Interaction of S 21007 with 5-HT3 receptors. In vitro and in vivo characterization.

The interaction of S 21007 [5-(4-benzyl piperazin-1-yl)4H pyrrolo [1,2-a]thieno[3,2-e]pyrazine] with serotonin 5-HT3 receptors was investigated using biochemical, electrophysiological and functional assays. Binding studies using membranes from N1E-115 neuroblastoma cells showed that S 21007 is a selective high affinity (IC50 = 2.8 nM) 5-HT3 receptor ligand. As expected of an agonist, S 21007 stimulated the uptake of [14C]guanidinium (EC50 approximately 10 nM) in NG 108-15 cells exposed to substance P, and this effect could be prevented by the potent 5-HT3 receptor antagonist ondansetron. In addition, like 5-HT and other 5-HT3 receptor agonists (phenylbiguanide and 3-chloro-phenylbiguanide), S 21007 (EC50 = 27 microM) produced a rapid inward current in N1E-115 cells. The 5-HT3 receptor agonist action of S 21007 was also demonstrated in urethane-anaesthetized rats as this drug (120 micrograms/kg i.v.) triggered the Bezold-Jarisch reflex (rapid fall in heart rate), and this action could be prevented by pretreatment with the potent 5-HT3 receptor antagonist zacopride. Finally, in line with its 5-HT3 receptor agonist properties, S 21007 also triggered emesis in the ferret. Evidence for 5-HT3 receptor antagonist-like properties of S 21007 was also obtained in some of these experiments since previous exposure to this compound prevented both the 5-HT-induced current in N1E-115 cells and the Bezold-Jarisch reflex elicited by an i.v. bolus of 5-HT (30 micrograms/kg) in urethane-anaesthetized rats. These data suggest that S 21007 is a selective 5-HT3 receptor agonist which can exhibit antagonist-like properties either by triggering a long lasting receptor desensitization or by a partial agonist activity at 5-HT3 receptors in some tissues.

Novel, potent, and selective 5-HT3 receptor antagonists based on the arylpiperazine skeleton: synthesis, structure, biological activity, and comparative molecular field analysis studies.

Synthesis and pharmacological evaluation of a series of condensed quinoline derivatives bearing a basic nitrogen on piperazine or [(dimethylamino)ethyl]thio moieties attached at the 2-position of the quinoline nucleus are described. 5-HT receptor binding studies revealed, for most of the compounds studied, nanomolar affinity for the 5-HT3 receptor subtype. The most active compound, benzopyrano[3,4-c]quinoline derivative 5f, displayed a Ki value very similar to that reported for quipazine along with an improved selectivity. Functional and in vivo testing carried out on three selected compounds showed that 5f,j,n are potent 5-HT3 receptor antagonists with potencies in the same range as the best known 5-HT3 receptor antagonists ondansetron, tropisetron, and zacopride. The crystal and molecular structures of compounds 5f,j,n were determined by single-crystal X-ray diffraction and used as starting structures for molecular modeling studies. Comparative molecular field analysis (CoMFA) was applied to binding constants of compounds 5a-p and 6a-h. The cross-validated r2, derived from partial least-squares calculations, indicated a good predictive capacity for affinity values in the series of compounds investigated. Evidence for the prediction capacity is provided in the form of plots of actual vs predicted pKi values. The steric and electrostatic features of the CoMFA-derived model are presented as standard coefficient contour maps of steric and electrostatic fields.

Cardiovascular effects of 5HT2 and 5HT3 receptor stimulation in the nucleus tractus solitarius of spontaneously hypertensive rats.

The effects of local application of 5-HT2- and 5-HT3-receptor agonists in the nucleus tractus solitarius (NTS) on the cardiovascular parameters were investigated in anaesthetized spontaneously hypertensive (SH) rats and their genetically normotensive precursors (WKY). Unilateral microinjection of picomolar doses of a 5HT2 receptor agonist, 2,5-dimethoxy-3-bromo-amphetamine (DOB, 0.025-0.5 pmol), produced a dose-dependent hypotension and bradycardia in both SH and WKY rats. These effects could be prevented by prior local microinjection of a 5-HT2 receptor antagonist, ketanserin (10 pmol). However, for both cardiovascular parameters, DOB was more potent in SH than in WKY rats. Thus, the dose-related responses to DOB were shifted to the left in SH as compared to WKY rats. Bilateral microinjection of the 5-HT3 receptor agonist, phenylbiguanide (1.7-5 nmol), produced an increase in blood pressure and reduced the cardiovagal component of the baroreflex. These effects were not significantly different in SH and WKY rats. These data suggest that 5-HT2 receptors, but not 5-HT3 receptors, are supersensitive in the NTS of SH rats.

5-HT2 receptors in the nucleus tractus solitarius: characterisation and role in cardiovascular regulation in the rat.

The effects of the local application of drugs acting on 5-HT2 receptors in the nucleus tractus solitarius (NTS) on the heart rate and blood pressure were investigated in normal and nodose ganglionectomized anaesthetized rats. The unilateral micro-injection of an agonist such as 2,5-dimethoxy-3-bromo-amphetamine (DOB) (0.1-0.5 pmol) or 2,5-dimethoxy-3-nitroamphetamine (DON) (0.1-0.5 pmol) produced a dose-dependent hypotension and bradycardia in both intact and ganglionectomized animals. These cardiovascular effects were similar to those observed after the unilateral micro-injection of low doses (pmol) of 5-HT, and could be prevented by the prior micro-injections of the 5-HT2 antagonists ketanserin, ritanserin and piremperone. These findings support the hypothesis that 5-HT2 receptors within the NTS play a role in the reflex regulation of blood pressure. In addition, it was also observed that the micro-injection of subthreshold doses of 5-HT or DOB significantly enhanced the hypotension and bradycardia produced by the unilateral micro-injection of N-methyl-D-aspartate (NMDA). The potentiation of NMDA depressor effects by 5-HT or DOB could be totally prevented by ketanserin or piremperone, suggesting that 5-HT acting upon 5-HT2 receptors in the NTS may intervene in the reflex control of blood pressure by modulating the glutamatergic transmission.

Baroreceptor reflex inhibition induced by the stimulation of serotonin3 receptors in the nucleus tractus solitarius of the rat.

Previous studies suggested that in the nucleus tractus solitarius, cardiovascular responses to serotonin may involve the simultaneous activation of more than one receptor subtype. In the present study, the cardiovascular effects of the local application of serotonin and different serotonin3 agonists and antagonists into the nucleus tractus solitarius were analysed in intact and unilaterally ganglionectomized rats. Unilateral injections of serotonin (5-15 nmol) produced a dose-dependent increase in blood pressure and partially antagonized the arterial baroreflex responses evoked by an i.v. injection of phenylephrine. Similar blood pressures response were obtained after unilateral microinjections of phenylbiguanide (5 nmol) and 2-methyl-serotonin (5 nmol), two serotonin3 receptor agonists. Bilateral microinjections of serotonin or phenylbiguanide produced more pronounced blood pressure effects and antagonized completely the baroreflex responses. Both blood pressure and baroreflex effects were antagonized by prior injections of specific serotonin3 antagonists such as zacopride (100 pmol) and ondansetron (100 pmol). Concomitant autoradiographic studies performed in intact and ganglionectomized rats, using [125I]iodozacopride, confirmed that serotonin3 receptors in the nucleus tractus solitarius are mainly located on vagal afferent fibers. In addition, serotonin microinjections made in the nucleus tractus solitarius ipsilateral to the ganglionectomy revealed a significant reduction in cardiovascular responses compared to intact animals. These results suggest that in the nucleus tractus solitarius of the rat, serotonin is involved in the reflex regulation of blood pressure through the stimulation of serotonin3 receptors presumably located on vagal afferent fibers. Since bicuculline antagonized the serotonin-mediated pressor responses, a serotonin3-dependent activation of an inhibitory GABAergic system within the nucleus tractus solitarius might be involved in blood pressure regulatory mechanisms.

[Preclinical pharmacology of amoxapine and amitriptyline. Implications of serotoninergic and opiodergic systems in their central effect in rats]. / Pharmacologie préclinique de l'amoxapine et de l'amitriptyline. Implications des systèmes sérotoninergiques et opioïdergiques dans leurs effets centraux chez le rat.

The effects of two antidepressant drugs, amoxapine and amitriptyline, that belong to distinct chemical classes, have been examined on various biochemical parameters related to serotoninergic and opioidergic neurotransmission in the rat brain and spinal cord. In vitro binding studies showed that both amoxapine and amitriptyline interact in the nanomolar range with 5-HT2 receptors labelled by [3H]ketanserin in cortical membranes. By contrast, neither amoxapine nor amitriptyline can be considered as possible ligands of 5-HT1A and 5-HT1B receptors because their affinities for these sites are in the micromolar range (or even worse). Interestingly, amoxapine binds with a good affinity (IC50 = 0.30 microM) to 5-HT3 receptors labelled by [3H]zacopride in cortical membranes. Complementary experiments using the 5-HT3-dependent Bezold-Jarisch reflex confirmed that amoxapine really acts in vivo as a 5-HT3 antagonist (IC50 = 50 micrograms/kg i.v.), whereas amitriptyline is essentially inactive on 5-HT3 receptors. The second part of this study consisted of looking for possible changes in central 5-HT receptors 24 h after either a single or a repeated (for 14 days) treatment with amoxapine (10 mg/kg i.p. each day) or amitriptyline (10 mg/kg i.p.). A marked decrease in the density of 5-HT2 receptors was found in the cerebral cortex in both treatment groups. By contrast, neither 5-HT1A nor 5-HT1B receptors were significantly affected in any brain region studied. Finally we explored whether acute and/or chronic administration of amoxapine or amitriptyline affected the levels of opioid peptides and the mu and delta classes of opioid receptors in various regions of the brain and the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Sleep changes induced by the local application of 5,7-dihydroxytryptamine into the nodose ganglia and aortic denervation in the rat.

The effects of a bilateral microinjection of 5,7-dihydroxytryptamine (5,7-DHT) into the nodose ganglia and aortic denervation on the daily amounts of sleep/wake states were studied in rats. Both lesions produced an increase in paradoxical sleep and provoked the onset of paradoxical sleep episodes without slow-wave-sleep transition ("narcolepsy-like" paradoxical sleep episodes). The increase in paradoxical sleep observed after 5,7-DHT injection was more important than that of the aortic denervation. In addition, both 5,7-DHT-treated and aortic-denervated animals exhibited a delayed decrease in slow-wave sleep associated with an increase in wakefulness. These results show that the peripheral messages coming from aortic serotonergic afferent fibres to the nucleus tractus solitarius play a modulatory role in the daily expression of paradoxical sleep in rats.

Cardiovascular effects of the local injection of 5,7-dihydroxytryptamine into the nodose ganglia and nucleus tractus solitarius in awake freely moving rats.

The role of the nucleus tractus solitarius (NTS) serotonergic afferents in cardiovascular (CV) regulation is yet to be established. However, several findings suggest that in this nucleus the serotonergic endings coming from the nodose ganglia (NG) are involved in the control of blood pressure (BP). The purpose of the present study was to identify the CV effects of the destruction of this NG-NTS serotonergic pathway. For that, the BP, BP variability (BPV) and heart rate (HR) effects of the local microinjection of 5,7-dihydroxytryptamine (5,7-DHT), into the NG and NTS were investigated in awake freely moving rats. The local degeneration of serotonergic elements was associated with a significant decrease in the 5-HT and 5-hydroxyindole acetic acid levels within the NG and NTS in 5,7-DHT treated rats. In addition, the microinjection of the neurotoxin in both structures produced a transient and significant increase in BP. This effect was of greater amplitude and associated with an increase in BPV in NG lesioned rats. These results may indicate that the NG-NTS serotonergic pathway participates in the transfer of the messages arising from the aortic baroreceptors. However, the vagal component of the baroreflex assessed with the phenylephrine test was not significantly modified in NG lesioned animals as compared to controls. Consequently, if the present data suggest that the NG-NTS serotonergic pathway plays a depressor role in BP regulation, its involvement in the reflex CV responses triggered by the stimulation of the aortic baroreceptors has yet to be established.

Serotonergic projections from the nodose ganglia to the nucleus tractus solitarius: an immunohistochemical and double labeling study in the rat.

Possible projections of serotonin (5-HT)-immunoreactive neurons in the nodose ganglia (NG) to the nucleus tractus solitarius (NTS) were investigated in the rat using a double labeling method combining retrograde transport and 5-HT immunohistochemistry. After injection of a complex of colloidal gold-apo-horseradish peroxidase into the medio-caudal and commissural parts of the NTS, most of the 5-HT-immunoreactive neurons were found to be labelled by the gold complex. The present study provides direct evidence for the existence, in the rat, of a serotonergic NG-NTS system. This system may be involved in the regulation of blood pressure and vigilance states.

Cardiovascular changes induced by the local application of glutamate-related drugs in the rat nucleus tractus solitarii.

The effects of the local application of drugs acting on glutamatergic receptors in the nucleus tractus solitarii (NTS) were investigated in anesthetized rats. Unilateral microinjection of agonists (L-glutamate, L-aspartate, N-methyl-D-aspartate (NMDA) and quisqualate) produced a dose-dependent hypotension and bradycardia. The effects of NMDA were prevented by low doses of the selective NMDA-receptor antagonist, 2-amino-5-phosphonovalerate (2-APV), or by the mixed NMDA/kainate antagonist, gamma-D-glutamylglycine. The response to all agonists and the bradycardia which was elicited in response to the intravenous administration of phenylephrine (vagal reflex response) could be prevented by the local microinjection of the glutamate antagonists kynurenic acid (3 nmol) and 2-APV (10 nmol) into the NTS. The present data suggest that in the NTS, NMDA and quisqualate receptors are implicated in blood pressure reflex regulation.