Cisplatin-induced conditioned taste aversion: attenuation by dexamethasone but not zacopride or GR38032F

Vagal sensory pathway for the gut-brain communication

The communication between the gut and brain is crucial for regulating various essential physiological functions, such as energy balance, fluid homeostasis, immune response, and emotion. The vagal sensory pathway plays an indispensable role in connecting the gut to the brain. Recently, our knowledge of the vagal gut-brain axis has significantly advanced through molecular genetic studies, revealing a diverse range of vagal sensory cell types with distinct peripheral innervations, response profiles, and physiological functions. Here, we review the current understanding of how vagal sensory neurons contribute to gut-brain communication. First, we highlight recent transcriptomic and genetic approaches that have characterized different vagal sensory cell types. Then, we focus on discussing how different subtypes encode numerous gut-derived signals and how their activities are translated into physiological and behavioral regulations. The emerging insights into the diverse cell types and functional properties of vagal sensory neurons have paved the way for exciting future directions, which may provide valuable insights into potential therapeutic targets for disorders involving gut-brain communication.

Conditioned nausea induced by cisplatin and emetine identified by a taste reactivity test in rats

No prior studies have shown that gaping reactions are produced with the avoidance of conditioned taste caused by cisplatin and emetine. Therefore, we tried to demonstrate it using a taste reactivity test in rats and found the gaping reactions induced when saccharin is readministered after gustatory conditioning that paired saccharin with cisplatin or emetine. Since conditioned gaping reactions indicate the aversion to saccharin taste and conditioned nausea, the present study suggest that the taste aversion is induced by cisplatin and emetine. It was also found that with intraperitoneal injections of emetine alone, gaping almost never occurs.

GDF-15 Neutralization Alleviates Platinum-Based Chemotherapy-Induced Emesis, Anorexia, and Weight Loss in Mice and Nonhuman Primates

Platinum-based cancer therapy is restricted by dose-limiting side effects and is associated with elevation of growth differentiation factor 15 (GDF-15). But whether this elevation contributes to such side effects has been unclear. Here, we explored the effects of GDF-15 blockade on platinum-based chemotherapy-induced emesis, anorexia, and weight loss in mice and/or nonhuman primate models. We found that circulating GDF-15 is higher in subjects with cancer receiving platinum-based chemotherapy and is positively associated with weight loss in colorectal cancer (NCT00609622). Further, chemotherapy agents associated with high clinical emetic score induce circulating GDF-15 and weight loss in mice. Platinum-based treatment-induced anorexia and weight loss are attenuated in GDF-15 knockout mice, while GDF-15 neutralization with the monoclonal antibody mAB1 improves survival. In nonhuman primates, mAB1 treatment attenuates anorexia and emesis. These results suggest that GDF-15 neutralization is a potential therapeutic approach to alleviate chemotherapy-induced side effects and improve the quality of life.

Ondansetron and promethazine have differential effects on hypothermic responses to lithium chloride administration and to provocative motion in rats

We recently reported that provocative motion (rotation in a home cage) causes hypothermic responses in rats, similar to the hypothermic responses associated with motion sickness in humans. Many stimuli inducing emesis in species with an emetic reflex also provoke hypothermia in the rat, therefore we hypothesized that a fall in body temperature may reflect a “nausea-like” state in these animals. As rats do not possess an emetic reflex, we employed a pharmacological approach to test this hypothesis. In humans, motion- and chemically-induced nausea have differential sensitivity to anti-emetics. We thus tested whether the hypothermia induced in rats by provocative motion (rotation at 0.7 Hz) and by the emetic LiCl (63 mg/kg i.p.) have a similar differential pharmacological sensitivity. Both provocations caused a comparable robust fall in core body temperature (−1.9 ± 0.3°C and −2.0 ± 0.2°C for chemical and motion provocations, respectively). LiCl⁻induced hypothermia was completely prevented by ondansetron (2mg/kg, i.p., a 5-HT₃ receptor antagonist that reduces cancer chemotherapy-induced nausea and vomiting), but was insensitive to promethazine (10 mg/kg, i.p., a predominantly histamine-H₁ and muscarinic receptor antagonist that is commonly used to treat motion sickness). Conversely, motion-induced hypothermia was unaffected by ondansetron but promethazine reduced the rate of temperature decline from 0.20 ± 0.02 to 0.11 ± 0.03°C/min (P < 0.05) with a trend to decrease the magnitude. We conclude that this differential pharmacological sensitivity of the hypothermic responses of vestibular vs. chemical etiology in rats mirrors the observations in other pre-clinical models and humans, and thus supports the idea that a “nausea-like” state in rodents is associated with disturbances in thermoregulation.

Evaluating the various phases of cisplatin-induced emesis in rats

Use of cisplatin as a chemotherapeutic agent causes acute and delayed emesis. Kaolin, saccharin solution and normal feed consumption have been evaluated as an index of cisplatin-induced emesis in rats; however, the most preferable of these methods for evaluating the various phases of emesis remains unclear. In the current study, kaolin, saccharin solution and normal feed consumption following cisplatin administration (6 mg/kg intraperitoneally) were simultaneously investigated in rats. Kaolin consumption increased significantly following cisplatin administration and was attenuated by granisetron administration 0-24 h following the injection. Saccharin solution consumption, however, decreased significantly 0-48 h following cisplatin administration, however, was attenuated by administration of granisetron within 0-24 h only. A reduced intake of normal feed was observed in the control group and was reversed by granisetron within the 0-72 h period. The present study indicates that kaolin consumption may be evaluated as an index of cisplatin-induced acute emesis and saccharin solution consumption may be evaluated as an index of delayed emesis, while normal feed consumption as an indicator of anorexia nervosa may be suitable to evaluate all phases of emesis and serve as an indicator of quality of life.

The role of area postrema neurons expressing H-channels in the induction mechanism of nausea and vomiting

The area postrema is one of the circumventricular organs, lacks a blood-brain barrier, and is well known as the chemoreceptor trigger zone for emesis. Area postrema neurons are sensitive to emetic chemical substances carried in the blood plasma. Our previous study demonstrated the presence of 3 types of neurons characterized by different ion channels expressed in each cell type, but the type or types of area postrema neurons involved in the induction of nausea and/or emesis have remained unclear. To clarify the role of the most populous cells, which express the hyperpolarization-activated cation channel (H-channel), in induction of nausea and/or emesis, we investigated the effects of ZD7288 (an H-channel inhibitor) on apomorphine-induced conditioned taste aversion (CTA) to saccharin and c-Fos expression in the area postrema. We found that ZD7288 inhibited the acquisition of CTA and reduced apomorphine-induced c-Fos expression in the area postrema, indicating the involvement of the cells expressing H-channels in the induction of nausea and/or emesis. Finally, we discuss the role of cells expressing H-channels in the mechanism of nausea and/or vomiting.

Pica as an adaptive response: Kaolin consumption helps rats recover from chemotherapy-induced illness

Clay consumption can occur during illness but there has been little work to understand why. To investigate whether consuming clay confers an advantage to the sick animal, we compared the recovery from illness of adult male rats with or without access to kaolin. Illness was induced by injection of 6 mg/kg, ip, cisplatin, a toxic chemotherapy agent, and recovery was assessed by changes in daily food intake, water intake, and body weight. Relative to saline-injected controls, cisplatin-injected rats reduced food and water intake and lost weight. However, those with access to kaolin ate more food and lost less body weight than did those without access to kaolin. Thus, clay consumption appeared beneficial in that it either protected the rats from illness or enhanced recovery and might prove useful as an adjunct therapy for other animals, including humans, experiencing visceral malaise.

Differential effects of dexamethasone, ondansetron and a tachykinin NK1 receptor antagonist (GR205171) on cisplatin-induced changes in behaviour, food intake, pica and gastric function in rats

This study aimed to dissect the mechanisms involved in malaise induced by the anti-cancer drug cisplatin by attempting to uncouple its effects on locomotor activity, arguably at least partly indicative of fatigue, from those effects indicative of emesis (pica, gastric stasis, reduced food intake) using pharmacological agents in the rat. Over 2 days cisplatin (6 mg/kg i.p.) reduced food intake, stimulated kaolin consumption, increased the wet weight of gastric contents and reduced locomotor activity. In animals treated with cisplatin: the 5-HT3 receptor antagonist ondansetron (1 mg/kg s.c. bd.) had no effect on either activity or weight of gastric contents but did increase food intake on day 1 (P<0.05) and the total over both days (27.6+/-1.8 vs. 19.9+/-2.3g, P<0.05), reducing kaolin consumption on day 2 (P<0.01) but not the total over both days; the NK1 receptor antagonist GR205171 (1 mg/kg s.c. bd.) was without effect on activity, but reduced the wet weight of gastric contents (P<0.05), increased food intake on day 2 (P<0.01) and total consumption over both days (28.1+/-1.7 g vs. 19.9+/-2.3 g; P<0.05) and reduced kaolin consumption on day 2 (P<0.05) but not over both days; dexamethasone (2 mg/kg s.c. bd.) blocked the cisplatin-induced reduction in activity on days 1 and 2 (P<0.01), reduced the wet weight of gastric contents by 43% (P<0.01), reduced kaolin consumption on both days (P<0.01) and arguably decreased the reduction in food intake caused by cisplatin. This study has revealed novel insights into the different spectra of activities of 5-HT3 and NK1 receptor antagonists and dexamethasone, which have implications for therapeutic strategies to alleviate the emetic, anorectic, dyspeptic and activity-reducing effects of anti-cancer chemotherapy.

Zingiber officinale exhibits behavioral radioprotection against radiation-induced CTA in a gender-specific manner

At the organismic level, exposure to radiation can produce taste aversion (CTA) learning and emesis, which have been proposed as behavioral endpoints that are mediated by harmful effects of radiations on peripheral systems, primarily the gastrointestinal system. Thus, the aim of the present investigation was to study the gastroprotective action of hydroalcoholic extract of zingiber rhizome (Zingiber officinale Rosc.) against radiation-induced conditioned taste aversion (CTA) in both male and female species of animals, for testing its potential as a behavioral radioprotector. Administration of zingiber extract 1 h before 2-Gy gamma-radiation was significantly effective in blocking the saccharin avoidance response, with 200 and 250 mg/kg b.wt. i.p., being the most effective doses for male and female rats, respectively. A comparison of the efficacy of zingiber extract with two antiemetic drugs, ondansteron and dexamethasone, revealed that the extract rendered comparable protection against radiation-induced CTA. Our experiments also confirmed the existence of sex dichotomy (i.e., the sex of animal greatly influenced response towards radiation exposure) in relation to behavioral responses (CTA) or differential metabolism. The observed gender variations were hypothesized to be a result of hormonal fluctuations and differences in pharmacological parameters in male and female rats. To correlate the mechanism of action, the free-radical-scavenging potential of zingiber extract to scavenge hydroxyl ion and nitric oxide was also tested, in cell-free system and a concentration of 1000 microg/ml, was found to be the most potent, which has been proposed as one the many activities assisting in its overall ability to modulate radiation-induced taste aversion. The results demonstrate that Z. officinale possesses antioxidant, radioprotective and neuromodulatory properties that can be effectively utilized for behavioral radioprotection and for efficiently mitigating radiation-induced CTA in both males and females species.

Granisetron attenuates exercise-induced conditioned taste aversion in the rat

A conditioned taste aversion (CTA) paradigm was used in the present study to investigate whether CTA produced by exercise could be attenuated by the 5-HT(3) receptor antagonist granisetron. Male Sprague-Dawley rats were randomly allocated to one of four groups (Ns=6) and were exposed to salty (0.128 M sodium chloride) or sour (0.00138M citric acid) solutions. Subjects were injected with either saline solution (1.0 ml, 0.9%) or granisetron (0.5mg/kg, IP) and were exposed to 30 min of forced wheel running exercise (70 revolutions/30min) 10 min after injection. Exercise induced CTA to both the salty (3.7 ml intake) and sour-flaroured (3.1ml intake) solutions as compared with no exercise (intake 14.0 and 13.7 ml), and administration of granisetron significantly attenuated the exercise-induced CTA to the salty- and sour-flavoured solutions.

Differential action of ondansetron and dexamethasone to modify cisplatin-induced acute and delayed kaolin consumption ("pica") in rats

The ability of cisplatin to induce acute (0-24 h) and delayed (24-48 and 48-72 h) phases of kaolin ingestion (pica) was investigated in the rat. Cisplatin 3 mg/kg, i.p., induced kaolin consumption during the 0-24- (P<0.001) and 48-72-h (P<0.05) periods that was antagonised by dexamethasone 1 mg/kg, i.p., administered every 12 h alone or in combination with ondansetron 2 mg/kg, i.p., administered every 12 h (P<0.05). As a single treatment, ondansetron 2 mg/kg, i.p., administered every 12 h potentiated cisplatin-induced kaolin consumption by 41% (P<0.05) during the 0-24-h period but had no action to modify the delayed response (P>0.05). Dexamethasone 1 mg/kg, i.p., administered every 12 h and cisplatin 3 and 6 mg/kg, i.p., but not ondansetron 2 mg/kg, i.p., administered every 12 h (P>0.05) reduced food consumption and decreased rat weight. The highest dose of cisplatin 6 mg/kg, i.p., induced acute (P<0.001) but not delayed kaolin ingestion (P>0.05). The action of cisplatin to induce acute and delayed pica is complicated and may be affected by drugs that modify appetite.

GR205171 blocks apomorphine and amphetamine-induced conditioned taste aversions

The tachykinin NK1 receptor antagonist, GR205171 ([2-methoxy-5-(5-trifluoromethyl-tetrazol-1-yl)-benzyl]-(2S-phenyl -piperidin-3S-yl)-amine), is a potent inhibitor of emesis induced by a wide variety of emetogens. This is in contrast to 5-HT3 (5-hydroxytryptamine3) receptor antagonists, such as ondansetron, which have a more restricted antiemetic profile. The present study evaluated the efficacy of GR205171, in comparison with ondansetron to block the acquisition of a conditioned taste aversion induced by either apomorphine (0.25 mg kg(-1) s.c.) or by amphetamine (0.5 mg kg(-1) s.c.) in rats. Pretreatment with GR205171 (0.1-1.0 mg kg(-1) s.c.) and ondansetron (0.001-0.1 mg kg(-1) s.c.) produced a dose-dependent blockade of conditioned taste aversions evoked by apomorphine. In contrast, the acquisition of conditioned taste aversions induced by amphetamine was inhibited by GR205171 (0.3-0.5 mg kg(-1) s.c.), but only attenuated by ondansetron (0.001-0.1 mg kg(-1) s.c.). These results suggest that tachykinin NK1 receptor antagonists may have potential in the treatment of drug-induced conditioned aversive behaviour and nausea.

5-HT3 receptors are not involved in conditioned taste aversions induced by 5-hydroxytryptamine, ipecacuanha or cisplatin

We have used the rat to examine the involvement of the 5-HT3 receptor in the mechanism(s) of conditioned taste aversion induced by 5-hydroxytryptamine (5-HT) and selected emetic drugs. 5-HT, ipecacuanha and cisplatin all induced conditioned taste aversion at doses known to induce emesis in other species but the responses were resistant to treatment with the 5-HT3 receptor antagonists ondansetron and granisetron. Further, m-chlorophenylbiguanide, a selective and potent 5-HT3 receptor agonist, failed to induce a conditioned taste aversion. The data provide strong evidence that the 5-HT3 receptor is not involved in conditioned taste aversion mechanisms in the rat. Results are discussed in terms of the usefulness of the rat conditioned taste aversion paradigm to anti-emetic research.

Discriminative stimulus properties of lithium chloride in rats

1. Adult male rats were trained to discriminate between an injection of lithium chloride (56 or 75 mg/kg) and saline in a two-lever operant chamber during a 20-minute session. 2. On training days, responding on the designated lever was reinforced under a fixed-ratio 20 (FR 20) schedule of food presentation, whereas responding on the other level had no programmed consequences. 3. Generalization testing with LiCl (10-100 mg/kg) was conducted after each subject reached a criterion of nine of ten sessions where 95% of overall responding occurred on the designated lever, and fewer than twenty responses were made on the other lever before presentation of the first reinforcer. 4. Substituting both lower and higher doses produced decreases in responding on the LiCl-appropriate lever while only higher doses decreased overall response rate. 5. Following generalization tests, animals were divided into two groups and varying doses of LiCl were given in combination with intraperitoneal injections of either dexamethasone (1 and 3.2 mg/kg) or ondansetron (0.32 and 1 mg/kg). 6. At doses that had little or no effect alone, neither ondansetron nor dexamethasone pretreatment blocked the discriminative stimulus properties of LiCl. 7. This research shows that LiCl can act as a highly discriminable stimulus in an operant drug-discrimination paradigm and suggests that the stimulus properties of LiCl do not derive from either direct activation of serotonin type-3 receptors or release of adrenocorticotropic hormone.

5HT3 receptor antagonists do not block nicotine induced hyperactivity in rats

The effects of 5-HT3 receptor antagonists (ondansetron 0.1 mg kg-1 SC 30 min; bemesetron 0.03 mg kg-1 SC 45 min) on nicotine-induced increases in locomotor activity were measured in male Sprague-Dawley rats. Intermittent daily injections of nicotine (0.3-1.2 mg kg-1 SC 30 min) resulted in increased locomotor activity as measured by photocell counts. The effect of nicotine was not affected by administration of the 5-HT3 receptor antagonists at doses that are reported to block nicotine- and morphine-induced place-preference conditioning. Neither of the 5-HT3 receptor antagonists tested affected activity counts in vehicle treated animals. Nicotine-induced hyperactivity was blocked by the dopamine antagonist haloperidol (0.03 mg kg-1 SC 2 h) and by the nicotinic antagonist mecamylamine (1 mg kg-1 SC 1 min). The effects of a range of doses (0-1 mg kg-1) of the 5-HT3 receptor antagonists ondansetron, bemesetron, granisetron and tropisetron on hyperactivity induced by 0.6 mg kg-1 nicotine were then assessed. Only tropisetron at 1 mg kg-1 attenuated nicotine-induced hyperactivity. To demonstrate the efficacy of the present range of doses of the 5-HT3 receptor antagonists in this study, conditioned taste aversion experiments were conducted. Ondansetron (0.1 mg kg-1) failed to attenuate a conditioned taste aversion to saccharin induced by nicotine (0.6 mg kg-1), but did induce a reduction in saccharin preference in choice tests following three saccharin-ondansetron pairings.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of food aversions in cancer patients during treatment

Food aversions are a common complication of cancer treatment. This study evaluated an approach for blocking the formation of aversions to dietary items in 209 cancer patients treated with chemo- and/or radiotherapy. Patients were exposed to a sensory stimulus (fruit beverage, halava, odor) before initial treatments to provide a target for aversion formation, thereby sparing dietary items. Patients who developed an aversion to the "scapegoat" stimulus experienced a statistically significant 30% reduction in dietary aversion formation relative to patients without a scapegoat aversion or those not exposed to the scapegoat. The most effective scapegoat was the beverage, probably because it was consumed in greatest quantity. Exposure of patients to a "scapegoat" food or beverage just before chemo- and, probably, radiotherapy can markedly reduce the incidence of treatment-related aversions to foods in the patients' customary diet.

Feeding behavior of grazing ruminants experiencing stress

The mechanisms underlying diet selection of ruminants are less studied than those for monogastrics. However, recent studies have shown that these mechanisms may be more similar in ruminants and monogastrics than previously believed. Food aversion learning is observed in both monogastrics and ruminants, and the hypothalamic-pituitary-adrenal axis appears to be involved in avoidance learning. Using leafy spurge (Euphorbia esula), an introduced weed whose expansion has costly ecological and economic implications in western North America, as a model for underconsumed plant species, we hypothesized that sheep experience increased cortisol levels when they first consume leafy spurge and that this may be related to their reluctance to graze it. We also hypothesized that preexposure to leafy spurge would attenuate the development of a spurge-based aversion. Correspondingly, we hypothesized that preexposed sheep would not experience increased blood cortisol levels with leafy spurge gavage during an aversion trial. None of our hypotheses were disproved by the experiments. Our results lend support to the hypothesis that stress is required for the development of conditioned taste aversions and extend it to ruminants. We suggest that activity of the hypothalamic-pituitary-adrenal axis is integral to food aversion learning in ruminants.

Behavioural pharmacology of 5-HT3 receptor antagonists: a critical update on therapeutic potential

There has been tremendous interest in 5-HT3 receptor antagonists since their discovery and the subsequent identification of 5-HT3 receptors in the CNS. Based on the results of early behavioural tests with these compounds, there has been substantial interest in their potential use for the treatment of various CNS disorders. In this review, Andrew Greenshaw attempts to clarify the status of the therapeutic potential of these drugs, discussing inconsistencies in preclinical findings and identifying areas in need of clarification through future research. 5-HT3 receptor antagonists are claimed to be potentially useful in the treatment of nausea, inflammatory pain (migraine and irritable bowel syndrome), anxiety, depression, schizophrenia, dementia and drug abuse!