Is nitric oxide involved in 5-HT3 receptor-mediated neurogenic relaxation of guinea pig proximal colon?

Antiproliferative Properties of the Serotonin Receptor Antagonist Ondansetron Correlate with Increased Nitric Oxides Release and Inducible Nitric Oxide Synthase Activity in the Acute Lymphoblastic Leukemia Cell Line REH

A recent report from our group described that the (serotonin receptor-3)-antagonist ondansetron exhibits antiproliferative effects in the B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cell line REH. Furthermore, after each application of ondansetron to cultured REH cells, significant increases (+23%) in the concentration of nitric oxides (NO) were observed in the cell supernatants after 72 hours incubation in standard conditions, and this effect was found to correlate with the described antiproliferative activity. This feature was further confirmed by using mRNA dot blot hybridizations with a specific gene probe for the inducible NO-synthase (iNOS), yielding significant increases (+100%) of iNOS mRNA, which were found to widely correlate with the detected increases of NO release, and also with the previously described antiproliferative effects. The presented results are the first report on high specific pro-inflammatory features of a (serotonin receptor 3)-antagonist in a BCP-ALL cell line, which are associated with previously described antiproliferative properties.

Involvement of nitric oxide in granisetron improving effect on scopolamine-induced memory impairment in mice

Granisetron, a serotonin 5-HT(3) receptor antagonist, widely used as an antiemetic drug following chemotherapy, has been found to improve learning and memory. In this study, effects of granisetron on spatial recognition memory and fear memory and the involvement of nitric oxide (NO) have been determined in a Y-maze and passive avoidance test. Granisetron (3, 10mg/kg, intraperitoneally) was administered to scopolamine-induced memory-impaired mice prior to acquisition, consolidation and retrieval phases, either in the presence or in the absence of a non-specific NO synthase inhibitor, l-NAME (3, 10mg/kg, intraperitoneally); a specific inducible NO synthase (iNOS) inhibitor, aminoguanidine (100mg/kg); and a NO precursor, l-arginine (750 mg/kg). It is demonstrated that granisetron improved memory acquisition in a dose-dependent manner, but it was ineffective on consolidation and retrieval phases of memory. The beneficial effect of granisetron (10mg/kg) on memory acquisition was significantly reversed by l-NAME (10mg/kg) and aminoguanidine (100mg/kg); however, l-arginine (750 mg/kg) did not potentiate the effect of sub-effective dose of granisetron (3mg/kg) in memory acquisition phase. It is concluded that nitric oxide is probably involved in improvement of memory acquisition by granisetron in both spatial recognition memory and fear memory. This article is part of a Special Issue entitled The Cognitive Neuroscience.

New benzimidazole derivatives: selective and orally active 5-HT3 receptor antagonists

The synthesis of new 5-HT(3) receptor antagonists is an interesting field of research because of their wide therapeutic use. The aim of this work is to functionally characterise a new series of benzimidazole derivatives previously described. These compounds bind to 5-HT(3) receptors and have been evaluated using in vitro (rat tunica muscularis mucosae) and in vivo tests (Bezold-Jarisch reflex in rat and gastrointestinal motility and spontaneous motility in mice). Ondansetron and 1-[4-amino-5-chloro-2-(3,5-dimethoxyphenil)methyloxy]-3-[1-[2-methylsulfonylamino]piperidin-4-yl]propan-1-one hydrochloride (RS 39604) were used as well known 5-HT(3) and 5-HT(4) receptor antagonists. These benzimidazole derivatives have proved to be 5-HT(3) receptor antagonists. Interestingly, they are as active as ondansetron when they are intraperitoneally (i.p.) or orally (p.o.) administered and, in mice, they seem to induce fewer behavioural changes at similar effective doses than does ondansetron. The present results confirm the usefulness of the previously proposed pharmacophore and justify the interest in these new benzimidazole derivatives.

5-HT-induced, 5-HT3 receptor-mediated, and ruthenium red- and capsaicin-sensitive positive chronotropic effects in the isolated guinea pig atrium

We investigated the mechanisms of 5-HT-induced tachycardia, which we reported previously to be triggered by 5-HT3 receptor stimulation, in the isolated guinea pig atrium in comparison with that induced by isoproterenol and histamine. We found that 5-HT-induced tachycardia was completely inhibited by ruthenium red. 5-HT-induced tachycardia was reduced in the capsaicin pre-treated atrium as well as in the presence of capsaicin. The effects of isoproterenol and histamine were not affected by ruthenium red or capsaicin treatment. Furthermore, 5-HT-induced tachycardia was found to be potentiated by thiorphan, an inhibitor of peptide degeneration. Calcitonin gene-related peptide (CGRP) (1-37), a full agonist of CGRP1-like receptors, was found to act selectively as a potent stimulator of chronotropic action. CGRP (8-37), an antagonist of CGRP1-type receptors, inhibited 5-HT-induced tachycardia as well as effects induced by CGRP (1-37). The observation that tetrodotoxin failed to affect 5-HT-induced tachycardia excluded the involvement of 5-hydroxytryptaminergic interneurons. Thus, we confirmed that the mechanism of 5-HT-induced tachycardia is distinct from that induced by isoproterenol and histamine. In conclusion, the activation of 5-HT3 receptors on the sensory nerve terminals brought about ruthenium red-sensitive Ca2+ influx and resulted in the release of CGRP from capsaicin-sensitive stores, and then CGRP stimulated CGRP1-like receptors to produce 5-HT-induced tachycardia.

Effects of NG-nitro-L-arginine methyl ester, 7-nitro indazole, and agmatine on pentylenetetrazol-induced discriminative stimulus in Long-Evans rats

This study was undertaken to determine any role that nitric oxide (NO) may play in the discriminative stimuli produced by pentylenetetrazol (PTZ). The PTZ-induced discriminative stimulus is pharmacologically similar to anxiety in humans and is used in a behavioral assay of anxiety (the PTZ model of anxiety). In the present study, effects of L-N(G)-nitro arginine methyl ester (L-NAME), 7-nitroindazole (7-NI) and agmatine, NO synthase (NOS) inhibitors, on PTZ-induced discriminative stimulus were investigated in male Long-Evans rats (330-350 g). Rats were trained to discriminate PTZ (16 mg/kg) from saline using a two-lever, food-reinforced choice procedure (FR 10). The rats that met the training criteria were injected with L-NAME (15, 30, and 60 mg/kg), 7-NI (15 and 30 mg/kg), agmatine (20, 40, and 60 mg/kg), and saline or vehicle intraperitoneally before each test. They were tested for the PTZ-discrimination to determine if the NOS inhibitors produce discriminative stimulus similar to PTZ or if they block PTZ-induced discrimination. Treatment with the NOS inhibitory drugs neither substituted for PTZ nor altered the PTZ lever selection in any other way. These findings suggest that PTZ-induced discriminative stimulus may not be related to NO-mediated central mechanisms.

The interaction of immunomodulatory muramyl dipeptide with peripheral 5-HT receptors: overview of the current state

Immunomodulator muramyl dipeptide (MDP) exerts also pronounced neuropharmacological activities which are probably mediated by an interaction with 5-HT receptors. Some of these effects are considered as undesirable by its clinical use. More precise information concerning MDP effects on 5-HT receptors with respect to their many subtypes could result from studies using isolated organs in vitro. Earlier conducted studies of this type provided data that are concisely overviewed and reinterpreted here from the view of current 5-HT receptor classification. Since new 5-HT receptor types have emerged recently, new studies are under way. The results might contribute to the development of novel immunomodulatory drugs devoid of adverse effects.