Roles of 5-HT receptors in the release and action of secretin on pancreatic secretion in rats

5-Hydroxytryptamine (serotonin, 5-HT) is a hormone and neurotransmitter regulating gastrointestinal functions. 5-HT receptors are widely distributed in gastrointestinal mucosa and the enteric nervous system. Duodenal acidification stimulates not only the release of both 5-HT and secretin but also pancreatic exocrine secretion. We investigated the effect of 5-HT receptor antagonists on the release of secretin and pancreatic secretion of water and bicarbonate induced by duodenal acidification in anesthetized rats. Both the 5-HT(2) receptor antagonist ketanserin and the 5-HT(3) receptor antagonist ondansetron at 1-100 microg/kg dose-dependently inhibited acid-induced increases in plasma secretin concentration and pancreatic exocrine secretion. Neither the 5-HT(1) receptor antagonists pindolol and 5-HTP-DP nor the 5-HT(4) receptor antagonist SDZ-205,557 affected acid-evoked release of secretin or pancreatic secretion. None of the 5-HT receptor antagonists affected basal pancreatic secretion or plasma secretin concentration. Ketanserin or ondansetron at 10 microg/kg or a combination of both suppressed the pancreatic secretion in response to intravenous secretin at 2.5 and 5 pmol x kg(-1) x h(-1) by 55-75%, but not at 10 pmol x kg(-1) x h(-1). Atropine (50 microg/kg) significantly attenuated the inhibitory effect of ketanserin on pancreatic secretion but not on the release of secretin. These observations suggest that 5-HT(2) and 5-HT(3) receptors mediate duodenal acidification-induced release of secretin and pancreatic secretion of fluid and bicarbonate. Also, regulation of pancreatic exocrine secretion through 5-HT(2) receptors may involve a cholinergic pathway in the rat.     

Role of Ca2+-activated K+ channels in duodenal mucosal ion transport and bicarbonate secretion

Stimulation of muscarinic receptors in the duodenal mucosa raises cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)), thereby regulating duodenal epithelial ion transport. However, little is known about the downstream molecular targets that account for this Ca(2+)-mediated biological action. Ca(2+)-activated K(+) (K(Ca)) channels are candidates, but the expression and function of duodenal K(Ca) channels are poorly understood. Therefore, we determined whether K(Ca) channels are expressed in the duodenal mucosa and investigated their involvement in Ca(2+)-mediated duodenal epithelial ion transport. Two selective blockers of intermediate-conductance Ca(2+)-activated K(+) (IK(Ca)) channels, clotrimazole (30 muM) and 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34; 10 muM), significantly inhibited carbachol (CCh)-induced duodenal short-circuit current (I(sc)) and duodenal mucosal bicarbonate secretion (DMBS) in mice but did not affect responses to forskolin and heat-stable enterotoxin of Escherichia coli. Tetraethylammonium, 4-aminopyridine, and BaCl(2) failed to inhibit CCh-induced I(sc) and DMBS. A-23187 (10 muM), a Ca(2+) ionophore, and 1-ethyl-2-benzimidazolinone (1-EBIO; 1 mM), a selective opener of K(Ca) channels, increased both I(sc) and DMBS. The effect of 1-EBIO was more pronounced with serosal than mucosal addition. Again, both clotrimazole and TRAM-34 significantly reduced A23187- or 1-EBIO-induced I(sc) and DMBS. Moreover, clotrimazole (20 mg/kg ip) significantly attenuated acid-stimulated DMBS of mice in vivo. Finally, the molecular identity of IK(Ca) channels was verified as KCNN4 (SK4) in freshly isolated murine duodenal mucosae by RT-PCR and Western blotting. Together, our results suggest that the IK(Ca) channel is one of the downstream molecular targets for [Ca(2+)](cyt) to mediate duodenal epithelial ion transport.     

Regulation of ion and water transport across the eel intestine: effects of acetylcholine and serotonin

Summary Both acetylcholine (ACh) and serotonin (5-HT) lowered the serosa-negative transepithelial potential difference (PD) and the short-circuit current (I_sc), accompanied by a decrease in NaCl and water absorption across the eel intestine. These inhibitory effects of ACh and 5-HT were blocked by atropine, a muscarinic receptor antagonist, and ICS-205930, a 5-HT₃ receptor antagonist, respectively. Even after blocking the ACh receptor with atropine, 5-HT inhibited the PD and I_sc, and ACh lowered them after blocking the 5-HT receptor with ICS-205930, indicating that ACh and 5-HT act independently. Similar inhibition in the PD and the I_sc was observed after electrical field stimulation (EFS) which is expected to release endogenous regulators. These effects of EFS were reduced by 70% after simultaneous addition of atropine and ICS-205930. Since atropine and ICS-205930 block ACh and 5-HT receptors, respectively, these results suggest that endogenous ACh and 5-HT are released by EFS.Abbreviations ACh acetylcholine - EFS electrical field stimulation - 5-HT serotonin - I _sc short-circuit current - PD transepithelial potential difference - R _t tissue resistance - TTX tetrodotoxin     

Protein kinase C potentiates cAMP-stimulated mouse duodenal mucosal bicarbonate secretion in vitro

PKC has been shown to regulate epithelial Cl(-) secretion in a variety of models. However, the role of PKC in duodenal mucosal bicarbonate secretion is less clear. We aimed to investigate the role of PKC in regulation of duodenal mucosal bicarbonate secretion. Bicarbonate secretion by murine duodenal mucosa was examined in vitro in Ussing chambers using a pH-stat technique. PKC isoform expression and activity were assessed by Western blotting and in vitro kinase assays, respectively. PMA (an activator of PKC) alone had no effect on duodenal bicarbonate secretion or short-circuit current (I(sc)). When PMA and dibutyryl-cAMP (db-cAMP) were added simultaneously, PMA failed to alter db-cAMP-stimulated duodenal bicarbonate secretion or I(sc) (P > 0.05). However, a 1-h preincubation with PMA potentiated db-cAMP-stimulated duodenal bicarbonate secretion and I(sc) in a concentration-dependent manner (from 10(-8) to 10(-5)M) (P < 0.05). PMA preincubation had no effects on carbachol- or heat-stable toxin-stimulated bicarbonate secretion. Western blot analysis revealed that PKCalpha, -gamma, -epsilon, -, -micro, and -iota/lambda were expressed in murine duodenal mucosa. Ro 31-8220 (an inhibitor active against PKCepsilon, -alpha, -beta, and -gamma), but not G? 6983 (an inhibitor active against PKCalpha, -gamma, -beta, and -delta), reversed the potentiating effect of PMA on db-cAMP-stimulated bicarbonate secretion. PMA also time- and concentration-dependently increased the activity of PKCepsilon, an effect that was prevented by Ro 31-8220 but not G? 6983. These results demonstrate that activation of PKC potentiates cAMP-stimulated duodenal bicarbonate secretion, whereas it does not modify basal secretion. The effect of PKC on cAMP-stimulated bicarbonate secretion is mediated by the PKCepsilon isoform.     

5-HT1a receptors positively coupled to C-AMP formation in the rabbit retina

Serotonin, 8-OH-DPAT, buspirone, ipsapirone, RU-24969, dopamine and isoproterenol all stimulate C-AMP production in rabbit retinal homogenates. The dopamine and isoproterenol responses are specifically antagonized by haloperidol and propranolol, respectively. In contrast the effects produced by the other substances are specifically nullified by spiroxatrine, a known 5-HT_1a antagonist. Since 5-HT₂ antagonists (methysergide, kentanserin), 5-HT_1b antagonist (propranolol), 5-HT₄ antagonist (ICS-205930), 5-HT₃ antagonist (MDL-72222, ICS-205930) or the primarily ₂-antagonist mianserin, had no influence on the stimulation of C-AMP caused by serotonin or 8-OH-DPAT, it is concluded that 5-HT_1a receptors, positively coupled to C-AMP production exist in the retina.     

Serotonin augments gut pacemaker activity via 5-HT3 receptors

Serotonin (5-hydroxytryptamine: 5-HT) affects numerous functions in the gut, such as secretion, muscle contraction, and enteric nervous activity, and therefore to clarify details of 5-HT's actions leads to good therapeutic strategies for gut functional disorders. The role of interstitial cells of Cajal (ICC), as pacemaker cells, has been recognised relatively recently. We thus investigated 5-HT actions on ICC pacemaker activity. Muscle preparations with myenteric plexus were isolated from the murine ileum. Spatio-temporal measurements of intracellular Ca(2+) and electric activities in ICC were performed by employing fluorescent Ca(2+) imaging and microelectrode array (MEA) systems, respectively. Dihydropyridine (DHP) Ca(2+) antagonists and tetrodotoxin (TTX) were applied to suppress smooth muscle and nerve activities, respectively. 5-HT significantly enhanced spontaneous Ca(2+) oscillations that are considered to underlie electric pacemaker activity in ICC. LY-278584, a 5-HT(3) receptor antagonist suppressed spontaneous Ca(2+) activity in ICC, while 2-methylserotonin (2-Me-5-HT), a 5-HT(3) receptor agonist, restored it. GR113808, a selective antagonist for 5-HT(4), and O-methyl-5-HT (O-Me-5-HT), a non-selective 5-HT receptor agonist lacking affinity for 5-HT(3) receptors, had little effect on ICC Ca(2+) activity. In MEA measurements of ICC electric activity, 5-HT and 2-Me-5-HT caused excitatory effects. RT-PCR and immunostaining confirmed expression of 5-HT(3) receptors in ICC. The results indicate that 5-HT augments ICC pacemaker activity via 5-HT(3) receptors. ICC appear to be a promising target for treatment of functional motility disorders of the gut, for example, irritable bowel syndrome.     

Identification of 5-HT receptor subtypes enhancing inhibitory transmission in the rat spinal dorsal horn in vitro

ABSTRACT: BACKGROUND: 5-hydroxytryptamine (5-HT) is one of the major neurotransmitters widely distributed in the CNS. Several 5-HT receptor subtypes have been identified in the spinal dorsal horn which act on both pre- and postsynaptic sites of excitatory and inhibitory neurons. However, the receptor subtypes and sites of actions as well as underlying mechanism are not clarified rigorously. Several electrophysiological studies have been performed to investigate the effects of 5-HT on excitatory transmission in substantia gelatinosa (SG) of the spinal cord. In the present study, to understand the effects of 5-HT on the inhibitory synaptic transmission and to identify receptor subtypes, the blind whole cell recordings were performed from SG neurons of rat spinal cord slices. RESULTS: Bath applied 5-HT (50 microM) increased the frequency but not amplitudes of spontaneous inhibitory postsynaptic currents (sIPSCs) in 58% of neurons, and both amplitude and frequency in 23 % of neurons. The frequencies of GABAergic and glycinergic mIPSCs were both enhanced. TTX (0.5 microM) had no effect on the increasing frequency, while the enhancement of amplitude of IPSCs was eliminated. Evoked-IPSCs (eIPSCs) induced by focal stimulation near the recording neurons in the presence of CNQX and APV were enhanced in both amplitude by 5-HT. In the presence of Ba2+ (1 mM), a potassium channel blocker, 5-HT had no effect on both frequency and amplitude. A 5-HT2Areceptor agonist, TCB-2 mimicked the 5-HT effect, and ketanserin, an antagonist of 5-HT2A receptor, inhibited the effect of 5-HT partially and TCB-2 almost completely. A 5-HT2C receptor agonist WAY 161503 mimicked the 5-HT effect and this effect was blocked by a 5-HT2C receptor antagonist, N-desmethylclozapine. The amplitude of sIPSCs were unaffected by both agonists. A 5-HT3 receptor agonist mCPBG enhanced both amplitude and frequency of sIPSCs. This effect was blocked by a 5-HT3 receptor antagonist ICS-205,930. The perfusion of 5-HT2B receptor agonist had no effect on sIPSCs. CONCLUSIONS: Our results demonstrated that 5-HT modulated the inhibitory transmission in SG by the activation of 5-HT2A and 5-HT2C receptors subtypes located predominantly at inhibitory interneuron terminals, and 5-HT3 receptors located at inhibitory interneuron terminals and soma-dendrites, consequently enhanced both frequency and amplitude.     

5-HT_(1A)受体参与学习记忆的分子机制研究进展

5-HT(五羟色胺)能神经元是起源最早的神经元之一,在传统的神经元形成前,成长中的轴突就可释放5-HT,并且通过5-HT的各种亚型受体来实现不同的功能。近年来,随着5-HT、5-HTRs(五羟色胺受体)的基因克隆及5-HT受体选择性激动剂和拮抗剂的研究发展,5-HT系统在学习记忆中的作用越发明确,许多研究结果表明:5-HT系统在记忆的巩固、短时程记忆(STM)及长时程记忆(LTM)中起重要作用,5-HT1A受体更是在非脊椎动物及哺乳动物的脑中都高度表达,并通过相似的信号转导途径参与学习与记忆的形成和巩固。本文将介绍5-HT1A受体、5-HT1A受体激动剂、5-HT1A受体拮抗剂及其与学习记忆的联系,重点综述5-HT1A受体参与学习记忆的信号转导途径研究进展,讨论5-HT1A受体参与学习记忆的可能性分子神经生物学机制。     

Involvement of 5-HT(2) receptor in imipramine-induced hyperglycemia in mice.

Effects of imipramine on plasma glucose levels were investigated in mice. Imipramine i. p. induced dose-dependent hyperglycemia, which was enhanced by pretreatment with 5-HT (1/2/5/7) receptor antagonist methysergide and 5-HT (2A/2B/2C) receptor antagonist LY 53857. 5-HT (2C/2B) receptor antagonist SB 206553 also augmented imipramine-induced hyperglycemia although 5-HT (1A) and 5-HT (1B) receptor antagonist (-)-propranolol,5-HT (2A) receptor antagonist ketanserin and 5-HT (3/4) receptor antagonist tropisetron each had no effect. Imipramine i. p.-induced hyperglycemia was antagonized by the 5-HT (2C/2B) receptor agonist 1-(3-chlorophenyl)piperazine (mCPP), while the 5-HT (2B) receptor agonist BW 723C86 had no effect. Intracerebroventricular injection of imipramine also elevated plasma glucose levels, which is enhanced by SB 206553. Hyperglycemia elicited by central injection of imipramine was abolished by adrenalectomy. These results suggest that imipramine-induced hyperglycemia in mice is related to its inhibition of the central 5-HT (2C) receptor. Moreover, our results indicate that adrenaline release is related to imipramine-induced hyperglycemia.     

Serotonergic modulation of retinal input to the mouse suprachiasmatic nucleus mediated by 5-HT1B and 5-HT7 receptors

Serotonin (5-HT) and 5-HT receptor agonists can modify the response of the mammalian suprachiasmatic nucleus (SCN) to light. It remains uncertain which 5-HT receptor subtypes mediate these effects. The effects of 5-HT receptor activation on optic nerve-mediated input to SCN neurons were examined using whole-cell patch-clamp recordings in horizontal slices of ventral hypothalamus from the male mouse. The hypothesis that 5-HT reduces the effect of retinohypothalamic tract (RHT) input to the SCN by acting at 5-HT1B receptors was tested first. As previously described in the hamster, a mixed 5-HT(1A/1B) receptor agonist, 1-[3-(trifluoromethyl)phenyl]-piperazine hydrochloride (TFMPP), reduced the amplitude of glutamatergic excitatory postsynaptic currents (EPSCs) evoked by selectively stimulating the optic nerve of wild-type mice. The agonist was negligibly effective in a 5-HT1B receptor knockout mouse, suggesting minimal contribution of 5-HT1A receptors to the TFMPP-induced reduction in the amplitude of the optic nerve-evoked EPSC. We next tested the hypothesis that 5-HT also reduces RHT input to the SCN via activation of 5-HT7 receptors. The mixed 5-HT(1A/7) receptor agonist, R(+)-8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT), reduced the evoked EPSC amplitude in both wild-type and 5-HT1B receptor knockout mice. This effect of 8-OH-DPAT was minimally attenuated by the selective 5-HT1A receptor antagonist WAY 100635 but was reversibly and significantly reduced in the presence of ritanserin, a mixed 5-HT(2/7) receptor antagonist. Taken together with the authors' previous ultrastructural studies of 5-HT1B receptors in the mouse SCN, these results indicate that in the mouse, 5-HT reduces RHT input to the SCN by acting at 5-HT1B receptors located on RHT terminals. Moreover, activation of 5-HT7 receptors in the mouse SCN, but not 5-HT1A receptors, also results in a reduction in the amplitude of the optic nerve-evoked EPSC. The findings indicate that 5-HT may modulate RHT glutamatergic input to the SCN through 2 or more 5-HT receptors. The likely mechanism of altered RHT glutamatergic input to SCN neurons is an alteration of photic effects on the SCN circadian oscillator.     

Aminotriazine 5-HT7 antagonists

The present studies have identified a series of aminotriazines as novel 5-HT(7) receptor antagonists. Compounds 10 and 17 have high affinity for the 5-HT(7) receptor and do not bind to either the 5-HT(2C) or 5-HT(6) receptors. These compounds produce no agonist effects by themselves, and shift the dose-response curve of 5-CT to the right in the manner of an antagonist.     

Modifying ligand-induced and constitutive signaling of the human 5-HT4 receptor

G protein-coupled receptors (GPCRs) signal through a limited number of G-protein pathways and play crucial roles in many biological processes. Studies of their in vivo functions have been hampered by the molecular and functional diversity of GPCRs and the paucity of ligands with specific signaling effects. To better compare the effects of activating different G-protein signaling pathways through ligand-induced or constitutive signaling, we developed a new series of RASSLs (receptors activated solely by synthetic ligands) that activate different G-protein signaling pathways. These RASSLs are based on the human 5-HT(4b) receptor, a GPCR with high constitutive G(s) signaling and strong ligand-induced G-protein activation of the G(s) and G(s/q) pathways. The first receptor in this series, 5-HT(4)-D(100)A or Rs1 (RASSL serotonin 1), is not activated by its endogenous agonist, serotonin, but is selectively activated by the small synthetic molecules GR113808, GR125487, and RO110-0235. All agonists potently induced G(s) signaling, but only a few (e.g., zacopride) also induced signaling via the G(q) pathway. Zacopride-induced G(q) signaling was enhanced by replacing the C-terminus of Rs1 with the C-terminus of the human 5-HT(2C) receptor. Additional point mutations (D(66)A and D(66)N) blocked constitutive G(s) signaling and lowered ligand-induced G(q) signaling. Replacing the third intracellular loop of Rs1 with that of human 5-HT(1A) conferred ligand-mediated G(i) signaling. This G(i)-coupled RASSL, Rs1.3, exhibited no measurable signaling to the G(s) or G(q) pathway. These findings show that the signaling repertoire of Rs1 can be expanded and controlled by receptor engineering and drug selection.     

5-HT activates ERK MAP kinase in cultured-human peripheral blood mononuclear cells via 5-HT1A receptors

In the present work, we tested the hypothesis that serotonin (5-hydroxytryptamine = 5-HT) might activate the extracellular signal-regulated kinase (ERK) pathway in human peripheral blood mononuclear cells (PBMC). PBMC were maintained in culture for 72 hrs at 37 degrees C prior to the addition of 5-HT. Our results showed an increase in ERK activation by 5-HT with a peak effect at 30 min and maximal stimulation with 5-HT at 1microM. This activation of ERK did not occur in adherent monocytes suggesting that the effect was on lymphocytes. In addition, p38 MAP kinase was not activated under these conditions. The effect of 5-HT on ERK activation appeared to be mediated through the activation of 5-HT1A receptors since similar results were obtained with R-+-8-hydroxy-DPAT, a selective 5-HT1A receptor agonist and WAY100635, a selective 5-HT1A receptor antagonist, reversed the 5-HT and the R-+-8-hydroxy-DPAT effects. Results from Western blot analysis confirmed the presence of 5-HT1A receptors on the PBMC. A 5-HT2A antagonist, ketanserin, and a 5-HT transport inhibitor, fluoxetine, both failed to block the activation of ERK by 5-HT. Our results indicate that 5-HT activates ERK, but not p38, MAP kinase of human PBMC via a 5-HT1A receptor.     

The effect of the selective 5-HT(3) receptor agonist on ferret gut motility

The effect of the selective 5-hydroxytryptamine (5-HT)(3) receptor agonist YM-31636 (2-(1H-imidazol-4-ylmethyl)-8H-indeno[1,2-d]thiazole monofumarate) on gut motility of fed ferrets was investigated. YM-31636 (0.1 mg/kg p.o.) induced a giant migrating contraction (GMC)-like, high-amplitude, ungrouped colonic contraction although it did not change the basal colonic motility pattern. This GMC-like contraction was always accompanied by defecation. Both GMC-like contraction and defecation were inhibited with the selective 5-HT(3) receptor antagonist ramosetron. YM-31636 affected gastric, duodenal and ileal motility pattern only slightly. These results suggest that 5-HT(3) receptor agonists such as YM-31636 are useful in treating constipation since they facilitate GMC-like contractions and defecation without undesired changes in gut motility pattern.     

Involvement of 5-HT receptors in the development and expression of methamphetamine-induced behavioral sensitization: 5-HT receptor channel and binding study

Methamphetamine (MAP) is one of the most commonly abused drugs in Asia, and previous studies suggest that serotonin 3 receptors (5-HT(3)) are involved in MAP-induced locomotion and reward. However, little is known about the role of 5-HT(3) receptors in MAP-induced behavioral sensitization. Here, we measured the effects of MDL 72222, a 5-HT(3) antagonist, and SR 57227 A, a 5-HT(3) agonist, on the development and expression of MAP-induced behavioral sensitization, and alternations of 5-HT(3) receptor binding labeled with the 5-HT(3)-selective antagonist, [(3)H]GR65630, in mice. In addition, we investigated the effects of MAP on 5-HT(3A) receptor channel activity in Xenopus laevis oocytes expressing 5-HT(3A) receptors. We found that MDL 72222 attenuated both the development and expression of behavioral sensitization to MAP (1.0 mg/kg, i.p.), and that this attenuating effect of MDL 72222 was reversed by pre-treatment with SR 57227 A. In oocytes expressing 5-HT(3A) receptor, MAP exhibited a dual modulation of 5-HT(3A) receptor channel activity, i.e. pre-treatment with a low dose of MAP (0.1 microm) enhanced 5-HT-induced inward peak current (I(5-HT)) but a high dose of MAP (100 microm) inhibited I(5-HT). The acute administration of MDL 72222 with MAP decreased [(3)H]GR65630 binding versus MAP alone in the mouse striatum. Our results suggest that MDL 72222 attenuates MAP-induced behavioral sensitization via 5-HT(3) receptors in the caudate putamen, and that 5-HT(3) receptor antagonists like MDL 72222 have potential as novel anti-psychotic agents for the treatment of MAP dependence and psychosis.     

Characterization of serotonin 5-HT2C receptor signaling to extracellular signal-regulated kinases 1 and 2

Serotonin 5-HT2C receptors (5-HT(2C)Rs) are almost exclusively expressed in the CNS, and implicated in disorders such as obesity, depression, and schizophrenia. The present study investigated the mechanisms governing the coupling of the 5-HT(2C)R to the extracellular signal-regulated kinases (ERKs) 1/2, using a Chinese hamster ovary (CHO) cell line stably expressing the receptor at levels comparable to those found in the brain. Using the non-RNA-edited isoform of the 5-HT(2C)R, constitutive ERK1/2 phosphorylation was observed and found to be modulated by full, partial and inverse agonists. Interestingly, agonist-directed trafficking of receptor stimulus was also observed when comparing effects on phosphoinositide accumulation and intracellular Ca2+ elevation to ERK1/2 phosphorylation, whereby the agonists, [+/-]-2,5-dimethoxy-4-iodoamphetamine (DOI) and quipazine, showed reversal of efficacy between the phosphoinositide/Ca2+ pathways, on the one hand, and the ERK1/2 pathway on the other. Subsequent molecular characterization found that 5-HT-stimulated ERK1/2 phosphorylation in this cellular background requires phospholipase D, protein kinase C, and activation of the Raf/MEK/ERK module, but is independent of both receptor- and non-receptor tyrosine kinases, phospholipase C, phosphoinositide 3-kinase, and endocytosis. Our findings underscore the potential for exploiting pathway-selective receptor states in the differential modulation of signaling pathways that play prominent roles in normal and abnormal neuronal signaling.     

Functional study of rat 5-HT2A receptors using antisense oligonucleotides

We studied the effects in rats of a 6-day intracerebroventricular (i.c.v) infusion of four different end-capped phosphorothioate-modified antisense oligonucleotides (AOs), specifically targeting different regions of the 5-hydroxytryptamine2A (5-HT2A) receptor mRNA, on central 5-HT2A receptor expression and 5-HT2A receptor-mediated behaviours. Only one of the AOs (sequence 4), directed against the 5'-untranslated region (from + 557 to + 577), specifically affected central 5-HT2A receptor expression and receptor-mediated behaviour. This AO (sequence 4) reduced binding of the 5-HT2A agonist 1-(2,5-dimethoxy-4-[125I]iodophenyl)-2-aminopropane ([125I]DOI) up to 25% in cortical areas, as measured by quantitative autoradiography. Cortical binding of the antagonist [3H]ketanserin was not affected. As the specific AO treatment presumably affects the synthesis of new receptor, we hypothesize that this newly synthesized receptor represents the major part of the functionally active, G protein coupled receptor. A 5-day infusion of AO (sequence 4) resulted in profound inhibition of the head-twitch response (HTR) to 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). In contrast, treatment with vehicle, sense oligonucleotides (SOs) and other AOs (sequences 1, 2 and 3) caused an increased DOM-induced HTR as well as a spontaneous HTR. The latter was abolished by treatment with the 5-HT2 receptor antagonist, ritanserin. Systematic investigation of the surgical and infusion procedures revealed that the enhanced HTR already appeared following drilling of the skull. This wounding can probably damage the blood-brain barrier and cause a stress-induced increase in serotonergic transmission. AO (sequence 4) treatment also abolished the spontaneous HTR. AO (sequence 4) treatment allowed the identification of specific central 5-HT2A receptor-mediated behaviours in the complex serotonergic syndrome induced by tryptamine in rats. Only bilateral convulsions and body tremors were significantly inhibited. The backward locomotion, hunched back and Straub tail were not affected, nor was cyanosis, an index of vasoconstriction induced by peripheral 5-HT2A receptor activation. Labelling of central 5-HT2C receptors by [3H]mesulergine, and 5-HT2C receptor-mediated anxiety were not attenuated by AO or SO treatment. Rats treated with AO (sequence 4) showed increased locomotor activity and a strong reactivity towards touching. We hypothesize that the down-regulation of functional 5-HT2A receptors may shift the balance between various 5-HT receptor subtypes. Our analysis of the behavioural consequences of AO treatment and the use of different AOs and SOs has shown that specific receptor-mediated behaviour can be identified.     

Azaadamantane benzamide 5-HT4 agonists: gastrointestinal prokinetic SC-54750

Azaadamantanone 1 was converted to a series of aminoazaadamantane benzamides 9a-d, which were profiled for serotonin receptor activity. Aminomethylazaadamantane SC-54750 is a potent 5-HT(4) agonist and 5-HT(3) antagonist with in vivo efficacy in gastroparesis models and also inhibits cisplatin-induced emesis.