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In contrast to cats and dogs, here we report that the α2-adrenergic receptor antagonist yohimbine is emetic and corresponding agonists clonidine and dexmedetomidine behave as antiemetics in the least shrew model of vomiting. Yohimbine (0, 0.5, 0.75, 1, 1.5, 2, and 3 mg/kg, i.p.) caused vomiting in shrews in a bell-shaped and dose-dependent manner, with a maximum frequency (0.85 ± 0.22) at 1 mg/kg, which was accompanied by a key central contribution as indicated by increased expression of c-fos, serotonin and substance P release in the shrew brainstem emetic nuclei. Our comparative study in shrews demonstrates that clonidine (0, 0.1, 1, 5, and 10 mg/kg, i.p.) and dexmedetomidine (0, 0.01, 0.05, and 0.1 mg/kg, i.p.) not only suppress yohimbine (1 mg/kg, i.p.)-evoked vomiting in a dose-dependent manner, but also display broad-spectrum antiemetic effects against diverse well-known emetogens, including 2-Methyl-5-HT, GR73632, McN-A-343, quinpirole, FPL64176, SR141716A, thapsigargin, rolipram, and ZD7288. The antiemetic inhibitory ID50 values of dexmedetomidine against the evoked emetogens are much lower than those of clonidine. At its antiemetic doses, clonidine decreased shrews' locomotor activity parameters (distance moved and rearing), whereas dexmedetomidine did not do so. The results suggest that dexmedetomidine represents a better candidate for antiemetic potential with advantages over clonidine. [ABSTRACT FROM AUTHOR]

Temsirolimus is a prodrug form of sirolimus (rapamycin). With its analogs (everolimus, ridaforolimus, and rapamycin), it forms a group of anticancer agents that block the activity of one of the two mammalian targets of rapamycin (mTOR) complexes, mTORC1. We investigated the emetic potential of varying doses (0, 0.5, 1, 2.5, 5, 10, 20, and 40 mg/kg, i.p.) of temsirolimus in the least shrew. Temsirolimus caused a bell-shaped and dose-dependent increase in both the mean vomit frequency and the number of shrews vomiting with maximal efficacy at 10 mg/kg (p < 0.05 and p < 0.02, respectively). Its larger doses (20 or 40 mg/kg) had no significant emetic effect. We also evaluated the emetic potential of its analogs (5, 10, and 20 mg/kg, i.p.), all of which exhibited a similar emetic profile. Our observational studies indicated that temsirolimus can reduce the shrew motor activity at 40 mg/kg, and subsequently, we examined the motor effects of its lower doses. At 10 and 20 mg/kg, it did not affect the spontaneous locomotor activity (distance moved) but attenuated the mean rearing frequency in a U-shaped manner at 10 mg/kg (p < 0.05). We then determined the broad-spectrum antiemetic potential of a 20 mg/kg (i.p.) dose of temsirolimus against diverse emetogens, including selective and nonselective agonists of 1) dopaminergic D2/3 receptors (apomorphine and quinpirole); 2) serotonergic 5-HT3 receptors [5-HT (serotonin) and 2-methyl-5-HT]; 3) cholinergic M1 receptors (pilocarpine and McN-A-343); 4) substance P neurokinin NK1 receptors (GR73632); 5) the L-type calcium (Ca2+) channel (LTCC) (FPL64176); 6) the sarcoplasmic endoplasmic reticulum Ca2+ ATPase inhibitor, thapsigargin; 7) the CB1 receptor inverse agonist/antagonist, SR141716A; and 8) the chemotherapeutic cisplatin. Temsirolimus prevented vomiting evoked by the aforementioned emetogens with varying degrees. The mechanisms underlying the pro- and antiemetic effects of temsirolimus evaluated by immunochemistry for c-fos expression demonstrated a c-fos induction in the AP and NTS, but not DMNX with the 10 mg/kg emetic dose of temsirolimus, whereas its larger antiemetic dose (20 mg/kg) had no significant effect. Our study is the first to provide preclinical evidence demonstrating the promising antiemetic potential of high doses of temsirolimus and possibly its analogs in least shrews. [ABSTRACT FROM AUTHOR]

Gq and Gβγ protein-dependent phospholipase C (PLC) activation is extensively involved in G protein-coupled receptor (GPCR)-mediated signaling pathways which are implicated in a wide range of physiological and pathological events. Stimulation of several GPCRs, such as substance P neurokinin 1-, dopamine D2/3-, histamine H1- and mu-opioid receptors, can lead to vomiting. The aim of this study was to investigate the role of PLC in vomiting through assessment of the emetic potential of a PLC activator (m-3M3FBS), and the antiemetic efficacy of a PLC inhibitor (U73122), in the least shrew model of vomiting. We find that a 50 mg/kg (i.p.) dose of m-3M3FBS induces vomiting in ∼90% of tested least shrews, which was accompanied by significant increases in c-Fos expression and ERK1/2 phosphorylation in the shrew brainstem dorsal vagal complex, indicating activation of brainstem emetic nuclei in m-3M3FBS-evoked emesis. The m-3M3FBS-evoked vomiting was reduced by pretreatment with diverse antiemetics including the antagonists/inhibitors of: PLC (U73122), L-type Ca2+ channel (nifedipine), IP3R (2-APB), RyR receptor (dantrolene), ERK1/2 (U0126), PKC (GF109203X), the serotoninergic type 3 receptor (palonosetron), and neurokinin 1 receptor (netupitant). In addition, the PLC inhibitor U73122 displayed broad-spectrum antiemetic effects against diverse emetogens, including the selective agonists of serotonin type 3 (2-Methyl-5-HT)-, neurokinin 1 receptor (GR73632), dopamine D2/3 (quinpirole)-, and muscarinic M1 (McN-A-343) receptors, the L-type Ca2+ channel (FPL64176), and the sarco/endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin. In sum, PLC activation contributes to emesis, whereas PLC inhibition suppresses vomiting evoked by diverse emetogens. [ABSTRACT FROM AUTHOR]

The introduction of second generation serotonin 5-HT 3 receptor (5-HT 3 ) antagonist palonosetron combined with long-acting substance P neurokinin NK 1 receptor (NK 1 ) antagonists (e.g. netupitant) has substantially improved antiemetic therapy against early- and delayed-phases of emesis caused by highly emetogenic chemotherapeutics such as cisplatin. However, the improved efficacy comes at a cost that many patients cannot afford. We introduce a new class of antiemetic, the antiasthmatic leukotriene CysLT1 receptor antagonist pranlukast for the suppression of cisplatin-evoked vomiting. Pranlukast (10 mg/kg) by itself significantly reduced the mean frequency of vomits (70%) and fully protected least shrews from vomiting (46%) during the delayed-phase of cisplatin (10 mg/kg)-evoked vomiting. Although, pranlukast tended to substantially reduce both the mean frequency of vomits and the number of shrews vomiting during the early-phase, these reductions failed to attain significance. When combined with a first (tropisetron)- or a second (palonosetron)-generation 5-HT 3 receptor antagonist, pranlukast potentiated their antiemetic efficacy during both phases of vomiting. In addition, pranlukast by itself prevented several intracellular signal markers of cisplatin-evoked delayed-vomiting such as phosphorylation of ERK1/2 and PKA. When pranlukast was combined with either palonosetron or tropisetron, these combinations suppressed the evoked phosphorylation of: i) ERK1/2 during both acute- and delayed-phase, ii) PKCα/β at the peak acute-phase, and iii) PKA at the peak delayed-phase. The current and our published findings suggest that overall behavioral and intracellular signaling effects of pranlukast via blockade of CysLT1 receptors generally appear to be similar to the NK 1 receptor antagonist netupitant with some differences. [ABSTRACT FROM AUTHOR]

Stimulation of 5-HT3 receptors (5-HT3Rs) by 2-methylserotonin (2-Me-5-HT), a selective 5-HT3 receptor agonist, can induce vomiting. However, downstream signaling pathways for the induced emesis remain unknown. The 5-HT3R channel has high permeability to extracellular calcium (Ca2+) and upon stimulation allows increased Ca2+ influx. We examined the contribution of Ca2+/calmodulin-dependent protein kinase IIα (Ca2+/CaMKIIα), interaction of 5-HT3R with calmodulin, and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling to 2-Me-5-HT-induced emesis in the least shrew. Using fluo-4 AM dye, we found that 2-Me-5-HT augments intracellular Ca2+ levels in brainstem slices and that the selective 5-HT3R antagonist palonosetron, can abolish the induced Ca2+ signaling. Pre-treatment of shrews with either: i) amlodipine, an antagonist of L-type Ca2+ channels present on the cell membrane; ii) dantrolene, an inhibitor of ryanodine receptors (RyRs) Ca2+-release channels located on the endoplasmic reticulum (ER); iii) a combination of their less-effective doses; or iv) inhibitors of CaMKII (KN93) and ERK1/2 (PD98059); dose-dependently suppressed emesis caused by 2-Me-5-HT. Administration of 2-Me-5-HT also significantly: i) enhanced the interaction of 5-HT3R with calmodulin in the brainstem as revealed by immunoprecipitation, as well as their colocalization in the area postrema (brainstem) and small intestine by immunohistochemistry; and ii) activated CaMKIIα in brainstem and in isolated enterochromaffin cells of the small intestine as shown by Western blot and immunocytochemistry. These effects were suppressed by palonosetron. 2-Me-5-HT also activated ERK1/2 in brainstem, which was abrogated by palonosetron, KN93, PD98059, amlodipine, dantrolene, or a combination of amlodipine plus dantrolene. However, blockade of ER inositol-1, 4, 5-triphosphate receptors by 2-APB, had no significant effect on the discussed behavioral and biochemical parameters. This study demonstrates that Ca2+ mobilization via extracellular Ca2+ influx through 5-HT3Rs/L-type Ca2+ channels, and intracellular Ca2+ release via RyRs on ER, initiate Ca2+-dependent sequential activation of CaMKIIα and ERK1/2, which contribute to the 5-HT3R-mediated, 2-Me-5-HT-evoked emesis. [ABSTRACT FROM AUTHOR]

The biochemical and histopathological changes in the lower esophageal sphincter (LES) in the pathogenesis of gastroesophageal reflux disease have gained interest. The least shrew is able to vomit in response to emetogens and provides a good model to study the histology of this phenomenon relative to the published reports in the commonly used but vomit-incompetent laboratory species. The LES is located at the junction of the esophagus and stomach. It typically closes at rest and opens in response to swallowing. Our findings demonstrate that the least shrew does not have a well-defined LES, lacks esophageal glands and has a mucosal valve-like projection from the terminal end of the esophagus before joining the gastric epithelium at the lesser curvature. In addition, the least shrew has thoracic and abdominal components prior to joining the gastric epithelium. The mucosal lining of the esophagus is folded, becoming clearly convoluted and forming a bucket-like structure at the level of the esophageocardiac junction (ECJ). No significant differences are to be found between the structure and thickness of the wall before and after the ECJ. Thus, the ECJ forming the LES is relatively less complex than those of other mammals including man. The distribution of enterochromaffin (EC) cells is confined to the lamina propria of the junction and is not associated with the cardiac glands, suggesting its functional involvement with the smooth muscle in and around the ECJ. In conclusion, the least shrew's anatomical sphincter appears ill-defined and is replaced by a less sturdy valve-like mucosal flap. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Previous studies have shown that cannabinoid CB1/2 and vanilloid TRPV1 agonists (delta-9-tetrahydrocannabinol (Δ9-THC) and resiniferatoxin (RTX), respectively) can attenuate the emetic effects of chemotherapeutic agents such as cisplatin. In this study we used the least shrew to demonstrate whether combinations of varying doses of Δ9-THC with resiniferatoxin can produce additive antiemetic efficacy against cisplatin-induced vomiting. RTX by itself caused vomiting in a bell-shaped dose-dependent manner with maximal vomiting at 18μg/kg when administered subcutaneously (s.c.) but not intraperitoneally (i.p.). Δ9-THC up to 10mg/kg provides only 80% protection of least shrews from cisplatin-induced emesis with an ID50 of 0.3–1.8mg/kg. Combinations of 1 or 5μg/kg RTX with varying doses of Δ9-THC completely suppressed both the frequency and the percentage of shrews vomiting with ID50 dose values 5–50 times lower than Δ9-THC doses tested alone against cisplatin. A less potent TRPV1 agonist, capsaicin, by itself did not cause emesis (i.p. or s.c.), but it did significantly reduce vomiting induced by cisplatin given after 30min but not at 2h. The TRPV1-receptor antagonist, ruthenium red, attenuated cisplatin-induced emesis at 5mg/kg; however, another TRPV1-receptor antagonist, capsazepine, did not. In summary, we present evidence that combination of CB1/2 and TRPV1 agonists have the capacity to completely abolish cisplatin-induced emesis at doses that are ineffective when used individually. [Copyright &y& Elsevier]

Abstract: Cisplatin-like chemotherapeutics cause vomiting via release of multiple neurotransmitters (dopamine, serotonin (5-HT), or substance P (SP)) from the gastrointestinal enterochromaffin cells and/or the brainstem via a calcium dependent process. Diverse channels in the plasma membrane allow extracellular Ca2+ entry into cells for the transmitter release process. Agonists of 5-HT3 receptors increase calcium influx through both 5-HT3 receptors and L-type Ca2+ channels. We envisaged that L-type calcium agonists such as FPL 64176 should cause vomiting and corresponding antagonists such as nifedipine would behave as broad-spectrum antiemetics. Administration of FPL 64176 did cause vomiting in the least shrew in a dose-dependent fashion. Nifedipine and the 5-HT3 receptor antagonist palonosetron, potently suppressed FPL 64176-induced vomiting, while a combination of ineffective doses of these antagonists was more efficacious. Subsequently, we investigated the broad-spectrum antiemetic potential of nifedipine against diverse emetogens including agonists of serotonergic 5-HT3- (e.g. 5-HT or 2-Me-5-HT), SP tachykinin NK1- (GR73632), dopamine D2- (apomorphine or quinpirole), and cholinergic M1- (McN-A-343) receptors, as well as the non-specific emetogen, cisplatin. Nifedipine by itself suppressed vomiting in a potent and dose-dependent manner caused by the above emetogens except cisplatin. Moreover, low doses of nifedipine potentiated the antiemetic efficacy of non-effective or semi-effective doses of palonosetron against vomiting caused by either 2-Me-5-HT or cisplatin. Thus, our findings demonstrate that activation of L-type calcium channels causes vomiting, whereas blockade of these ion channels by nifedipine-like antagonists not only provides broad-spectrum antiemetic activity but can also potentiate the antiemetic efficacy of well-established antiemetics such as palonosetron. L-type calcium channel antagonists should also provide antiemetic activity against drug-induced vomiting as well as other emetogens including bacterial and viral proteins. [Copyright &y& Elsevier]

Abstract: Scant information is available regarding the effects of cisplatin on the expression profile of tachykinin NK1 receptors and downstream signaling during cisplatin-induced emesis. Cisplatin causes peak early- and delayed-phase emesis in the least shrew at 1–2 and 33h post-injection. To investigate the expression profile of NK1 receptor during both emetic phases, we cloned the cDNA corresponding to a ∼700 base pairs of mRNA flanked by two stretches of nucleotides conserved among different species and demonstrated that the shrew NK1 receptor nucleotide sequence shares ∼90% sequence identity with the human NK1 receptor. Of the 12 time-points tested, significant increases in expression levels of NK1 receptor mRNA in the shrew brainstem occurred at 2 and 28h post-cisplatin injection, whereas intestinal NK1 receptor mRNA was increased at 28h. Shrew brainstem and intestinal substance P mRNA levels also tended to increase during the two phases. Furthermore, expression levels of NK1 receptor protein were significantly increased in the brainstem at 2, 8, and 33h post-cisplatin. No change in brainstem 5-HT3 receptor protein expression was observed. The temporal enhancements in NK1 receptor protein expression were mirrored by significant increases in the phosphorylation status of the brainstem ERK1/2 at 2, 8, and 33h post-cisplatin. Phosphorylation of PKA significantly increased at 33rd and 40th hour. Our results indicate associations between cisplatin’s peak immediate- and delayed-phase vomiting frequency with increased: (1) expression levels of NK1 receptor mRNA and its protein level, and (2) downstream NK1 receptor-mediated phosphorylation of ERK1/2 and PKA signaling. [Copyright &y& Elsevier]

Abstract: Significant electrophysiological and biochemical findings suggest that receptor cross-talk occurs between serotonergic 5-HT3- and tachykininergic NK1-receptors in which co-activation of either receptor by ineffective doses of their corresponding agonists (serotonin (5-HT) or substance P (SP), respectively) potentiates the activity of the other receptor to produce a response. In contrast, selective blockade of any one of these receptors attenuates the increase in abdominal vagal afferent activity caused by either 5-HT or SP. This interaction has important implications in chemotherapy-induced nausea and vomiting (CINV) since 5-HT3- and NK1-receptor antagonists are the major classes of antiemetics used in cancer patients receiving chemotherapy. The purpose of this study was to demonstrate whether the discussed interaction produces effects at the behavioral level in a vomit-competent species, the least shrew. Our results demonstrate that pretreatment with either a 5-HT3 (tropisetron)- or an NK1 (CP99,994)-receptor specific antagonist, attenuates vomiting caused by a selective agonist (2-methyl 5-HT or GR73632, respectively) of both emetic receptors. In addition, relative to each antagonist alone, their combined doses were 4–20 times more potent against vomiting caused by each emetogen. Moreover, combined sub-maximal doses of the agonists 2-methyl 5-HT and GR73632, produced 8–12 times greater number of vomits relative to each emetogen tested alone. However, due to large variability in vomiting caused by the combination doses, the differences failed to attain significance. The antiemetic dose–response curves of tropisetron against both emetogens were U-shaped probably because larger doses of this antagonist behave as a partial agonist. The data demonstrate that 5-HT3- and NK1-receptors cross-talk to produce vomiting, and that synergistic antiemetic effects occur when both corresponding antagonists are concurrently used against emesis caused by each specific emetogen. [Copyright &y& Elsevier]

Abstract: Although the neurotransmitter basis of chemotherapy-induced vomiting (CIV) is thought to be multifactorial, it is generally accepted that acute (immediate) CIV is mainly due to the release of serotonin (5-HT) within the gastrointestinal tract, while the delayed phase occurs following substance P (SP) release in the brainstem. The aim of the current study was to test this dogma in the least shrew model of vomiting. Thus, we initially investigated the temporal development of cisplatin''s immediate and delayed emetic effects in the least shrew and subsequently determined the concomitant changes in the turnover of major emetic neurotransmitters both in the central and peripheral loci associated with CIV. Cisplatin (0, 5, 10 and 20 mg/kg, i.p.) caused dose- and time-dependent emetic effects. A 10 mg/kg dose of cisplatin produced both phases of emesis with corresponding peak mean frequencies occurring at 2–3 and 33 h post-treatment, at 5 mg/kg it failed to cause significant emesis in either phase, while its 20 mg/kg dose induced both phases earlier but toxicity restricted the full 47 hour observation. Cisplatin (10 mg/kg, i.p.)-induced peak immediate and delayed phases were associated with concomitant increases in the turnover of 5-HT, dopamine and SP in both the shrew brainstem and jejunum. The discussed increases during both phases appear to be site specific since neurotransmitter release was not persistently altered in the shrew frontal cortex or duodenum, although occasionally increases or decreases did occur. Our findings suggest that the least shrew appears to be a sensitive and rapid emesis model for both phases of CIV, and both emetic phases are associated with specific increases in the release of all of the cited neurotransmitters in both the brainstem and jejunum. Thus, the generally accepted neurotransmitter dogma needs to be updated since more recent neurochemical studies in humans as well as other clinical findings support the current basic results obtained in the least shrew. [Copyright &y& Elsevier]

Abstract: Xenobiotic cannabinoid CB1/CB2‐receptor agonists appear to possess broad‐spectrum antiemetic activity since they prevent vomiting produced by a variety of emetic stimuli including the chemotherapeutic agent cisplatin, serotonin 5‐HT3‐receptor agonists, dopamine D2/D3‐receptor agonists and morphine, via the stimulation of CB1‐receptors. The purpose of this study was to evaluate whether structurally‐diverse cannabinoids [Δ9‐THC, (delta‐9‐tetrahydrocannabinol); (Δ8‐THC, delta‐8‐tetrahydrocannabinol); WIN55,212‐2, (R (+)‐[2,3‐dihydro‐5‐methyl‐3‐[(morpholinyl)), methyl] pyrolol [1,2,3‐de]‐1,4 benzoxazinyl]‐(1‐naphthalenyl) methenone mesylate); and CP55,940, ((−)‐3‐[2‐hydroxy‐4‐(1,1‐dimethylheptyl]‐4‐[3‐hydroxypropyl] cyclohexane‐1‐ol)), can prevent radiation‐induced emesis. Exposure to total body radiation (0, 5, 7.5 and 10 Gy) caused robust emesis in the least shrew (Cryptotis parva) in a dose‐dependent manner (ED50 = 5.99 (5.77–6.23) Gy) and all animals vomited at the highest tested dose of radiation. In addition, the radiation exposure reduced locomotor behaviors to a significant but mild degree in a non‐dose‐dependent fashion up to one hour post‐treatment. Radiation‐induced emesis (10 Gy) was blocked in a dose‐dependent manner by the CB1/CB2‐receptor agonists with the following ID50 potency order: CP55,940 (0.11 (0.09–0.12) mg/kg) > WIN55,212,2 (3.65 (3.15–4.23) mg/kg) = Δ8‐THC (4.36 (3.05–6.22) mg/kg) > Δ9‐THC (6.76 (5.22–8.75) mg/kg). Although the greater antiemetic potency and efficacy of Δ8‐THC relative to its isomer Δ9‐THC is unusual as the latter cannabinoid possesses higher affinity and potency for cannabinoid receptors in functional assays, the current data support the results of a clinical study in children suggestive of complete protection from emesis by Δ8‐THC. This effect has not been clinically observed for Δ9‐THC in cancer patients receiving chemo‐ or radiation‐therapy. Cannabinoids prevented the induced emesis via the stimulation of cannabinoid CB1‐receptors because the CB1 (SR141716A) – and not the CB2 (SR144528) – receptor antagonist reversed both the observed reduction in emesis frequency and shrew emesis protection afforded by either Δ9‐THC or CP55,940 against radiation‐induced emesis. These findings further suggest that the least shrew can be utilized as a versatile and inexpensive small animal model to rapidly screen the efficacy of investigational antiemetics for the prevention of radiation‐induced emesis. [Copyright &y& Elsevier]

Abstract: The principal psychoactive component of marijuana, delta-9-tetrahydrocannabinol (Δ9-THC), suppresses nausea and vomiting in cancer patients caused by chemotherapeutics such as cisplatin. Cisplatin induces vomiting via a number of emetic stimuli, including dopamine. Currently, there is controversy as to whether Δ9-THC can prevent emesis produced by dopaminergic agonists such as apomorphine. The present investigation utilizes the least shrew to evaluate the antiemetic potential and the cannabinoid receptor by which Δ9-THC may prevent emesis produced by four dopamine receptor agonists with differing selectivity for D2 and D3 receptors, i.e., a nonselective dopamine receptor agonist (apomorphine), a D2-preferring receptor agonist (quinpirole), and two D3-preferring receptor agonists (quinelorane and 7-OH DPAT). In addition, relative to its antiemetic doses, the motor suppressive doses of Δ9-THC in dopamine D2/D3-receptor-agonist-treated shrews were also evaluated. Thus, different groups of shrews were injected with either vehicle (V) or varying doses of Δ9-THC [0.5, 1, 2.5, 5, or 10 mg/kg, intraperitoneal (i.p.)] 10 min prior to administration of a 2 mg/kg dose of one of the four cited D2/D3 agonists. Immediately after the last injection, the frequency of vomiting for each shrew was recorded for the next 30 min. To investigate which cannabinoid receptor is involved in the antiemetic action of Δ9-THC, various doses of the CB1 receptor antagonist SR 141716A [0, 5, 10, and 20 mg/kg, subcutaneous (s.c.)] were administered to shrews 10 min prior to an injection of a fully effective antiemetic dose of Δ9-THC (5 mg/kg, i.p.). Ten minutes later, each treated shrew was administered with a 2 mg/kg dose of apomorphine. The emesis frequency was recorded for the next 30 min. For locomotor studies, different groups of shrews received either vehicle or various doses of Δ9-THC (0, 5, 10, 20, or 30 mg/kg) 10 min prior to an injection of vehicle or a 2 mg/kg dose of one of the four D2/D3 receptor agonists. The triad of motor behaviors (spontaneous locomotor activity, total duration of movement, and rearing frequency) were recorded for the next 30 min by a computerized video tracking system. Δ9-THC dose-dependently attenuated the frequency of emesis as well as fully protecting shrews from vomiting produced by each one of the four cited dopamine D2/D3 receptor agonists with ID50s ranging from 1 to 4 mg/kg. SR 141716A reversed the antiemetic activity of Δ9-THC against apomorphine-induced emesis. Δ9-THC also differentially suppressed the triad of motor activities in dopamine D2/D3-receptor-agonist-treated shrews with ID50s ranging from 7 to 21 mg/kg. The results suggest that Δ9-THC prevents emesis via cannabinoid CB1 receptors in a potent and dose-dependent manner in D2/D3-receptor-agonist-treated shrews at doses well below those which cause significant motor depression. [Copyright &y& Elsevier]

Ca 2+ plays a major role in maintaining cellular homeostasis and regulates processes including apoptotic cell death and side-effects of cancer chemotherapy including vomiting. Currently we explored the emetic mechanisms of FPL64176, an L-type Ca 2+ channel (LTCC) agonist with maximal emetogenic effect at its 10 mg/kg dose. FPL64176 evoked c-Fos immunoreactivity in shrew brainstem sections containing the vomit-associated nuclei, nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus. FPL64176 also increased phosphorylation of proteins ERK1/2, PKCα/βII and Akt in the brainstem. Moreover, their corresponding inhibitors (PD98059, GF 109203X and LY294002, respectively) reduced FPL64176-evoked vomiting. A 30 min subcutaneous (s.c.) pretreatment with the LTCC antagonist nifedipine (10 mg/kg) abolished FPL64176-elicited vomiting, c-Fos expression, and emetic effector phosphorylation. Ryanodine receptors (RyRs) and inositol trisphosphate receptors (IP 3 Rs) mediate intracellular Ca 2+ release from the sarcoplasmic/endoplasmic reticulum. The RyR antagonist dantrolene (i.p.), or a combination of low doses of nifedipine and dantrolene, but not the IP 3 R antagonist 2-APB, significantly attenuated FPL64176-induced vomiting. The serotonin type 3 receptor (5-HT 3 R) antagonist palonosetron (s.c.), the neurokinin 1 receptor (NK 1 R) antagonist netupitant (i.p.) or a combination of non-effective doses of netupitant and palonosetron showed antiemetic potential against FPL64176-evoked vomiting. Serotonin (5-HT) and substance P immunostaining revealed FPL64176-induced emesis was accompanied by an increase in 5-HT but not SP-immunoreactivity in the dorsomedial subdivision of the NTS. These findings demonstrate that Ca 2+ mobilization through LTCCs and RyRs, and subsequent emetic effector phosphorylation and 5-HT release play important roles in FPL64176-induced emesis which can be prevented by 5-HT 3 R and NK 1 R antagonists. [ABSTRACT FROM AUTHOR]

Shrews are abundant in most areas of toxic chemical contamination and bioaccumulate pollutants at much higher rates than sympatric rodent species. As a part of studies to provide information concerning the toxicity of 1,3-dinitrobenzene (DNB) in least shrews (Cryptotis parva), groups of 10 females and 10 males received DNB at 0 (control), 0.7, 2.9, 11.6, and 46.3 µl/L (equivalent mean daily dosage of 0, 0.26, 1.06, 4.26, and 17.0 mg/kg body wt in each sex) in their diet for 14 d. Leukocytosis present at the 0.26 mg/kg body weight/d dosage established the lowest-observed-adverse effect level (LOAEL). Adrenal enlargement was noted at the 1.06 mg/kg body weight/d level. Splenic enlargement and reductions in hematocrit and hemoglobin values occurred at the 4.26 mg/kg body weight/d treatment. Enlargements in the liver and heart and reductions in brown fat weight, granulocyte numbers, and alanine aminotransferase levels were present at high dose levels. Histopathologic examinations showed Kupffer's cell hemosiderosis and suggested testicular damage at the two highest tested doses but failed to confirm brain lesions. Least shrews do not follow standard scaling estimates for lifespan or metabolic rates. The LOAEL calculated from the standard terrestrial screening benchmark equation was higher than our findings, suggesting that these estimates must be viewed with caution. [ABSTRACT FROM AUTHOR]

Cytoplasmic calcium (Ca 2+ ) mobilization has been proposed to be an important factor in the induction of emesis. The selective sarcoplasmic/endoplasmic reticulum Ca 2+ -ATPase (SERCA) inhibitor thapsigargin, is known to deplete intracellular Ca 2+ stores, which consequently evokes extracellular Ca 2+ entry through cell membrane-associated channels, accompanied by a prominent rise in cytosolic Ca 2+ . A pro-drug form of thapsigargin is currently under clinical trial as a targeted cancer chemotherapeutic. We envisioned that the intracellular effects of thapsigargin could cause emesis and planned to investigate its mechanisms of emetic action. Indeed, thapsigargin did induce vomiting in the least shrew in a dose-dependent and bell-shaped manner, with maximal efficacy (100%) at 0.5 mg/kg (i.p.). Thapsigargin (0.5 mg/kg) also caused increases in c-Fos immunoreactivity in the brainstem emetic nuclei including the area postrema (AP), nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMNX), as well as enhancement of substance P (SP) immunoreactivity in DMNX. In addition, thapsigargin (0.5 mg/kg, i.p.) led to vomit-associated and time-dependent increases in phosphorylation of Ca 2+ /calmodulin kinase IIα (CaMKIIα) and extracellular signal-regulated protein kinase 1/2 (ERK1/2) in the brainstem. We then explored the suppressive potential of diverse chemicals against thapsigargin-evoked emesis including antagonists of: i) neurokinin-1 receptors (netupitant), ii) the type 3 serotonin receptors (palonosetron), iii) store-operated Ca 2+ entry (YM-58483), iv) L-type Ca 2+ channels (nifedipine), and v) SER Ca 2+ -release channels inositol trisphosphate (IP 3 Rs) (2-APB)-, and ryanodine (RyRs) (dantrolene)-receptors. In addition, the antiemetic potential of inhibitors of CaMKII (KN93) and ERK1/2 (PD98059) were investigated. All tested antagonists/blockers attenuated emetic parameters to varying degrees except palonosetron, however a combination of non-effective doses of netupitant and palonosetron exhibited additive antiemetic efficacy. A low-dose combination of nifedipine and 2-APB plus dantrolene mixture completely abolished thapsigargin-evoked vomiting, CaMKII-ERK1/2 activation and SP elevation. In addition, pretreatment with KN93 or PD98059 suppressed thapsigargin-induced increases in SP and ERK1/2 activation. Intracerebroventricular injection of netupitant suppressed vomiting caused by thapsigargin which suggests that the principal site of evoked emesis is the brainstem. In sum, this is the first study to demonstrate that thapsigargin causes vomiting via the activation of the Ca 2+ -CaMKII-ERK1/2 cascade, which is associated with an increase in the brainstem tissue content of SP, and the evoked emesis occurs through SP-induced activation of neurokinin-1 receptors. [ABSTRACT FROM AUTHOR]

Abstract: The dihydropyridine l-type calcium (Ca2+) channel blockers nifedipine and amlodipine reduce extracellular Ca2+ entry into cells. They are widely used for the treatment of hypertensive disorders. We have recently demonstrated that extracellular Ca2+ entry via l-type Ca2+ channels is involved in emesis and that nifedipine has broad-spectrum antiemetic activity. The aim of this study was to evaluate the antiemetic efficacy of the longer-acting l-type Ca2+ channel blocker, amlodipine. Fully effective emetic doses of diverse emetogens such as the l-type Ca2+ channel agonist (FPL 64176) as well as selective and/or nonselective agonists of serotonergic 5-HT3 (e.g. 5-HT or 2-Me-5-HT)-, dopamine D2 (e.g. apomorphine or quinpirole)-, cholinergic M1 (e.g. pilocarpine or McN-A343)- and tachykininergic NK1 (e.g. GR73632)-receptors, were administered intraperitoneally (i.p.) in the least shrew to induce vomiting. The broad-spectrum antiemetic potential of amlodipine was evaluated against these emetogens. Subcutaneous (s.c.) administration of amlodipine (0.5–10mg/kg) attenuated in a dose-dependent and potent manner both the frequency and percentage of shrews vomiting in response to intraperitoneal (i.p.) administration of FPL 64176 (10mg/kg), 5-HT (5mg/kg), 2-Me-5-HT (5mg/kg), apomorphine (2mg/kg), quinpirole (2mg/kg), pilocarpine (2mg/kg), McN-A343 (2mg/kg), or GR73632 (5mg/kg). A combination of non-effective doses of amlodipine (0.5mg/kg, s.c.) and the 5-HT3 receptor antagonist palonosetron (0.05mg/kg, s.c.) was more effective against FPL 64176-induced vomiting than their corresponding doses tested alone. Amlodipine by itself suppressed the frequency of acute cisplatin (10mg/kg, i.p)-induced vomiting in a dose-dependent manner. Moreover, a combination of a non-effective dose of amlodipine (1mg/kg) potentiated the antiemetic efficacy of a semi-effective dose of palonosetron (0.5mg/kg, s.c.) against acute vomiting caused by cisplatin. We confirm that influx of extracellular Ca2± ion underlies vomiting due to diverse causes and demonstrate that l-type Ca2+ channel blockers are a new class of broad-spectrum antiemetics. [Copyright &y& Elsevier]

Abstract: Complete control of emesis caused by cyclophosphamide (CPA) is of immense interest to both patients and physicians. Serotonin 5-HT3- and tachykinin NK1-receptor antagonists are widely used antiemetics in clinic, but they fail to completely control CPA-induced emesis. New antiemetic targets for the full control of CPA-induced vomiting are lacking. We therefore examined the effects of CPA on emetic targets downstream of 5-HT3- and NK1- receptors in an attempt to better understand the molecular bases of CPA-induced emesis. Acute CPA (200mg/kg, i.p.) administration in the least shrew caused a biphasic pattern of emesis over a 40h observation period, with maximal peak vomit frequency during the 1st hour of treatment (acute phase), followed by a delayed-phase which peaks at 27th hour. The NK1 receptor mRNA levels increased significantly at 8h post-CPA treatment in the brainstem, and at 28h in the whole intestine. Substance P mRNA levels tended to increase both in the brainstem and intestine at most time-points post-CPA injection, however due to large variability, they failed to attain significance. Likewise, protein expression profiles of both NK1- and 5-HT3 -receptors in the brainstem were unchanged at any time-point. However, phosphorylation levels of protein kinase A (PKA), but not of extracellular signal-regulated protein kinase 1/2 (ERK1/2), were increased at 2, 8, 22, 28, and 33h time-points after the treatment with CPA. Moreover, brainstem but not frontal cortex cAMP tissue levels tended to be elevated at most time-points, but significant increases occurred only at 1 and 2h post-CPA treatment. The phosphodiesterase inhibitor, rolipram, caused significant increases in shrew brainstem cAMP levels which were associated with its capacity to produce vomiting, while pretreatment with SQ22536, an inhibitor of adenylyl cyclase, prevented rolipram-induced emesis. The results demonstrate that accumulation of cAMP and subsequent activation of PKA in the brainstem may help to initiate and sustain emesis induced by CPA in the least shrew. Our findings suggest that suppression of the cAMP/PKA cascade may have antiemetic potential in the management of CPA-induced emesis. [Copyright &y& Elsevier]

Abstract: Cisplatin chemotherapy frequently causes severe vomiting in two temporally separated clusters of bouts dubbed the acute and delayed phases. Cannabinoids can inhibit the acute phase, albeit through a poorly understood mechanism. We examined the substrates of cannabinoid-mediated inhibition of both the emetic phases via immunolabeling for serotonin, Substance P, cannabinoid receptors 1 and 2 (CB1, CB2), and the neuronal activation marker Fos in the least shrew (Cryptotis parva). Shrews were injected with cisplatin (10mg/kg i.p.), and one of vehicle, Δ9-THC, or both Δ9-THC and the CB1 receptor antagonist SR141716A (2mg/kg i.p.), and monitored for vomiting. Δ9-THC-pretreatment caused concurrent decreases in the number of shrews expressing vomiting and Fos-immunoreactivity (Fos-IR), effects which were blocked by SR141716A-pretreatment. Acute phase vomiting induced Fos-IR in the solitary tract nucleus (NTS), dorsal motor nucleus of the vagus (DMNX), and area postrema (AP), whereas in the delayed phase Fos-IR was not induced in the AP at all, and was induced at lower levels in the other nuclei when compared to the acute phase. CB1 receptor-IR in the NTS was dense, punctate labeling indicative of presynaptic elements, which surrounded Fos-expressing NTS neurons. CB2 receptor-IR was not found in neuronal elements, but in vascular-appearing structures. All areas correlated with serotonin- and Substance P-IR. These results support published acute phase data in other species, and are the first describing Fos-IR following delayed phase emesis. The data suggest overlapping but separate mechanisms are invoked for each phase, which are sensitive to antiemetic effects of Δ9-THC mediated by CB1 receptors. [Copyright &y& Elsevier]

With its five receptor subtypes (D 1 – 5), dopamine is implicated in a myriad of neurological illnesses. Dopamine D 2 receptor-based agonist therapy evokes nausea and vomiting. The signaling mechanisms by which dopamine D 2 receptors evoke vomiting remains unknown. Phosphatidylinositol 3-kinases (PI3K)- and protein kinase C (PKC)-related signaling cascades stimulate vomiting post-injection of various emetogens in emetically competent animals. This study investigated potential mechanisms involved in dopamine D 2 receptor-mediated vomiting using least shrews. We found that vomiting evoked by the selective dopamine D 2 receptor agonist quinpirole (2 mg/kg, i.p.) was significantly suppressed by: i) a dopamine D 2 preferring antagonist, sulpiride (s.c.); ii) a selective PI3K inhibitor, LY294002 (i.p.); iii) a PKCαβII inhibitor, GF109203X (i.p.); and iv) a selective inhibitor of extracellular signal-regulated protein kinase1/2 (ERK1/2), U0126 (i.p.). Quinpirole-evoked c-fos immunofluorescence in the nucleus tractus solitarius (NTS) was suppressed by pretreatment with sulpiride (8 mg/kg, s.c.). Western blot analysis of shrew brainstem emetic loci protein lysates revealed a significant and time-dependent increase in phosphorylation of Akt (protein kinase B (PKB)) at Ser473 following a 30-min exposure to quinpirole (2 mg/kg, i.p.). Pretreatment with effective antiemetic doses of sulpiride, LY294002, GF109203X, or U0126 significantly reduced quinpirole-stimulated phosphorylation of emesis-associated proteins including p-85PI3K, mTOR (Ser2448/2481), PKCαβII (Thr638/641), ERK1/2 (Thr202/204), and Akt (Ser473). Our results substantiate the implication of PI3K/mTOR/Akt and PI3K/PKCαβII/ERK1/2/Akt signaling pathways in dopamine D 2 receptor-mediated vomiting. Potential novel antiemetics targeting emetic proteins associated with these signaling cascades may offer enhanced potency and/or efficacy against emesis. [Display omitted] • Dopamine D 2 receptor agonist quinpirole induces emesis in shrews. • Quinpirole phosphorylates PI3K/mTOR/Akt and PI3K/PKCαβII/ERK1/2/Akt pathways in brainstems. • Sulpiride prevents emesis in shrews. • Sulpiride inhibits PI3K/mTOR/Akt and PI3K/PKCαβII/ERK1/2/Akt pathways phosphorylation in brainstems. • The above signaling pathways function possibly through synergetic/parallel actions. [ABSTRACT FROM AUTHOR]

Akt (protein kinase B) signaling is frequently activated in diverse cancers. Akt inhibitors such as perifosine and MK-2206 have been evaluated as potential cancer chemotherapeutics. Although both drugs are generally well tolerated, among their most common side-effects vomiting is a major concern. Here we investigated whether these Akt inhibitors evoke emesis in the least shrew model of vomiting. Indeed, both perifosine and MK-2206 induced vomiting with maximal efficacies of 90% at 50 mg/kg (i.p.) and 100% at 10 mg/kg (i.p.), respectively. MK-2206 (10 mg/kg, i.p.) increased c-Fos immunoreactivity both centrally in the shrew brainstem dorsal vagal complex (DVC) emetic nuclei, and peripherally in the jejunum. MK-2206 also evoked phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in both the DVC emetic nuclei and the enteric nervous system in the jejunum. The ERK1/2 inhibitor U0126 suppressed MK-2206-induced emesis dose-dependently. We then evaluated the suppressive efficacy of diverse antiemetics against MK-2206-evoked vomiting including antagonists/inhibitors of the: L-type Ca2+ channel (nifedipine at 2.5 mg/kg, subcutaneously (s.c.)); glycogen synthase kinase 3 (GSK-3) (AR-A014418 at 10 mg/kg and SB216763 at 0.25 mg/kg, i.p.); 5-hydroxytryptamine 5-HT 3 receptor (palonosetron at 0.5 mg/kg, s.c.); substance P neurokinin NK 1 receptor (netupitant at 10 mg/kg, i.p.) and dopamine D 2/3 receptor (sulpride at 8 mg/kg, s.c.). All tested antagonists/blockers attenuated emetic parameters to varying degrees. In sum, this is the first study to demonstrate how pharmacological inhibition of Akt evokes vomiting via both central and peripheral mechanisms, a process which involves multiple emetic receptors. [Display omitted] • Akt inhibitors (perifosine and MK-2206) are proemetic in the least shrew. • MK-2206 evokes c-Fos expression and ERK1/2 phosphorylation in central and peripheral emetic loci. • ERK1/2 inhibitor U0126, LTCC antagonist nifedipine or GSK-3 inhibitors reduces MK-2206-induced vomiting. • 5-hydroxytryptamine 5-HT 3 , neurokinin NK 1 , or dopamine D 2/3 receptor antagonists reduces MK-2206-induced vomiting. [ABSTRACT FROM AUTHOR]

Activation of serotonergic 5-HT 3 receptors by its selective agonist 2-methyl serotonin (2-Me-5-HT) induces vomiting, which is sensitive to selective antagonists of both 5-HT 3 receptors (palonosetron) and L-type calcium channels (LTCC) (amlodipine or nifedipine). Previously we demonstrated that 5-HT 3 receptor activation also causes increases in a palonosetron-sensitive manner in: i) intracellular Ca 2+ concentration, ii) attachment of calmodulin (CaM) to 5-HT 3 receptor, and iii) phosphorylation of Ca 2+ /calmodulin-dependent protein kinase IIα (CaMKIIα) and extracellular-signal-regulated kinase 1/2 (ERK1/2). Here, we investigate the role of the short-acting LTCC blocker nifedipine on 2-Me-5-HT-evoked intracellular Ca 2+ increase and on downstream intracellular emetic signaling, which have been shown to be coupled with 2-Me-5-HT׳s emetic effects in the least shrew. Using the cell-permeant Ca 2+ indicator fluo-4 AM, here we present evidence for the contribution of Ca 2+ influx through LTCCs (sensitive to nifedipine) in 2-Me-5-HT (1 µM) -evoked rise in cytosolic Ca 2+ levels in least shrew brainstem slices. Nifedipine pretreatment (10 mg/kg, s.c.) also suppressed 2-Me-5-HT-evoked interaction of 5-HT 3 receptors with CaM as well as phosphorylation of CaMKIIα and ERK1/2 in the least shrew brainstem, and 5-HT 3 receptors -CaM colocalization in jejunum of the small intestine. In vitro exposure of isolated enterochromaffin cells of the small intestine to 2-Me-5-HT (1 µM) caused CaMKIIα phosphorylation, which was also abrogated by nifedipine pretreatment (0.1 µM). In addition, pretreatment with the CaMKII inhibitor KN62 (10 mg/kg, i.p.) suppressed emesis and also the activation of CaMKIIα, and ERK in brainstem caused by 2-Me-5-HT (5 mg/kg, i.p.). This study provides further mechanistic explanation for our published findings that nifedipine can dose-dependently protect shrews from 2-Me-5-HT-induced vomiting. [ABSTRACT FROM AUTHOR]

Stimulation of 5-HT3 receptors (5-HT3Rs) by 2-methylserotonin (2-Me-5-HT), a selective 5-HT3 receptor agonist, can induce vomiting. However, downstream signaling pathways for the induced emesis remain unknown. The 5-HT3R channel has high permeability to extracellular calcium (Ca2+) and upon stimulation allows increased Ca2+ influx. We examined the contribution of Ca2+/calmodulin-dependent protein kinase IIα (Ca2+/CaMKIIα), interaction of 5-HT3R with calmodulin, and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling to 2-Me-5-HT-induced emesis in the least shrew. Using fluo-4 AM dye, we found that 2-Me-5-HT augments intracellular Ca2+ levels in brainstem slices and that the selective 5-HT3R antagonist palonosetron, can abolish the induced Ca2+ signaling. Pre-treatment of shrews with either: i) amlodipine, an antagonist of L-type Ca2+ channels present on the cell membrane; ii) dantrolene, an inhibitor of ryanodine receptors (RyRs) Ca2+-release channels located on the endoplasmic reticulum (ER); iii) a combination of their less-effective doses; or iv) inhibitors of CaMKII (KN93) and ERK1/2 (PD98059); dose-dependently suppressed emesis caused by 2-Me-5-HT. Administration of 2-Me-5-HT also significantly: i) enhanced the interaction of 5-HT3R with calmodulin in the brainstem as revealed by immunoprecipitation, as well as their colocalization in the area postrema (brainstem) and small intestine by immunohistochemistry; and ii) activated CaMKIIα in brainstem and in isolated enterochromaffin cells of the small intestine as shown by Western blot and immunocytochemistry. These effects were suppressed by palonosetron. 2-Me-5-HT also activated ERK1/2 in brainstem, which was abrogated by palonosetron, KN93, PD98059, amlodipine, dantrolene, or a combination of amlodipine plus dantrolene. However, blockade of ER inositol-1, 4, 5-triphosphate receptors by 2-APB, had no significant effect on the discussed behavioral and biochemical parameters. This study demonstrates that Ca2+ mobilization via extracellular Ca2+ influx through 5-HT3Rs/L-type Ca2+ channels, and intracellular Ca2+ release via RyRs on ER, initiate Ca2+-dependent sequential activation of CaMKIIα and ERK1/2, which contribute to the 5-HT3R-mediated, 2-Me-5-HT-evoked emesis. [ABSTRACT FROM AUTHOR]

Serotonin is an important neurotransmitter in the central (CNS) and peripheral (PNS) nervous systems. It is involved in a variety of physiological processes both in the gut and in the CNS. The present study examined the distribution of serotonin containing enterochromaffin cells in the gastrointestinal tract (GIT) of a vomit competent species, the least shrew. These cells were easily recognized by their globular granules stained with the H&E and serotonin immune-positive stain. The immunoreactive enterochromaffin cells (IERCs) were mainly confined to the basal portion of the glandular epithelium and were distributed throughout the shrew stomach, small and large intestine. None was found to be associated with the mucosal epithelial lining. Moreover, their distribution and count varied in different regions of the GIT suggesting specific functions for these regions. The highest concentration of IERCs was found in the colon followed by the Jejunum. Appreciable numbers of IERCs were found in the stomach especially at the esophageo-gastric junction. The gastric location of the IERCs was mainly in the basal portion of the gland. However, some IERCs were associated with the parietal cells of the stomach. Two types of IERCs were observed: One with globular secretory granules in their apical portion of the cytoplasm which were located within the glandular epithelial cells facing the glandular lumen which release their secretions into the lumen; and the second were basally located, facing the lamina propria of the mucosa. Their secretory granules were not distinct in shape, and are most probably paracrine in their mode of secretions. [ABSTRACT FROM AUTHOR]

Abstract: Many chemotherapeutic agents activate multiple signaling systems, including potentially emetogenic arachidonic acid metabolites. Of these messengers, the emetic role of the leukotriene family has been neglected. The aims of this study were to test the emetic potential of key leukotrienes (LTA4, LTB4, LTF4, and the cysteinyl leukotrienes LTC4, LTD4 and LTE4), and to investigate whether the leukotriene CysLT1 receptor antagonist pranlukast or mixed leukotriene CysLT1/2 receptor antagonist Bay u9773 can prevent the LTC4-induced emesis. Least shrews were injected with varying doses of one of the six tested leukotrienes and vomiting parameters were measured for 30min. LTC4 and LTD4 were most efficacious, and significantly increased both the frequency and percentage of animals vomiting at doses from 0.1 and 0.05mg/kg, respectively. The other tested leukotrienes were either weakly emetic or ineffective at doses up to 4mg/kg. The relative emetogenic activities of the cysteinyl leukotrienes (LTC4 =LTD4 >LTE4) suggest that leukotriene CysLT2 receptors have a key role in emesis. However, pranlukast dose-dependently, and at 10mg/kg completely, blocked LTC4-induced vomiting, implicating a leukotriene CysLT1 receptor-mediated emetic effect. Bay u9773 dose-dependently reduced the percentage of animals vomiting, but did not significantly reduce vomiting frequency. Fos immunoreactivity, measured subsequent to LTC4-induced vomiting to define its putative anatomical substrates, was significantly increased in the enteric nervous system and medullary dorsal vagal complex following LTC4 (P <0.05) versus vehicle injections. This study is the first to show that some leukotrienes induce emesis, possibly involving both central and peripheral leukotriene CysLT1 and/or leukotriene CysLT2 receptors. [Copyright &y& Elsevier]

Abstract: Cisplatin and related chemotherapeutics are potent emetogens in humans and least shrews, a small animal emesis model which also vomits in response to substance P (SP). The SP-producing preprotachykinin-1 (PPT1) mRNA is transcribed from the Tac1 gene, which has been sequenced from several animal species and humans and is highly conserved. Despite its prominent role in chemotherapy-induced vomiting, the tachykininergic system is not well-characterized in emesis-competent species. This study was undertaken to further establish Cryptotis parva as an emesis model, by sequencing and characterizing SP mRNA, and then comparing the least shrew tachykininergic system to other mammalian species (vomiting and non-vomiting). The cDNA for least shrew β-PPT1 was successfully cloned and partially sequenced, and found to be 90% homologous to the human sequence, with the SP-producing portion identical to humans. Initial in situ hybridization results demonstrated induction of β-PPT1 mRNA in the gut following cisplatin administration. These were followed up with mRNA quantification (via QPCR) at multiple time points following cisplatin injection. PPT1 mRNA levels in the brain spiked at 4 h (19-fold increase) and 24 h (20-fold increase) in correlation with cisplatin-induced emesis. PPT1 mRNA in the gut spiked at 28 h (∼6.5-fold increase), correlated with the later phase of vomiting. These results validate the least shrew as a tachykinin model at the molecular level. [Copyright &y& Elsevier]

Abstract: 5-HT3 receptor antagonists (e.g. tropisetron) combined with dexamethasone are effective for the acute phase of cisplatin (CIS)-induced emesis. This study determined the possible additive or synergistic antiemetic efficacy of Δ9-THC when combined with tropisetron or dexamethasone (DEX). Δ9-THC (0–10 mg/kg i.p.) was injected in combination with tropisetron (0–5 mg/kg i.p.) or dexamethasone (0–20 mg/kg i.p.) prior to CIS (20 mg/kg i.p.) in the least shrew, and the induced emesis was recorded for 60 min. CIS-induced vomiting was dose-dependently and significantly attenuated by individual administration of Δ9-THC (59–97% reductions) and tropisetron (79–100% attenuation), but not dexamethasone (26–40%), although a trend (p <0.1) towards reduced vomiting frequency following DEX was noted. Low doses of Δ9-THC (0.25 or 0.5 mg/kg) when combined with low doses of tropisetron (0.025, 0.1, or 0.25 mg/kg) were more efficacious in reducing emesis frequency than when given individually, but Δ9-THC had no antiemetic interactions with DEX. However, no tested combination provided a significantly greater effect on the number of animals vomiting than their individually-administered counterparts. The modest interaction of Δ9-THC with tropisetron suggests they activate overlapping antiemetic mechanisms, while the lack of interaction with dexamethasone needs further clarification. [Copyright &y& Elsevier]