvate carboxykinase. LBW-T0.4 tended to have a lower protein abundance of sodium-glucose co-transporter 1 in the jejunum. In comparison with LBW-T0, LBW-T0.4 and LBW-T0.8 had a lower transcript of hepatic acetyl-CoA carboxylase, and LBW-T0.4 had a higher transcript of 3-hydroxyacyl-CoA dehydrogenase. Blocking 5-HT3 receptors with ondansetron reduced the feed intake in all groups, with a transient effect on LBW-T0, but more persistent effect on LBW-T0.8 and NBW-T0. In conclusion, Trp supplementation reduced the hepatic lipogenesis and gluconeogenesis, but increased the glycolysis in LBW piglets. Peripheral serotonin is likely involved in the regulation of feeding behavior, particularly in LBW piglets fed diets supplemented with a higher dose of Trp.

Contrasting effects of 5-HT3 receptor stimulation of the nucleus accumbens or ventral tegmentum on food intake in the rat

Although serotonin (5-HT) signaling is known to regulate food intake and energy homeostasis, the roles of the 5-HT₃ receptor in feeding processes have been elusive. 5-HT₃ receptors are found throughout mesolimbic circuitry that promote feeding not only in response to hunger, but also to the palatable and rewarding properties of food. These experiments examined if stimulation or blockade of the 5-HT₃ receptor of the nucleus accumbens (NAcc) or ventral tegmentum affected food intake in the rat in response to hunger or the presence of a palatable diet. Rats (N=6-9/group) received bilateral injections of the 5-HT₃ agonist m-chlorophenylbiguanide hydrochloride (mCPBG; at 0.0, 10.0, or 20.0μg/0.5μl/side) or the 5-HT₃ antagonist ondansetron hydrochloride (at 0.0, 1.0, 2.0, or 5.0μg/0.5μl/side) into either the NAcc or the ventral tegmentum. NAcc 5-HT₃ receptor stimulation significantly increased 2-h food intake in food-deprived animals offered rat chow and in a separate group of unrestricted rats offered a sweetened fat diet. In contrast to the feeding increase seen with NAcc treatments, stimulation of 5-HT₃ receptors of the ventral tegmentum significantly reduced food and water intake in food-restricted animals; reductions of intake in non-restricted rats offered the palatable diet did not approach significance. Blockade of the 5-HT₃ receptor had no effect on feeding in either brain region. These data support a functional role for serotonergic signaling in the mesolimbic pathway on motivated behavior, and demonstrate that 5-HT₃ receptors differentially modulate food consumption in a region-dependent manner.

Role of 5-HT3 receptor on food intake in fed and fasted mice

Background

Many studies have shown that 5-hydroxytryptamine (5-HT) receptor subtypes are involved in the regulation of feeding behavior. However, the relative contribution of 5-HT₃ receptor remains unclear. The present study was aimed to investigate the role of 5-HT₃ receptor in control of feeding behavior in fed and fasted mice.

Methodology/Principal Findings

Food intake and expression of c-Fos, tyrosine hydroxylase (TH), proopiomelanocortin (POMC) and 5-HT in the brain were examined after acute treatment with 5-HT₃ receptor agonist SR-57227 alone or in combination with 5-HT₃ receptor antagonist ondansetron. Food intake was significantly inhibited within 3 h after acute treatment with SR 57227 in fasted mice but not fed mice, and this inhibition was blocked by ondansetron. Immunohistochemical study revealed that fasting-induced c-Fos expression was further enhanced by SR 57227 in the brainstem and the hypothalamus, and this enhancement was also blocked by ondansetron. Furthermore, the fasting-induced downregulation of POMC expression in the hypothalamus and the TH expression in the brain stem was blocked by SR 57227 in the fasted mice, and this effect of SR 57227 was also antagonized by ondansetron.

Conclusion/Significance

Taken together, our findings suggest that the effect of SR 57227 on the control of feeding behavior in fasted mice may be, at least partially, related to the c-Fos expression in hypothalamus and brain stem, as well as POMC system in the hypothalamus and the TH system in the brain stem.

Review article: the role of gastric motility in the control of food intake

BACKGROUND

From a classical point of view, gastric motility acts to clear the stomach between meals, whereas postprandial motility acts to provide a reservoir for food, mixing and grinding the food and to assure a controlled flow of food to the intestines.

AIM

To summarise findings that support the role of gastric motility as a central mediator of hunger, satiation and satiety.

METHODS

A literature review using the search terms 'satiety', 'satiation' and 'food intake' was combined with specific terms corresponding to the sequence of events during and after food intake.

RESULTS

During food intake, when gastric emptying of especially solids is limited, gastric distension and gastric accommodation play an important function in the regulation of satiation. After food intake, when the stomach gradually empties, the role of gastric distension in the determination of appetite decreases and the focus will shift to gastric emptying and intestinal exposure of the nutrients. Finally, we have discussed the role of the empty stomach and the migrating motor complex in the regulation of hunger signals.

CONCLUSIONS

Our findings indicate that gastric motility is a key mediator of hunger, satiation and satiety. More specifically, gastric accommodation and gastric emptying play important roles in the regulation of gastric (dis)tension and intestinal exposure of nutrients and hence control satiation and satiety. Correlations between gastric accommodation, gastric emptying and body weight indicate that gastric motility can also play a role in the long-term regulation of body weight.

Action of ondansetron and CP-99,994 on cisplatin-induced emesis and locomotor activity in Suncus murinus (house musk shrew)

Species possessing the emetic reflex are useful for anti-emetic screening. Assessing the potential of novel drugs to simultaneously reduce nausea and emesis in animals is problematic, however. In the present studies, therefore, the behavioural repertoire of Suncus murinus in response to the emetic chemotherapeutic drug cisplatin was studied in an attempt to characterize behaviours (including spontaneous locomotor activity) that may be relevant to nausea status. Cisplatin at 30 mg/kg, intraperitoneal, induced a robust emetic response but did not induce novel behaviour and failed to affect spontaneous locomotor activity. Ondansetron at 3 mg/kg, subcutaneous, and CP-99,994 at 10 mg/kg, subcutaneous, reduced emesis by 98% and 40.7%, respectively. Both ondansetron and CP-99,994, however, were inactive in modifying spontaneous locomotor activity in either cisplatin-treated or normal animals. Results are discussed in relation to other animal models of nausea and emesis.

CCK and 5-HT act synergistically to suppress food intake through simultaneous activation of CCK-1 and 5-HT3 receptors

Cholecystokinin (CCK) and serotonin (5-HT) systems have been shown to cooperate interdependently in control of food intake. To assess mechanisms by which CCK and 5-HT systems interact in control of food intake we examined: (1) participation of CCK-1 and 5-HT3 receptors in 5-HT-induced suppression of sucrose intake; (2) the interaction between CCK and 5-HT in suppression of food intake; (3) the role of CCK-1 and 5-HT3 receptors in mediating this interaction. Intraperitoneal administration of 5-HT (0.25, 0.5 and 1.0 mg/kg) significantly reduced intake compared to control in a dose responsive fashion (r2=0.989). Suppression of food intake by 5-HT was significantly attenuated by prior treatment with the 5-HT3 receptor antagonist ondansetron at each 5-HT dose tested (P<0.05), while blockade of CCK-1 receptors by lorglumide had no effect on 5-HT-induced suppression of intake. Administration of CCK-8 (0.5 microg/kg) or 5-HT (0.5 mg/kg) alone significantly reduced sucrose intake by 22.9 and 22.2% respectively, compared to control (P<0.0001). Co-administration of CCK and 5-HT resulted in a synergistic suppression of intake leading to an overall 48.4% reduction in sucrose intake compared to saline (P<0.0001). Concomitant CCK-1 and 5-HT3 receptor blockade by lorglumide and ondansetron respectively, resulted in a complete reversal of the combined CCK and 5-HT-induced suppression of intake. Independent administration of lorglumide or ondansetron did not alter intake compared to control. These studies provide evidence that 5-HT causes suppression in food intake by acting at 5-HT3, not CCK-1 receptors. Furthermore, CCK and 5-HT interact to produce an enhanced suppression of food intake, an effect mediated through concomitant activation of CCK-1 and 5-HT3 receptors.

Serotonin-type 3 receptors mediate intestinal Polycose- and glucose-induced suppression of intake

Ondansetron, a selective serotonin-type 3 (5-HT(3)) receptor antagonist, was used to test the hypothesis that duodenal infusion of isosmotic solutions of Polycose or its hydrolytic product glucose suppressed intake through 5-HT(3) receptors. Polycose suppressed sucrose intake across both concentrations infused (132 mM, 7.6 +/- 0.6 ml; 263 mM, 2.3 +/- 0.5 ml), compared with intake under control conditions (12.6 +/- 0.3 ml, P <0.001). Pretreatment with 1.0 mg/kg ondansetron attenuated reduction of sucrose intake induced only by the highest concentration of Polycose (4.6 +/- 0.8 ml, P = 0.004). Dose-response testing revealed that suppression of food intake by 263 mM Polycose was equally attenuated by ondansetron administered at 1.0, 2.0, and 5.0 mg/kg but not when given at 0.125, 0.25, and 0.5 mg/kg. Acarbose, an alpha-glucosidase inhibitor, attenuated Polycose-induced suppression of food intake, and pretreatment with 1.0 mg/kg ondansetron had no further effect. Suppression of intake after 990 mM glucose but not mannitol infusion was attenuated by pretreatment with 1.0 mg/kg ondansetron. The competitive SGLT(1) inhibitor, phloridzin, had no effect on 60-min 990 mM glucose-induced suppression of intake or the ability of ondansetron to attenuate this suppression of intake. Conversely, glucose-induced suppression of intake was attenuated by phloridzin at earlier time points and further attenuated when rats were pretreated with 1.0 mg/kg ondansetron. Ondansetron administration alone had no effect on intake at any dose tested. We conclude that 5-HT(3) receptors participate in the inhibition of food intake by intraduodenal infusion of carbohydrate solutions through a posthydrolytic, preabsorptive mechanism.

Action of ondansetron and CP-99,994 to modify behavior and antagonize cisplatin-induced emesis in the ferret

The action of ondansetron (1 mg/kg, i.p.) and (+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine (CP-99,994; 10 mg/kg, i.p.) on spontaneous behavior and the emesis induced by cisplatin (10 mg/kg, i.p.) was studied in the ferret. Ondansetron was inactive to modify behavior, but CP-99,994 reduced spontaneous locomotor activity and lip licking by 48% (P<0.01) and 79% (P<0.01), respectively; CP-99,994 also abolished spontaneous burrowing activity (P<0.05). Treatment of animals with cisplatin induced an emetic response that was abolished by both ondansetron and CP-99,994 (P<0.01). However, cisplatin did not significantly modify other behavioral measures although animals that received CP-99,994, cisplatin, or CP-99,994 in combination with cisplatin exhibited more episodes of defecation than animals that received ondansetron (P<0.05). The action of CP-99,994 to modify behavior in this species is discussed in relation to animal models of nausea.

Cholecystokinin-induced satiety is mediated through interdependent cooperation of CCK-A and 5-HT3 receptors

Recent evidence supports a role for the serotonin-3 (5-HT3) receptors in the modulation of cholecystokinin (CCK)-induced satiation. Likewise, 5-HT's anorectic response has been linked to recruitment of peripheral CCK-A receptors. Evidence to date, however, does not elucidate whether there is a concomitant interaction between CCK-A and 5-HT3 receptors or whether each receptor functions independently in the negative feedback control of food intake elicited by CCK. In the present study, we used selective receptor antagonists to investigate the roles of CCK-A and 5-HT3 receptors in CCK-induced satiation. Intraperitoneal administration of CCK-8 reduced 30-min 15% sucrose intake in a dose-responsive manner. Prior treatment with ondansetron (1.0 mg/kg ip), a highly selective 5-HT3 receptor antagonist, attenuated CCK-induced suppression of food intake in a dose-responsive manner. Pretreatment with lorglumide (1.0 mg/kg ip), a selective CCK-A receptor antagonist, reversed CCK-induced inhibition of sucrose intake. Finally, simultaneous blockade of CCK-A and 5-HT3 receptors by lorglumide and ondansetron, as well as concomitant administration of the two antagonists with CCK, produced a significant synergistic increase in sucrose intake compared with intakes after administration of saline, CCK, or either antagonist alone. These findings support evidence that CCK-A and 5-HT3 receptors cooperate interdependently in control of short-term food intake. Most likely, this interconnection exists through a feed-forward parallel model arising from CCK-A and 5-HT3 receptors, where activation of one system engages the other to intensify the overall satiety signal.

Serotonin receptor blockade increases food intake and body weight after total gastrectomy in rats

BACKGROUND

Total gastrectomy often results in early satiety and loss of body weight. Serotonin inhibits food intake, and postprandial serotonin release is increased after total gastrectomy. Serotonin might contribute to early satiety and loss of body weight after total gastrectomy.

METHODS AND MATERIALS

Food intake and body weight were investigated with an automated recording system in gastrectomized rats 1-12 months postoperatively. Rats were treated with metergoline, a 5-hydroxytryptamine (5-HT)(1/2) receptor antagonist, two different 5-HT(3) receptor antagonists, a combination of metergoline and devazepide, a cholecystokinin (CCK) a receptor antagonist, or vehicle. In addition, metergoline or vehicle was applied continuously by an intraperitoneal osmotic minipump for 7, 28, or 84 days after total gastrectomy.

RESULTS

Metergoline treatment resulted in a dose-dependent increase in food intake in gastrectomized rats. 5-HT(3) receptor antagonist treatment had no effect, and devazepide in addition to metergoline did not further stimulate food intake. Metergoline increased food intake at 1, 3, and 6 months postoperatively by up to 45% (24-h cumulative food intake [FI], 6 months: vehicle 3.83 +/- 0.10, metergoline 5.52 +/- 0.15 g/100 g body weight (BW), P < 0.0001). Chronic metergoline treatment for 7, 28, or 84 days significantly increased food intake after total gastrectomy compared to vehicle treatment (FI 7 days: vehicle 30.83 +/- 0.71, metergoline 36.27 +/- 0.85 g/100 g BW; P < 0.0002; average weekly FI during 28 days; vehicle 31.23 +/- 0.22, metergoline 36.83 +/- 0.33 g/100 g BW, P < 0.0001; average weekly FI during 84 days: vehicle 33.02 +/- 0.59, metergoline 35.07 +/- 0.48 g/100g BW, P < 0.008), and there was a significant body weight increase compared to vehicle treatment (7 days: DeltaBW vehicle -0.7 +/- 1.2 g vs DeltaBW metergoline 9.0 +/- 2.1 g, P < 0.001; 28 days: DeltaBW vehicle 0.3 +/- 2.2 vs DeltaBW metergoline 13.0 +/- 2.3, P < 0.001; 84 days: DeltaBW vehicle 25.7 +/- 10.2 vs DeltaBW metergoline 49.5 +/- 7.2, P < 0.04). Treatment for 84 days resulted in a significant body weight gain, while vehicle treatment had no effect (vehicle: 438 +/- 11 g vs 464 +/- 12 g, P < 0.2, n.s.; metergoline: 448 +/- 9 g vs 498 +/- 10 g, P < 0.007).

CONCLUSIONS

Inhibition of food intake by serotonin might contribute to early satiety and loss of body weight after total gastrectomy.

Intestinal serotonin acts as paracrine substance to mediate pancreatic secretion stimulated by luminal factors

We recently demonstrated that luminal factors such as osmolality, disaccharides, and mechanical stimulation evoke pancreatic secretion by activating 5-hydroxytryptamine subtype 3 (serotonin-3, 5-HT3) receptors on mucosal vagal afferent fibers in the intestine. We hypothesized that 5-HT released by luminal stimuli acts as a paracrine substance, activating the mucosal vagal afferent fibers to stimulate pancreatic secretion. In the in vivo rat model, luminal perfusion of maltose or hypertonic NaCl increased 5-HT level threefold in intestinal effluent perfusates. Similar levels were observed after intraluminal 10(-5) M 5-HT perfusion. These treatments did not affect 5-HT blood levels. In a separate study, intraduodenal, but not intraileal, 5-HT application induced a dose-dependent increase in pancreatic protein secretion, which was not blocked by the CCK-A antagonist CR-1409. Acute vagotomy, methscopolamine, or perivagal or intestinal mucosal application of capsaicin abolished 5-HT-induced pancreatic secretion. In conscious rats, luminal 10(-5) M 5-HT administration produced a 90% increase in pancreatic protein output, which was markedly inhibited by the 5-HT3 antagonist ondansetron. In conclusion, luminal stimuli induce 5-HT release, which in turn activates 5-HT3 receptors on mucosal vagal afferent terminals. In this manner, 5-HT acts as a paracrine substance to stimulate pancreatic secretion via a vagal cholinergic pathway.

Ondansetron attenuates CCK induced satiety and c-fos labeling in the dorsal medulla

Serotonin 5-HT(3) antagonists have been suggested for treatment of several disorders involving altered gastrointestinal (GI) function. CCK also has well documented GI actions on both food intake and vago-vagal reflexes. To evaluate potential interactions, the effect of a 5-HT(3) antagonist, ondansetron, on exogenous CCK induced satiety and c-fos activation was determined. Ondansetron reduced both actions of CCK by approximately 50%. The reduction in c-fos was localized to a specific subregion of the dorsal medulla, suggesting that a distinct subpopulation of CCK receptive fibers are modulated by 5-HT(3) ligands. Treatments using 5-HT(3) antagonists also may affect endogenous CCK functions.

Lack of evidence for a role of serotonin in interleukin-1-induced hypophagia

Interleukin-1 (IL-1) administration depresses food intake in rodents. IL-1 is known to increase the metabolism of serotonin, which is known to affect feeding behavior. Thus, serotonin is an obvious candidate for a mediator of the hypophagic response to IL-1. Therefore, we tested the ability of serotonergic agonists and antagonists to alter the hypophagic responses to IL-1 and bacterial lipopolysaccharide (LPS). Hypophagia was assessed in ad lib-fed mice by recording the intake of sweetened milk in a 30-min period. Acute intraperitoneal administration of mouse IL-1beta reliably decreased milk intake. This hypophagic response was not affected by any of the serotonin antagonists tested, including 5-HT(1A) (WAY100135 and propranolol), 5-HT(1B) (GR127935), 5-HT(2) (ritanserin, ketanserin, SB206553, and RS102221), mixed 5-HT(1/2) (methysergide and metergoline), and 5-HT(3) (tropisetron) receptor antagonists. The 5-HT(1A) agonists (8-OH-DPAT and ipsapirone) and a 5-HT(1B) agonist (CGS12066B) known to decrease the activity of serotonergic neurons, also had no effect. Mice pretreated with 5,7-dihydroxytryptamine to deplete brain serotonin ate less, but, nevertheless, displayed similar hypophagic responses to mIL-1beta or LPS. The results suggest that serotonin is not involved in the decrease in short-term milk intake induced by mIL-1beta or LPS in mice that have been fed ad lib.

Comparison of effects of a range of 5-HT receptor modulators on consumption and preference for a sweetened ethanol solution in rats

This study assessed the effects of a range of serotonergic agents on preference for a slightly sweetened ethanol solution (10% ethanol, 3% glucose) in rats. A two-bottle, free-choice paradigm was used following induction of ethanol consumption. The model used provides a robust and reliable level of ethanol self-administration in normal laboratory rats. Ethanol consumption was significantly and selectively reduced by the 5-hydroxytryptamine-1A (5-HT1A) full agonist 8-OH-DPAT (0.3-1.0 mg/kg) and the 5-HT3 antagonist granisetron (0.1-1.0 mg/kg). Non-specific reductions in fluid consumption were induced by the 5-HT1B agonist RU 24969 (0.1-1.0mg/kg) and the 5-HT2 antagonist ritanserin (1.0-6.0 mg/kg). These studies thus confirm the potential for decreasing ethanol consumption and ethanol preference of 5-HT1A agonists and 5-HT3 antagonists, but failed to find any selective effects for agents acting at 5-HT1B or 5-HT2 receptors.

Effects of peripheral 5-HT2 and 5-HT3 receptor agonists on food intake in food-deprived and 2-deoxy-D-glucose-treated rats

Peripherally administered, the 5-HT2 receptor agonist, alpha-methyl-5-hydroxytryptamine (alpha-methyl-5-HT), significantly suppressed the food intake of food-deprived rats. alpha-Methyl-5-HT also inhibited 2-deoxy-D-glucose-induced hyperphagia in rats. The alpha-methyl-5-HT-induced hypophagia was antagonized by the 5-HT2A receptor antagonist, ketanserin. The alpha-methyl-5-HT-induced decrease in food intake of food-deprived rats was not inhibited by prior adrenodemedullation. The peripheral 5-HT3 receptor agonist, 2-methyl-5-HT, did not affect food intake in food-deprived or 2-deoxy-D-glucose-treated rats. These results suggest that the peripheral 5-HT2A receptor may participate in the regulation of food intake and that its hypophagic effects are not associated with its adrenaline-releasing effects from the adrenal gland. Lastly, the peripheral 5-HT3 receptor did not participate in feeding control.

A novel test of visual learning in the rat: effects of 8 -OH-DPAT and WAY-100579

The 5-HT(1A) agonist 8-OH-DPATand the 5-HT(3) antagonist WAY-100579 were tested in a novel computerized visual learning task. Since rats show substantial learning of new problems within each single session, drug effects on new learning could be compared within subjects. Both the reaction time (RT) and choice accuracy were measured. A dose of 0.3 mg/kg of 8-OH-DPAT lengthened the RTs while 0.1 mg/kg of 8-OH-DPAT and 0.1 mg/kg of WAY-100579 shortened the RTs. In the absence of drugs, accuracy was independent of the RT for RTs > 1.5 s. Therefore, in order to unconfound the drug effects on accuracy from motor effects, only responses with longer RTs were analysed. Both 0.3 and 0.1 mg/kg of 8-OH-DPAT and 0.1 mg/kg of WAY-100579 significantly impaired accuracy, though some learning was seen in all cases. These findings may have implications for animal models of Alzheimer's disease.

Temperature, food intake, and locomotor activity effects of a 5-HT3 receptor agonist and two 5-HT3 receptor antagonists in rats

This study investigated three physiologic functions known to be modulated by serotonin-temperature, food intake and locomotor activity - using the 5-HT3 receptor agonist, m-chlorophenylbiguanide (m-CPBG), and two 5-HT3 antagonists, MDL-72222 and ondansetron. m-CPBG produced dose-dependent elevations in rectal temperature. MDL-72222, which had no effects on temperature when given alone, significantly attenuated m-CPBG-induced hyperthermia. Food intake in food-deprived rats was reduced during the first hour by the highest dose of m-CPBG. Food intake was also dose-dependently reduced by MDL-72222; m-CPBG plus MDL-72222 led to greater reductions in food intake. Food intake in freely fed rats was unaffected by m-CPBG or MDL-72222. Locomotor activity was unaffected by m-CPBG, but was dose-dependently reduced by MDL-72222, an effect which may have contributed to its hypophagic effects. Ondansetron, used in ten-fold lower doses than MDL-72222, was inactive in all of these paradigms. These data: (1) provide some evidence for 5-HT3 receptor-mediated changes in temperature; (2) are in agreement with two prior studies which reported locomotor activity reductions following 5-HT3 antagonists; but (3) do not support an important role for 5-HT3 receptors in the regulation of food intake in rats.