tropisetron and alpha-methylserotonin

5-HT receptor subtypes are widely expressed in primary sensory neurons, yet so far little is known about the interaction among them. This study aimed to investigate whether the activation of 5-HT2 and 5-HT1 receptors could modulate 5-HT3 receptor mediated current in rat trigeminal ganglion (TG) neurons using whole-cell patch clamp technique. The majority of TG neurons examined responded to 5-HT (10(-7)-10(-3) M) with a fast activating and rapid desensitizing inward current (77.2%, 71/92). This 5-HT activated current (I(5-HT)) was blocked by ICS 205-930 and mimicked by 2-methyl-5-HT, indicating that it was mediated by 5-HT3 receptor. With alpha-methyl-5-HT applied prior to 5-HT application, I(5-HT) was potentiated in a concentration-dependent manner, with the maximal modulatory effect at 10(-9) M of alpha-methyl-5-HT. The concentration-response curve for I(5-HT) pretreated with alpha-methyl-5-HT shifts upwards compared with that for I(5-HT) without alpha-methyl-5-HT pretreatment, the maximal I(5-HT) value having increased by (60.3 +/- 5.7)% of its control while the EC50 values of the two curves being very close, i.e. (2.0 +/- 0.3) x 10(-5) M vs (1.7 +/- 0.2) x 10(-5) M, respectively. The alpha-methyl-5-HT potentiation of I(5-HT) was removed by intracellular dialysis of either GDP-beta-S, a non-hydrolyzable GDP analog, or GF109203X, a selective PKC inhibitor, almost completely. Preapplication of R-(+)-UH-301, a selective agonist of 5-HT(1A) receptor, had no modulatory effect on I(5-HT). These results suggest that in the membrane of TG neurons, the activation of 5-HT2 receptors can exert an enhancing effect on the function of coexistent 5-HT3 receptors while that of 5-HT(1A) receptors cannot.

Topics: Animals; Cell Separation; Dose-Response Relationship, Drug; Guanosine Diphosphate; In Vitro Techniques; Indoles; Maleimides; Membrane Potentials; Neurons; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin, 5-HT1; Receptors, Serotonin, 5-HT3; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Thionucleotides; Trigeminal Ganglion; Tropisetron

The aim of this study was to identify the receptor type(s) by which 5-hydroxytryptamine applied to the intestinal mucosa excites the terminals of myenteric AH neurons. The AH neurons have been identified as the intrinsic primary afferent (sensory) neurons in guinea-pig small intestine and 5-hydroxytryptamine has been identified as a possible intermediate in the sensory transduction process. Intracellular recordings were taken from AH neurons located within 1mm of intact mucosa to which 5-hydroxytryptamine was applied. Trains of action potentials and/or slow depolarizing responses were recorded in AH neurons in response to mucosal application of 5-hydroxytryptamine (10 or 20microM) or the 5-hydroxytryptamine-3 receptor agonist, 2-methyl-5-hydroxytryptamine (1 or 3mM), and to electrical stimulation of the mucosa. The 5-hydroxytryptamine-2 receptor agonist, alpha-methyl-5-hydroxytryptamine (100microM), and the 5-hydroxytryptamine-1,2,4 receptor agonist, 5-methoxytryptamine (10microM), did not elicit such responses. The 5-hydroxytryptamine-3 receptor-selective antagonist, granisetron (typically 1microM), and the 5-hydroxytryptamine-3,4 receptor antagonist, tropisetron (typically 1microM), each reduced or abolished the responses to 5-hydroxytryptamine, while the selective 5-hydroxytryptamine-4 receptor antagonist, SB 204070 (1microM), did not. It is concluded that application of 5-hydroxytryptamine to the mucosa activates a 5-hydroxytryptamine-3 receptor that triggers action potential generation in the mucosal nerve terminals of myenteric AH neurons.

Topics: 5-Methoxytryptamine; Action Potentials; Animals; Dioxanes; Granisetron; Guinea Pigs; Ileum; Indoles; Myenteric Plexus; Neurons, Afferent; Piperidines; Presynaptic Terminals; Receptors, Serotonin; Receptors, Serotonin, 5-HT3; Serotonin; Signal Transduction; Tropisetron

1 Whole cell patch clamp techniques were used on thin brainstem slices to investigate the effects of 5-hydroxytryptamine (5-HT) on gastrointestinal-projecting dorsal motor nucleus of the vagus (DMV) neurones. Neurones were identified as projecting to the stomach (n=122) or intestine (n=84) if they contained the fluorescent tracer Dil after it had been applied to the gastric fundus, corpus or antrum/pylorus or to the duodenum or caecum. 2 A higher proportion of intestinal neurones (69%) than gastric neurones (47%) responded to 5-HT with a concentration-dependent inward current which was antagonized fully by the 5-HT2A receptor antagonist ketanserin (1 microM). 3 Stimulation of the nucleus tractus solitarius (NTS) induced inhibitory synaptic currents that were reduced in amplitude by application of the 5-HT1A receptor agonist 8-OHDPAT (1 microM) or the 5-HT1A/1B receptor agonist TFMPP (1 microM) in 61% and 52% of gastric- and intestinal-projecting neurones, respectively. 5-HT also significantly reduced the frequency but not the amplitude of spontaneous inhibitory currents. 4 These data show that 5-HT excites directly a larger proportion of intestinal projecting neurones than gastric-projecting neurones, as well as inhibiting synaptic transmission from the NTS to the DMV. These data imply that the response to DMV neurones to 5-HT may be determined and classified by their specific projections.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Cesium; Chlorides; Dose-Response Relationship, Drug; Electric Stimulation; Electrophysiology; Excitatory Postsynaptic Potentials; Female; In Vitro Techniques; Indoles; Intestines; Ketanserin; Ligands; Male; Membrane Potentials; Motor Neurons; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT1B; Receptors, Serotonin; Receptors, Serotonin, 5-HT1; Receptors, Serotonin, 5-HT3; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Solitary Nucleus; Stomach; Synaptic Transmission; Tropisetron; Vagus Nerve

1. Activation of abdominal sympathetic afferents during ischaemia reflexly excites the cardiovascular system. We have shown previously that exogenous 5-hydroxytryptamine (5-HT, i.e. serotonin) stimulates abdominal sympathetic afferent nerve endings, and recently have documented increased concentrations of 5-HT in intestinal lymph and portal venous plasma during brief abdominal ischaemia. The present investigation evaluated the role of endogenously produced 5-HT in activation of ischaemically sensitive abdominal sympathetic afferents. 2. Nerve activity of single-unit C fibre afferents innervating duodenum, mesentery, pancreas, portal hepatis, bile duct, gall bladder and jejunum was recorded from the right thoracic sympathetic chain of anaesthetized cats. Ischaemically sensitive C fibre afferents were identified according to their response to 5-10 min of abdominal ischaemia. 3. Intra-arterial injection of 5-HT (20 microg kg-1) increased discharge activity of twelve afferents from 0. 23 +/- 0.05 to 0.96 +/- 0.09 impulses s-1 after an onset latency of 5.7 +/- 1.4 s. Also, 2-methylserotonin (100 microg kg-1, i.a.), a 5-HT3 receptor agonist, stimulated eleven of twelve afferents to significantly increase their discharge activity from 0.25 +/- 0.05 to 0.90 +/- 0.10 impulses s-1 after a latency of 3.3 +/- 0.4 s. Furthermore, intravenous injection of tropisetron (200 microg kg-1), a 5-HT3 receptor antagonist, significantly attenuated the increase in activity of twelve other C fibre afferents during 10 min of abdominal ischaemia from 1.62 +/- 0.18 to 0.94 +/- 0.22 impulses s-1, and eliminated the response of eleven other afferents to 5-HT. 4. Both the 5-HT2 receptor agonist, alpha-methylserotonin (100 microg kg-1, i.a.), and the 5-HT1 receptor agonist, 5-carboxamidotryptamine (100 microg kg-1, i.a.), did not alter the impulse activity of these twelve afferents (0.29 +/- 0.05 to 0.31 +/- 0.06, and 0.26 +/- 0.06 to 0.29 +/- 0.06 impulses s-1, respectively). 5. Treatment with indomethacin (5 mg kg-1, i.v.) in eight different cats did not alter the response of nine C fibre afferents to exogenous 5-HT (0.91 +/- 0. 17 vs. 1.19 +/- 0.25 impulses s-1, P > 0.05). 6. The results suggest that, during mesenteric ischaemia, endogenous 5-HT contributes to the activation of abdominal sympathetic afferents, mainly through direct stimulation of 5-HT3 receptors and that the action of 5-HT on these afferents appears to be independent of the cyclo-oxygenase pathway.

Topics: Adrenergic Fibers; Animals; Anti-Inflammatory Agents, Non-Steroidal; Cats; Electrophysiology; Female; Ganglia, Sympathetic; Indoles; Indomethacin; Ischemia; Male; Neurons, Afferent; Pain; Prostaglandins; Receptors, Serotonin; Receptors, Serotonin, 5-HT3; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Splanchnic Circulation; Tropisetron; Viscera

The effects of 5-hydroxytryptamine (5-HT) and its receptor subtype agonists on spontaneous propulsive activities of the segment, and on changes in tension of the muscle strips were examined in the guinea-pig isolated distal colon. 5-HT, 5-carboxamidotryptamine (5-CT), alpha-methyl-5-HT and t-methoxytryptamine (5-MeOH), applied to the serosal side of the segment, inhibited spontaneous propulsive activities, but 2-methyl-5-HT did not. On the indomethacin-treated segment, 5-HT and its receptor subtype agonists all stimulated propulsive activity. 5-HT, 5-CT, alpha-methyl-5-HT and 5-MeOH relaxed circular muscle strips, which were inhibited in the presence of tetrodotoxin. However, these agonists showed contractile effects on the indomethacin-treated circular muscle strips. These results suggest that 5-HT may inhibit spontaneous propulsive activities of the colonic segment via release of endogenous PGs (e.g., E and I types) in the circular muscle cells mediated by an inhibitory neurotransmitter, which release was stimulated by 5-HT1-like 5-HT2 and 5-HT4 receptors on the myenteric neurones in the circular muscle layer.

Topics: 5-Methoxytryptamine; Animals; Colon; Dose-Response Relationship, Drug; Guinea Pigs; In Vitro Techniques; Indoles; Indomethacin; Ketanserin; Male; Muscle Contraction; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tetrodotoxin; Tropisetron

5-Hydroxytryptamine (5-HT) contracts and relaxes isolated stomach preparations. This study attempts to characterise receptors involved in the contractile response using electrically stimulated circular muscle strips from guinea pig stomach. Electrically induced contractions were abolished by atropine and tetrodotoxin. 5-HT enhanced contractions in corpus and fundus strips with pEC50% values (-log10 of the concentrations causing a 50% increase in twitch height) of 9.6 and 9.1, respectively. 5-Carboxamidotryptamine and 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), 5-HT1A receptor agonists, and alpha-methyl-5-HT, an agonist at 5-HT2 receptors, reduced contractions. The 5-HT3 receptor agonist, 2-methyl-5-HT, increased contractions. The effect of 2-methyl-5-HT but not of 5-HT was antagonized by the 5-HT3 receptor antagonist, tropisetron (10(-7) M). The 5-HT3 receptor antagonists, tropisetron, MDL 72222 (1 alpha H,3 alpha,5 alpha H-tropan-3-yl-3,5-dichlorobenzoate), grainsetron and ondansetron, did not modify twitch responses at concentrations below 10(-7) M. Renzapride and metoclopramide, agonists at 5-HT4 receptors, increased contractions and this effect was inhibited by the 5-HT4 receptor antagonist SDZ 205-557 (2-methoxy-4-amino-5-chloro-benzoic acid 2-(diethylamino) ethyl ester) with a pA2 of 7.4. The effect of 5-HT at a submaximal concentration of 10(-8) M was blocked by SDZ 205-557 (10(-6) M). It is concluded that electrically induced contractions in guinea pig stomach strips are enhanced by activation of 5-HT3- and 5-HT4 receptors and are diminished by 5-HT1 receptor agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 4-Aminobenzoic Acid; 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Atropine; Benzamides; Binding Sites; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Electric Stimulation; Female; Guinea Pigs; In Vitro Techniques; Indoles; Ligands; Male; Metoclopramide; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; para-Aminobenzoates; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Stomach; Tetrodotoxin; Tropanes; Tropisetron

1. Despite the fact that 5-hydroxytryptamine (5-HT)-induced contractions of the rabbit isolated renal artery are mediated by a receptor belonging to the heterogeneous 5-HT1-like category, we observed that the so-called selective 5-HT3 receptor agonist, 2-methyl-5-HT, caused a concentration-dependent contraction of this vessel. This study was therefore undertaken to analyze the effects of 2-methyl-5-HT in the renal artery segments, either quiescent or precontracted with U46619 (10(-7) M). alpha-Methyl-5-HT and 5-methoxytryptamine, which have high affinities for 5-HT2 and 5-HT4 receptors, respectively, were used for comparison. 2. In the precontracted vessel segments, the maximum contractile responses obtained with 2-methyl-5-HT, alpha-methyl-5-HT, 5-methoxytryptamine and 5-HT were similar to those in the quiescent segments. However the pD2 values were higher in the precontracted segments, making them about 4-100 fold more sensitive. 3. Neither MDL 72222 (10(-6) M) nor tropisetron (3 x 10(-6) M) suppressed renal artery contractions elicited by 5-HT, 2-methyl-5-HT, alpha-methyl-5-HT or 5-methoxytryptamine, thus ruling out the involvement of 5-HT3 as well as 5-HT4 receptors. 4. On the other hand, both methiothepin (10(-8) and 10(-7) M) and ketanserin (10(-7) and 10(-6) M) caused a rightward shift of agonist concentration-effect curves.The two antagonists had similar pA2 values against the different agonists tested on either quiescent or precontracted vessels, but ketanserin (apparent pA2: 6.6 to 7.0) was between 20-100 fold less potent than methiothepin (apparent pA2: 8.4 to 8.8).5. The results of this functional study permit us to conclude that the contractile effects of 2-methyl-5-HT as well as ct-methyl-5-HT and 5-methoxytryptamine on the rabbit isolated renal artery are mediated by a 5-HT1-like receptor. Since, in addition, the reported ligand binding affinity of 2-methyl-5-HT at 5-HT3 receptors is similar to both the ligand binding affinity and the functional pD2 at 5-HTI sites, this compound cannot be regarded as a selective 5-HT3 receptor agonist. Similarly, a-methyl-5-HT and 5-methoxytryptamine have only a limited selectivity for 5-HT2 and 5-HT4 receptors, respectively.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; In Vitro Techniques; Indoles; Muscle Contraction; Muscle, Smooth, Vascular; Prostaglandin Endoperoxides, Synthetic; Rabbits; Receptors, Serotonin; Renal Artery; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tropanes; Tropisetron; Vasoconstriction

Intravenously administered 5-HT and the 5-HT3 selective agonist, 2CH3-5-HT, and the 5-HT2 selective agonist, alpha-CH3-5-HT, transiently increased heart rate in conscious, instrumented dogs. 5-HT, alpha-CH3-5-HT and 2CH3-5-HT increased systolic blood pressure in conscious dogs. The increase in blood pressure produced by alpha-CH3-5-HT was blocked by the 5-HT2 selective antagonist, LY53857, supporting a role for vascular 5-HT2 receptors in the pressor response to these amines. In contrast, LY53857 did not antagonize tachycardia produced by 2CH3-5-HT. Furthermore, propranolol also did not block 2CH3-5-HT-induced tachycardia, indicating that an indirect neuronal effect to release norepinephrine cannot explain the increase in heart rate to 2CH3-5-HT. Tachycardia to 2CH3-5-HT (as well as to isoproterenol) was modestly inhibited, but never abolished by interruption of the autonomic nervous system with atropine or hexamethonium. 5-HT3 receptor antagonists, zacopride, ICS 205-930 and GR38032F, dose-dependently blocked the tachycardia and pressor response to 2CH3-5-HT. These data establish the presence of a 5-HT3 receptor mediating a direct positive chronotropic effect of 5-HT in conscious dogs, an effect that depends, only minimally, on the presence of an intact autonomic nervous system.

Topics: Animals; Benzamides; Blood Pressure; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Dogs; Ergolines; Heart Rate; Hexamethonium; Hexamethonium Compounds; Imidazoles; Indoles; Male; Ondansetron; Receptors, Serotonin; Serotonin; Tropisetron

1. 5-Hydroxytryptamine (5-HT) was applied by microiontophoresis in the vicinity of identified sympathetic preganglionic neurones in the upper thoracic spinal cord of the rat, in vivo. 2. Sympathetic preganglionic neurones responded in one of three ways to 5-HT: by (a) excitation (76%), (b) inhibition (4%) or (c) in a biphasic manner (5%). 3. The excitatory responses evoked by 5-HT were mimicked by 5-carboxamidotryptamine (5-CT) and alpha-methyl-5-hydroxytryptamine (alpha-Me-5-HT). The inhibitory and biphasic responses evoked by 5-HT were mimicked by 2-methyl-5-hydroxytryptamine (2-Me-5-HT). The observed responses evoked by 5-HT and selective agonists may be different on the same cell. In several instances a single neurone excited by one agonist was inhibited by another agonist. 4. The 5-HT2-receptor antagonists, ketanserin and LY 53857, failed to abolish selectively the excitatory responses evoked by 5-HT and alpha-Me-5-HT, when applied by microiontophoresis. The antagonists non-selectively reduced the excitatory responses evoked by 5-HT, 5-CT, alpha-Me-5-HT, D,L-homocysteic acid (DLH) and noradrenaline (NA). A reduction in synaptically evoked activity was also observed. 5. The 5-HT3-receptor antagonist, ICS 205-930, failed to abolish the inhibitory responses evoked by 5-HT. 6. It was concluded that the excitatory responses evoked by 5-HT are mediated by a receptor that is neither 5-HT2 or 5-HT3, but shows similarities to the 5-HT1-like receptor profile. The inhibitory actions of 5-HT are mimicked by 2-Me-5-HT, but the receptor is not 5-HT3, or 5-HT1-like or 5-HT2.

Topics: Anesthesia; Animals; Electric Stimulation; Ergolines; Ganglia, Sympathetic; Homocysteine; Indoles; Iontophoresis; Ketanserin; Male; Neurons; Norepinephrine; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Tropisetron