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Sumatriptan has been among the top choices in the management of migraine headaches. The association between migraine and epilepsy highlights the possible effect of sumatriptan on seizures. In this regard, we investigated sumatriptan effects on PTZ-induced seizures thresholds and delineated the modulatory role of 5-HT1B/D receptors and NOS/NO pathway. Our data revealed the anti-convulsant effects of lower doses of sumatriptan, and pro-convulsant effects of higher doses of sumatriptan. GR 127935, a selective 5-HT1B/D antagonist, could abolish the sumatriptan anti-convulsant effects, but it was ineffective against the sumatriptan pro-convulsant effects. Serotonin depletion by consecutive administration of p-CPA, a selective irreversible inhibitor of tryptophan hydroxylase, could not affect the anti-convulsant effects of sumatriptan. The anti-convulsant effects of sumatriptan was potentiated by L-NAME, a non-selective NOS inhibitor, 7-NI, a selective nNOS inhibitor, but not AG, an iNOS inhibitor. It was also neutralized by L-ARG, a NO precursor. The pro-convulsant effects of sumatriptan were blocked by L-NAME and AG, but not 7-NI. It was also potentiated by L-ARG. Our data revealed that anti-convulsive effects of sumatriptan is mediated by interaction between non-serotonergic 5-HT1B/D receptors and nNOS/NO pathway. Besides, the pro-convulsive effect of sumatriptan is mediated by iNOS/NO pathway independent of 5-HT1B/D receptors. For the first time, this study reported the biphasic effect of sumatriptan on an animal model of GCS and its modulatory pathways.

The psychoactive effects of mephedrone are commonly compared with those of 3,4-methylenedioxymethamphetamine, but because of a shorter duration of action, users often employ repeated administration to maintain its psychoactive effects. This study examined the effects of repeated mephedrone administration on locomotor activity, body temperature and striatal dopamine and 5-hydroxytryptamine (5-HT) levels and the role of dopaminergic and serotonergic neurons in these responses. Adult male Lister hooded rats received three injections of vehicle (1 ml/kg, i.p.) or mephedrone HCl (10 mg/kg) at 2 h intervals for radiotelemetry (temperature and activity) or microdialysis (dopamine and 5-HT) measurements. Intracerebroventricular pre-treatment (21 to 28 days earlier) with 5,7-dihydroxytryptamine (150 µg) or 6-hydroxydopamine (300 µg) was used to examine the impact of 5-HT or dopamine depletion on mephedrone-induced changes in temperature and activity. A final study examined the influence of i.p. pre-treatment (-30 min) with the 5-HT1A receptor antagonist WAY-100635 (0.5 mg/kg), 5-HT1B receptor antagonist GR 127935 (3 mg/kg) or the 5-HT7 receptor antagonist SB-258719 (10 mg/kg) on mephedrone-induced changes in locomotor activity and rectal temperature. Mephedrone caused rapid-onset hyperactivity, hypothermia (attenuated on repeat dosing) and increased striatal dopamine and 5-HT release following each injection. Mephedrone-induced hyperactivity was attenuated by 5-HT depletion and 5-HT1B receptor antagonism, whereas the hypothermia was completely abolished by 5-HT depletion and lessened by 5-HT1A receptor antagonism. These findings suggest that stimulation of central 5-HT release and/or inhibition of 5-HT reuptake play a pivotal role in both the hyperlocomotor and hypothermic effects of mephedrone, which are mediated in part via 5-HT1B and 5-HT1A receptors.

Item does not contain fulltext Serotonin is well known for its role in psychiatric disorders like depression and autism, but it is less clear how aberrant behaviour associated with these disorders are shaped by serotonergic alterations during prenatal and postnatal development. The use of serotonergic antidepressant agents and other drugs during pregnancy and breastfeeding can change brain development, and the behavioural consequences may depend on the stage of development; prenatal, early and late postnatal. The aim of this review is to provide an overview of the behavioural consequences of changes in serotonin levels during these three critical developmental stages. The studies together demonstrate that risk for mood disorders (including social deficits) is related to serotonergic perturbations during the prenatal and postnatal phases, whereas risk for autism-like features and sexual abnormalities increases when serotonin levels are increased during the postnatal period. This insight may inform timed strategies to reduce risk for psychiatric disorders.

RU 24969 is a widely used, but non-selective, 5-HT1B/1A agonist that decreases fluid consumption and increases forward locomotion. The mechanism underlying these behavioural responses is not, however, well understood. Accordingly, effects of the selective 5-HT1A and 5-HT1B antagonists, WAY 100635, and GR 127935, respectively, on these two responses to RU 24969 were determined. RU 24969 (0.03-3.0mg/kg, s.c.) dose-dependently decreased water consumption in water deprived rats. This effect was attenuated by GR 127935 (3.0mg/kg), but not by WAY 100635 (1.0mg/kg). RU 24969 (0.3-3.0mg/kg) dose-dependently increased forward locomotion but a higher dose was required to produce this response than the adipsic response. The increased locomotor response was attenuated by WAY 100635 (1.0mg/kg), but not GR 127935 (3.0mg/kg). These results suggest that RU 24969-induced adipsia is mediated by 5-HT1B mechanisms, while RU 24969-induced hyperlocomotion is mediated by 5-HT1A mechanisms.

Perinatal exposure of rats to selective serotonin reuptake inhibitors (SSRIs) produces sensory and social abnormalities paralleling those seen in autistic spectrum disorders (ASDs). However, the possible mechanism(s) by which this exposure produces behavioral abnormalities is unclear. We hypothesized that the lasting effects of neonatal SSRI exposure are a consequence of abnormal stimulation of 5-HT1A and/or 5-HT1B receptors during brain development. We examined whether such stimulation would result in lasting sensory and social deficits in rats in a manner similar to SSRIs using both direct agonist stimulation of receptors as well as selective antagonism of these receptors during SSRI exposure. Male and female rat pups were treated from postnatal days 8 to 21. In Experiment 1, pups received citalopram (20 mg/kg/day), saline, (±)-8-hydroxy-dipropylaminotetralin hydrobromide (8-OH-DPAT; 0.5 mg/kg/day) or 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo[1,2-a]-quinoxaline dimaleate (CGS-12066B; 10 mg/kg/day). In Experiment 2, a separate cohort of pups received citalopram (20 mg/kg/day), or saline which was combined with either N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclo-hexanecarboxamide maleate (WAY-100635; 0.6 mg/kg/day) or N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)-1-1′-biphenyl-4-carboxamide (GR-127935; 6 mg/kg/day) or vehicle. Rats were then tested in paradigms designed to assess sensory and social response behaviors at different time points during development. Direct and indirect neonatal stimulation of 5-HT1A or 5-HT1B receptors disrupts sensory processing, produces neophobia, increases stereotypic activity, and impairs social interactions in manner analogous to that observed in ASD. Increased stimulation of 5-HT1A and 5-HT1B receptors plays a significant role in the production of lasting social and sensory deficits in adult animals exposed as neonates to SSRIs.

Numerous data indicated a significance for the brain dopaminergic pathways in the behavioral effects of cocaine, however recent research also demonstrated involvement of serotonin (5-HT) neurotransmission and particularly 5-HT(1B) receptors in the reinforcing, discriminative stimulus and sensitizing effects of cocaine. In order to substantiate a role of these receptors in incentive motivation for cocaine, we used the extinction/reinstatement model to examine the effects of the 5-HT(1B) receptor ligands on reinstatement of extinguished cocaine-seeking behavior and food-taking behavior. Rats trained to self-administer cocaine (0.5 mg/kg/infusion) subsequently underwent extinction procedures. They were then tested for the cocaine-primed or cocaine-associated cue-induced reinstatement of extinguished cocaine-seeking behavior. Other groups of rats were trained to self-administer food (sweet milk), and after extinction they were tested for the reinstatement of food-taking behavior induced by contingent food presentation. The 5-HT(1B) receptor antagonists SB 216641 (2.5-7.5 mg/kg) and GR 127935 (2.5-10 mg/kg) dose-dependently attenuated the cocaine (10 mg/kg)- and cocaine-associated cue-induced reinstatement of cocaine-seeking behavior whereas they failed to alter reinstatement of food-taking behavior. The 5-HT(1B) receptor agonist CP 94253 (2.5 or 5 mg/kg) combined with a subthreshold priming dose of cocaine (2.5 mg/kg) potentiated reinstatement of the drug seeking-behavior, but inhibited cocaine seeking induced by a submaximal dose (10 mg/kg) of cocaine or the cocaine-associated cue. Moreover, the 5-HT(1B) receptor agonist attenuated reinstatement of food-taking behavior. Facilitatory effect of CP 94253 on cocaine-seeking behavior and its inhibitory effect on food-taking behavior were blocked by SB 216641, but its inhibitory effect on cocaine-seeking behavior remained unaffected by this 5-HT(1B) receptor antagonist. Our results indicate that tonic activation of 5-HT(1B) receptors is involved in cocaine- and cue-induced reinstatement of cocaine-seeking behavior and that the inhibitory effects of 5-HT(1B) receptor antagonists on these phenomena are directly related to motivational aspects of cocaine abuse. The facilitatory 5-HT(1B) receptor-mediated effect of the 5-HT(1B) receptor agonist on cocaine seeking may be related to the earlier reported enhancement of the rewarding properties of cocaine, while its inhibitory effect on cocaine-seeking behavior, unrelated to the 5-HT(1B) receptor activation, may result from a general reduction of motivation.

Preclinical Research TRIM, a selective neuronal NOS inhibitor, had anxiolytic effects in the elevated plus-maze (EPM) test. The aim of the present study was to evaluate the involvement of serotonergic system in the anxiolytic-like effect of TRIM in the EPM test, a widely used animal model of anxiety. The anxiolytic-like effect of TRIM (50 mg/kg, i.p.) in adult Wistar albino male rats in the EPM test was antagonized by pretreatment with the 5-HT depleting agent; parachlorophenylalanine methyl ester (3 × 150 mg/kg i.p.) that inhibits 5-HT synthesis; methiothepin (0.1 mg/kg, i.p.), a nonselective 5-HT receptor antagonist; WAY 100635 (0.1 mg/kg i.p.), a selective 5-HT1A receptor antagonist; GR 127935 (3 mg/kg i.p.), a selective 5-HT1B/1D receptor antagonist; cyproheptadine (3 mg/kg i.p.), a 5-HT2 receptor antagonist; or ketanserin (5 mg/kg i.p.), a 5-HT2A/2C receptor antagonist. The anxiolytic-like effects of TRIM thus appear to be mediated in part by 5-HT1 and 5-HT2 receptors.

BACKGROUND: We have recently shown that levetiracetam, administered systemically, exerts an antihyperalgesic effect in a rat inflammatory pain model. In this study, we examined whether levetiracetam has local peripheral antihyperalgesic/antiedematous effects in the same model of localized inflammation and whether opioidergic, adrenergic, purinergic, 5-HTergic, and GABAergic receptors are involved in its antihyperalgesic action. METHODS: Rats were intraplantarly (IPL) injected with carrageenan. A paw pressure test was used to determine the effect/s of (a) levetiracetam when applied IPL, on carrageenan-induced hyperalgesia, and (b) naloxone (a nonselective opioid receptor antagonist), CTAP (a selective mu-opioid receptor antagonist); yohimbine (a selective alpha(2)-adrenoceptor antagonist), BRL 44408 (a selective alpha(2A)-adrenoceptor antagonist), MK-912 (a selective alpha(2C)-adrenoceptor antagonist); caffeine (a nonselective adenosine receptor antagonist), DPCPX (a selective adenosine A(1) receptor antagonist); methysergide (a nonselective 5-HT receptor antagonist), GR 127935 (a selective 5-HT1B/1D receptor antagonist); and bicuculline (a selective GABA(A) receptor antagonist), all applied IPL, on the levetiracetam-induced antihyperalgesia. Moreover, levetiracetam's influence on paw inflammatory edema was measured by plethysmometry. RESULTS: Levetiracetam (200-1000 nmol/paw) produced a significant dose-dependent reduction of the paw inflammatory hyperalgesia and edema induced by carrageenan. Naloxone (75-300 nmol/paw), CTAP (1-5 nmol/paw); yohimbine (130-520 nmol/paw), BRL 44408 (50-200 nmol/paw), MK-912 (5-20 nmol/paw); caffeine (500-1500 nmol/paw), DPCPX (3-30 nmol/paw); methysergide (10-100 nmol/paw) and GR 127935 (50-200 nmol/paw); but not bicuculline (400 nmol/paw), significantly depressed the antihyperalgesic effects of levetiracetam (1000 nmol/paw). The effects of levetiracetam and antagonists were attributed to local peripheral effects because they were not observed after administration into the contralateral hindpaw. CONCLUSIONS: Our results show that levetiracetam produces local peripheral antihyperalgesic and antiedematous effects in a rat model of localized inflammation. Antihyperalgesia is at least in part mediated by peripheral mu-opioid, alpha(2A,C)-adrenergic, A(1) adenosine, and 5-HT1B/1D receptors, but not by GABA(A) receptors. These findings could contribute toward a better understanding of the analgesic effects of levetiracetam, and improved treatments of inflammatory pain with a lower incidence of systemic side effects and drug interactions of levetiracetam. (Anesth Analg, 2012;115:1457-66)

Acute exposure to ±3,4-methylenedioxymethamphetamine (MDMA) preferentially increases release of serotonin (5-HT), and a role of 5-HT in many of the behavioral effects of acute exposure to MDMA has been demonstrated. A role of 5-HT in MDMA self-administration in rats has not, however, been adequately determined. Therefore, the present study measured the effect of pharmacological manipulation of some 5-HT receptor subtypes on self-administration of MDMA. Rats received extensive experience with self-administered MDMA prior to tests with 5-HT ligands. Doses of the 5-HT1A antagonist, WAY 100635 (0.1-1.0mg/kg), 5-HT1B antagonist, GR 127935 (1.0-3.0mg/kg), and the 5-HT2A antagonist, ketanserin (1.0-3.0mg/kg) that have previously been shown to decrease self-administration of other psychostimulants and that decreased MDMA-produced hyperactivity in the present study did not alter MDMA self-administration. Experimenter-administered injections of MDMA (10.0mg/kg, ip) reinstated extinguished drug-taking behavior, but this also was not decreased by any of the antagonists. In contrast, both WAY 100635 and ketanserin, but not GR 127935, decreased cocaine-produced drug seeking in rats that had been trained to self-administered cocaine. The 5-HT1A agonist, 8-OH-DPAT (0.1-1.0mg/kg), but not the 5-HT1B/1A agonist, RU 24969 (0.3-3.0mg/kg), decreased drug-seeking produced by the reintroduction of a light stimulus that had been paired with self-administered MDMA infusions. These findings suggest a limited role of activation of 5-HT1A, 5-HT1B or 5-HT2 receptor mechanisms in MDMA self-administration or in MDMA-produced drug-seeking following extinction. The data suggest, however, that 5-HT1A agonists inhibit cue-induced drug-seeking following extinction of MDMA self-administration and might, therefore, be useful adjuncts to therapies to limit relapse to MDMA use.

Inductive signals mediating the differentiation of neural precursors into serotonergic (5-HT) or dopaminergic neurons have not been clarified. We have recently shown that in cell aggregates obtained from rat mesencephalic precursors, reduction of serotonin levels induces a marked increase in generation of dopaminergic neurons. In the present study we treated rat neurospheres with antagonists of the main subtypes of 5-HT receptors, 5-HT transport inhibitors, or 5-HT receptor agonists, and studied the effects on generation of dopaminergic neurons. Cultures treated with Methiothepin (5-HT(1,2,5,6,7) receptor antagonist), the 5-HT(4) receptor antagonist GR113808;67:00-.or the 5-HT(7) receptor antagonist SB 269970 showed a significant increase in generation of dopaminergic cells. Treatment with the 5-HT(1B/1D) antagonist GR 127935, the 5-HT(2) antagonist Ritanserin, the 5-HT transporter inhibitor Fluoxetine, the dopamine and norepinephrine transport inhibitor GBR 12935, or with both inhibitors together, or 5-HT(4) or 5-HT(7) receptor agonists induced significant decreases in generation of dopaminergic cells. Cultures treated with WAY100635 (5-HT(1A) receptor antagonist), the 5-HT(3) receptor antagonist Ondasetron, or the 5-HT(6) receptor antagonist SB 258585 did not show any significant changes. Therefore, 5-HT(4) and 5-HT(7) receptors are involved in the observed serotonin-induced decrease in generation of dopaminergic neurons from proliferating neurospheres of mesencephalic precursors. 5-HT(4) and 5-HT(7) receptors were found in astrocytes and serotonergic cells using double immunolabeling and laser confocal microscopy, and the glial receptors appeared to play a major role.

The 5-HT1B/1D receptor antagonist, GR-127935, inhibits hypotensive responses produced by the 5-HT1A, 5-HT1B/1D and 5-HT7 receptor agonist, and 5-HT5A/5B receptor ligand, 5-carboxamidotryptamine (5-CT), in rats. This work further characterized the above mechanism using more selective 5-HT1B and 5-HT1D receptor antagonists. Also, expression of 5-HT5A and 5-HT5B receptor mRNAs in blood vessels was searched by reverse transcription polymerase chain reaction. Decreases in diastolic blood pressure induced by 5-CT (0.001-10 μg/kg, intravenously) were analyzed in anesthetized rats that had received intravenous vehicle (1 mL/kg), SB-224289 (5-HT1B antagonist; 0.3 and 1.0 mg/kg), BRL15572 (5-HT1D antagonist; 0.3 and 1.0 mg/kg), SB-224289 + BRL15572 (0.3 mg/kg, each), or SB-224289 + BRL15572 (0.3 mg/kg, each) + GR-127935 (1 mg/kg). Because only the latter treatment inhibited 5-CT-induced hypotension, suggestive of a mechanism unrelated to 5-HT1B/1D receptors, the effects of antagonists/ligands at 5-HT5A (SB-699551, 1 mg/kg), 5-HT6 (SB-399885, 1 mg/kg), and 5-HT1B/1D/5A/5B/7 receptors (ergotamine, 0.1 mg/kg) on 5-CT-induced hypotension were tested. Interestingly, only ergotamine blocked 5-CT-induced responses; this effect closely paralleled that of SB-224289 + BRL-15572 + GR-127935. Neither did ergotamine nor GR-127935 inhibit hypotensive responses induced by the 5-HT7 receptor agonist, LP-44. Faint but clear bands corresponding to 5-HT5A and 5-HT5B receptor mRNAs in aorta and mesenteric arteries were detected. Results suggest that the GR-127935-sensitive mechanism mediating hypotension in rats is unrelated to 5-HT1B, 5-HT1D, 5-HT5A, 5-HT6, and 5-HT7 receptors. This mechanism, however, resembles putative 5-HT5B receptors.

The aim of the present study was to determine whether donitriptan and sumatriptan decreased jugular venous oxygen saturation and increased carbon dioxide partial pressure in venous blood. However, previous studies conducted with these compounds cannot discriminate whether the decrease of venous oxygen saturation is dependent of cranial vasoconstrictor. In the present study, vehicle (n = 10), donitriptan (2.5, 10, and 40 microg/kg; n = 8) or sumatriptan (630 microg/kg; n = 8) were infused into the carotid artery in the anesthetized rat. Regional blood flows were evaluated in the presence of donitriptan (10 microg/kg; n = 6) or vehicle (n = 6). Jugular venous oxygen saturation was significantly decreased by donitriptan (from 10 microg/kg) with maximal changes of -32.9 +/- 8.0%. Jugular carbon dioxide partial pressure was increased by donitriptan, reaching maximal changes of 17.7 +/- 4.6% (P0.05 versus vehicle). Similarly, sumatriptan significantly decreased venous oxygen saturation and increased jugular carbon dioxide partial pressure. These changes induced by donitriptan are abolished by the 5-hydroxytryptamine (5-HT)(1B/1D) receptor antagonist GR 127935 (N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2-[-methyl-4(5-methyl-1,2,4)-oxadiazol-3-yl]-(1,1 biphenyl)-4-carboxamide dihydrochloride). In addition, donitriptan was devoid of significant effects on systemic arterial pressure, heart rate, or regional blood flows, including systemic arterial-jugular venous anastomotic, systemic, or cranial. The results demonstrate that donitriptan increases cerebral oxygen consumption by 5-HT(1B/1D) receptor activation in the absence of cranial vasoconstriction.

The authors have investigated 5-HT1B receptor function in prefrontal cortex and dorsal hippocampus as well as the HPA axis response after subchronic (24 h) and chronic (15 days) treatment with the SSRI citalopram. All experiments were carried out in presence of citalopram to prevent rapid resensitization of the 5-HT1B receptors. Moreover, this more closely resembles the clinical situation. The concentration of citalopram was measured in both brain areas to ensure comparable levels in the different treatment groups. Using microdialysis, the authors found that under those conditions the effect of the 5-HT1B receptor antagonists SB 224289 and the mixed 5-HT1B/1D receptor antagonist GR 127935 on extracellular levels of 5-HT was unaltered by duration of treatment. Basal levels of 5-HT, however, were increased in the dorsal hippocampus following chronic treatment. In addition, plasma levels of the catecholamines adrenaline and noradrenaline and the HPA axis hormones ACTH and corticosterone were all decreased after chronic treatment. (C0 2005 Elsevier Inc. All rights reserved.

Effects of the 5-hydroxytryptamine (5-HT)(1A/1B/2C) receptor agonist N-[3-(trifluoromethyl)phenyl] piperazine (TFMPP, 0-3.0 mg/kg s.c.) and the 5-HT2C receptor agonist 8,9-dichloro-2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a]quinoxalin-5(6H)-one (WAY 161503, 0-3.0 mg/kg s.c.) in place conditioning were measured in male Sprague-Dawley rats. Effects of TFMPP, alone and with the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl]-N-2-pyridinyl-cyclohexanecarboxamine (WAY 100635), the 5-HT(1B) receptor antagonist N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-1,1'-biphenyl-4-carboxamide (GR 127935) or the 5-HT2C receptor antagonist 6-chloro-5-methyl-1-[[2-(2-methylpyrid-3-yloxy)pyrid-5-yl]carbamoyl]indoline (SB 242084) and of WAY 161503 alone and with SB 242084 on locomotor activity were also assessed. Neither TFMPP nor WAY 161503 induced place conditioning. WAY 161503 (1.0 and 3.0 mg/kg s.c.) decreased locomotor activity; SB 242084 (1.0 mg/kg i.p.) blocked this effect. Reduced locomotor activity following TFMPP was blocked by SB 242084 but not WAY 100635 (0.1 mg/kg s.c.) or GR 127935 (3.0 mg/kg s.c.). Behaviourally relevant levels of 5-HT2C receptor stimulation may not exert reinforcing effects, although other studies indicate that such manipulations alter reinforcing effects of drugs of abuse.

1 Although an important regulatory role for serotonin (5-HT) in seizure activation and propagation is well established, relatively little is known of the function of specific 5-HT receptor subtypes on seizure modulation. 2 The aim of the present study was to investigate the role of 5-HT1A, 1B and 1D receptors in modulating generalised seizures in the rat maximal electroshock seizure threshold (MEST) test. 3 The mixed 5-HT receptor agonists SKF 99101 (5–20 mg kg−1 i.p.) and RU 24969 (1–5 mg kg−1 i.p.), 0.5 h pretest, both produced marked dose-related increases in seizure threshold. These agents share high affinity for 5-HT1A, 1B and 1D receptors. 4 Antiseizure effects induced by submaximal doses of these agonists were maintained following p-chlorophenylalanine (150 mg kg−1 i.p. × 3 days)-induced 5-HT depletion. 5 The anticonvulsant action of both SKF 99101 (15 mg kg−1 i.p.) and RU 24969 (2.5 mg kg−1 i.p.) was dose-dependently abolished by the selective 5-HT1B receptor antagonist SB-224289 (0.1–3 mg kg−1 p.o., 3 h pretest) but was unaffected by the selective 5-HT1A receptor antagonist WAY 100635 (0.01–0.3 mg kg−1 s.c., 1 h pretest). This indicates that 5-HT1B receptors are primarily involved in mediating the anticonvulsant properties of these agents. 6 In addition, the ability of the 5-HT1B/1D receptor antagonist GR 127935 (0.3–3 mg kg−1 s.c., 60 min pretest) to dose-dependently inhibit SKF 99101-induced elevation of seizure threshold also suggests possible downstream involvement of 5-HT1D receptors in the action of this agonist, although confirmation awaits the identification of a selective 5-HT1D receptor antagonist. 7 Overall, these data demonstrate that stimulation of postsynaptic 5-HT1B receptors inhibits electroshock-induced seizure spread in rats. British Journal of Pharmacology (2005) 144, 628–635. doi:10.1038/sj.bjp.0706027

In the present study, we examined effects of the selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor citalopram, the 5-HT/noradrenaline reuptake inhibitor imipramine, the selective noradrenaline reuptake inhibitor desipramine or the monoamine oxidase-A inhibitor moclobemide, administered in combination with the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridynyl)cyclohexanecarboxamide (WAY 100635) or the 5-HT(1B/1D) receptor antagonist N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-[1,2,4]oxadiazol-3-yl)1,1'-biphenyl-4-carboxamide (GR 127935) and the 5-HT(1B) receptor antagonist N-[3-(2-dimethylamino) ethoxy-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1'-biphenyl)-4-carboxamide (SB 216641) in the forced swimming test in rats. When given alone, citalopram (20 and 30 mg/kg), imipramine (20 mg/kg), desipramine (20 mg/kg), moclobemide (20 mg/kg), WAY 100635 (0.1 and 1 mg/kg), GR 127935 (10 and 20 mg/kg) or SB 216641 (2 mg/kg) did not shorten the immobility time of rats. Co-administration of WAY 100635 (0.1 and 1 mg/kg) and citalopram (20 mg/kg), or imipramine (20 mg/kg), or moclobemide (20 mg/kg) did not affect the immobility time of rats, whereas WAY 100635 given jointly with desipramine (20 mg/kg) induced a weak anti-immobility effect. GR 127935 (10 and 20 mg/kg) or SB 216641 (2 mg/kg) co-administered with imipramine, desipramine or moclobemide, but not citalopram, produced a significant anti-immobility action in the forced swimming test in rats. These results indicate that the blockade of 5-HT(1B) rather than 5-HT(1A) receptors may facilitate the anti-immobility effect of imipramine, desipramine or moclobemide in the forced swimming test. No interaction was observed between 5-HT(1A) or 5-HT(1B/1D) receptor antagonists and citalopram.

The role of serotonin (5-HT)1B receptors in the mechanism of action of selective serotonin re-uptake inhibitors (SSRI) was studiedbyusingintracerebralinvivomicrodialysisinconscious, freely moving wild-type and 5-HT1B receptor knockout (KO 5-HT1B) mice in order to compare the effects of chronic administration of paroxetine via osmotic minipumps (1 mg per kg per day for 14 days) on extracellular 5-HT levels ([5-HT]ext) in the medial prefrontal cortex and ventral hippocampus. Basal [5-HT]ext values in the medial prefrontal cortex and ventral hippocampus, ! 20 h after removing the minipump, were not altered by chronic paroxetine treatment in both genotypes. On day 15, in the ventral hippocampus, an acute paroxetine challenge (1 mg/kg i.p.) induced a larger increase in [5-HT]ext in saline-pretreated mutant than in wild-type mice. This difference between the two genotypes in the effect of the paroxetine challenge persisted following chronic paroxetine treatment. Conversely, in the medial prefrontal cortex, the paroxetine challenge increased [5-HT]ext similarly in saline-pretreated mice of both genotypes. Such a challenge produced a further increase in cortical [5-HT]ext compared with that in salinepretreated groups of both genotypes, but no differences were foundbetweengenotypesfollowingchronictreatment.Toavoid the interaction with raphe 5-HT1A autoreceptors, 1 lM paroxetinewasperfusedlocallythroughthedialysisprobeimplantedin the ventral hippocampus; similar increases in hippocampal [5-HT]ext were found in acutely or chronically treated wild-type mice. Systemic administration of the mixed 5-HT1B/1D receptor antagonist GR 127935 (4 mg/kg) in chronically treated wildtype mice potentiated the effect of a paroxetine challenge dose on [5-HT]ext in the ventral hippocampus, whereas systemic administration of the selective 5-HT1A receptor antagonist WAY 100635 did not. By using the zero net flux method of quantitative microdialysis in the medial prefrontal cortex and ventral hippocampus of wild-type and KO 5-HT1B mice, we found that basal [5-HT]ext and the extraction fraction of 5-HT were similar in the medial prefrontal cortex and ventral hippocampus of both genotypes, suggesting that no compensatory response to the constitutive deletion of the 5-HT1B receptor involving changes in 5-HT uptake capacity occurred in vivo. As steady-state brain concentrations of paroxetine at day 14 were similar in both genotypes, it is unlikely that differences in the effects of a paroxetine challenge on hippocampal [5-HT]ext are due to alterations of the drug’s pharmacokinetic properties in mutants. These data suggest that there are differences between the ventral hippocampus and medial prefrontal cortex in activation of terminal 5-HT1B autoreceptors and their role in regulating dialysate 5-HT levels. These presynaptic receptors retain their capacity to limit 5-HT release mainly in the ventral

Agonists acting at the serotonin-1B receptor (5-HT1BR) and 5-HT2CR have been reported to potentiate and block, respectively, the discriminative stimulus effects of cocaine. The present investigation reassessed the antagonistic effects of the mixed 5-H2C/1BR agonist m-chlorophenylpiperazine (mCPP) on the discriminative stimulus effects of cocaine in the presence or absence of selective antagonism of the 5-HT1BR or 5-HT2CR. The stimulus effects of cocaine were attenuated by mCPP at doses that reduced response rates. The selective 5-HT2CR antagonist SB 242084, but not the selective 5-HT1BR antagonist GR 127935, reversed the mCPP-evoked attenuation of the cocaine cue and the suppression of response rates. These results demonstrate that the suppressive effects of mCPP on cocaine discrimination are related to stimulation of the HT2CR.

Onset of action is a key unmet need in the treatment of depression. However, very few preclinical models in which the effects of antidepressants can be shown are suitable for screening for onset. In this context, previous literature suggests that a slow onset of action of selective serotonin reuptake inhibitors (SSRIs) is observed in schedule-induced polydipsia (SIP). The current investigation was performed to determine the latency to reduce SIP of the SSRI, fluoxetine, and of two treatments known to facilitate 5-HT neurotransmission to a greater extent than an SSRI alone. These treatments included interaction studies for fluoxetine+the 5-HT 1A antagonist, WAY 100635, and for fluoxetine+the 5-HT 1B partial agonist, GR 127935. Food-restricted rats were trained on a fixed interval schedule with drinking water freely available. Once water intake was stable, rats were randomly assigned to vehicle of treatment groups. Daily treatment was continued for 3 (interaction studies) or 18 days (fluoxetine alone study). Fluoxetine significantly reduced SIP after 5–6 days of treatment, with the maximal effect evidenced after 8 days. WAY 100635 and GR 127935 accelerated the onset of action of fluoxetine, with significant effects observed on treatment day 1. These data suggest that SIP may be useful to assess the onset of action of serotonin enhancers.

Continuous infusions of 5-hydroxytryptamine (5-HT) inhibit the tachycardiac responses to preganglionic (C7-T1) sympathetic stimulation in pithed rats pretreated with desipramine. The present study identified the pharmacological profile of this inhibitory action of 5-HT. The inhibition induced by intravenous (i.v.) continuous infusions of 5-HT (5.6 microg x kg-1x min-1) on sympathetically induced tachycardiac responses remained unaltered after i.v. treatment with saline or the antagonists GR 127935 (5-HT1B/1D), the combination of WAY 100635 (5-HT1A) plus GR 127935, ritanserin (5-HT2), tropisetron (5-HT3/4), LY215840 (5-HT7) or a cocktail of antagonists/inhibitors consisting of yohimbine (alpha2), prazosin (alpha1), ritanserin, GR 127935, WAY 100635 and indomethacin (cyclooxygenase), but was abolished by methiothepin (5-HT1/2/6/7 and recombinant 5-ht5A/5B). These drugs, used in doses high enough to block their respective receptors/mechanisms, did not modify the sympathetically induced tachycardiac responses per se. I.v. continuous infusions of the agonists 5-carboxamidotryptamine (5-CT; 5-HT1/7 and recombinant 5-ht5A/5B), CP 93129 (r5-HT1B), sumatriptan (5-HT1B/1D), PNU-142633 (5-HT1D) and ergotamine (5-HT1B/1D and recombinant 5-ht5A/5B) mimicked the above sympatho-inhibition to 5-HT. In contrast, the agonists indorenate (5-HT1A) and LY344864 (5-ht1F) were inactive. Interestingly, 5-CT-induced cardiac sympatho-inhibition was abolished by methiothepin, the cocktail of antagonists/inhibitors, GR 127935 or the combination of SB224289 (5-HT1B) plus BRL15572 (5-HT1D), but remained unchanged when SB224289 or BRL15572 were given separately. Therefore, 5-HT-induced cardiac sympatho-inhibition, being unrelated to 5-HT2, 5-HT3, 5-HT4, 5-ht6, 5-HT7 receptors, alpha1/2-adrenoceptor or prostaglandin synthesis, seems to be primarily mediated by (i). 5-HT1 (probably 5-HT1B/1D) receptors and (ii). a novel mechanism antagonized by methiothepin that, most likely, involves putative 5-ht5A/5B receptors.

The effects of donitriptan on systemic arterial-jugular venous oxygen saturation difference were evaluated in pentobarbitone-anesthetized pigs. Oxygen and carbon dioxide partial pressures in systemic arterial and jugular venous blood as well as hemoglobin oxygen saturation were determined by conventional blood gas analysis. Vehicle (40% polyethyleneglycol in saline, n = 9) or donitriptan (0.01, 0.04, 0.16, 0.63, 2.5, 10, and 40 microg/kg, n = 7) were cumulatively infused over 15 min/dose. The involvement of 5-hydroxytryptamine(1B) (5-HT(1B)) receptors was assessed in the presence of the 5-HT(1B/1D) receptor antagonist, GR 127935. Donitriptan decreased markedly and dose dependently jugular venous oxygen saturation [ED(50) 0.5 (0.3-1.1) microg/kg], in parallel with increases in carotid vascular resistance [ED(50) 0.9 (0.7-1.1) microg/kg]. Since arterial oxygen saturation and partial pressure remained unchanged, donitriptan significantly increased arteriovenous oxygen saturation difference from 0.63 microg/kg (maximal variation: 57 +/- 18%, P0.05 compared with vehicle). Unexpectedly, donitriptan from 2.5 microg/kg induced marked and significant increases in carbon dioxide partial pressure (pVCO(2)) in venous blood (maximal increase 18.8 +/- 5.7%; P0.05 compared with vehicle). Pretreatment with GR 127935 (0.63 mg/kg, n = 5) abolished the fall in venous oxygen saturation and the increase in carotid vascular resistance and reduced the increases in pVCO(2) induced by donitriptan. The results demonstrate that donitriptan, via 5-HT(1B) receptor activation, decreases the oxygen saturation of venous blood draining the head, concomitantly with cranial vasoconstriction. Since donitriptan also increased pVCO(2), an effect upon cerebral oxygen consumption and metabolism is suggested in addition to cranial vasoconstriction, which may be relevant to its headache-relieving effects.

The sympathetic nervous system that innervates the peripheral circulation is regulated by several mechanisms/receptors. It has been reported that prejunctional 5-HT1A, 5-HT1B, 5-HT1D, D2-like receptors and α2-adrenoceptors mediate the inhibition of the vasopressor sympathetic outflow in pithed rats. In addition, ergotamine, an antimigraine drug, displays affinity at the above receptors and may explain some of its adverse/therapeutic effects. Thus, the aims of this study were to investigate in pithed rats: (i) whether ergotamine produces inhibition of the vasopressor sympathetic outflow; and (ii) the major receptors involved in this effect. For this purpose, male Wistar pithed rats were pre-treated with gallamine (25 mg/kg; i.v.) and desipramine (50 µg/kg) and prepared to stimulate the vasopressor sympathetic outflow (T7-T9; 0.03-3 Hz) or to receive i.v. bolus of exogenous noradrenaline (0.03-3 µg/kg). I.v. continuous infusions of ergotamine (1 and 1.8 μg/kgmin) dose-dependently inhibited the vasopressor responses to sympathetic stimulation but not those to exogenous noradrenaline. The sympatho-inhibition elicited by 1.8 μg/kg min ergotamine was (i) unaffected by saline (1 ml/kg); (ii) partially antagonised by WAY 100635 (5-HT1A; 30 μg/kg) and rauwolscine (α2-adrenoceptor; 300 μg/kg), and (iii) dose-dependently blocked by GR 127935 (5-HT1B/1D; 100 and 300 μg/kg) or raclopride (D2-like; 300 and 1000 μg/kg), The above doses of antagonists did not modify per se the sympathetically-induced vasopressor responses. The above results suggest that ergotamine induces inhibition of the vasopressor sympathetic outflow by activation of prejunctional 5-HT1A, 5-HT1B/1D, α2-adrenoceptors and D2-like receptors in pithed rats.

We used knockout mice and receptor antagonist strategies to investigate the contribution of the serotonin (5-hydroxytryptamine, 5-HT) 5-HT1B receptor subtype in mediating the effects of selective serotonin reuptake inhibitors (SSRIs). Using in vivo intracerebral microdialysis in awake mice, we show that a single systemic administration of paroxetine (1 or 5 mg/kg, i.p.) increased extracellular serotonin levels [5-HT]ext in the ventral hippocampus and frontal cortex of wild-type and mutant mice. However, in the ventral hippocampus, paroxetine at the two doses studied induced a larger increase in [5-HT]ext in knockout than in wild-type mice. In the frontal cortex, the effect of paroxetine was larger in mutants than in wild-type mice at the 1 mg/kg dose but not at 5 mg/kg. In addition, either the absence of the 5-HT1B receptor or its blockade with the mixed 5-HT1B/1D receptor antagonist, GR 127935, potentiates the effect of a single administration of paroxetine on [5-HT]ext more in the ventral hippocampus than in the frontal cortex. Furthermore, we demonstrate that SSRIs decrease immobility in the forced swimming test; this effect is absent in 5-HT1B knockout mice and blocked by GR 127935 in wild-type suggesting therefore that activation of 5-HT1B receptors mediate the antidepressant-like effects of SSRIs. Taken together these data demonstrate that 5-HT1B autoreceptors appear to limit the effects of SSRI on dialysate 5-HT levels particularly in the hippocampus while presynaptic 5-HT1B heteroreceptors are likely to be required for the antidepressant activity of SSRIs.

Recent studies have shown that antagonists of serotonin (5-HT)1B receptors attenuate cocaine-induced locomotor hyperactivity, whereas agonists enhance reinforcing and discriminative stimulus effects of the psychostimulant. The present study was designed to determine how 5-HT1B receptor ligands affected the development or the expression phase of sensitization to the cocaine-induced locomotor response in rats. In Experiment 1, rats were treated repeatedly (for 5 days) with cocaine (10 mg/kg) in combination with either saline, GR 127935 (5-HT1B antagonist), CP 94,253 (5-HT1B agonist) or GR 127935 + CP 94,253. On day 10, they received a challenge dose of cocaine (10 mg/kg). In Experiment 2, animals received either saline or cocaine (10 mg/kg) for 5 days, and were then challenged with cocaine (10 mg/kg) in combination with saline, GR 127935, CP 94,253 or GR 127935 + CP 94,253, on day 10. In Experiment 3, rats received either saline, cocaine or CP 94,253 for 5 days; on day 10 they received challenge doses of CP 94,253 or cocaine. In rats treated repeatedly with cocaine, the locomotor hyperactivity induced by a challenge dose of the psychostimulant was about twice as high as that observed after its first administration. The effect evoked by cocaine challenge was further increased in animals treated repeatedly with CP 94,253 + cocaine, but not with GR 127935 + CP 94,253 + cocaine. No difference was observed in the response to cocaine challenge in rats treated repeatedly with cocaine or GR 127935 + cocaine (Experiment 1). In animals treated repeatedly with the psychostimulant, the behavioral response to a challenge dose of cocaine was dose-dependently increased when that drug was combined with CP 94,253, but not with GR 127935 + CP 94,253. No difference was observed in the locomotor response of rats challenged with cocaine or GR 127935 + cocaine (Experiment 2). When rats were treated repeatedly with cocaine, a challenge dose of CP 94,253 produced an about threefold increase in the locomotor effect compared to the animals treated likewise with saline (Experiment 3). Our results indicate that 5-HT1B receptors are involved in neither the development nor the expression of sensitization to cocaine-induced locomotor hyperactivity. On the other hand, they also show that pharmacological activation of 5-HT1B receptors enhances both phases of this phenomenon, and that repeated administration of cocaine leads to an increased functional reactivity of these receptors.

This study has further investigated the pharmacological profile of the GR127935-sensitive 5-HT1 receptors mediating vasoconstriction in the internal carotid bed of anaesthetized vagosympathectomized dogs. One-minute intracarotid infusions of the agonists 5-hydroxytryptamine (5-HT; 0.1–10 μg min−1; endogenous ligand) and sumatriptan (0.3–10 μg min−1; 5-HT1B/1D), but not PNU-142633 (1–1000 μg min−1; 5-HT1D) or LY344864 (1–1000 μg min−1; 5-ht1F), produced dose-dependent decreases in internal carotid blood flow without changing blood pressure or heart rate. The responses to 5-HT were apparently resistant to blockade by i.v. administration of the antagonists SB224289 (300 μg kg−1; 5-HT1B), BRL15572 (300 μg kg−1; 5-HT1D) or ritanserin (100 μg kg−1; 5-HT2). In contrast, the responses to sumatriptan were antagonized by SB224289, but not by BRL15572. In the animals receiving SB224289, but not those receiving BRL15572, the subsequent administration of ritanserin abolished the 5-HT-induced vasoconstriction and unmasked a vasodilator component. Similarly, in ritanserin-treated animals, the subsequent administration of SB224289, but not BRL15572, completely blocked the 5-HT-induced vasoconstriction, revealing vasodilatation. In animals receiving initially BRL15572, the subsequent administration of SB224289 did not affect (except at 10 μg min−1) the vasoconstrictor responses to 5-HT. Notably, in animals pretreated with 1000 μg kg−1 of mesulergine, a 5-HT2/7 receptor antagonist, 5-HT produced a dose-dependent vasoconstriction, which was practically abolished by SB224289. After BRL15572, no further blockade was produced and the subsequent administration of ritanserin was similarly inactive. These results suggest that the GR127935-sensitive 5-HT1 receptors mediating canine internal carotid vasoconstriction resemble the 5-HT1B but not the 5-HT1D or 5-ht1F, receptor subtype. British Journal of Pharmacology (2001) 132, 991–998; doi:10.1038/sj.bjp.0703913

5-HT1A, 5-HT1B and 5-HT1D receptors are known to function as 5-HT autoreceptors in the rat dorsal raphe nucleus (DRN), modulating local 5-HT efflux. However, there are no studies on the simultaneous blockade of these receptors in the DRN. We investigated the effect of 5-HT1B and 5-HT1D receptor antagonists on 5-HT efflux in rat DRN, alone and in the presence of 5-HT1A receptor antagonists, using the technique of fast cyclic voltammetry. The 5-HT1A receptor antagonist, WAY 100635, and the 5-HT1B receptor antagonist, SB-224289, had no effect on 5-HT efflux while the 5-HT1B/1D receptor antagonist, GR 127935, produced a small decrease in 5-HT efflux. In contrast, the 5-HT1D receptor antagonist, BRL 15572, produced a significant increase in 5-HT efflux. Co-perfusion of WAY 100635 and SB-224289 significantly increased 5-HT efflux. In addition, WAY 100635 reversed the small inhibition of 5-HT efflux observed with GR 127935 but had no effect on the BRL 15572-induced increase. Antagonism of all three 5-HT autoreceptors with SB-224289, BRL 15572 and WAY 100635 significantly increased 5-HT efflux. These data confirm that 5-HT efflux within the DRN is under the control of 5-HT1A, 5-HT1B and 5-HT1D autoreceptors and elevation of 5-HT efflux was greatest following antagonism of 5-HT1A and 5-HT1B receptors.

Glucocorticoid hormones are known to be elevated in depression, and to interact with serotonin 5-HT(1A) receptors at both the presynaptic and postsynaptic levels. Since one of the presumed mechanisms of action of antidepressant drugs is induction of changes in sensitivity of 5-HT(1A) and also 5-HT(1B) receptors, the effects of repeated administration of corticosterone (50 mg/kg s.c. b.i.d. for 10 days) on activities of these receptors were determined using in vivo microdialysis in freely moving rats. Presynaptic 5-HT(1A) receptor activity, as measured by the effect of a challenge dose (0.2 mg/kg s.c.) of the 5-HT(1A) agonist 8-hydroxy-2 (di-n-propylamino) tetralin (8-OH-DPAT) to reduce 5-HT levels in the hypothalamus, was not affected by corticosterone administration. Presynaptic 5-HT(1B) receptor activity, as measured by the effect of the 5-HT(1B) receptor antagonist (N-[4-methoxy-3-(4-methyl-1-piperizinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazole-3-yl)[1,1'-biphenyl]-carboxamide (GR 127935) (5 mg/kg s.c.) to increase 5-HT levels, was increased in hypothalamus but not hippocampus of corticosterone-treated rats. Postsynaptic 5-HT(1A) receptor activity, as measured by the effect of 8-OH-DPAT to increase cyclic AMP levels in the hippocampus, was not affected by corticosterone administration. The decrease in presynaptic 5-HT(1B) receptor activity after chronic administration of antidepressant drugs complements the increases in 5-HT(1B) receptor number observed in animal models of depression.

Electrical stimulation of the superior sagittal sinus in the cat activated neurones in the trigeminal nucleus caudalis. The mean latency of these responses (10.1 ms) was consistent with activation of Adelta-fibres. Microiontophoretic ejection of either the selective serotonin(1A) (5-HT(1A)) agonist (+)8-OH-DPAT or the 5-HT(1B/1D) agonist alniditan resulted in the reversible suppression of the response to superior sagittal sinus stimulation of 29/46 and 18/20 trigeminal neurones, respectively. The response to sagittal sinus stimulation was suppressed by 39+/-5% (n=46) by (+)8-OH-DPAT and 65+/-5% (n=20) by alniditan. Microiontophoretic ejection of the selective 5-HT(1A) receptor antagonist WAY-100635 significantly antagonised the effect of (+)8-OH-DPAT (effect reduced by 30%, P0.05). The ejection of GR-127935, a selective 5-HT(1B/1D), antagonist, significantly antagonised the effect of alniditan (effect reduced by 52%, P0.02). In eight neurones the response to convergent facial receptive field stimulation was also tested in the presence of alniditan. Only 4/8 receptive field responses were suppressed by alniditan (compared to 8/8 sagittal sinus responses) and alniditan had significantly less quantitative effect on the response to receptive field stimulation than on the response to sagittal sinus stimulation in the same neurones (mean reduction 36+/-14% and 66+/-8%, respectively, P0.05). These results suggest that pharmacological modulation of the trigeminovascular system can occur at the first central synapse and that, in addition to 5-HT(1B/1D) receptors, 5-HT(1A) receptors may be involved in the modulation of sensory neurotransmission in the trigeminovascular system.

Subchronic administration of fluoxetine to rats has been shown to induce subsensitivity of presynaptic 5-HT 1A and 5-HT 1B autoreceptors, and also postsynaptic 5-HT 1A receptors in the hypothalamus. We investigated the effects of administration of fluoxetine (10 mg/kg i.p.) to rats for 6 days on presynaptic 5-HT 1A receptor activity in the hypothalamus, postsynaptic 5-HT 1A receptor activity in the hippocampus, and presynaptic 5-HT 1B autoreceptor activity in both areas, using in vivo microdialysis. The effect of the 5-HT 1B/1D antagonist ( N -[4-methoxy-3-(4-methyl-1-piperizinyl)phenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazole-3-yl)[1,1′-biphenyl]-carboxamide (GR 127935) (5 mg/kg s.c.) to elevate 5-hydroxytryptamine (5-HT) levels was reduced in hippocampus but not hypothalamus of fluoxetine-treated rats. Fluoxetine did not alter either presynaptic 5-HT 1A autoreceptor activity, as measured by the effect of injection of 8-hydroxy-2(di- n -propylamino)tetralin (8-OH-DPAT) (0.2 mg/kg or 50 μg/kg s.c.) on 5-HT levels in the hypothalamus, or postsynaptic 5-HT 1A receptor activity, as measured by the effect of 8-OH-DPAT (0.2 mg/kg s.c.) on cyclic AMP accumulation, in the hippocampus.

By taking up serotonin (5-hydroxytryptamine, 5-HT) released in the extracellular space, the 5-HT transporter (5-HTT) regulates central 5-HT neurotransmission. Possible adaptive changes in 5-HT neurotransmission in knock-out mice that do not express the 5-HT transporter were investigated with special focus on 5-HT1A and 5-HT1B receptors. Specific labelling with radioligands and antibodies, and competitive RT-PCR, showed that 5-HT1A receptor protein and mRNA levels were significantly decreased in the dorsal raphe nucleus (DRN), increased in the hippocampus and unchanged in other forebrain areas of 5-HTT-/- vs. 5-HTT+/+ mice. Such regional differences also concerned 5-HT1B receptors because a decrease in their density was found in the substantia nigra (-30%) but not the globus pallidus of mutant mice. Intermediate changes were noted in 5-HTT+/- mice compared with 5-HTT+/+ and 5-HTT-/- animals. Quantification of [35S]GTP-gamma-S binding evoked by potent 5-HT1 receptor agonists confirmed such changes as a decrease in this parameter was noted in the DRN (-66%) and the substantia nigra (-30%) but not other brain areas in 5-HTT-/- vs. 5-HTT+/+ mice. As expected from actions mediated by functional 5-HT1A and 5-HT1B autoreceptors, a decrease in brain 5-HT turnover rate after i.p. administration of ipsapirone (a 5-HT1A agonist), and an increased 5-HT outflow in the substantia nigra upon local application of GR 127935 (a 5-HT1B/1D antagonist) were observed in 5-HTT+/+ mice. Such effects were not detected in 5-HTT-/- mice, further confirming the occurrence of marked alterations of 5-HT1A and 5-HT1B autoreceptors in these animals.

Pharmacokinetic and pharmacodynamic parameters of the selective serotonin reuptake inhibitor 1-(3-dimethylaminopropyl)-1-(4-nuorophenyl)-5-phtalancarbonitril (citalopram) were determined in order to find optimal conditions for augmentation of its effect on extracellular serotonin [5-hydroxytryptamine (5-HT)] through blockade of 5-HT1A and 5-HT1B autoreceptors. Citalopram dose-dependently (0.3-10 mu mol/kg s.c.) increased serotonin levels in ventral hippocampus of conscious rats. At plasma levels above approximately 0.15 mu M, the effect of citalopram on extracellular 5-HT was augmented by both a 5-HT1A [N-[2-[4-(2-mehoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridil)cyclohexanecarboxamide trihydrochloride (Way 100635), 1 mu mol/kg s.c.] and a 5-HT1B receptor antagonist (2'-methyl-4'-(5-methyl-[1,2,4]oxadiazol-3-yl)biphenyl-4-carboxylic acid [4-methoxy]-3-(4-methylpiperazin-1-yl)phenyl]amide (GR 127935), 1 mu mol/kg s.c.). However, at plasma levels of the selective serotonin reuptake inhibitor below 0.15 mu M, the effects of the antagonists diverged viz. the 5-HT1B receptor antagonist was still able to potentiate citalopram's effect on extracellular 5-HT, while the 5-HT1B receptor antagonist was no longer effective. These results suggest that in contrast to 5-HT1B autoreceptors, indirect activation of 5-HT1A autoreceptors by citalopram is critically related to the dose of selective serotonin reuptake inhibitor administered. The latter may have consequences for selective serotonin reuptake inhibitor augmentation strategies with 5-HT1A receptor antagonists in the therapy of depression and anxiety disorders. (C) 2000 Elsevier Science B.V. All rights reserved.

Rationale: Young rodents emit ultrasonic vocalizations (USVs) when separated from their dams and littermates. Pharmacological agents that act on GABAA and/or 5-HT receptors and that alleviate anxiety in humans reduce the emission of these calls. Objectives: 1) to investigate specific 5-HT1 receptor subtypes that modulate maternal separation-induced USVs in mice; 2) to assess the behavioral specificity of these effects; and 3) to compare 5-HT1 agonists with a positive neurosteroid modulator of the GABAA receptor complex. Methods: Seven-day old CFW mouse pups were isolated from their littermates and placed onto a 20°C surface for 4 min. USVs between 30 and 80 kHz, grid crossing, and rectal temperature were measured in separate groups of mouse pups following subcutaneous administration of 5-HT1A and 5-HT1B receptor agonists and antagonists, the neurosteroid allopregnanolone, or the benzodiazepine midazolam. Results: The 5-HT1A agonists (+)8-OH-DPAT (0.01–0.1 mg/kg) and flesinoxan (0.3–1.0 mg/kg), the selective 5-HT1B agonist CP-94,253 (0.03–30.0 mg/kg), and the mixed 5-HT1B/2C receptor agonist TFMPP (0.1–10.0 mg/kg) dose-dependently reduced USVs. These effects were reversed by the 5-HT1A receptor antagonist WAY 100,635 (0.1 mg/kg) or the 5-HT1B/D receptor antagonist GR 127935 (0.1 mg/kg). The effects of TFMPP were biphasic; low doses (i.e. 0.01 and 0.03 mg/kg) increased the rate of vocalization. Midazolam and allopregnanolone also reduced USVs. The highest doses of flesinoxan, (+)8-OH-DPAT, and allopregnanolone suppressed locomotion, whereas CP-94,253, TFMPP, and midazolam stimulated motor activity. Conclusions: These experiments confirm that agonists at the 5-HT1 receptors and a positive allosteric modulator of the GABAA receptor complex decrease maternal separation-induced USVs in mice, with 5-HT1B manipulations dissociating the effects on vocalizations from sedative effects.

Rationale: Prepulse inhibition (PPI) is the normal reduction of the startle response which occurs when an abrupt startling stimulus is preceded by a weak pre-stimulus and is decreased in several neuropsychiatric disorders. Objective: The role of the serotonin 1B (5-HT1B) receptor in modulating PPI was investigated using 5-HT-releasing agents in wild-type (WT) and 5-HT1B knockout (1BKO) mice. Whether the differential effects of 5-HT-releasing agents on PPI in WT and 1BKO mice resulted from lack of the 5-HT1B receptor or altered development was also assessed. Methods: PPI was assessed in WT and 1BKO mice treated with the 5-HT-releasing agents (+)3,4-methylenedioxy-N-methylamphetamine (MDMA: 0, 10 mg/kg) or (±)N-methyl-1-(1,3-benzodioxol-5-yl)-2-butanamine (MBDB: 0, 10 mg/kg). Additionally, intact 129 Sv mice received pre-treatments of the 5-HT1B/1D antagonist GR 127935 (0, 0.75, 1.5, 3.0 mg/kg) and treatments of MDMA (10 mg/kg). Results: MDMA and MBDB increased PPI in 1BKO mice, but did not alter PPI in WT mice. Intact 129 Sv mice receiving 3.0 mg/kg GR 127935 and 10 mg/kg MDMA exhibited increases in PPI. Conclusions: The ability of GR 127935 to increase PPI in intact MDMA-treated mice suggests that lack of the 5-HT1B receptor, and not altered development, is responsible for the PPI-increasing effects of 5-HT releasers in 1BKO mice. 5-HT release activates multiple 5-HT receptor subtypes, which individually may increase or decrease PPI and together have a combined effect on PPI. Our finding that MDMA and MBDB increase PPI in 1BKO, but not WT mice, indicates that the activation of 5-HT1B receptors by 5-HT disrupts PPI.

The characteristics of the spontaneous firing of serotoninergic neurons in the dorsal raphe nucleus and its control by serotonin (5-hydroxytryptamine, 5-HT) receptors were investigated in wild-type and 5-HT1B knock-out (5-HT1B-/-) mice of the 129/Sv strain, anaesthetized with chloral hydrate. In both groups of mice, 5-HT neurons exhibited a regular activity with an identical firing rate of 0.5-4.5 spikes/s. Intravenous administration of the 5-HT reuptake inhibitor citalopram or the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) induced a dose-dependent inhibition of 5-HT neuronal firing which could be reversed by the selective 5-HT1A antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohe xane carboxamide (WAY 100635). Both strains were equally sensitive to 8-OH-DPAT (ED50 approximately 6.3 microgram/kg i.v.), but the mutants were less sensitive than wild-type animals to citalopram (ED50 = 0.49 +/- 0.02 and 0.28 +/- 0.01 mg/kg i.v., respectively, P < 0.05). This difference could be reduced by pre-treatment of wild-type mice with the 5-HT1B/1D antagonist 2'-methyl-4'-(5-methyl-[1,2,4]oxadiazol-3-yl)-biphenyl-4-carbox yli c acid [4-methoxy-3-(4-methyl-piperazine-1-yl)-phenyl]amide (GR 127935), and might be accounted for by the lack of 5-HT1B receptors and a higher density of 5-HT reuptake sites (specifically labelled by [3H]citalopram) in 5-HT1B-/- mice. In wild-type but not 5-HT1B-/- mice, the 5-HT1B agonists 3-(1,2,5, 6-tetrahydro-4-pyridyl)-5-propoxypyrrolo[3,2-b]pyridine (CP 94253, 3 mg/kg i.v.) and 5-methoxy-3-(1,2,3, 6-tetrahydropyridin-4-yl)-1H-indole (RU 24969, 0.6 mg/kg i.v.) increased the firing rate of 5-HT neurons (+22.4 +/- 2.8% and +13.7 +/- 6.0%, respectively, P < 0.05), and this effect could be prevented by the 5-HT1B antagonist GR 127935 (1 mg/kg i.v.). Altogether, these data indicate that in the mouse, the firing of 5-HT neurons in the dorsal raphe nucleus is under both an inhibitory control through 5-HT1A receptors and an excitatory influence through 5-HT1B receptors.

The cardiovascular pharmacological profiles of a series of novel indorenate analogs, including methyl 3-amino-(1H-indol-3-yl) propanoate hydrochloride and 3-amino-2-(1H-indol-3-yl)propanol oxalate 5-substituted analogs, were evaluated. The antihypertensive effects in anesthetized spontaneously hypertensive rats (SHR), direct action on blood pressure in the pithed rat preparation, on canine basilar artery vascular tone, and on the tension develop by rat aortic rings were assessed for the 5-methoxy, 5-fluor and 5 benzyloxy esters, and alcohol derivatives. 5-Alkoxytryptamine derivatives caused a short-lasting, dose-dependent immediate antihypertensive response, after which blood pressure returned to baseline. Ester derivatives induced both a significant long-lasting and dose-dependent increase in arterial blood pressure and elicited concentration-dependent contractions of the canine basilar artery. This last response was potently blocked by selective 5-HT1B/1D antagonist GR 127935 (1 nM). Unlike the canine basilar artery, the rat aorta was almost insensitive to these alcohols and ester indorenate derivatives. Fluoro derivative 4 and the benzyloxy compounds 5 and 6 significantly inhibited phenylephrine-induced contractions of rat aorta rings at high concentrations. It is concluded that: 1) substitution of a 5-fluoro group instead of a 5-alcoxyl group increases affinity for 5-HT1 subtype receptors; 2) the 5-alcoxy group is an important requirement for the antihypertensive effect; and 3) a β-carbomethoxy group in the lateral chain increases potency. Drug Dev. Res. 48:130–137, 1999. © 1999 Wiley-Liss, Inc.

Behavioural and neurochemical evidence indicates a facilitatory effect of 5-hydroxytryptamine (5-HT), acting via 5-HT1B receptors, on dopamine (DA) systems. To explore this interaction further, these experiments examined the effects of the 5-HT1A/1B agonist RU-24969 on behaviours known to involve the mesolimbic DA system. These behaviours were locomotor activity, intravenous self-administration of d-amphetamine, responding for a conditioned reward (CR), and the response potentiating effects of amphetamine on CR responding. Locomotor activity was enhanced by 1 and 3 mg/kg RU 24969, and both doses also reduced responding for d-amphetamine (60 microg/kg/infusion). Changing the unit dose produced a characteristic U-shaped dose-response curve. This dose-response relationship was not apparent following injection of RU-24969. Across all unit infusion doses of amphetamine, the level of responding was fairly constant. In the CR experiments, rats responded for a conditioned stimulus that was previously paired with water. RU-24969 completely disrupted responding for CR, and also abolished CR responding in rats injected with 3 microg d-amphetamine in the nucleus accumbens. RU-24969 also markedly suppressed responding for water. The suppressant actions of RU-24969 on amphetamine self-administration and CR responding involve stimulation of 5-HT1B receptors, since they were reversed by the 5-HT1B/1D antagonist GR 127935 (3 mg/kg), but not by the 5-HT1A antagonist WAY-100635 (1 mg/kg). None of the behavioural effects of RU-24969 are consistent with a selective action to enhance mesolimbic DA function. Rather, global activation of 5-HT1B receptors appear to exert a general disruptive effect on operant responding.

The releases of [3H]5-hydroxytryptamine ([3H]5-HT) and of endogenous glutamic acid and their modulation through presynaptic h5-HT1B autoreceptors and h5-HT1D heteroreceptors have been investigated in synaptosomal preparations from fresh neocortical samples obtained from patients undergoing neurosurgery. The inhibition by 5-HT of the K+ (15 mM)-evoked overflow of [3H]5-HT was antagonized by the 5-HT1B/5-HT1D receptor ligand GR 127935, which was ineffective on its own; this drug was previously found to behave as a full agonist at the h5-HT1D heteroreceptor regulating glutamate release. The recently proposed selective h5-HT1B receptor ligand SB-224289 also prevented the effect of 5-HT at the autoreceptor, being inactive on its own; in contrast, SB-224289, at 1 μM, was unable to interact with the h5-HT1D heteroreceptor. The inhibitory effect of 5-HT on the K+-evoked overflow of glutamate was antagonized by the h5-HT1D receptor ligand BRL-15572; added in the absence of 5-HT the compound was without effect. BRL-15572 (1 μM) was unable to modify the effect of 5-HT at the autoreceptor regulating [3H]5-HT release. The selective 5-HT1A receptor antagonist (+)-WAY 100135, previously found to be an agonist at the h5-HT1D heteroreceptor regulating glutamate release, could not interact with the h5-HT1B autoreceptor when added at 1 μM. It is concluded that native h5-HT1B and h5-HT1D receptors exhibit a hitherto unexpected pharmacological diversity. British Journal of Pharmacology (1999) 126, 607–612; doi:10.1038/sj.bjp.0702336

3,4-Methylenedioxymethamphetamine (MDMA) is a psychoactive drug of abuse which is increasingly popular in human recreational drug use. In rats, the drug has been shown to stimulate locomotion while decreasing exploratory behavior. MDMA acts as an indirect agonist of serotonin (5-HT) receptors by inducing 5-HT release by a 5-HT reuptake transporter-dependent mechanism, although it is not known which 5-HT receptors are important for the behavioral effects of the drug. In order to examine the role of specific 5-HT receptors, we assessed the behavioral effects of MDMA on knockout mice lacking the 5-HT1B receptor. Knockout animals show a reduced locomotor response to MDMA, although delayed locomotor stimulation is present in these animals. This finding indicates that the locomotor effects of MDMA are dependent upon the 5-HT1B receptor, at least in part. In contrast, MDMA eliminates exploratory behavior in both normal and knockout mice, suggesting that the exploratory suppression induced by MDMA occurs through mechanisms other than activation of the 5-HT1B receptor. To confirm these findings, we tested the effects of MDMA on the locomotor and exploratory behavior of wild-type mice pretreated with GR 127935, a 5-HT1B/1D receptor antagonist. These mice had an attenuated locomotor response to MDMA, but still exhibited the drug-induced suppression of exploration.

Hippocampal serotonin (5-hydroxytryptamine, 5-HT) synthesis, as determined by the accumulation of 5-hydroxytryptophan (5-HTP) following inhibition of L-aromatic amino acid decarboxylase with NSD 1015, was inhibited by systemic administration of the selective serotonin reuptake inhibitors fluoxetine (10 mg/kg i.p.) and paroxetine (3 mg/kg i.p.). Pretreatment of rats with the selective 5-HT1A receptor antagonist WAY 100635 for a period of 7 days using subcutaneously implanted osmotic minipumps (1 mg/kg/day) was sufficient to block the inhibition of 5-HT synthesis following the 5-HT 1A receptor agonist 8-OH-DPAT (0.3 mg/kg s.c.), but failed to inhibit the decrease of hippocampal 5-HT synthesis by fluoxetine (10 mg/kg i.p.) or paroxetine (3 mg/kg i.p.). Similarly, pretreatment of rats with GR 127935 (5 mg/kg i.p.), an antagonist with high affinity for 5-HT1B/D receptors, blocked the reduction of hippocampal 5-HT synthesis following the 5-HT receptor agonist TFMPP (3 mg/kg s.c.) without affecting the reduction of hippocampal 5-HT synthesis by either fluoxetine or paroxetine. In contrast, pretreatment with WAY 100635 (1 mg/kg/day, for 7 days s.c. in osmotic minipumps) in combination with GR 127935 (5 mg/kg i.p.) significantly attenuated the decrease of hippocampal 5-HT synthesis by both fluoxetine and paroxetine. These results indicate that both 5-HT1A and 5-HT1B/1D receptors, which function in the rat as inhibitory somatodendritic and nerve terminal autoreceptors, independently regulate hippocampal 5-HT synthesis and must be simultaneously blocked to prevent the inhibition of 5-HT synthesis by selective serotonin reuptake inhibitors which increase 5-HT availability at both nerve terminals in hippocampus and 5-HT cell bodies in the raphe nuclei. Synapse 31:13–19, 1999. © 1999 Wiley-Liss, Inc.

1. 1. Recent clinical evidence suggests that the nonselective 5-HT 1A receptor antagonist pindolol may enhance the antidepressive efficacy of selective serotonin reuptake inhibitors (SSRIs); an effect generally ascribed to a presumed blockade of somatodendritic 5-HT 1A receptors by pindolol. 2. 2. The present study investigated whether blockade of 5-HT 1A receptors similarly potentiates the previously reported anti-alcohol effects of the SSRI fluoxetine. 3. 3. Pindolol and the selective 5-HT 1A receptor antagonist WAY-100635 were tested alone and in combination with fluoxetine in cAA rats, a genetic model of alcoholism. However, as pindolol has also a high affinity to 5-HT 1B receptors, the effects of selective 5-HT 1B receptor agonists and antagonists were evaluated as well. 4. 4. Neither pindolol (3–30 mg/kg, IP), nor WAY-100635 (1–10 mg/kg, IP) affected alcohol intake when tested alone. In contrast, the 5-HTm receptor agonists CP-94,253 and TFMPP (both 1–10 mg/kg, IP), and antagonists metergoline (1–10 mg/kg, IP) and GR 127935 (3–30 mg/kg, IP) were found to reduce alcohol intake with different degrees of selectivity (that is, the extent to which reductions in ethanol intake could be separated from reductions in food- and/or total fluid intake) and specificity (that is, the degree to which effects on ethanol intake coincided with effects on ethanol preference). 5. 5. Because the behavioral profile of pindolol resembles that of WAY-100635, and not that of the 5-HT 1B receptors ligands, combination experiments with fluoxetine were only performed with the former two compounds. Neither pindolol (30 mg/kg), nor WAY-100635 (3 mg/kg) potentiated the anti-alcohol effects of fluoxetine (10 mg/kg, IP). Moreover, WAY-100635 tended to shift the anti-alcohol effect of fluoxetine towards a less selective and specific profile. It is concluded that acute blockade of 5-HT 1A receptors does not potentiate the anti-alcohol effects of fluoxetine. In addition, it is suggested that different mechanisms underly the antidepressive and anti-alcohol effects of SSR.

It has been suggested that the inhibition of sympathetically-induced vasopressor responses produced by 5-hydroxytryptamine (5-HT) in pithed rats is mediated by 5-HT1-like receptors. The present study has re-analysed this suggestion with regard to the classification schemes recently proposed by the NC-IUPHAR subcommittee on 5-HT receptors. Intravenous (i.v.) continuous infusions of 5-HT and the 5-HT1 receptor agonists, 8-OH-DPAT (5-HT1A), indorenate (5-HT1A), CP 93,129 (5-HT1B) and sumatriptan (5-HT1B/1D), resulted in a dose-dependent inhibition of sympathetically-induced vasopressor responses. The sympatho-inhibitory responses induced by 5-HT, 8-OH-DPAT, indorenate, CP 93,129 or sumatriptan were analysed before and after i.v. treatment with blocking doses of the putative 5-HT receptor antagonists, WAY 100635 (5-HT1A), cyanopindolol (5-HT1A/1B) or GR 127935 (5-HT1B/1D). Thus, after WAY 100635, the responses to 5-HT and indorenate, but not to 8-OH-DPAT, CP 93,129 and sumatriptan, were blocked. After cyanopindolol, the responses to 5-HT, indorenate and CP 93,129 were abolished, whilst those to 8-OH-DPAT and sumatriptan (except at the lowest frequency of stimulation) remained unaltered. In contrast, after GR 127935, the responses to 5-HT, CP 93,129 and sumatriptan, but not to 8-OH-DPAT and indorenate, were abolished. In additional experiments, the inhibition induced by 5-HT was not modified after 5-HT7 receptor blocking doses of mesulergine. The above results suggest that the 5-HT1-like receptors, which inhibit the sympathetic vasopressor outflow in pithed rats, display the pharmacological profile of the 5-HT1A, 5-HT1B and 5-HT1D, but not that of 5-HT7, receptors.

In previous studies, we have shown that several 5-HT1B/1D receptor agonists, including sumatriptan, potently constrict porcine carotid arteriovenous anastomoses. This effect seems to be of high predictive value for antimigraine activity. In the present experiments, we studied the effects of a new non-indole 5-HT1B/1D receptor agonist, alniditan, on systemic and carotid haemodynamics in anaesthetised pigs. In control animals, no significant changes in either systemic or carotid haemodynamics were observed after four consecutive i.v. injections of physiological saline (0.5 ml each, every 20 min; n = 4). On the other hand, i.v. doses of alniditan (3, 10, 30 and 100 microg kg(-1) in 0.5 ml saline, every 20 min; n = 6) dose-dependently decreased total carotid conductance (maximum change: -31 +/- 6%) by a selective vasoconstrictor action on arteriovenous anastomoses (maximum change: -72 +/- 5%); the nutrient vascular bed dilated in response to alniditan (maximum change: +103 +/- 39%). The dose of alniditan that decreased arteriovenous anastomotic conductance by 50% was 24 +/- 8 microg kg(-1) (64 +/- 20 nmol kg(-1)). Alniditan produced a slight bradycardia (maximum change: -4 +/- 1%) and a more pronounced hypotensive effect (maximum change: -23 +/- 5%). In six animals pre-treated with the potent and selective 5-HT1B/1D receptor antagonist, GR127935, the alniditan-induced changes in carotid haemodynamics were clearly antagonised, whereas the bradycardia and hypotension remained unaffected. These results suggest that alniditan selectively constricts porcine carotid arteriovenous anastomoses mainly via 5-HT1B/1D receptors and should be able to abort migraine headaches. The latter has indeed been confirmed in initial clinical studies in man.

1. 5-Hydroxytryptamine (5-HT) exerts both contractile and relaxant effects in the marmoset isolated aorta, actions that are unaffected by the 5-HT2 antagonist ketanserin. The aim of the present study was to define the receptors mediating the contractile activity of 5-HT in the marmoset aorta. 2. Contractile responses were elicited in aortic rings that were either: (i) precontracted submaximally with the thromboxane A2 agonist U44069 in order to amplify the responses; or (ii) exposed to N(omega)-nitro-L-arginine (100 micromol/L) plus LY 53857 (0.1 micromol/L; a 5-HT2 receptor antagonist shown previously to inhibit relaxation). The effect of 5-HT on adenosine 3',5'-cyclic monophosphate (cAMP) formation was also investigated. 3. The effects of agonists and antagonists comprised: (i) agonist potencies in the order 5-carboxamidotryptamine > 5-HT > sumatriptan > 8-hydroxy-2-(di-n-propylamino)tetralin; (ii) inhibition of contractile action of 5-HT by the 5-HT1D antagonist GR 127935; (iii) a contractile response to methysergide; (iv) a lack of effect of tropisetron, an antagonist of 5-HT3 and 5-HT4 receptors; and (v) inhibition of forskolin-stimulated cAMP formation by 5-HT (in the presence of LY 53857), indicative of negative coupling to adenylate cyclase. 4. The above effects fulfill the criteria for a 5-HT1-like receptor. In view of the previous finding that this contractile response is insensitive to ketanserin, it is concluded that the contractile effects of 5-HT in the marmoset aorta are mediated exclusively by a 5-HT1-like receptor.

5-HT receptor antagonists with selectivity for 5-HT 1A WAY-100635 ( N -[2-[-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N -(2-pyridinyl)cyclohexanecarboxamide), 5-HT 1B GR 127935 ( N -[methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2′-methyl-4′(5-methyl-1,2,4-oxadiazol-3-yl)[1,1-biphenyl]-4-carboxamide·HCl), 5-HT 2C SB 200646A ( N -(1-methyl-5-indolyl)- N ′-(3-pyridyl)urea·HCl) and 5-HT 2A (ketanserin, fananserin and MDL 100,151 1 ((±)- α -(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4-piperidinemethanol) receptors were tested for cataleptogenic responses in rats. WAY-100635 (0.1–3 mg/kg, s.c.), ketanserin (0.1–3 mg/kg, s.c.), MDL 100,151 (0.3–3 mg/kg, s.c.) and fananserin (RP 62203; 3 mg/kg, s.c.) induced a significant catalepsy. GR 127935 (1 mg/kg, s.c.), SB 200646A (without effect per se at 10 mg/kg, s.c.) and MDL 100,151 (0.3 mg/kg, s.c.) did not inhibit the cataleptic response to the dopamine D 2 receptor antagonist, loxapine (0.3 mg/kg, s.c.). Catalepsy induced by MDL 100,151 (3 mg/kg) was blocked by co-treatment with clozapine, but not by SB 200646A (both at 10 mg/kg, s.c.). Although clozapine displays significant affinity to 5-HT 1A , 5-HT 1B , 5-HT 2A and 5-HT 2C receptors, the present results suggest that blockade of these receptors is not responsible for clozapine's anticataleptic activity.

The release of glutamic acid and its modulation by 5-hydroxytryptamine (5-HT) in the human brain has been investigated in synaptosomal preparations from fresh neocortical samples obtained from patients undergoing neurosurgery to reach deeply sited tumours. The Ca2+-dependent K+ (15 mM)-evoked overflow of glutamate was inhibited by 5-HT in a concentration-dependent manner (EC50=2.9 nM; maximal effect ≃50%). The inhibition caused by 5-HT was antagonized by the 5-HT1/5-HT2 receptor antagonist methiothepin. The 5-HT1B/5-HT1D receptor agonist sumatriptan mimicked 5-HT (EC50=6.4 nM; maximal effect ≃50%); the effect of sumatriptan was also methiothepin-sensitive. Selective 5-HT1A receptor antagonists could not prevent the inhibition of glutamate release by 5-HT. The 5-HT1B/5-HT1D receptor ligand GR 127935 and the 5-HT2C/5-HT1B/5-HT1D receptor ligand metergoline were unable to prevent the 5-HT effect; instead they inhibited glutamate release, their effects being abolished by methiothepin. Some 5-HT1A receptor antagonists also displayed intrinsic agonist activity. The effect of sumatriptan was prevented by ketanserin, a drug known to display much higher affinity for recombinant h 5-HT1D than for h 5-HT1B receptors. We propose that neocortical glutamatergic nerve terminals in human brain cortex possess release-inhibiting presynaptic heteroreceptors that appear to belong to the h 5-HT1D subtype. British Journal of Pharmacology (1998) 123, 45–50; doi:10.1038/sj.bjp.0701581

1 The receptors involved in mediating the haemodynamic effects of three 5-HT1B/D receptor agonists were investigated in pentobarbitone anaesthetized rats (n = 6-17 per group). 2 Cumulative intravenous (i.v.) infusions of rizatriptan and sumatriptan (from 0.63 to 2500 microg kg(-1); each dose over 5 min) induced dose-dependent and marked hypotension (-42+/-6 and -34+/-4 mmHg at the highest dose, respectively; both P

The effects of 5-HT1B/D receptor agonists anpirtoline, S-CM-GTNH2 and CP93129 were examined in locomotor activity tests in mice. Anpirtoline and S-CM-GTNH2 both significantly increased locomotor activity (ambulation) (minimum affective doses; 3 and 30 mg/kg respectively). CP 93129 injected subcutaneously was without effect, but increased locomotor activity when given i.c.v. Thus activation of central 5-HT1B receptors results in increased locomotor activity. The effects of anpirtoline and S-CM-GTNH2 were blocked by the antagonist GR 127935 suggesting that GR 127935 is an effective antagonist of 5-HT1B receptors in vivo. © 1997 John Wiley & Sons, Ltd.

Texto completo: acesso restrito. p.749–754 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-02-01T11:57:25Z No. of bitstreams: 1 -SILVA.pdf: 252821 bytes, checksum: 841efc1839f806a8b2ad9e05d8af69b7 (MD5) Made available in DSpace on 2013-02-01T11:57:25Z (GMT). No. of bitstreams: 1 -SILVA.pdf: 252821 bytes, checksum: 841efc1839f806a8b2ad9e05d8af69b7 (MD5) Previous issue date: 1997 DE CASTRO-E-SILVA, E., C. SARMENTO, T. A. NASCIMENTO, C. P. LUZ, T. SOARES, C. A. MARINHO, M. CUNHA, C. BULCÃO, I. R. DE OLIVEIRA AND J. B. FREGONEZE. Effect of third ventricle administration of L-694,247, a selective 5-HT1D receptor agonist, on water intake in rats. PHARMACOL BIOCHEM BEHAV 57[4]749–754, 1997.—L-694,247, a selective 5-HT1D receptor agonist, injected directly into the third ventricle (2.5, 5.0, and 10.0 μg/rat) of dehydrated rats induced a dose-dependent partial blockade of water intake. Injected in this way, the compound abolishes drinking behavior induced by third ventricle administration of carbachol (2 μg/rat), angiotensin II (5 ng/rat), and isoproterenol (40 μg/rat). In addition, intraventricular injections of L-694,247 did not modify water intake in normohydrated rats. The effects of L-694,247 are due to a specific interaction with 5-HT1D receptors, because its inhibitory effect on water intake in dehydrated rats is blocked by the previous administration of a 5-HT1D antagonist, GR 127935 (5 μg/rat), directly into the third ventricle. It is concluded that central 5-HT1D receptor activation disrupts the functional integrity of central pathways related to drinking behavior.

1. Selective 5-hydroxytryptamine (5-HT; serotonin) reuptake inhibitors (SSRIs) cause a greater increase in extracellular 5-HT in the forebrain when the somatodendritic 5-HT1A autoreceptor is blocked. Here, we investigated whether blockade of the terminal 5-HT1B autoreceptor influences a selective 5-HT reuptake inhibitor in the same way, and whether there is an additional effect of blocking both the 5-HT1A and 5-HT1B autoreceptors. 2. Extracellular 5-HT was measured in frontal cortex of the anaesthetized rat by use of brain microdialysis. In vivo extracellular recordings of 5-HT neuronal activity in the dorsal raphe nucleus (DRN) were also carried out. 3. The selective 5-HT reuptake inhibitor, paroxetine (0.8 mg kg-1, i.v.), increased extracellular 5-HT about 2 fold in rats pretreated with the 5-HT1A receptor antagonist, WAY100635. When administered alone neither paroxetine (0.8 mg kg-1, i.v.) nor WAY100635 (0.1 mg kg-1, i.v.) altered extracellular 5-HT levels. 4. Paroxetine (0.8 mg kg-1, i.v.) did not increase 5-HT in rats pretreated with the 5-HT1B/D receptor antagonist, GR127935 (1 mg kg-1, i.v.). GR127935 (1 and 5 mg kg-1, i.v.) had no effect on extracellular 5-HT when administered alone. 5. Interestingly, paroxetine (0.8 mg kg-1, i.v.) caused the greatest increase in 5-HT (up to 5 fold) when GR127935 (1 or 5 mg kg-1, i.v.) was administered in combination with WAY100635 (0.1 mg kg-1, i.v.). Administration of GR127935 (5 mg kg-1, i.v.) plus WAY100635 (0.1 mg kg-1, i.v.) without paroxetine, had no effect on extracellular 5-HT in the frontal cortex. 6. Despite the lack of effect of GR127935 on 5-HT under basal conditions, when 5-HT output was elevated about 3 fold (by adding 1 microM paroxetine to the perfusion medium), the drug caused a dose-related (1 and 5 mg kg-1, i.v.) increase in 5-HT. 7. By itself, GR127935 slightly but significantly decreased 5-HT cell firing in the DRN at higher doses (2.0-5.0 mg kg-1, i.v.), but did not prevent the inhibition of 5-HT cell firing induced by paroxetine. 8. In summary, our results suggest that selective 5-HT reuptake inhibitors may cause a large increase in 5-HT in the frontal cortex when 5-HT autoreceptors on both the somatodendrites (5-HT1A) and nerve terminals (5-HT1B) are blocked. This increase is greater than when either set of autoreceptors are blocked separately. The failure of a 5-HT1B receptor antagonist alone to enhance the effect of the selective 5-HT reuptake inhibitor in our experiments may be related to a lack of tone on the terminal 5-HT1B autoreceptor due to a continued inhibition of 5-HT cell firing. These results are discussed in relation to the use of 5-HT autoreceptor antagonists to augment the antidepressant effect of selective 5-HT reuptake inhibitors.