Receptor Antagonist SB Research Articles

Potential anxiolytic and antidepressant effects of the selective 5-HT 7 receptor antagonist SB 269970 after intrahippocampal administration to rats

Using conflict drinking and forced swimming tests in rats, we examined the anxiolytic- and the antidepressant-like activity, respectively, of (2 R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]-pyrrolidine (SB 269970), a selective 5-HT 7 receptor antagonist, after its intrahippocampal administration. SB 269970 at doses of 0.3, 1 and 3 μg showed an anticonflict effect which was weaker than that of diazepam (40 μg), whereas SB 269970 at doses of 3 and 10 μg had marked anti-immobility action comparable to that of imipramine (0.1 μg). Importantly, the anxiolytic- and antidepressant-like activity of SB 269970 seemed to be specific, since that agent − when given by the same route in doses effective in either model – affected neither the shock threshold, nor the non-punished water consumption, nor the exploratory activity of rats. The obtained results indicate that the hippocampus is one of the neuroanatomical structures involved in the potential anxiolytic and, in particular, antidepressant activity of SB 269970.

The effects of the 5-HT2C receptor antagonist SB242084 on locomotor activity induced by selective, or mixed, indirect serotonergic and dopaminergic agonists

The 5-HT(2C) receptor modulates mesolimbic dopamine (DA) function and the expression of DA-dependent behaviors, including stimulant-induced hyperactivity. The 5-HT(2C) receptor may also be involved in drug-induced locomotion that is 5-HT-dependent. This study investigated the effects of the 5-HT(2C) receptor antagonist 6-chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-indoline (SB242084) on hyperlocomotion induced by psychomotor stimulants with selective, or mixed, actions on serotonergic and/or dopaminergic systems. Male Sprague-Dawley rats were treated in the presence or absence of SB242084 with releasers/reuptake inhibitors of DA (amphetamine and methylphenidate), 5-HT (fenfluramine and citalopram), or both 5-HT and DA (MDMA and cocaine). In addition, the effects of SB242084 combined with nicotine, morphine, or the 5-HT(1A/1B) receptor agonist RU24969 were examined. Locomotor activity was recorded for 2 h. SB242084 potentiated hyperactivity induced by MDMA (2.5-5 mg/kg), amphetamine (0.5 mg/kg), fenfluramine (5 mg/kg), cocaine (10 mg/kg), and methylphenidate (5 mg/kg). SB242084 modestly potentiated nicotine-induced (0.2-0.4 mg/kg) and morphine-induced (2.5 mg/kg) hyperactivity. SB242084 failed to influence hyperactivity induced by RU24969 (0.5-1 mg/kg) or citalopram (10-20mg/kg). SB242084 potentiated the locomotor stimulant effects of both indirect DA and 5-HT agonists. This potentiation may reflect two distinct mechanisms. The first involves direct enhancement of DA activity as shown by potentiation of the effects of amphetamine and methylphenidate. The second mechanism reflects an unmasking of stimulatory 5-HT receptors activated by 5-HT releasers (possibly 5-HT(1B/2A)) through blockade of inhibitory 5-HT(2C) receptors. The failure of SB242084 to potentiate the effect of citalopram might reflect differences between changes in synaptic levels of 5-HT produced by release compared to reuptake inhibition.

Effect of the selective 5-HT 7 receptor antagonist SB 269970 in animal models of anxiety and depression

The aim of the present study was to examine the effect of the selective 5-HT 7 receptor antagonist SB 269970 (0.25–20 mg/kg) in the behavioral tests commonly used for predicting anxiolytic- and antidepressant-like activity. Diazepam and imipramine were used as standard drugs. SB 269970 (in one medium dose of 0.5 or 1 mg/kg) exerted a specific antianxiety-like effect in the Vogel drinking test in rats, in the elevated plus-maze test in rats and in the four-plate test in mice. Moreover, SB 269970 (in one medium dose of 5 or 10 mg/kg) showed antidepressant-like activity in the forced swimming and the tail suspension tests in mice. At the same time, the tested compound at doses of 1–20 mg/kg did not change the spontaneous locomotor activity of mice. The potential anxiolytic and antidepressant effects produced by SB 269970 were weaker than those of the reference drugs employed. It is noteworthy that the active doses of SB 269970 were devoid of any visible motor side-effects. In conclusion, the results of our studies indicate that 5-HT 7 receptor antagonists may play a role in the therapy of both anxiety and depression.

Effects of the 5-HT 7 receptor antagonist SB-269970 on rat hormonal and temperature responses to the 5-HT 1A/7 receptor agonist 8-OH-DPAT

The physiological function of 5-HT 7 receptors is not yet fully determined. This study was designed to characterize the involvement of 5-HT 7 receptor in rat body temperature regulation and in adrenocorticotropic hormone (ACTH) and corticosterone secretion. In the first part of our study, acute administration of SB-269970 (0.1–1 mg/kg, i.p.), a potent and selective 5-HT 7 receptors antagonist, dose-dependently prevented 5-HT 1A/7 receptor agonist 8-OH-DPAT (0.1 mg/kg, s.c.)-induced hypothermia and when the 5-HT 1A receptor antagonist WAY-100,635 was co-injected with SB-269970, a reduction of the latter hypothermia was obtained in an additive manner. In contrast, 1 mg/kg (i.p.) of SB-269970 failed to prevent 8-OH-DPAT (0.5 mg/kg, s.c.)-induced increase of ACTH and corticosterone plasma levels. In conclusion, the present results unveil an additive effect of both 5-HT 1A and 5-HT 7 receptors in core body temperature regulation.

Contractile mechanisms coupled to TRPA1 receptor activation in rat urinary bladder

TRPA1 is a member of the transient receptor potential (TRP) channel family present in sensory neurons. Here we show that vanilloid receptor (TRPV1) stimulation with capsaicin and activation of TRPA1 with allyl isothiocyanate or cinnamaldehyde cause a graded contraction of the rat urinary bladder in vitro. Repeated applications of maximal concentrations of the agonists produce desensitization to their contractile effects. Moreover, contraction caused by TRPA1 agonists generates cross-desensitization with capsaicin. The TRP receptor antagonist ruthenium red (10–100 μM) inhibits capsaicin (0.03 μM), allyl isothiocyanate (100 μM) and cinnamaldehyde (300 μM)-induced contractions in the rat urinary bladder. The selective TRPV1 receptor antagonist SB 366791 (10 μM) blocks capsaicin-induced contraction, but partially reduces allyl isothiocyanate- or cinnamaldehyde-mediated contraction. However, allyl isothiocyanate and cinnamaldehyde (10–1000 μM) completely fail to interfere with the specific binding sites for the TRPV1 agonist [ 3H]-resiniferatoxin. Allyl isothiocyanate or cinnamaldehyde-mediated contractions of rat urinary bladder, which rely on external Ca 2+ influx, are significantly inhibited by tachykinin receptor antagonists as well as by tetrodotoxin (1 μM) or indomethacin (1 μM). Allyl isothiocyanate-induced contraction is not changed by atropine (1 μM) or suramin (300 μM). The exposure of urinary bladders to allyl isothiocyanate (100 μM) causes an increase in the prostaglandin E 2 and substance P levels. Taken together, these results indicate that TRPA1 agonists contract rat urinary bladder through sensory fibre stimulation, depending on extracellular Ca 2+ influx and release of tachykinins and cyclooxygenase metabolites, probably prostaglandin E 2. Thus, TRPA1 appears to exert an important role in urinary bladder function.

Characterization of Intracavernous Pressure Increase Induced by Ym348, a Novel 5-HT 2C Receptor Agonist, in Anesthetized Rats

We investigated the effects of the novel 5-HT2C receptor agonist YM348 [(S)-2-(7-ethyl-1H-furo[2,3-g]indazol-1-yl)-1-methylethylamine] on ICP in anesthetized rats and clarified whether behavioral changes such as hypolocomotion induced at a high dose are a cause of the inverted U-shaped PE dose-response curves in conscious rats.Male Wistar rats (Japan SLC, Shizuoka, Japan) weighing 250 to 315 gm were used. The pro-erectile effect of YM348 (2.03 to 67.7 microg/kg subcutaneously) was examined in conscious rats. ICP was also monitored after YM348 treatment (0.677 to 67.7 mug/kg subcutaneously) in anesthetized rats. Response number, latency, duration, peak pressure and area under the curve were measured. The selective 5-HT2C receptor antagonist SB242084 [(6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy) pyridin-3-yl carbamoyl] indoline)] (0.03 to 1 mg/kg intraperitoneally) was administered 30 minutes before YM348 treatment.YM348 induced PE and ICP increases, and was significantly inhibited by SB242084. Dose-response curves for the number of PEs and ICP increases were an inverted U shape. YM348 decreased the latency of but did not affect the quality of ICP (duration, peak pressure and area under the curve) even at the highest dose.Activation of 5-HT2C receptor increased ICP and, as a result, induced PE. Since the dose-response curve for the number of ICP increases under anesthetized, behavior independent conditions still showed an inverted U shape, behavioral changes were not likely to have contributed to the inverted U-shaped dose-response curves for the number of PEs in conscious rats. Furthermore, the certain magnitude of ICP increases was likely to have occurred despite the stimulus intensity after the level of 5-HT2C receptor activation crossed the threshold.

Serotonin 1B and 2C receptor interactions in the modulation of feeding behaviour in the mouse

To examine the functional relationship between 5-HT1B receptors (5-HT1B-R) and 5-HT2C receptors (5-HT2C-R) in the control of food intake. To compare the hypophagic effect of the 5-HT(2C/1B)-R agonist m-chlorophenylpiperazine (mCPP), with that of the selective 5-HT1B-R agonist CP-94,253 in both wildtype (WT) and 5-HT2C knockout (KO) mice. The hypophagic effects of mCPP (1, 3 and 5.6 mg/kg) and CP-94,253 (5, 10 and 20 mg/kg) were assessed in WT and 5-HT2C KO mice using the behavioural satiety sequence paradigm. The effects of pre-treatment with the selective 5-HT2C-R antagonist SB 242,084 (0.5 and 1.5 mg/kg) were assessed in two groups of WT mice, with each group given only mCPP or CP-94,253. The 5-HT(2C/1B) receptor agonist mCPP and the selective 5-HT1B receptor agonist CP-94,253 both suppressed food intake in WT mice. 5-HT2C KO mice were insensitive to the hypophagic effects of mCPP but were more sensitive to CP-94,253-induced hypophagia than WT controls. mCPP induced a significant increase in post-prandial activity in 5-HT2C KO mice, but this effect was absent in 5-HT2C KO mice who were given CP-94,253. Data from WT mice, who were pre-treated with the 5-HT2C receptor antagonist SB 242,084 and then challenged with either mCPP or CP-94,253, were similar to those obtained from 5-HT2C KO mice. 5-HT2C-R and 5-HT1B-R activation are each sufficient to induce a hypophagic response. However, concurrent 5-HT2C-R inactivation can potentiate the hypophagic response to 5-HT1B-R activation, consistent with an inhibitory role for the 5-HT2C-R in behaviour mediated by the activation of other 5-HT receptors. These results also confirm that 5-HT1B-R activation alone cannot account for the hyperactive response of 5-HT2C KO mice to mCPP.

Investigation of the SSRI augmentation properties of 5-HT 2 receptor antagonists using in vivo microdialysis

Recent evidence that 5-HT 2 receptors exert a negative influence on central 5-hydroxytryptamine (5-HT) neurones suggests that 5-HT 2 receptor antagonists may augment the effects of serotonin selective reuptake inhibitors (SSRIs). The present study investigated whether pre-treatment with 5-HT 2 receptor antagonists enhances the effect of SSRI administration on hippocampal extracellular 5-HT of freely moving rats. Administration of the SSRI citalopram at a low (2 mg kg −1) and higher (4 mg kg −1) dose, increased dialysate 5-HT by 5- and 8-fold, respectively. Pre-treatment with the 5-HT 2 receptor antagonist ketanserin (4 mg kg −1) augmented the effect of 4 mg kg −1 but not 2 mg kg −1 citalopram. The effect of 4 mg kg −1 citalopram was also augmented by pre-treatment with either the 5-HT 2C receptor antagonist SB 242084 (0.5 mg kg −1) or the 5-HT 2A receptor antagonist MDL 100907 (0.5 mg kg −1). As with citalopram, fluoxetine elevated dialysate 5-HT at both a low (5 mg kg −1) and higher (20 mg kg −1) dose. However, neither dose of fluoxetine was augmented by ketanserin (4 mg kg −1). These results confirm recent findings that 5-HT 2 receptor antagonists augment the effect of citalopram on extracellular 5-HT, and indicate the involvement of 5-HT 2C and possibly 5-HT 2A receptors. The lack of augmentation of fluoxetine might reflect the intrinsic 5-HT 2 receptor antagonist properties of this drug.

Antiobesity-like effects of the 5-HT 2C receptor agonist WAY-161503

WAY-161503 ((4a R)-8,9-dichloro-2,3,4,4a-tetrahydro-1 H-pyrazino[1,2-a]quinoxalin-5(6 H)-one), a 5-HT 2B/C receptor agonist, was characterized in vitro using stable Chinese hamster ovary cell lines expressing each of the human 5-HT 2 receptors and in vivo in animal models of obesity. WAY-161503 displaced both agonist ([ 125I]2,5-dimethoxy-4-iodoamphetamine (DOI)) and antagonist ([ 3H]mesulergine) radioligand binding to the human 5-HT 2C receptor with derived Ki values of 3.3 ± 0.9 and 32 ± 6 nM, respectively. Relative to 5-HT 2C receptor binding, WAY-161503 was approximately 6-fold less potent at human 5-HT 2A receptors ([ 125I]DOI) with a derived Ki value of 18 nM and 20-fold less potent at human 5-HT 2B receptors ([ 3H]5-HT) with a derived Ki value of 60 nM. In functional studies, WAY-161503 was a full agonist in stimulating 5-HT 2C-receptor-coupled [ 3H]inositol phosphate (IP) formation and calcium mobilization with EC 50 values of 8.5 nM and 0.8 nM, respectively. WAY-161503 was also a 5-HT 2B agonist (EC 50s of 6.9 and 1.8 nM for IP and calcium, respectively). In IP studies, WAY-161503 was a weak 5-HT 2A partial agonist (EC 50, 802 nM) yet potently stimulated calcium mobilization (EC 50, 7 nM) in 5-HT 2A receptor-expressing cells. Functionally, WAY-161503 also stimulated the phospholipase A 2-coupled arachidonic acid release in 5-HT 2C receptor expressing cells albeit with lower potency (EC 50, 38 nM) and efficacy (Emax, 77%) compared with activation of the PLC pathway. In vivo, WAY-161503 produced dose-dependent decreases in 2-h food intake in 24 h fasted normal Sprague–Dawley rats, diet-induced obese mice, and obese Zuker rats with ED 50 values of 1.9 mg/kg, 6.8 mg/kg, and 0.73 mg/kg, respectively. The reduction in food intake in normal Sprague–Dawley rats was reversed by administration of the 5-HT 2C receptor antagonist SB-242084. Following chronic administration (10 days) in growing Sprague–Dawley rats, WAY-161503 decreased food intake and attenuated body weight gain. Finally, following chronic administration (15 days) of WAY-161503 to obese Zuker rats, the rats maintained a 30% decrease in food intake over the 15-day period combined with a 25 g decrease in body weight relative to vehicle-treated controls demonstrating a lack of tolerance to its anorectic effects.

Investigation of mechanisms mediating 8-OH-DPAT-induced impairment of spatial memory: Involvement of 5-HT 1A receptors in the dorsal hippocampus in rats

The purpose of this study was to identify mechanisms that mediate the impairment of spatial memory induced by 8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT), a 5-HT 1A/5-HT 7 receptor agonist, in the eight-arm radial maze in rats. WAY-100635 and NAN-190, 5-HT 1A receptor antagonists, reversed the impairment of spatial memory induced by systemic injection of 8-OH-DPAT (1 mg/kg, i.p.). On the other hand, the α 1-adrenoceptor antagonist prazosin and a selective 5-HT 7 receptor antagonist SB269970 had no effect on 8-OH-DPAT-induced impairment of spatial memory. Bilateral microinjection of 8-OH-DPAT (4 μg/side) impaired spatial memory when injected into the dorsal hippocampus (DH). Contrastingly, spatial memory was unaffected by microinjections of 8-OH-DPAT into the other six areas examined: ventral hippocampus (VH), central amygdaloid nucleus (ACE), lateral hypothalamus (LH), nucleus accumbens (NAc), and dorsal (DR) and median (MR) raphe nucleus. Furthermore, NAN-190 significantly reversed the impairment of spatial memory induced by intra-DH injection of 8-OH-DPAT. These findings suggest that 5-HT 1A receptors in the DH play an important role in the mechanisms underlying the 8-OH-DPAT-induced impairment of spatial memory in rats.

P.2.d.012 Behavioural and molecular effects of the combined treatment fluoxetine plus acetylsalicylic acid in a rat model of depression

Agomelatine, a novel melatonin analogue and anti-depressant that acts as an agonist on melatonin receptors 1 and 2 and as an antagonist at the 5HT2C receptor, was tested for its effects on cell proliferation in the dentate gyrus of the adult rat hippocampus under intact and flattened corticosterone rhythm conditions. Agomelatine stimulated mitosis rates in the intact male rat. Flattening the daily corticosterone rhythm by inserting a subcutaneous pellet of this steroid prevented the action of agomelatine. However, adding a daily injection of corticosterone at CT1200 to rats with implanted corticosterone pellets failed to restore agomelatine’s efficacy on cell proliferation. The 5HT2C receptor antagonist SB242084 stimulated progenitor cell proliferation in the dentate gyrus, while a 5HT2C agonist (RO600175) had no effect on cell proliferation alone, but counteracted that of agomelatine. These results suggest that agomelatine, a new anti-depressant, can stimulate progenitor cell mitosis in the dentate gyrus. Its action requires an intact diurnal corticosterone rhythm. The action of agomelatine on neurogenesis is likely to reside in its antagonism of the 5HT2C receptor, and suggests a mechanism distinct from that of fluoxetine, another anti-depressant, which, as previous work shows, acts through the 5HT1A receptor, but whose action is also blocked by a flattened corticosterone rhythm.

Serotonin increases protective duodenal bicarbonate secretion via enteric ganglia and a 5-HT4-dependent pathway

Objective. Serotonin (5-HT) is present in much larger amounts in the gut than in the central nervous system and is predominantly synthesized and stored in mucosal enterochromaffin cells. Bicarbonate secretion by the duodenal mucosa is the major mechanism in maintaining mucosal integrity, neutralizing invading protons within the surface mucus gel. In this study the role of local 5-HT in the control of the protective secretion was investigated. Material and methods. A segment of proximal duodenum was perfused in situ in anaesthetized rats and the alkaline secretion was continuously recorded by pH-stat. Intracellular calcium signalling was measured in clusters of human and rat duodenal enterocytes devoid of neural tissue. After loading with the fluorescent probe, fura-2, the clusters were attached to the bottom of a temperature-controlled perfusion chamber. Results. Close intra-arterial infusion to the duodenal segment of 5-HT (20–200 nmol kg−1 h−1) dose-dependently increased duodenal mucosal HCO3 secretion. A higher dose (2000 nmol kg−1 h−1) did not further increase secretion. Responses were inhibited by the ganglionic blocker and nicotinic receptor antagonist hexamethonium, and were abolished by the 5-HT4 receptor antagonist SB 204070. The 5-HT3 antagonist tropisetron, in contrast, caused only slight inhibition. Viable human and rat duodenal enterocytes responded to 5-HT (100–500 nM) with an increase in intracellular calcium concentration. Pretreatment with SB 204070 or removal of external calcium abolished the response. Conclusions. Stimulation of the duodenal protective secretion by 5-HT thus involves receptors of the 5-HT4 subtype as well as nicotinic transmission, the myenteric plexus being a likely location. In addition, serotonin acts on enterocyte membrane receptors, inducing intracellular calcium signalling.

Luminal hypotonicity increases duodenal mucosal permeability by a mechanism involving 5‐hydroxytryptamine

To investigate whether 5-hydroxytryptamine (5-HT) participates in the mediation of the hypotonicity-induced increase in duodenal mucosal permeability. Proximal duodenum in anaesthetized rats was perfused in situ with a hypotonic NaCl solution and effects on duodenal motility, net fluid flux, mucosal permeability [blood-to-lumen clearance of (51)Cr-ethylenediaminetetraacetic acid (EDTA)] and the release of 5-HT into the luminal solution studied in the presence of the cyclooxygenase inhibitor indomethacin. Perfusion of the duodenum with 50 mm NaCl increased mucosal permeability eightfold, increased the luminal output of 5-HT twofold and induced net fluid absorption. This rise in permeability was enhanced 25% by 5-HT (3 x 10(-3) m), reduced by the 5-HT(3)-receptor antagonists granisetron (10(-4)-3 x 10(-4) m) or ondansetron (10(-5)-10(-4) m) or by the 5-HT(4) receptor antagonist SB 203186 (10(-4) m). The 5-HT(3/4) receptor antagonist tropisetron, at 10(-4) m, did not affect while 3 x 10(-4) and 3 x 10(-3) m augmented the hypotonicity-induced increase in mucosal permeability. Lidocaine (1.1 x 10(-3) m) similarly potentiated while tetrodotoxin (TTX) (5 x 10(-5) m) inhibited the hypotonicity-induced increase in mucosal permeability. Compared with animals treated with indomethacin alone ondansetron and granisetron augmented (by 30-40%) while tropisetron and lidocaine reduced (by 60-70%) the hypotonicity-induced net fluid absorption. Tetrodotoxin and all 5-HT receptor antagonists, except tropisetron, depressed duodenal motility. Luminal hypotonicity increases duodenal mucosal permeability by a neural mechanism involving 5-HT acting on 5-HT(3) and 5-HT(4) receptors. 5-HT also appears to participate in the regulation of the hypotonicity-induced fluid flux.

Role for hypocretin in mediating stress-induced reinstatement of cocaine-seeking behavior

Hypocretin-1 and -2 (Hcrt-1 and Hcrt-2), also referred to as orexin-A and -B, are neuropeptides synthesized by a few thousand neurons in the lateral hypothalamus. Hypocretin-containing neurons project throughout the brain, with a prominent input to basal forebrain structures involved in motivation, reward, and stress. However, the role of hypocretins in addiction-related behaviors remains largely unexplored. Here we show that intracerebroventricular infusions of Hcrt-1 lead to a dose-related reinstatement of cocaine seeking without altering cocaine intake in rats. Hcrt-1 also dramatically elevates intracranial self-stimulation thresholds, indicating that, unlike treatments with reinforcing properties such as cocaine, Hcrt-1 negatively regulates the activity of brain reward circuitries. Hypocretin-induced reinstatement of cocaine seeking was prevented by blockade of noradrenergic and corticotropin-releasing factor systems, suggesting that Hcrt-1 reinstated drug seeking through induction of a stress-like state. Consistent with this interpretation, the selective Hcrt-1 receptor antagonist SB-334867 blocked footshock-induced reinstatement of previously extinguished cocaine-seeking behavior. These findings reveal a previously unidentified role for hypocretins in driving drug seeking through activation of stress pathways in the brain.

Effects of the 5-HT 7 receptor antagonist SB-269970 microinjected into the dorsal raphe nucleus on REM sleep in the rat

The effects of SB-269970, a selective 5-HT 7 receptor antagonist, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. SB-269970 was infused directly into the dorsal raphe nucleus (DRN) during the light phase. The 5-HT 7 receptor antagonist (0.25–1.0 mM) induced a significant reduction of REM sleep and of the number of REM periods whereas REM sleep latency was augmented. Pretreatment with the GABA A receptor agonist muscimol (1.0–2.0 mM), which by itself did not affect sleep variables, prevented the decrease of REM sleep induced by SB-269970 (1.0 mM). Our results indicate that the 5-HT 7 receptor is involved in the effect of DRN serotonergic (5-HT) neurons on brainstem structures that act to promote and induce REM sleep. We propose that the SB-269970-induced suppression of REM sleep is dependent upon the inhibition of GABA release in the DRN.

5-HT7 Receptors Modulate Peristalsis and Accommodation in the Guinea Pig Ileum

The 5-hydroxytryptamine 7 (5-HT7) receptors mediate intestinal smooth muscle relaxation. In this study, we evaluated the expression of 5-HT7 receptors in the guinea pig ileum and their role in peristalsis and accommodation of the circular muscle. We used immunohistochemistry and confocal microscopy with whole tissue and cultured myenteric neurons. Peristalsis was induced by delivering a solution into the oral end of an isolated ileal segment. The effect of the selective 5-HT7 receptor antagonist SB-269970 (100 nmol/L) on peristaltic activity was evaluated at 30, 60, and 90 minutes and compared with control. 5-HT7 receptor immunoreactivity was localized to numerous myenteric neurons, a few submucosal neurons, and a few smooth muscle cells of the ileum. In enteric cultured neurons, 5-HT7 receptor immunoreactivity was observed in subpopulations of after hyperpolarizing neurons and descending neurons as identified by neuron-specific nuclear protein or calbindin and neuronal nitric oxide synthase or vasoactive intestinal peptide antibodies, respectively. SB-269970 significantly increased the threshold pressure by 33.3% +/- 2.2% (P < .001) and by 27.2% +/- 1.6% (P < .05) at 60 and 90 minutes, respectively, without modifying the threshold volume. The accommodation significantly decreased by 27.5% both at 60 and 90 minutes (P < .05). Our results indicate that endogenous 5-HT is involved in the modulation of circular muscle accommodation during the preparatory phase of peristalsis via the activation of 5-HT7 receptors expressed by neurons in addition to smooth muscle cells. Overstimulation of these receptors leading to an exaggerated accommodation of circular muscle might contribute to abdominal symptoms in functional bowel disorders.

Orexin 1 Receptor Activation Attenuates Neurogenic Dural Vasodilation in an Animal Model of Trigeminovascular Nociception

The pathophysiology underlying the pulsating quality of the pain of a migraine attack is not fully understood, although trigeminal vascular afferents containing the sensory neuropeptide calcitonin gene-related peptide (CGRP) must have a role. Antimigraine drugs, such as triptans, serotonin 5-hydroxytryptamine(1B/1D) receptor agonists, reproducibly block neurogenic vasodilation associated with CGRP release. We examined the effects of the hypothalamic neuropeptides orexin A and orexin B on neurogenic dural vasodilation, dissecting out the receptor pharmacology with the novel orexin 1 (OX1) receptor antagonist N-(2-methyl-6-benzoxazolyl)-N''-1,5-naphthyridin-4-yl urea (SB-334867). Electrical stimulation of dural afferents (50-300 microA) resulted in reproducible dural vasodilation of 136 +/- 9%. Orexin A 30 microg kg(-1), but not 3 and 10 microg kg(-1), inhibited the dilation brought about by electrical stimulation over 60 min and maximally after 15 min by 60% (t7= 7.138; P < 0.001; n = 8). This response was reversed by pretreatment with the OX1 receptor antagonist SB-334867. Addition of CGRP(8-37) at the point of maximal effect of orexin A produced a further significant decrease in neurogenic dural vasodilation compared with orexin A only. CGRP administration (1 microg kg(-1)) produced a reproducible dural blood vessel dilation of 145 +/- 7% that was not inhibited by intravenous administration of orexin A (30 microg kg(-1)). Orexin B had no significant effect even at the highest dose. The current study demonstrates that orexin A is able to inhibit neurogenic dural vasodilation via activation of the OX1 receptor, resulting in inhibition of prejunctional release of CGRP from trigeminal neurons.

Implication of 5-HT 2A subtype receptors in DOI activity in the four-plates test–retest paradigm in mice

The four-plates test (FPT) is an animal model of anxiety which allows the detection of anxiolytic effect not only of benzodiazepines (BZDs) but also of other non-BZDs anxiolytic compounds such as antidepressants (ADs). Furthermore, DOI, a 5-HT 2A/2C agonist, has been shown to exert an anxiolytic-like effect in this model. Retesting mice in animal models of anxiety (test–retest paradigm) induces an anxiogenic-like and a loss of anxiolytic-like effects in response to BZDs and ADs. On the contrary, DOI has been reported to oppose the fear potentiation induced by trial 1 in the FPT. Despite DOI is considered as one of the most selective 5-HT 2A available, it acts as agonist at all three 5-HT 2 receptor subtypes (5-HT 2A, 5-HT 2B and 5-HT 2C). The aim of this study was thus to investigate in the FPT test–retest paradigm, which 5-HT 2 receptor subtype(s) was involved in the DOI-induced effect in experienced mice. The effect of DOI (0.25–4 mg/kg) and the agonists, 5-HT 2B, BW 723C86 (1–16 mg/kg) and 5-HT 2C, RO 60-0175 (0.25–4 mg/kg) have also been studied. Then, antagonism studies were conducted combinating the 5-HT 2A receptor antagonist SR 46349B, the 5-HT 2B/2C receptor antagonist SB 206553 or the selective 5-HT 2C receptor antagonist RS 10-2221 (at the doses of 0.1 and 1 mg/kg) with the DOI (1 mg/kg). Our study shows that the BW 723C86 had no effect on retesting mice, whereas it exerted an anxiolytic-like effect in naive mice. By contrast to DOI, the RO 60-0175 had no effect neither in naive nor experienced mice. Furthermore, only the SR 46349B antagonized the DOI-induced anti-punishment effect. Diazepam included as a positive control also increased in each case the number of punished passages in naive mice. Our findings altogether also suggest that DOI exerts its anxiolytic-like effect in the FPT test–retest paradigm through 5-HT 2A receptors.

Bicyclic heteroarylpiperazines as selective brain penetrant 5-HT 6 receptor antagonists

Starting from the potent and selective but poorly brain penetrant 5-HT 6 receptor antagonist SB-271046, a successful strategy for improving brain penetration was adopted involving conformational constraint with concomitant reduction in hydrogen bond count. This provided a series of bicyclic heteroarylpiperazines with high 5-HT 6 receptor affinity. 5-Chloroindole 699929 combined high 5-HT 6 receptor affinity with excellent brain penetration and also had good oral bioavailability in both rat and dog.

Despite Similar Anxiolytic Potential, the 5-Hydroxytryptamine 2C Receptor Antagonist SB-242084 [6-Chloro-5-methyl-1-[2-(2-methylpyrid-3-yloxy)-pyrid-5-yl Carbamoyl] Indoline] and Chlordiazepoxide Produced Differential Effects on Electroencephalogram Power Spectra

Serious efforts have been made to develop anxiolytics with improved clinical utility and reduced side effects. 5-Hydroxytryptamine (5-HT)(2C) receptor antagonists are potential anxiolytics; however, their effects on vigilance are not well characterized. To compare the effects of benzodiazepines and subtype-selective 5-HT(2C) receptor antagonists on anxiety, vigilance, and electroencephalogram (EEG) power density, social interaction test and polygraphic recordings were performed in male Sprague-Dawley rats after chlordiazepoxide (CDP; 4.0 mg/kg i.p.) and SB-242084 (6-chloro-5-methyl-1-[2-(2-methylpyrid-3-yloxy)-pyrid-5-yl carbamoyl] indoline) (0.1, 0.3, and 1.0 mg/kg i.p.) treatment. CDP and SB-242084 (0.3 and 1.0 mg/kg) had similar anxiolytic effects. Spectral analysis of EEG in wakefulness (W) and paradoxical sleep (PS) showed an opposite effect on activity (5-9 Hz); it decreased after CDP, whereas it increased after SB-242084 (even at 0.1 mg/kg). In addition, CDP significantly decreased slow-wave activity (0.5-4 Hz) in deep slow-wave sleep (SWS-2) and increased power at frequencies above 12 Hz mainly in W and PS. A markedly increased intermediate stage of sleep was also found after CDP treatment. At the highest dose, SB-242084 increased W and decreased SWS-2. In summary, low but potent anxiolytic doses of the subtype-selective 5-HT(2C) receptor antagonist SB-242084 did not affect vigilance states but caused an increased activity in W, raising the possibility of a cognitive-enhancing effect of the drug. In contrast, acute CDP administration, based on spectral analysis of the EEG, produced a more superficial sleep along with a decreased activity.