Pharmacological evaluation of a novel corticotropin-releasing factor 1 receptor antagonist T-3047928 in stress-induced animal models in a comparison with alosetron.

BACKGROUND: The major symptoms of irritable bowel syndrome (IBS) are changes in bowel habits and abdominal pain. Psychological stress is the major pathophysiological components of IBS. Corticotropin-releasing factor (CRF) is a well-known integrator in response to psychological stress. In this study, a novel CRF1 receptor antagonist T-3047928 was evaluated in stress-induced IBS models of rats to explore its potency for IBS. METHODS: Plasma adrenocorticotropic hormone (ACTH) levels after intravenous oCRH challenge were measured as a pharmacodynamic marker. Efficacies of oral T-3047928 were compared with oral alosetron, a 5-HT3 antagonist, on conditioning fear stress (CFS)-induced defecation, restraint stress (RS)-induced acute visceral pain, specific alteration of rhythm in temperature (SART) stress-induced chronic visceral pain, and normal defecation. RESULTS: T-3047928 (1-10 mg/kg, p.o.) demonstrated a dose-dependent inhibition on oCRH-induced ACTH secretion. In disease models, T-3047928 suppressed fecal pellet output induced by CFS and improved both acute and chronic visceral hypersensitivity induced by RS and SART stress, respectively. Alosetron was also efficacious in stress-induced defecation and visceral pain models at 1 and 10 mg/kg, respectively. Alosetron, however, also suppressed normal defecation at lower those. On the other hand, T-3047928 did not change normal defecation even at higher dose than those in disease models. CONCLUSION: T-3047928 is an orally active CRF1 antagonist that demonstrated potent inhibitory effects in stress-associated IBS models with no effect on normal defecation. Therefore, it is suggested that T-3047928 may have a potency as a novel option for IBS-D therapy with minimal constipation risk.

Prolongation of bronchopulmonary C-fiber-mediated apnea by prenatal nicotinic exposure in rat pups: role of 5-HT3 receptors.

Prenatal nicotinic exposure (PNE) reportedly sensitizes bronchopulmonary C-fibers (PCFs) and prolongs PCF-mediated apnea in rat pups, contributing to the pathogenesis of sudden infant death syndrome. Serotonin, or 5-hydroxytryptamine (5-HT), induces apnea via acting on 5-HT receptor 3 (5-HT3R) in PCFs, and among the 5-HT3R subunits, 5-HT3B is responsible for shortening the decay time of 5-HT3R-mediated currents. We examined whether PNE would promote pulmonary 5-HT secretion and prolong the apnea mediated by 5-HT3Rs in PCFs via affecting the 5-HT3B subunit. To this end, the following variables were compared between the control and PNE rat pups: 1) the 5-HT content in bronchoalveolar lavage fluid, 2) the apneic response to the right atrial bolus injection of phenylbiguanide (a 5-HT3R agonist) before and after PCF inactivation, 3) 5-HT3R currents and the stimulus threshold of the action currents of vagal pulmonary C-neurons, and 4) the immunoreactivity (IR) and mRNA expression of 5-HT3A and 5-HT3B in these neurons. Our results showed that PNE up-regulated the pulmonary 5-HT concentration and strengthened the PCF 5-HT3R-mediated apnea. PNE significantly facilitated neural excitability by shortening the decay time of 5-HT3R currents, lowering the stimulus threshold, and increasing 5-HT3B IR. In summary, PNE prolongs the apnea mediated by 5-HT3Rs in PCFs, likely by increasing 5-HT3B subunits to enhance the excitability of 5-HT3 channels.-Zhao, L., Gao, X., Zhuang, J., Wallen, M., Leng, S., Xu, F. Prolongation of bronchopulmonary C-fiber-mediated apnea by prenatal nicotinic exposure in rat pups: role of 5-HT3 receptors.

Opposing effects of bronchopulmonary C-fiber subtypes on cough in guinea pigs.

We have addressed the hypothesis that the opposing effects of bronchopulmonary C-fiber activation on cough are attributable to the activation of C-fiber subtypes. Coughing was evoked in anesthetized guinea pigs by citric acid (0.001-2 M) applied topically in 100-µl aliquots to the tracheal mucosa. In control preparations, citric acid evoked 10 ± 1 coughs cumulatively. Selective activation of the pulmonary C fibers arising from the nodose ganglia with either aerosols or continuous intravenous infusion of adenosine or the 5-HT3 receptor-selective agonist 2-methyl-5-HT nearly abolished coughing evoked subsequently by topical citric acid challenge. Delivering adenosine or 2-methyl-5-HT directly to the tracheal mucosa (where few if any nodose C fibers terminate) was without effect on citric acid-evoked cough. These actions of pulmonary administration of adenosine and 2-methyl-5-HT were accompanied by an increase in respiratory rate, but it is unlikely that the change in respiratory pattern caused the decrease in coughing, as the rapidly adapting receptor stimulant histamine also produced a marked tachypnea but was without effect on cough. In awake guinea pigs, adenosine failed to evoke coughing but reduced coughing induced by the nonselective C-fiber stimulant capsaicin. We conclude that bronchopulmonary C-fiber subtypes in guinea pigs have opposing effects on cough, with airway C fibers arising from the jugular ganglia initiating and/or sensitizing the cough reflex and the intrapulmonary C fibers arising from the nodose ganglia actively inhibiting cough upon activation.

Contrasting effects of 5-HT3 receptor stimulation of the nucleus accumbens or ventral tegmentum on food intake in the rat.

Although serotonin (5-HT) signaling is known to regulate food intake and energy homeostasis, the roles of the 5-HT3 receptor in feeding processes have been elusive. 5-HT3 receptors are found throughout mesolimbic circuitry that promote feeding not only in response to hunger, but also to the palatable and rewarding properties of food. These experiments examined if stimulation or blockade of the 5-HT3 receptor of the nucleus accumbens (NAcc) or ventral tegmentum affected food intake in the rat in response to hunger or the presence of a palatable diet. Rats (N=6-9/group) received bilateral injections of the 5-HT3 agonist m-chlorophenylbiguanide hydrochloride (mCPBG; at 0.0, 10.0, or 20.0µg/0.5µl/side) or the 5-HT3 antagonist ondansetron hydrochloride (at 0.0, 1.0, 2.0, or 5.0µg/0.5µl/side) into either the NAcc or the ventral tegmentum. NAcc 5-HT3 receptor stimulation significantly increased 2-h food intake in food-deprived animals offered rat chow and in a separate group of unrestricted rats offered a sweetened fat diet. In contrast to the feeding increase seen with NAcc treatments, stimulation of 5-HT3 receptors of the ventral tegmentum significantly reduced food and water intake in food-restricted animals; reductions of intake in non-restricted rats offered the palatable diet did not approach significance. Blockade of the 5-HT3 receptor had no effect on feeding in either brain region. These data support a functional role for serotonergic signaling in the mesolimbic pathway on motivated behavior, and demonstrate that 5-HT3 receptors differentially modulate food consumption in a region-dependent manner.

Sleep Deprivation-Induced Blood-Brain Barrier Breakdown and Brain Dysfunction are Exacerbated by Size-Related Exposure to Ag and Cu Nanoparticles. Neuroprotective Effects of a 5-HT3 Receptor Antagonist Ondansetron.

Military personnel are often subjected to sleep deprivation (SD) during combat operations. Since SD is a severe stress and alters neurochemical metabolism in the brain, a possibility exists that acute or long-term SD will influence blood-brain barrier (BBB) function and brain pathology. This hypothesis was examined in young adult rats (age 12 to 14 weeks) using an inverted flowerpot model. Rats were placed over an inverted flowerpot platform (6.5 cm diameter) in a water pool where the water levels are just 3 cm below the surface. In this model, animals can go to sleep for brief periods but cannot achieve deep sleep as they would fall into water and thus experience sleep interruption. These animals showed leakage of Evans blue in the cerebellum, hippocampus, caudate nucleus, parietal, temporal, occipital, cingulate cerebral cortices, and brain stem. The ventricular walls of the lateral and fourth ventricles were also stained blue, indicating disruption of the BBB and the blood-cerebrospinal fluid barrier (BCSFB). Breakdown of the BBB or the BCSFB fluid barrier was progressive in nature from 12 to 48 h but no apparent differences in BBB leakage were seen between 48 and 72 h of SD. Interestingly, rats treated with metal nanoparticles, e.g., Cu or Ag, showed profound exacerbation of BBB disruption by 1.5- to 4-fold, depending on the duration of SD. Measurement of plasma and brain serotonin showed a close correlation between BBB disruption and the amine level. Repeated treatment with the serotonin 5-HT3 receptor antagonist ondansetron (1 mg/kg, s.c.) 4 and 8 h after SD markedly reduced BBB disruption and brain pathology after 12 to 24 h SD but not following 48 or 72 h after SD. However, TiO2-nanowired ondansetron (1 mg/kg, s.c) in an identical manner induced neuroprotection in rats following 48 or 72 h SD. However, plasma and serotonin levels were not affected by ondansetron treatment. Taken together, our observations are the first to show that (i) SD could induce BBB disruption and brain pathology, (ii) nanoparticles exacerbate SD-induced brain damage, and (iii) serotonin 5-HT3 receptor antagonist ondansetron is neuroprotective in SD that is further potentiated byTiO2-nanowired delivery, not reported earlier.

Tropisetron diminishes demyelination and disease severity in an animal model of multiple sclerosis.

Tropisetron, a selective 5-HT3 receptor (5-HT3R) antagonist, has been widely used to counteract chemotherapy-induced emesis. New investigations described the immunomodulatory properties of tropisetron which may not be 5HT3R mediated. In the present study, we assessed the potential effects of tropisetron on an animal model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). EAE was induced in C57BL/6 mice by myelin oligodendrocyte glycoprotein peptide (MOG35-55) immunization. Animals were treated with tropisetron (5 mg/kg/day); m-chlorophenylbiguanide (mCPBG), a selective 5-HT3R agonist (10 mg/kg/day); tropisetron (5 mg/kg/day) plus mCPBG (10 mg/kg/day), and granisetron (5 mg/kg/day) intraperitoneally on days 3-35 post-immunization. Treatment with tropisetron and granisetron markedly suppressed the clinical symptoms of EAE (p<0.001) and reduced leukocyte infiltration as well as demyelination in the spinal cord (p<0.05). In addition, in vivo tropisetron, granisetron or tropisetron plus mCPBG therapy greatly reduced in vitro MOG35-55-stimulated proliferation of mononuclear cells from spleens, and MOG35-55-induced IL-2, IL-6 and IL-17 production by splenocytes isolated from EAE-induced mice (p<0.05). Concurrent administration of tropisetron and mCPBG did not significantly alter the histological damage in the spinal cord. mCPBG had no effect on the mentioned parameters. Taken together, these findings indicate that tropisetron has considerable immunoregulatory functions in EAE and may be promising for the treatment of MS or other autoimmune and inflammatory diseases of the CNS. Furthermore, beneficial effects of tropisetron in this setting seem to be both receptor dependent and receptor independent in the early phase of the disease.