Natural compounds boldine and menthol are antagonists of human 5-HT3 receptors: implications for treating gastrointestinal disorders.

BACKGROUND: Impaired 5-HT3 receptor function is likely involved in the pathogenesis of functional gastrointestinal disorders (FGID) and 5-HT3 receptor antagonists are effective treatments for chemotherapy-induced nausea and vomiting (CINV) and irritable bowel syndrome (IBS). The monoterpene alcohol menthol and the aporphine alkaloid boldine combat symptoms of gastrointestinal diseases; both interact with other members of the Cys-loop ligand-gated ion channel family and may therefore also act on 5-HT3 receptors. METHODS: The impact of boldine and menthol on human recombinant homomeric 5-HT3 A- and heteromeric 5-HT3 AB receptors in HEK293 cells was determined by radioligand binding, a luminescence-based Ca(2+) assay, and a membrane potential assay. 5-HT3 protein and mRNA expression was assessed in human colon tissue. KEY RESULTS: Boldine and menthol inhibited the 5-HT-induced activation of 5-HT3 receptors in the low and middle micromolar range, respectively. Boldine was a competitive antagonist of both receptors being 6.5- to 10-fold more potent at 5-HT3 A- vs 5-HT3 AB receptors. Menthol non-competitively and stereoselectively inhibited both receptors: In contrast to (+)-menthol, (-)-menthol was significantly more potent toward 5-HT3 A- vs 5-HT3 AB receptors. We show co-expression of 5-HT3A and 5-HT3B subunits in the human gut epithelium, the lamina propria, the myenteric plexus, and the muscular cell layer. CONCLUSIONS & INFERENCES: The demonstrated 5-HT3 inhibitory effects may be relevant for boldine's and menthol's alleviating properties on FGID and may encourage clinical studies with the compounds or the plant extracts for CINV and IBS treatment. The found receptor-discriminative properties make boldine and (-)-menthol to potentially useful tools for analyzing structural differences between these receptor subtypes.

Assessment of dopamine (DA) synthesis rate in selected parts of the rat brain with central noradrenergic lesion after administration of 5-HT3 receptor ligands.

INTRODUCTION: The study objective was to determine the effect of central noradrenergic system lesions performed in the early extrafetal life period on dopamine synthesis in the rat brain. The content of L-dihydroxyphenylalanine (L-DOPA) was assessed in the frontal lobe, thalamus, hypothalamus and brain stem of rats by high-pressure chromatography with electrochemical detection (HPLC/ED) after administration of 5-HT3 receptor ligands. MATERIAL AND METHODS: Adult male Wistar rats which underwent central noradrenergic lesions by DSP-4 administration (50 mg/kg m.c. i.p.) on day 1 and 3 of life received i.p. injections of the aromatic amino acid decarboxylase inhibitor (NSD-1050) in a dose of 100 mg/kg b.w. Next, 30 min after NSD-1050 injection, the animals were decapitated by guillotine. Selected brain structures were dissected and L-DOPA content was determined by HPLC/ED. RESULTS AND CONCLUSIONS: A statistically significant reduction was found in DA synthesis in the group of animals with DSP-4 lesions induced by PBG (1-phenylbiguanide, 7.5 mg/kg b.w. i.p.) and ondansetron (1.0 mg/kg b.w. i.p.). Morphine and PBG had no major effect on DA synthesis in the cerebral cortex of both control animals and in rats with noradrenergic lesions. The assessment of the effect of DSP-4 lesions on L-DOPA content in the brain stem after administration of morphine (7.5 mg/kg b.w. s.c.), PBG (7.5 mg/kg b.w. i.p.) or ondansetron (1.0 mg/kg b.w. i.p.) separately or jointly showed a statistically significant increase in the synthesis of DA in animals with DSP-4 lesions, as compared to the control group exposed to 0.9% NaCl and morphine. The analysis of the effect of DSP-4 lesions on L-DOPA content in the thalamus and hypothalamus revealed no statistically significant differences between the control groups of rats and those with DSP-4 lesions. As shown by this model, permanent noradrenergic lesions in animals in the early extra-fetal period result in increased reactivity of the central dopamine system.

Effects of an Atractylodes lancea rhizome extract and a volatile component ß-eudesmol on gastrointestinal motility in mice.

AIM OF THE STUDY: The rhizomes of Atractylodes lancea DC (Compositae) are used clinically to treat gastrointestinal symptoms, including functional dyspepsia and gastroparesis, in China and Japan, but their influence and mechanism on gastrointestinal motility are not yet proven in detail. MATERIALS AND METHODS: This study examined the effects of an Atractylodes lancea extract, and isolated ß-eudesmol, on gastric emptying and small intestinal motility in atropine-, dopamine-, and 5-hydroxytryptamine (5-HT)-treated mice. RESULTS AND CONCLUSIONS: The extract (500 or 1000mg/kg) and ß-eudesmol (50 or 100mg/kg), as well as itopride hydrochloride (a dopamine D(2) receptor antagonist, 10 or 50mg/kg), stimulated small intestinal motility in normal mice. They inhibited reductions in gastric emptying and gastrointestinal motility induced by dopamine (1mg/kg, intraperitoneal injection, ip). The extract (1000mg/kg) and ß-eudesmol (100mg/kg) inhibited the atropine-induced decrease in small intestinal motility, but not gastric emptying. Furthermore, the extract (500 or 1000mg/kg) and ß-eudesmol (25, 50, or 100mg/kg) inhibited reductions in gastric emptying and small intestinal motility caused by 5-HT (4mg/kg, ip) or the 5-HT(3) receptor agonist 1-(3-chlorophenyl) biguanide (0.5mg/kg, ip), but not a 5-HT(2C) receptor agonist. These findings suggest that the extract of Atractylodes lancea and ß-eudesmol may stimulate gastric emptying or small intestinal motility by inhibiting the dopamine D(2) receptor and 5-HT(3) receptor.

Attenuation of 1-(m-chlorophenyl)-biguanide induced hippocampus-dependent memory impairment by a standardised extract of Bacopa monniera (BESEB CDRI-08).

Bacopa monniera is a well-known medhya-rasayana (memory enhancing and rejuvenating) plant in Indian traditional medical system of Ayurveda. The effect of a standardized extract of Bacopa monniera (BESEB CDRI-08) on serotonergic receptors and its influence on other neurotransmitters during hippocampal-dependent learning was evaluated in the present study. Wistar rat pups received a single dose of BESEB CDRI-08 during postnatal days 15-29 showed higher latency during hippocampal-dependent learning accompanied with enhanced 5HT(3A) receptor expression, serotonin and acetylcholine levels in hippocampus. Furthermore, 5HT(3A) receptor agonist 1-(m-chlorophenyl)-biguanide (mCPBG) impaired learning in the passive avoidance task followed by reduction of 5HT(3A) receptor expression, 5HT and ACh levels. Administration of BESEB CDRI-08 along with mCPBG attenuated mCPBG induced behavioral, molecular and neurochemical alterations. Our results suggest that BESEB CDRI-08 possibly acts on serotonergic system, which in turn influences the cholinergic system through 5-HT(3) receptor to improve the hippocampal-dependent task.

Moringa oleifera induced potentiation of serotonin release by 5-HT(3) receptors in experimental ulcer model.

ETHNOPHARMACOLOGICAL RELEVANCE: moringa oleifera (Moringaceae), a perennial plant is widely cultivated throughout the world. Extensive pharmacological studies revealed its promising role in modulation of various disorders like antispasmodic, diuretic, abortifacient, antimicrobial antibacterial, antitubercular, antiviral, antifertility, depressant, anti-inflammatory and anticancer property which promoted us to conduct the study to elucidate its role on experimental gastric ulceration. AIM OF THE STUDY: the aim of the present study was to assess the efficacy of its aqueous leaf extract on protection of gastric ulceration and characterize the possible modulatory mechanism underlying the phenomenon. MATERIALS AND METHODS: adult Holtzman strain albino rats (weight 150-200 g) of either sex were used for the study. Ulceration was induced using aspirin (500 mg/kg body weight) and using Moringa oleifera (MO), a herbal formulation, the modulatory mechanism has been studied and compared with a commonly used antagonist of 5-HT(3) receptors, ondansetron by assessing parameters like mean ulcer index, 5-HT content, EC cell count and mucosal thickness. RESULTS: the results of our study suggest that MO protects ulcer formation by modulating 5-HT secretion through EC cell via 5-HT(3) receptors in gastrointestinal tract. INTERPRETATION AND CONCLUSION: MO showed maximum protective activity at a dose of 300 mg/kg body weight against above-mentioned experimental rat ulcer model by modulating 5-HT secretion through EC cell via 5-HT(3) receptors in gastrointestinal tract which has given a glimpse of a therapeutic approach for gastric ulcer management, which may be beneficially used in contrast to the classical antacid, antihistamine or surgical treatment. Further investigations and proper screening regarding various phytochemicals, alkaloids present within MO leaf will help to formulate effective herbal preparation that will be used to combat gastrointestinal disorders in future.

Mode of action of peppermint oil and (-)-menthol with respect to 5-HT3 receptor subtypes: binding studies, cation uptake by receptor channels and contraction of isolated rat ileum.

Peppermint oil (Mentha × piperita L. (Lamiaceae) has been shown to exert potent antiemetic properties, but its mode of action has not yet been elucidated. Among its active constituents (-)-menthol is the most important. Three different in vitro models were used to investigate the effects on 5-HT(3) receptors (serotonin receptor subtype): [(14)C]guanidinium influx into N1E-115 cells which express 5-HT(3) receptors, isotonic contractions of the isolated rat ileum and equilibrium competition binding studies using a radioactively labelled 5-HT(3) receptor antagonist ([(3)H]GR65630) (3-(5-methyl-1H-imidazol-4-yl)-1-(1-methyl-1H-indol-3-yl)-1-propanone). Both peppermint oil and (-)-menthol inhibited [(14)C]guanidinium influx through 5-HT(3) receptor channels as well as contractions of the ileum induced by serotonin. Neither the peppermint oil nor (-)-menthol, however, was able to displace [(3)H]GR65630 from 5-HT(3) binding sites. It may be concluded that peppermint oil and (-)-menthol exert their antiemetic effect at least partly by acting on the 5-HT(3) receptor ion-channel complex, probably by binding to a modulatory site distinct from the serotonin binding site.

Involvement of opioid, adenosine and 5-HT(3) receptors in antinociceptive effects of an ayurvedic polyherbal formulation.

OBJECTIVE: The present study was undertaken to evaluate the antinociceptive effects of an ayurvedic polyherbal formulation in rats and mice employing the tail immersion test and acetic acid-induced writhing test, respectively. MATERIALS AND METHODS: With the tail immersion method, rats received two different doses (270 and 405 mg/kg BW, p.o.) of a formulation, pethidine (5.4 mg/kg BW, p.o.) as a reference standard and the combination of the higher dose of the formulation with naloxone (2 mg/kg, i.p.), an opioid receptor antagonist, and caffeine (16 mg/kg, i.p.), used as an adenosine receptor antagonist. In the acetic acid-induced writhing test, mice received two different doses (390 and 585 mg/kg, BW, p.o.) of formulation, diclofenac sodium (15 mg/kg, BW, p.o.) as a reference standard and the combination of the higher dose of the polyherbal formulation with ondansetron (0.5 mg/kg, i.p.), a serotonin receptor antagonist. RESULTS: The polyherbal formulation (405 mg/kg) exhibited a significant (p < 0.01) antinociceptive effect using the tail immersion method. In the acetic acid-induced writhing test, the formulation showed significant (p < 0.01) dose-dependent activity. The antinociceptive effect of the polyherbal formulation apparently involved an opiate-like mechanism, since its antinociceptive action was attenuated by naloxone pretreatment. In addition, antinociceptive activity was attenuated by caffeine and reversed by ondansetron pretreatment. CONCLUSION: Our data suggest that the polyherbal formulation possessed centrally and peripherally mediated antinociceptive properties. The activity could be mediated through opioid, adenosine, and serotonin receptors and via inhibition of cyclo-oxygenase- and/or lipoxygenase-dependent pathways.

Effects of protostane-type triterpenoids on the 5-HT3A receptor-mediated ion current in Xenopus oocytes.

Alisol derivatives are unique protostane-type triterpenoid compounds that are isolated from Alismatis rhizoma, which is a well-known traditional medicine in East Asia. In the present study, we investigated the effects of protostane-type triterpenoids (AA, Alisol A; AB, Alisol B; AB-ac, Alisol B 23-acetate; AC-ac, Alisol C 23-aceteate) on 5-HT-induced currents mediated by the human 5-HT(3)A receptor expressed in Xenopus laevis oocytes. Co-treatment with triterpenoids regulated the 5-HT-induced inward peak current in a concentration-dependent and reversible manner. In addition, regulation of I(5-HT) by triterpenoids occurred in a non-competitive manner. Taken together, these results indicate that triterpenoids may regulate the 5-HT(3)A receptors that are expressed in Xenopus oocytes. Furthermore, this regulation of the ligand-gated ion channel activity by triterpenoids may be one of the pharmacological actions of Alismatis rhizoma.

Effects of a bicarbonate-alkaline mineral water on digestive motility in experimental models of functional and inflammatory gastrointestinal disorders.

This study investigates the effects of Uliveto, a bicarbonate-alkaline mineral water, in experimental models of diarrhea, constipation and colitis. Rats were allowed to drink Uliveto or oligomineral water (control) for 30 days. Diarrhea and constipation were evoked by 16,16-dimethyl-prostaglandin E(2) (dmPGE(2)) or loperamide, respectively. Colitis was induced by 2,4-dinitrobenzenesulfonic acid (DNBS) or acetic acid. Gastric emptying, small-intestinal and colonic transit were evaluated. dmPGE(2)-induced diarrhea reduced gastric emptying and increased small-intestinal and colonic transit. In this setting, Uliveto water enhanced gastric emptying, and this effect was prevented by L-365,260 (gastrin receptor antagonist). Loperamide-induced constipation reduced gastric emptying, small-intestinal and colonic transit, and these effects were prevented by Uliveto water. L-365,260 counteracted the effects of Uliveto on gastric emptying, while alosetron (serotonin 5-HT(3) receptor antagonist) blunted the effect of Uliveto on colonic transit. Gastric emptying, small-intestinal and colonic transit were reduced in DNBS-induced colitis, and Uliveto water enhanced gastric emptying and normalized small-intestinal and colonic transit. Gastric emptying, small-intestinal and colonic transit were also reduced in acetic acid-induced colitis, and Uliveto increased both gastric emptying and small-intestinal transit. In conclusion, Uliveto water exerts beneficial effects on gastrointestinal motility in the presence of bowel motor dysfunctions. The effects of Uliveto water on gastric emptying depend on gastrin-mediated mechanisms, whereas the activation of serotonergic pathways accounts for the modulation of colonic functions.

Wood creosote prevents CRF-induced motility via 5-HT3 receptors in proximal and 5-HT4 receptors in distal colon in rats.

Wood creosote has been used as an herbal medicine against acute diarrhea caused by food poisoning and has an inhibitory effect on colonic motility and enterotoxin-induced ion secretion. Since no previous studies have examined the effects of wood creosote on stress-induced alteration of colonic motility, we examined the effects on the colonic motility altered by intracerebroventricular (i.c.v.) injection of corticotropin-releasing factor (CRF), which is a key mediator in responses to stress. We recorded motor activity in proximal and distal colon of unrestrained conscious rats via two manometory catheters. The frequencies of phase III-like contraction and the % motor indices in both proximal and distal colon were measured. At the same time the number of fecal pellets excreted was counted. I.c.v. injection of CRF increased the motor activity in both proximal and distal colon, and these effects were completely antagonized by i.c.v. injection of a selective CRF type 1 antagonist but not by a CRF type 2 antagonist. Changes in colonic motility induced by CRF were reversed by intravenously administered wood creosote. Intraluminal administration of the 5-HT(3) receptor antagonist granisetron, or the 5-HT(4) receptor antagonist SB 204070 blocked the increase in colonic motility induced by i.c.v. injection of CRF. Wood creosote prevented the increase in colonic motility induced by the 5-HT(3) receptor agonist SR57227A in the proximal colon, while it prevented the increase in colonic motility induced by the 5-HT(4) receptor agonist RS67506 in the distal colon. These results indicate that wood creosote prevents the increase in colonic motility induced by CRF via 5-HT(3) receptors in the proximal colon, and via 5-HT(4) receptors in the distal colon, suggesting that wood creosote might be useful to treat stress-induced diarrhea.

A study of the role of serotonin in the anxiolytic effect of nitrous oxide in rodents.

RATIONALE: In earlier studies, we have shown that nitrous oxide (N2O)-induced behavioral effects in rats and mice are mediated by benzodiazepine receptors. OBJECTIVES: This two-part study was conducted in order to investigate the possible role of serotonin (5-HT) in the behavioral effects of N2O by clarifying its effects on regional brain concentrations of 5-HT and assessing the influence of 5-HT antagonist and reuptake inhibiting drugs on the anxiolytic-like behavioral effect of N2O. METHODS: In experiment A, male, 150-200 g Sprague-Dawley rats were killed following a 15-min exposure to room air or 70% N2O. The frontal cortex, hippocampus, corpus striatum and hypothalamus were dissected out and analyzed by HPLC with electrochemical detection for content of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA); dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) were also measured. In experiment B, male 18-22 g NIH Swiss mice were pretreated with the 5-HT2 antagonist cinanserin, the 5-HT3 antagonist LY-278,584, the 5-HT reuptake inhibitor fluoxetine or saline and tested in the light/dark exploration test under 70% N2O 30 min after pretreatment. RESULTS: In experiment A, N2O produced differential effects on 5-HT neurons in distinct brain areas. There was increased 5-HT turnover in the hypothalamus, decreased turnover in the frontal cortex but no changes in either hippocampus or corpus striatum. By comparison, dopamine turnover in these brain regions was unaltered by N2O exposure. In experiment B, pretreatment with neither cinanserin, LY-278,584 nor fluoxetine had any appreciable effect on the N2O-induced increase in time spent in the light compartment. Only cinanserin significantly reduced the N2O-induced increase in transitions. CONCLUSIONS: While neurochemical results suggest an effect of N2O on brain 5-HT function, there was no effect of 5-HT2 or 5-HT3 antagonists or 5-HT reuptake inhibitor on N2O-induced anxiolytic-like behavior.

Effect of ginseng saponins on a rat visceral hypersensitivity model.

The 5-hydroxytryptamine3A (5-HT3) receptor is closely related with irritable bowel syndrome (IBS) in enteric nervous systems. We previously demonstrated that ginseng total saponins (GTS, also called ginsenosides), the active ingredients of Panax ginseng, inhibit the activity of 5-HT3A receptor channels expressed in Xenopus laevis oocytes. Here, we further investigated whether the in vitro inhibitory effect of ginsenosides on 5-HT3A receptor channel activity is coupled to in vivo attenuation of IBS. A rat model of IBS was induced by colorectal distention (CRD) and intracolonic infusion of 0.6% acetic acid (CRD-acetic acid), and visceral hypersensitivity was assessed by counting the contractions in the external oblique muscles of conscious rats during the 10 min distention period. We found that oral administration of GTS significantly and dose-dependently inhibited CRD-acetic acid-induced visceral hypersensitivity. The EC50 was 5.5+/-4.7 mg/kg (95% confidence intervals: 1.2-15.7) and the inhibitory effect of GTS against visceral hypersensitivity persisted for 4 h. When we compared the effects of protopanaxadiol (PD) ginsenosides and protopanaxatriol (PT) ginsenosides against CRD-acetic acid-induced visceral hypersensitivity, we found that PT but not PD ginsenosides significantly attenuated the CRD-acetic acid-induced visceral hypersensitivity. These results indicate that PT ginsenosides of Panax ginseng might be the main active components for the attenuation of experimentally CRD-acetic acid-induced visceral hypersensitivity, and may be clinically relevant for the future treatment of IBS.

Stimulation of the lateral hypothalamus produces antinociception mediated by 5-HT1A, 5-HT1B and 5-HT3 receptors in the rat spinal cord dorsal horn.

The lateral hypothalamus is part of an efferent system that modifies pain at the spinal cord dorsal horn, but the mechanisms by which lateral hypothalamus-induced antinociception occur are not fully understood. Previous work has shown that antinociception produced from electrical stimulation of the lateral hypothalamus is mediated in part by spinally projecting 5-hydroxytryptamine (5-HT) neurons in the ventromedial medulla. To further examine the role of the lateral hypothalamus in antinociception, the cholinergic agonist carbamylcholine chloride (125 nmol) was microinjected into the lateral hypothalamus of female Sprague-Dawley rats and nociceptive responses measured on the tail-flick and foot-withdrawal tests. Intrathecal injections of the selective 5-HT1A, 5-HT1B, 5-HT3 receptor antagonists, WAY 100135, SB-224289, and tropisetron, respectively, and the non-specific antagonist methysergide, were given. Lateral hypothalamus stimulation with carbamylcholine chloride produced significant antinociception that was blocked by WAY 100135, tropisetron, and SB-224289 on both the tail-flick and foot-withdrawal tests. Methysergide was not different from controls on the tail flick test, but increased foot-withdrawal latencies compared with controls. These results suggest that the lateral hypothalamus modifies nociception in part by activating spinally projecting serotonin neurons that act at 5-HT1A, 5-HT1B, and 5-HT3 receptors in the dorsal horn.

5-HT3 receptor blocking activity of arylalkanes isolated from the rhizome of Zingiber officinale.

Different extracts (ethanolic, hexane, aqueous) of ginger (rhizomes of Zingiber officinale) and the essential oil were tested using [14C]guanidinium influx into N1E-115 cells and the isolated rat ileum in order to identify their activity in inhibiting 5-HT3 receptor function. The hexane extract proved to be the most active and yielded upon bioassay-guided fractionation nine constituents: [6]-, [8]-, [10]-gingerols, [6]- and [8]-shogaols which were previously shown as active in vivo against cytotoxic drug-induced emesis; [4]-gingerol, [6]-gingerdiol, diacetyl-[6]-gingerdiol and [6]-dehydrogingerdione have not been previously tested for anti-emetic or 5-HT3 receptor antagonistic effects. Even though the latter four compounds are only minor constituents, their identification contributed towards the characterisation of a structure-activity relationship of this class of compounds. The order of potency for the nine constituents in the N1E-115 cell system was [6]-gingerdiol approximately diacetyl-[6]-gingerdiol approximately [6]-dehydrogingerdione approximately [6]-shogaol > or = [8]-shogaol approximately [8]-gingerol > [10]-gingerol > or = [6]-gingerol > [4]-gingerol.

Cancer chemotherapy-induced nausea and vomiting: role of mediators, development of drugs and treatment methods.

The development of serotonin 5-HT3 receptor antagonists dramatically improved the treatment of chemotherapy-induced nausea and vomiting. Ondansetron, a serotonin 5-HT3 receptor antagonist in combination with dexamethasone is widely used to treat chemotherapy-induced nausea and vomiting. This treatment regimen is effective against acute nausea and vomiting, but fails to control delayed nausea and vomiting. Metoclopramide along with other antiemetics are used to treat delayed nausea and vomiting. The high doses of metoclopramide needed may produce extra pyramidal side effects. The recent developments of 5-HT3 and dopamine D2 dual receptor antagonists have been found to exhibit a broad spectrum of activity against peripherally and centrally acting stimuli, but are not much effective against delayed emesis associated with chemotherapy. In various animal models, neurokinin NK1 receptor antagonists showed promising results against acute and delayed emesis, but the clinical trials revealed that triple therapy (NK1 receptor antagonist, 5-HT3 receptor antagonist and dexamethasone) is superior than standard therapy (5-HT3 receptor antagonist & dexamethasone) or NK1 receptor antagonist alone, in controlling acute as well as delayed nausea and vomiting. Ginger, which is used traditionally for controlling emesis induced by various stimuli, also showed good activity against chemotherapy-induced nausea and vomiting in animal models. Non-pharmacological methods such as acupressure and acustimulation are good adjunct methods in treating nausea and vomiting. Since many mediators are involved in emesis induced by chemotherapy, cocktail treatment is proven to be more efficacious than a single drug, but increases treatment costs. So there is a need of further research in this field to get economically useful methods for the treatment of acute and delayed chemotherapy-induced nausea and vomiting.

A vertical flow chamber for Xenopus oocyte electrophysiology and automated drug screening.

Xenopus laevis oocytes are used extensively in the study of ion channel coupled receptors. Efficient use of oocytes for ion channel characterization requires a system that is inherently stable, reproducible, minimizes drug volumes, and maximizes oocyte longevity. We have constructed a vertical flow oocyte recording chamber to address the aforesaid issues, where the oocyte is placed in a funnel-shaped chamber and perfused from the bottom of the funnel. The vertical rather than horizontal flow of perfusate results in an unusually stable environment for oocyte recording. Two-electrode voltage clamp recordings from a single oocyte are acquired easily and routinely over several hours while maintaining stable baseline currents and reproducible response profiles. Chamber characteristics were tested using a serotonin ligand-gated ion channel receptor (5-HT3R). Data obtained from this system corresponds well with published data. To further test the stability and reliability of this perfusion chamber, we constructed an automated oocyte perfusion system utilizing a commonly available HPLC autosampler. We were able to obtain dose-response curves for various 5-HT3AR ligands using the automated perfusion system with minimal user intervention. Such a system can easily satisfy need for automated oocyte electrophysiology in academic settings, especially small to medium sized laboratories.

Effect of ginseng saponins on the recombinant serotonin type 3A receptor expressed in xenopus oocytes: implication of possible application as an antiemetic.

OBJECTIVES: Nausea and vomiting are the most frequently reported side-effects by patients who are given general anesthesia perioperatively and patients with cancer who undergo chemotherapy or radiotherapy. Serotonin (5-hydroxytryptamine, 5HT) type 3A receptor (5HT(3A) receptor) is known to mediate nausea and vomiting and its antagonists have been used effectively to prevent and/or reduce the incidence and severity of nausea and vomiting. However, the adverse effects on cardiac function, such as QT interval prolongation, limit their routine use by these patients. This study was designed to elucidate the effect of ginseng saponins on the recombinant 5HT(3A) receptor expressed in the xenopus oocyte. DESIGN: After in vitro transcription of the recombinant human 5HT(3A) receptor in the Xenopus laevis oocyte, we examined Panax ginseng saponins (total saponin [TS], panaxadiol saponin [PD] fraction, panaxatriol saponin [PT] fraction, and ginsenoside-Rb1 and -Rg1) for their ability to inhibit current flow through the 5HT(3A) receptor using the voltage-clamp technique. RESULTS: All saponin fractions (TS, PD, PT fraction, as well as ginsenoside-Rb1 and -Rg1) inhibited the peak current induced by the agonist 5HT on the 5HT(3A) receptor in a concentration-dependent, reversible, and voltage-independent manner. The PT fraction inhibited 5HT-induced currents in 5HT(3A) receptor more than the PD fraction; meanwhile, there was a similar degree of inhibition between ginsenoside-Rg1 and -Rb1, the main substitutes of PT fraction and PD saponin fractions, respectively. CONCLUSIONS: These results indicate that ginseng saponins, especially PT fraction, have substantial inhibitory effects on the recombinant 5HT(3A) receptor, suggesting that some of the specific types of ginsenoside might have an antagonistic action against 5HT(3A) receptor related to nausea and vomiting.