WAY-100635 Research Articles

Ginsenoside Re attenuates 8-OH-DPAT-induced serotonergic behaviors in mice via interactive modulation between PKCδ gene and Nrf2

It has been recognized that serotonergic blocker showed serious side effects, and that ginsenoside modulated serotonergic system with the safety. However, the effects of ginsenoside on serotonergic impairments remain to be clarified. Thus, we investigated ginsenoside Re (GRe), a major bioactive component in the mountain-cultivated ginseng on (±)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT), a 5-HT1A receptor agonist. In the present study, we observed that the treatment with GRe resulted in significant inhibition of protein kinase C δ (PKCδ) phosphorylation induced by the 5-HT1A receptor agonist (±)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT) in the hypothalamus of the wild-type (WT) mice. The inhibition of GRe was comparable with that of the PKCδ inhibitor rottlerin or the 5-HT1A receptor antagonist WAY100635 (WAY). 8-OH-DPAT-induced significant reduction in nuclear factor erythroid-2-related factor 2 (Nrf2)-related system (i.e., Nrf2 DNA binding activity, γ-glutamylcysteine ligase modifier (GCLm) and γ-glutamylcysteine ligase catalytic (GCLc) mRNA expression, and glutathione (GSH)/oxidized glutathione (GSSG) ratio) was significantly attenuated by GRe, rottlerin, or WAY in WT mice. However, PKCδ gene knockout significantly protected the Nrf2-dependent system from 8-OH-DPAT insult in mice. Increases in 5-hydroxytryptophan (5-HT) turnover rate, overall serotonergic behavioral score, and hypothermia induced by 8-OH-DPAT were significantly attenuated by GRe, rottlerin, or WAY in WT mice. Consistently, PKCδ gene knockout significantly attenuated these parameters in mice. However, GRe or WAY did not provide any additional positive effects on the serotonergic protective potential mediated by PKCδ gene knockout in mice. Therefore, our results suggest that PKCδ is an important mediator for GRe-mediated protective activity against serotonergic impairments/oxidative burden caused by the 5-HT1A receptor.

Antinociceptive effects of flower extracts and the active fraction from Styrax japonicus

Ethnopharmacological relevanceFlowers from Styrax japonicus sieb. et Zucc. have been used as a Chinese folk medicine to alleviate pain such as toothache and sore throat. Aim of the studyTo testify the analgesic effect of flowers from Styrax japonicus, analyze components of the active fraction, and investigate the mechanism of analgesia. Materials and methodsFlower extracts were obtained by ethanol, petroleum ether and hydrodistillation extraction. Different fractions of ethanol extracts (EE) were isolated by silica gel column chromatography and preparative liquid chromatography. Analgesic effects of EE, petroleum ether extracts (PEE), hydrodistillation extracts (HDE), and fractions of EE were evaluated using hot plate, acetic acid-induced writhing and formalin tests on mice. Components of the active fraction 1 (F1) were determined by the ultrahigh-performance liquid chromatography Q extractive mass spectrometry (UHPLC-QE-MS). Anti-inflammatory and sedative effects involving analgesic mechanisms were evaluated by carrageenan induced hind paw oedema and pentobarbital sodium sleep tests, respectively. In addition, antagonists including naloxone hydrochloride (NXH), flumazenil (FM), SCH23390 (SCH) and WAY100635 (WAY) were used to investigate the possible mechanism of analgesia. Contents of neurotransmitters and relevant metabolites in different brain regions of mice were also quantified by the ultraperformance liquid chromatography with a fluorescence detector (UPLC-FLD). ResultsEE rather than PEE and HDE at medium and high doses (150 mg/kg and 300 mg/kg) significantly prolonged the latency time of the response of mice to the thermal stimulation in the hot plate test. Moreover, EE significantly decreased number of writhes in the acetic acid-induced writhing test, and reduced licking time in both two phases of the formalin test in a dose-dependent manner. The F1 (50 mg/kg) showed effective antinociceptive responses in all mice models. However, fraction 2 (F2) and fraction 3 (F3) at 50 mg/kg performed no analgesic action. Kaempferol-3-O-rutinoside, isorhamnetin-3-O-rutinoside, pinoresinol-4-O-glucoside, forsythin and arctiin were identified from components of the F1. Furthermore, F1 (50 mg/kg) did not significantly affect hind paw oedema of mice induced by carrageenan but significantly shortened sleep latency and increased sleep duration in the pentobarbital sodium sleep test. In addition, the antinociceptive response of F1 was not affected by NXH in two mice models, but significantly blocked by FM and WAY in the hot plate test. In the formalin test, FM avoided the effect of F1 only in the first phase, while the analgesic activity of F1 was totally suppressed by WAY in both two phases. Otherwise, contents of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) increased significantly in hippocampus and striatum of mice in the F1 group. ConclusionEE from flowers of Styrax japonicus, and F1, the active part isolated from EE, showed significant antinociceptive activities. The analgesic effect of F1 appeared to be related to the sedative effect, partially mediated by the GABAergic system, and highly involved in the serotonergic system. This was the first study confirming the analgesic effect of Styrax japonicus flower, which provided a candidate for the development of non-opioid analgesics.

Evidence for intact 5-HT1A receptor-mediated feedback inhibition following sustained antidepressant treatment in a rat model of depression

Serotonin (5-HT) neurons are strongly implicated in mood disorders such as depression and are importantly regulated by feedback inhibition mediated by 5-HT1A receptors. These receptors may play a role, albeit a poorly understood one, in the generation of mood disorders, treatment response to antidepressants and delayed therapeutic efficacy. Here we sought to gain insight into the role of 5-HT1A receptor-mediated feedback inhibition in these processes by studying Fos protein expression within serotonin neurons in a rat model of stress-related mood disorder, early life maternal separation (MS), combined with two-week treatment with the antidepressant fluoxetine (FLX) in adulthood. We gauged 5-HT1A receptor-mediated feedback inhibition by the ability of the antagonist, WAY-100635 (WAY), to disinhibit Fos expression in 5-HT neurons. We found that two-week FLX treatment dramatically inhibited Fos expression in serotonin neurons and that this effect was reversed by blocking 5-HT1A receptors with WAY. Together these observations reveal that after prolonged exposure to SSRIs, endogenous 5-HT1A receptors continue to exert feedback inhibition of serotonin neurons. Furthermore we found unique effects of pharmacological treatments after MS in that the WAY effect was greatest in MS rats treated with FLX, a phenomenon selective to the rostral 2/3 of the dorsal raphe nucleus (B7). These results indicate that the balance between activation and feedback inhibition of serotonin neurons in B7 is altered and uniquely sensitive to FLX after early-life stress.

The Role of 5-HTR6 in Mossy Fiber Sprouting: Activating Fyn and p-ERK1/2 in Pilocarpine-Induced Chronic Epileptic Rats

Objective: Our primary objective is to verify whether 5-HTR6 is involved in the development of mossy fiber sprouting (MFS), and to determine how the progression of MFS is affected by 5-HTR6. Methods: A total of 90 male adult Sprague-Dawley rats were allocated into either the control group (n=36) or the epileptic group (n=54). Status epilepticus (SE) of rats was induced by the intraperitoneal (i.p.) injection of LiCl-pilocarpine. We conducted our experiments in two stages. The first stage involves equally dividing 36 epileptic rats into three groups with treatments of none, 5-HTR6 antagonist SB-27104 (SB) and vehicle DMSO. Then behavior and electroencephalogram (EEG) of rats were monitored by video-EEG. The second stage involves dividing 126 epileptic rats into seven groups with treatments of none, 10% DMSO, SB (100 µg/kg), Fyn antagonist PP₂ (50 µg/kg), p-ERK1/2 antagonist PD-98059 (30 µg/kg), SB (100 µg/ kg) + PP₂ (50 µg/kg); SB (100 µg/kg) + PD-98059 (30 µg/kg). We also treated 18 rats in the control group of the first stage with 100 µg/kg 5-HTR6 agonist WAY-181187 (WAY). MFS of rats was detected through the approach of Timm’s staining. Finally, expressions of 5-HTR6, Fyn, p-ERK1/2 and GAP-3 were qualified and semi-quantified via western blotting or RT-PCR. Results: Induction of SE could stimulate formation of MFS and increased GAP-43 expressions. Expressions of 5-HTR6, Fyn and p-ERK1/2 were also up-regulated with increasing time after establishment of SE models. The development of MFS was remarkably inhibited by SB, PP₂ and PD. Compared to the single antagonist, such an inhibitory effect was enhanced by SB+PD or SB+PP. Moreover, treatment of healthy rats with WAY would contribute to up-regulated Fyn and p-ERK1/2 expressions, as well as development of MFS (P < 0.05). Suppression of Fyn triggered a down-regulating trend of p-ERK1/2 (P < 0.05), however, suppressed p-ERK1/2 did not have such a significant effect on Fyn expression. Conclusion: HTR6 may affect the progression of MFS by activating both p-ERK1/2 and Fyn, which further modulate the expression of GAP-43.

RGS Regulation of Gαi2 in the Mouse Hippocampus Modulates 5‐HT1A Receptor Mediated Antidepressant‐Like Activity

Regulators of G‐protein signaling (RGS) are negative regulators of heterotrimeric G protein coupled receptor signaling. A single point mutation (G184S) in Gαi2 abolishes the RGS negative regulatory effects. Mice expressing two knock‐in copies of this RGS insensitive (RGSi) Gαi2 protein display a robust antidepressant‐like phenotype due to increased 5‐HT1A receptor (5‐HT1AR) signaling. The objective of this study was to test the hypothesis that the 5‐HT1ARs in the hippocampus are critical determinants of the phenotype.Mice (C57BL6) expressing RGSi‐Gαi2 and their wild‐type littermates were implanted with intra‐hippocampal drug infusion cannulae. Antidepressant‐like activity was evaluated by measuring time spent immobile in the tail suspension test (TST). The RGSi‐Gαi2 mice showed decreased immobility in the TST and this was reversed by infusion of the selective 5‐HT1AR antagonist WAY‐100635 (WAY) directly into the hippocampus. Conversely, direct hippocampal infusion of the 5‐HT1AR agonist 8‐OH‐DPAT produced decreased immobility in wild type mice that was reversed by the peripheral administration of WAY. Peripheral, but not hippocampal, administration of 8‐OH‐DPAT to wild‐type mice caused a 5‐HT1AR‐mediated hypothermia. The mutant mice showed no differences in 5‐HT1AR or Gα protein expression in the hippocampus compared with their wild‐type littermates.These results are consistent with the hypothesis that the antidepressant‐like phenotype in the RGSi‐Gαi2 knock‐in mice is due to altered 5‐HT1AR signaling in the hippocampus. These findings identify hippocampal 5‐HT1AR specifically coupled to Gαi2, and the RGS proteins that regulate them, as potential targets for antidepressant medications. Supported by MH097012 and GM007767.

Plurality of anxiety and depression alteration mechanism by oleanolic acid.

Our study sought to evaluate the anxiolytic and antidepressant activities of oleanolic acid as well as the neural mechanisms involved. Animal models such as barbiturate sleep-induction, light-dark box, elevated plus maze, forced swimming test, tail suspension test and open field test were conducted. Male Albino Swiss mice were treated orally with vehicle 10 mL/kg, fluoxetine 20 mg/kg, imipramine 15 mg/kg, diazepam 1 mg/kg or oleanolic acid 5-40 mg/kg. Pretreatment (intraperitoneal) of animals with pentylenetetrazole (PTZ) 20 mg/kg, 1-(2-methoxyphenyl)-4-[4- (2-phthalimido) butyl]piperazine hydrobromide (NAN-190) 0.5 mg/kg, p-chlorophenylalanine methyl ester (PCPA) 100 mg/kg or α-methyl-p-tyrosine (AMPT) 100 mg/kg, WAY100635 (WAY) 0.3 mg/kg, prazosin (PRAZ) 1 mg/kg, yohimbine 2 mg/kg as well as monoamine oxidase assay and hippocampal brain-derived neurotrophic factor (BDNF) quantification were carried out. Oleanolic acid potentiated the hypnotic effect of barbiturate and demonstrated an anxiolytic effect in both the light-dark box and elevated plus maze. This effect was not reversed by PTZ. Acute and/or chronic oral treatment of mice with oleanolic acid (5-20 mg/kg) elicited an antidepressant effect in the forced swimming test and the tail suspension test without interfering with the locomotor activity. The antidepressant effect of oleanolic acid was attenuated by NAN-190, AMPT, PCPA, WAY and PRAZ. Although monoamine oxidase activity remained unaltered by oleanolic acid, chronic administration of oleanolic acid augmented hippocampal BDNF level. These findings demonstrate multiple mechanisms of the anxiolytic and antidepressant effect of oleanolic acid.

Experimental study of 5-hydroxytryptamine 1A receptor agonist to improve the voiding dysfunction in diabetic rats

Objective To investigate the effect of 5-hydroxytryptamine 1A (5-HT1A) receptor agonists to improve micturition function in rats with diabetes mellitus (DM).Methods Fourteen female SD rats with the weight of 250 to 275 g were used.Seven rats were in the DM model group with intraperitoneal injection streptozotocin (STZ,65 mg/kg).Rats in the control group and DM group were anesthetized with urethane (1.3 g/kg) 8 weeks later.A polyethylene (PE)-50 catheter were placed in the left jugular vein for intravenous drug administration.A PE-90 catheter was inserted into the bladder,with the other end connected to a syringe pump for continuous infusion of saline and a pressure transducer for intravesical pressure monitor.Dose-response curves for 8-OH-DPAT were followed by WAY-100635 test.The capacity,residual volume,micturition volume,and EUS-EMG were measured.Results Compared to normal control,DM rats had a higher bladder capacity,residual volume,and a lower voiding efficiency.With increasing dose of 8-OH-DPAT (0.003-1.000 mg/kg,i.v.),the micturition volume increased from (2.15±0.49) ml to (2.85±0.21) ml,the residual volume decreased from (3.40±0.74)ml to (1.82±0.48) ml and voiding efficiency changed from (39.0±9.3)％ to (61.6±6.9)％.Control rats showed little change in cystometic variable.During the micturition,there was a dose-dependent increased phasic EUS activity correlated with the improved voiding efficiency.WAY-100635 (0.300 mg/kg,i.v.) reversed the 8-OH-DPAT-induced changes.Conclusions Both the bladder voiding efficiency and the periodic EUS activity decrease in DM rats.5-HT1A receptor agonist could promote periodic EUS activity and improve voiding efficiency. Key words: Rats; Diabetes mellitus; Micturition; Receptor, serotonin, 5-HT1A; Serotonin agonists

Independent of 5-HT1A receptors, neurons in the paraventricular hypothalamus mediate ACTH responses from MDMA

Acute and chronic complications from the substituted amphetamine 3,4-methylenedioxymethamphetamine (MDMA) are linked to activation of the hypothalamic–pituitary–adrenal (HPA) axis. How MDMA activates the HPA axis is not known. HPA responses to stress are known to be mediated through the paraventricular (PVH) hypothalamus and to involve serotonin-1a (5-HT1A) receptors. We sought to determine if the PVH and 5-HT1A receptors were also involved in mediating HPA responses to MDMA. Rats were pretreated with either saline or a 5-HT1A antagonist, WAY-100635 (WAY), followed by a systemic dose of MDMA (7.5mg/kg i.v.). Animals pretreated with WAY had significantly lower plasma ACTH concentrations after MDMA. To determine if neurons in the PVH were involved, and if their involvement was mediated by 5-HT1A receptors, rats implanted with guide cannulas targeting the PVH were microinjected with the GABAA receptor agonist muscimol, aCSF, or WAY followed by MDMA. Compared to aCSF, microinjections of muscimol significantly attenuated the MDMA-induced rise in plasma ACTH (126 vs. 588pg/ml, P=<0.01). WAY had no effect. Our data demonstrates that neurons in the PVH, independent of 5-HT1A receptors, mediate ACTH responses to MDMA

Involvement of serotonin receptor subtypes in the antidepressant-like effect of beta receptor agonist Amibegron (SR 58611A): An experimental study

New therapeutic strategies against depression, with less side effects and thus greater efficacy in larger proportion of depressed patients, are needed. Amibegron (SR58611A) is the first selective β3 adrenergic agent that has been shown to possess a profile of antidepressant activity in rodents. To investigate the involvement of serotonin receptors in the effects of amibegron, we used the serotonin 5HT1A receptor antagonist WAY-100635 (WAY) or serotonin 5HT2A-2C receptor antagonist ketanserin or serotonin 5HT3 receptor antagonist ondansetron in mice forced swimming test (FST). The locomotor activity was evaluated by measuring the total distance moved in the apparatus and the speed of the animals in the open field test. Imipramine (30mg/kg) significantly reduced immobility time compared to vehicle-treated group while amibegron (5 and 10mg/kg) dose dependently reduced immobility time in the FST. WAY(0.1mg/kg), ondansetron (1mg/kg), ketanserin(5mg/kg) had no effect on immobility time in naive mice while all of the drugs partially and significantly reversed amibegron (10mg/kg) induced decreasement in the immobility time in FST. None of the drugs alter locomotor activity in the open field test. The antidepressant-like effect of amibegron in the FST seems to be mediated by an interaction with serotonin 5-HT1A, serotonin 5-HT2A-2C and serotonin 5-HT3 receptors.

Effect of 5-serotonin 1 receptor agonists on acetic acid stimulated micturition in chronic spinal cord injury cats

Objective To evaluate the effects of 5-serotonin 1 (5-HT1) receptor agonists on acetic acid stimulated micturition in cats with chronic spinal cord injury (SCI).Methods Chloralose-anesthetized SCI cats were catheterized through the bladder dome for filling cystometry during 0.5％ acetic acid infusion.Dose-response curves for ( R)-8-OH-DPAT (0.30-30.00 μg/kg,i.v.) or GR 46611 (0.03-300.00 μg/kg,i.v.) were followed by 5-HT1A antagonist WAY-100635 (300.00 μg/kg).Threshold volume,bladder capacity,residual volume,micturition volume,and arterial pressure were measured and the external urethral sphincter electromyogram (EUS-EMG) was recorded.Results Acid-infused SCI cats responded to (R)-8-OH-DPAT but not GR-46611 with dose-dependent increases in threshold volume,capacity,and residual volume,significantly at the dose above 10 μg/kg.Effects of (R)-8-OH-DPAT were largely reversed by WAY 100635.Neither (R)-8-OH-DPAT nor GR-46611 augmented EUS-EMG activity.Conclusion Because 5-HT1A receptor agonists increase bladder capacity under either saline or acid infused conditions,they are promising candidates for reducing bladder hyperactivity and increasing bladder capacity in patients with chronic SCI. Key words: Spinal cord injury; Micturition; 5-serotonin receptor; Cat

The Influence of Repeated Treatment with 5‐HT1A Receptor Ligands on the Quinpirole‐induced Hyperactivity in Rats

The effects of repeated (twice daily, 21 days) administration of the 5-HT1A A receptor partial agonists buspirone (2.5 mg kg−1) and ipsapirone (5 mg kg−1), antagonist (S)-N-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-l-yl]-2-phenylpropanamide dihydrochloride ((S)-WAY 100135, 10 mg kg−1), and full agonist 8-hydroxy-2-(di-n-propylamino)tetralin (0.5 mg kg−1), or the antidepressant imipramine (10 mg kg−1), as well as of short-term (twice daily, 3 days) administration of buspirone and imipramine on the hyperactivity induced by quinpirole (0.25 mg kg−1, 24 h after the last dose of the investigated compounds), a response mediated by dopamine D2 receptors, were examined. Of the examined 5-HT1A receptor ligands, only buspirone—like imipramine—administered repeatedly, but not on a short-term basis, potentiated the locomotor hyperactivity induced by quinpirole. The results indicate that the effect of buspirone, which points to sensitization of the postsynaptic D2 receptor, is not connected with the drug's interaction with 5-HT1A receptors.

Cystometric evaluation of partial urinary bladder outlet obstruction model in conscious rats

Urinary frequency and urgency in benign prostatic hyperplasia (BPH) are associated with involuntary detrusor contractions. Animals with partial bladder outlet obstruction (BOO) exhibit detrusor instability showing non-micturition contractions (NMC) on cystometrogram (CMG). We investigated the conscious CMG and natural voidings (NV) of rats with BOO. The effect of 5-HT1A antagonist WAY100635 (WAY) on NMC was also evaluated in the BOO rats. The proximal urethra was loosely ligated. NV and CMG were measured 2–6 weeks post BOO. The ligature was removed and the bladder was cannulated 2 days prior to CMG. The bladder weight of BOO was increased significantly 3–6 weeks post BOO. [Bladder weight (g): BOO 0.53±0.04 (n=18), sham 0.18±0.01 (n=16)]. Histopathological abnormalities were seen in the bladders and kidneys in BOO rats. No NV difference was observed between BOO and sham. The void pressure (VP), void interval (VI) and void volume (VV) were not significantly different within 3–6 week BOO rats, however the VI and VV were increased and significantly different from sham rats. [VI (min): BOO 13.8±0.8, sham 6.16±0.4 (p<0.01); VV (ml): BOO 2.7±0.3, sham 1.3±0.1 (p<0.01)]. NMC was exhibited in 9 of 17 BOO rats, but not in sham controls. WAY (0.1 mg/kg, iv) significantly inhibited NMC. [Inhibition time (min): WAY 7.4±3.1, veh 0±0 (n=4, p<0.05); Amplitude inhibition (mmHg): WAY −11.3±2.9, veh −0.5±1.2; (n=4, p<0.05)]. These results indicate that BOO could induce increased bladder capacity and void interval and NMC in conscious rats. WAY100635 produced inhibitory effect on NMC, suggesting that 5-HT1A antagonist may inhibit detrusor instability associated with outlet obstruction in BPH.

5-HT1a receptor antagonists block perforant path-dentate LTP induced in novel, but not familiar, environments

Numerous studies suggest roles for monoamines in modulating long-term potentiation (LTP). Previously, we reported that both induction and maintenance of perforant path-dentate gyrus LTP is enhanced when induced while animals explore novel environments. Here we investigate the contribution of serotonin and 5-HT1a receptors to the novelty-mediated enhancement of LTP. In freely moving animals, systemic administration of the selective 5-HT1a antagonist WAY-100635 (WAY) attenuated LTP in a dose-dependent manner when LTP was induced while animals explored novel cages. In contrast, LTP was completely unaffected by WAY when induced in familiar environments. LTP was also blocked in anesthetized animals by direct application of WAY to the dentate gyrus, but not to the median raphe nucleus (MRN), suggesting the effect of systemic WAY is mediated by a block of dentate 5-HT1a receptors. Paradoxically, systemic administration of the 5-HT1a agonist 8-OH-DPAT also attenuated LTP. This attenuation was mimicked in anesthetized animals following application of 8-OH-DPAT to the MRN, but not the dentate gyrus. In addition, application of a 5-HT1a agonist to the dentate gyrus reduced somatic GABAergic inhibition. Because serotonergic projections from the MRN terminate on dentate inhibitory interneurons, these data suggest 5-HT1a receptors contribute to LTP induction via inhibition of GABAergic interneurons. Moreover, activation of raphe 5-HT1a autoreceptors, which inhibits serotonin release, attenuated LTP induction even in familiar environments. This suggests that serotonin normally contributes to dentate LTP induction in a variety of behavioral states. Together, these data suggest that serotonin and dentate 5-HT1a receptors play a permissive role in dentate LTP induction, particularly in novel conditions, and presumably, during the encoding of novel, hippocampus-relevant information.

Serotonergic involvement in stress-induced vasopressin and oxytocin secretion.

To investigate the involvement of serotonin (5-hydroxytryptamine - 5-HT) receptors in mediation of stress-induced arginine vasopressin (AVP) and oxytocin (OT) secretion in male rats. Experiments on laboratory rats with control groups. Different stress paradigms were applied after pretreatment with intracerebroventricular infusion of saline or different 5-HT antagonists. Restraint stress (5 min), hypotensive hemorrhage or dehydration for 24 h increased AVP secretion fivefold and OT secretion threefold. Swim stress for 3 min had no effect on AVP secretion, but increased OT secretion threefold. Ether vapor or hypoglycemia had no effect on AVP or OT secretion. The restraint stress-induced AVP response was inhibited by pretreatment with the 5-HT(2A+2C) antagonists ketanserin (KET) and LY-53857 (LY) and the 5-HT(3+4) antagonist ICS-205930 (ICS), whereas the 5-HT(1A) antagonist WAY-100635 (WAY) had no effect. The OT response to restraint stress was inhibited by WAY, KET and LY but not by ICS. KET and LY inhibited OT response to dehydration, and LY inhibited OT response to hemorrhage. Neither of the antagonists affected AVP responses to dehydration or hemorrhage, nor the swim stress-induced OT response. 5-HT(2A), 5-HT(2C) and possibly 5-HT(3) and 5-HT(4) receptors, but not 5-HT(1A) receptors, are involved in the restraint stress-induced AVP secretion. 5-HT does not seem to be involved in the dehydration- or hemorrhage-induced AVP response. The restraint stress-induced OT response seems to be mediated via 5-HT(1A), 5-HT(2A) and 5-HT(2C) receptors. The dehydration and hemorrhage-induced OT responses are at least mediated by the 5-HT(2A) and 5-HT(2C) receptors. The 5-HT(3) and 5-HT(4) receptors are not involved in stress-induced OT secretion.

Visualisation of serotonin-1A (5-HT1A) receptors in the central nervous system.

The 5-HT1A subtype of receptors for the neurotransmitter serotonin is predominantly located in the limbic forebrain and is involved in the modulation of emotion and the function of the hypothalamus. Since 5-HT1A receptors are implicated in the pathogenesis of anxiety, depression, hallucinogenic behaviour, motion sickness and eating disorders, they are an important target for drug therapy. Here, we review the radioligands which are available for visualisation and quantification of this important neuroreceptor in the human brain, using positron emission tomography (PET) or single-photon emission tomography (SPET). More than 20 compounds have been labelled with carbon-11 (half-life 20 min), fluorine-18 (half-life 109.8 min) or iodine-123 (half-life 13.2 h): structural analogues of the agonist, 8-OH-DPAT, structural analogues of the antagonist, WAY 100635, and apomorphines. The most successful radioligands thus far are [carbonyl-11C] WAY-100635 (WAY), [carbonyl-11C]desmethyl-WAY-100635 (DWAY), p-[18F]MPPF and [11C]robalzotan (NAD-299). The high-affinity ligands WAY and DWAY produce excellent images of 5-HT1A receptor distribution in the brain (even the raphe nuclei are visualised), but they cannot be distributed to remote facilities and they probably cannot be used to measure changes in endogenous serotonin. Binding of the moderate-affinity ligands MPPF and NAD-299 may be more sensitive to serotonin competition and MPPF can be distributed to PET centres within a flying distance of a few hours. Future research should be directed towards: (a) improvement of the metabolic stability in primates; (b) development of a fluorinated radioligand which can be produced in large quantities and (c) production of a radioiodinated or technetium-labelled ligand for SPET.

Radioligands for the study of brain 5-HT 1A receptors in vivo–development of some new analogues of way

ABSTRACT. [ Carbonyl- 11C]WAY-100635 (WAY) has proved to be a very useful radioligand for the imaging of brain 5-HT 1A receptors in human brain in vivo with positron emission tomography (PET). WAY is now being applied widely for clinical research and drug development. However, WAY is rapidly cleared from plasma and is also rapidly metabolised. A comparable radioligand, with a higher and more sustained delivery to brain, is desirable since these properties might lead to better biomathematical modelling of acquired PET data. There are also needs for other types of 5-HT 1A receptor radioligands, for example, ligands sensitive to elevated serotonin levels, ligands labelled with longer-lived fluorine-18 for distribution to “satellite” PET centres, and ligands labelled with iodine-123 for single photon emission computerised tomography (SPECT) imaging. Here we describe our progress toward these aims through the exploration of WAY analogues, including the development of [ carbonyl- 11C]desmethyl-WAY (DWAY) as a promising, more brain-penetrant radioligand for PET imaging of human 5-HT 1A receptors, and ( pyridinyl-6-halo)-analogues as promising leads for the development of radiohalogenated ligands.

Use of PET and the radioligand [ carbonyl- 11C]WAY-100635 in psychotropic drug development

Positron-emission tomography (PET) provides potential in neuropsychiatric drug development by expanding knowledge of drug action in the living human brain and reducing time consumption and costs. The 5-hydroxytryptamine 1A (5-HT 1A) receptor is of central interest as a target for the treatment of anxiety, depression, and schizophrenia. Research on the clinical significance of the 5-HT 1A receptor now benefits from the highly selective radioligand [ carbonyl- 11C]WAY-100635 (WAY) for quantitative determination of 5-HT 1A receptors in the primate and human brain in vivo using PET. In this paper, three studies are reviewed to demonstrate the suitability of WAY as radioligand for quantification of central 5-HT 1A receptors in brain and as an applicable tool for drug development. In the first study a monkey model was used to characterize WAY binding. It was confirmed that the reference ligand 8-OH-DPAT and psychoactive drugs such as buspirone and pindolol occupies 5-HT 1A receptors in the primate brain. Pindolol is an β-adrenoreceptor antagonist with a high affinity to 5-HT 1A receptors. This drug has been suggested in combination with selective serotonin reuptake inhibitors for the treatment of depression and was given to healthy males in the second study. Pindolol induced a marked inhibition of central 5-HT 1A receptors as calculated by the ratio-analysis method and simplified reference tissue model, 2 h after administration of 10 mg as a single oral dose. This observation suggests that pindolol may have a role for the suggested potentiation of selective serotonin reuptake inhibitor treatment of depression. The third study was on robalzotan (NAD-299), a recently developed 5-HT 1A receptor antagonist and putative drug with implications for the treatment of depression. In the cynomolgus monkey brain, robalzotan in the dose range 2–100 μg/kg IV occupied 5-HT 1A receptors in a dose-dependent and saturable manner with a maximal calculated occupancy of 70–80%. The relationship between robalzotan plasma concentration and 5-HT 1A receptor occupancy could be described by a hyperbolic function that was used to guide the selection of appropriate doses in man. In a subsequent PET study of robalzotan binding to 5-HT 1A receptors in the living human brain, similar results have been replicated recently. These studies reviewed here illustrate and corroborate that quantitative neuroimaging of receptor binding has potential for the evaluation and dose finding of new central nervous system drugs.

Neonatal organizational effects of the 5-HT 2 and 5-HT 1A subsystems on adult behavior in the rat

Males, females, neonatally androgenized females, and neonatally castrated males were treated over the second week of life with 0.25 mg/kg of either the 5-HT 2 agonist 1-(2,5-dimethoxy-3-iodophenyl)-2-aminopropane HCl (DOI), the 5-HT 2 antagonist ritanserin (Rit), the 5-HT 1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), or the 5-HT 1A antagonist WAY100135 (WAY). Exploration, anxiety, sociosexual preferences, and sexual behavior were measured in adulthood. Agents acting on 5-HT 1A receptors do not appear to affect organization of any of the behavioral systems studied. DOI increased exploratory activity but in females only, which suggests that testosterone antagonizes the stimulatory effect of 5-HT 2 activity on exploration. Neonatal ritanserin selectively reduced anxiety in females, and DOI had a similar effect in androgenized females. This indicates that neonatal 5-HT 2 activity is anxiogenic in normal females, anxiolytic in androgenized females, and has no effect on anxiety in males. Males and androgenized females both showed a preference for the female teaser that was abolished by the 5-HT 2 agonist, DOI. These results point out that 5-HT 2 activity selectively suppresses heterosexual preference induced in the presence of neonatal testosterone. DOI also reduced both male sexual behavior in males and female sexual behavior in androgenized females. Thus, the 5-HT 2 system antagonizes the action of testosterone in stimulating heterosexual orientation and sexual activity, and this is independent of genetic sex.