Doses Of WAY Research Articles

Cannabidiol Interferes with Establishment of Δ9-Tetrahydrocannabinol-Induced Nausea Through a 5-HT1A Mechanism.

Introduction: Cannabinoid hyperemesis syndrome (CHS) is characterized by intense nausea and vomiting brought on by the use of high-dose Δ9-tetrahydrocannabinol (THC), the main psychotropic compound in cannabis. Cannabidiol (CBD), a nonpsychotropic compound found in cannabis, has been shown to interfere with some acute aversive effects of THC. In this study, we evaluated if CBD would interfere with THC-induced nausea through a 5-HT1A receptor mechanism as it has been shown to interfere with nausea produced by lithium chloride (LiCl). Since CHS has been attributed to a dysregulated stress response, we also evaluated if CBD would interfere with THC-induced increase in corticosterone (CORT). Materials and Methods: The potential of CBD (5 mg/kg, ip) to suppress THC-induced conditioned gaping (a measure of nausea) was evaluated in rats, as well as the potential of the 5-HT1A receptor antagonist, WAY-100635 (WAY; 0.1 mg/kg, ip), to reverse the suppression of THC-induced conditioned gaping by CBD. Last, the effect of CBD (5 mg/kg, ip) on THC-induced increase in serum CORT concentration was evaluated. Results: Pretreatment with CBD (5 mg/kg, ip) interfered with the establishment of THC-induced conditioned gaping (p=0.007, relative to vehicle [VEH] pretreatment), and this was reversed by pretreatment with 0.1 mg/kg WAY. This dose of WAY had no effect on gaping on its own. THC (10 mg/kg, ip) significantly increased serum CORT compared with VEH-treated rats (p=0.04). CBD (5 mg/kg, ip) pretreatment reversed the THC-induced increase in CORT. Conclusions: CBD attenuated THC-induced nausea as well as THC-induced elevation in CORT. The attenuation of THC-induced conditioned gaping by CBD was mediated by its action on 5-HT1A receptors, similar to that of LiCl-induced nausea.

The Effects of a Selective Serotonin 2C (5HT2C) Receptor Agonist WAY 163909 on Cocaine Self‐Administration in Male and Female Rhesus Macaques Exposed to Early Life Stress

Cocaine use disorder represents a prominent health concern in the United States, and there are currently no accepted pharmacotherapies for the treatment of ongoing cocaine use. Additionally, the occurrence of stressors early in life, such as physical abuse and neglect, is a major predictor in the emergence of cocaine abuse later in life. Rhesus monkeys demonstrate a similar prevalence rate of infant abuse and rejection as humans, and serve as ideal candidates to examine the relationship between early life stress (ELS) and cocaine use. Finally, previous data suggest serotonin 2C (5HT2C) agonists may be viable candidates in the treatment of ongoing drug use. Accordingly, the effectiveness of the 5HT‐2C agonist WAY 163909 (WAY) to decrease cocaine self‐administration was examined in male and female rhesus macaques.Subjects were 8 adolescent male and female rhesus macaques who experienced infant maltreatment (MALT) or competent maternal care (MALT males n=4; MALT females, n=2; Control males, n=0; Control females, n=2). During adolescence, animals were trained to respond under a fixed‐ratio 20 response (FR 20) schedule of reinforcement to receive an infusion of cocaine (0.01–0.1 mg/kg/infusion). After meeting criteria for stable self‐administration (SA), animals progressed through a full dose‐effect curve to establish the dose that engendered the highest response rate (EDMax), and were then examined under maintenance conditions. During each testing week, WAY pretreatments (3 consecutive daily treatments administered 45 minutes prior to sessions) were preceded by normal maintenance sessions without any pretreatments, which provided a baseline of responding. Each WAY dose (0.1–1 mg/kg IM) was tested weekly interspersed by weeks of vehicle treatment.WAY dose‐dependently decreased cocaine self‐administration in males and females, with males demonstrating significantly lower response rates in comparison to females at 0.3 mg/kg WAY. MALT animals also demonstrated an overall lower response rate across doses of WAY in comparison to control subjects.These preliminary data suggest that females may be more resistant to serotonergic interventions of ongoing cocaine SA, given that females from MALT and Control groups were less sensitive to the effects of WAY in comparison to males. Furthermore, MALT animals overall showed a lower response rate in comparison to control animals across doses of WAY, suggesting that MALT subjects may be uniquely sensitive to serotonergic interventions aimed at decreasing ongoing drug use. The addition of male controls will be critical in determining whether robust sex differences persist, and if male controls demonstrate a similar response pattern as female controls.Support or Funding InformationThis research was supported by USPHS grants DA 038588 (MMS/LLH), DA 010344 (LLH), DA 031246 (LLH), and P51OD11132 (YNPRC).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Anxiolytic- and antidepressant-like activities of a methanolic extract of Morinda citrifolia Linn. (noni) fruit in mice: Involvement of benzodiazepine-GABAAergic, serotonergic and adrenergic systems

This study presents anxiolytic- and antidepressant-like effects of a methanolic extract of Morinda citrifolia Linn. (noni) fruit (MMC) in well-established mouse models of anxiety and depression. The administration of MMC (1 g/kg, p.o.) and diazepam (1 mg/kg, i.p.) significantly attenuated anxiety-like behaviour in mice by increasing the percentage of time spent and number of entries in the open arms in the elevated plus maze (EPM), and significantly enhanced the exploration in the light box in the light/dark test (LDT). The pre-treatment with flumazenil (6 mg/kg, i.p.) or bicuculline (3 mg/kg, i.p.) or WAY 100635 (1 mg/kg, i.p.) antagonized the anxiolytic-like effect elicited by MMC (1 g/kg, p.o.). These results suggest the possible involvement of benzodiazepine-GABAAergic and serotonergic mechanisms in the anxiolytic-like effect of noni fruit. Meanwhile, in the antidepressant study, the administration of MMC (0.5 and 0.75 g/kg, p.o.) and desipramine (30 mg/kg, i.p.) significantly reduced the duration of immobility in the tail suspension test (TST). Furthermore, pre-treatment of mice with 4-chloro-DL-phenylalanine methyl ester hydrochloride (PCPA; 100 mg/kg, i.p., an inhibitor of serotonin synthesis) for four consecutive days or a single dose of WAY 100635 (1 mg/kg, i.p., 5HT1A receptor antagonist) or α-methyl-DL-tyrosine (AMPT; 100 mg/kg, i.p., an inhibitor of noradrenaline synthesis) significantly reversed the anti-immobility effect of MMC (0.5 g/kg, p.o.) in TST by indicating the specific involvement of the serotonergic and noradrenergic systems in the antidepressant-like effect of noni fruit. Taken together, these findings suggest that MMC has both anxiolytic- and antidepressant-like activities to be resorted as a valuable alternative therapy for comorbid anxiety and depressive conditions.

Effects of a Serotonin 2C Agonist and a 2A Antagonist on Actigraphy-Based Sleep Parameters Disrupted by Methamphetamine Self-Administration in Rhesus Monkeys.

Sleep disorders and substance abuse are highly comorbid and we have previously shown that methamphetamine self-administration significantly disrupts activity-based sleep parameters in rhesus monkeys. To the best of our knowledge, no study has evaluated the effectiveness of any pharmacological intervention to attenuate the effects of methamphetamine on nighttime activity under well-controlled conditions in laboratory animals. Thus, we examined the effects of a 5-HT2C receptor agonist, WAY163909, and a 5-HT2A receptor antagonist, M100907, given alone and in combination, on actigraphy-based sleep parameters disrupted by methamphetamine self-administration in non-human primates. Adult male/female rhesus monkeys self-administered methamphetamine (0.03 mg/kg/injection, i.v.) under a fixed-ratio 20 schedule of reinforcement (60-min sessions once a day, 5 days per week). Nighttime activity was evaluated using Actiwatch monitors. WAY163909 (0.1, 0.3, and 1.0 mg/kg), M100907 (0.03, 0.1, and 0.3 mg/kg), and a combination (0.1 mg/kg M100+0.3 mg/kg WAY) were administered i.m. before lights-out. Each dose was given for five consecutive days during which self-administration took place in the morning. Both drugs improved activity-based sleep measures disrupted by methamphetamine by decreasing sleep latency and increasing sleep efficiency compared with vehicle. By combining these drugs, their individual effects were significantly enhanced. Agonists at the 5-HT2C receptor and antagonists at the 5-HT2A receptor show promise as potential treatments for the sleep-disrupting effects of stimulants when used alone and in combination. Combining subthreshold doses of WAY and M100 produced significant improvements in nighttime activity measures while avoiding the general motor-decreasing effects of the high dose of WAY.

Restoration of serotonin neuronal firing following long-term administration of bupropion but not paroxetine in olfactory bulbectomized rats.

Background:Olfactory bulbectomized rats generally manifest many of the neurochemical, physiological, and behavioral features of major depressive disorder in humans. Another interesting feature of this model is that it responds to chronic but not acute antidepressant treatments, including selective serotonin reuptake inhibitors. The purpose of the present study was first to characterize the firing activity of dorsal raphe serotonin neurons in olfactory bulbectomized rats and then examine the effects of 2 antidepressants, bupropion and paroxetine.Methods:Olfactory bulbectomy was performed by aspirating olfactory bulbs in anesthetized rats. Vehicle and drugs were delivered for 2 and 14 days via subcutaneously implanted minipumps. In vivo electrophysiological recordings were carried out in male anesthetized Sprague-Dawley rats.Results:Following ablation of olfactory bulbs, the firing rate of serotonin neurons was decreased by 36%, leaving those of norepinephrine and dopamine neurons unchanged. In olfactory bulbectomized rats, bupropion (30mg/kg/d) restored the firing rate of serotonin neurons to the control level following 2- and 14-day administration and also induced an increase in the tonic activation of serotonin1A receptors; paroxetine (10mg/kg/d) did not result in a return to normal of the attenuated firing of serotonin neurons in olfactory bulbectomized rats. In the hippocampus, although at a higher dose of WAY 100635 than that required in bupropion-treated animals, paroxetine administration also resulted in an increase in the tonic activation of serotonin1A receptors.Conclusions:The present results indicate that unlike paroxetine, bupropion administration normalized serotonin neuronal activity and increased tonic activation of the serotonin1A receptors in hippocampus.

Serotonergic control of ingestive and post-ingestive behaviors in pigeons (Columba livia): The role of 5-HT1A receptor-mediated central mechanisms

Central injections of serotonin (5-HT) produce hyperdipsic and hypnogenic behavioral effects that are correlated to decreased Fos-immunorreactivity of 5-HT neurons in free-feeding pigeons. We herein (1) probed the role of 5-HT1A receptors on the 5-HT- or 8-OH-DPAT-evoked postprandial behaviors and (2) described the sleep–waking states (waking, W; drowsiness, D; slow-wave sleep, SWS; rapid-eye movement sleep, REMS) and sleep architecture of free-feeding pigeons after these treatments. Latency, frequency and duration of feeding, drinking, preening, exploratory and sleep-like behaviors (SLB) were examined after intracerebroventricular (ICV) injections of 5-HT (0, 50 or 150nmol) or 8-OH-DPAT (DPAT, 0 or 30nmol) in pigeons pretreated with the 5-HT1A antagonist WAY100635 (WAY, 0, 0.1, 0.3 or 1nmol). Additionally, the acute (1h) waking-sleep-related electrographic activity in the hippocampus (HP) was examined after ICV injections of 5-HT (150 or 300nmol) or DPAT (30 or 60nmol) in pigeons pretreated with WAY (0 or 1nmol). 5-HT and DPAT acutely increased drinking and then sleep: all doses of WAY attenuated the 5-HT (50nmol) -induced dipsogenic effect, but left unchanged the effects of the 150nmol 5-HT dose. The WAY 0.1nmol dose blocked the SLB induced by the 5-HT 50nmol dose. Given before the vehicle (VEH) injections, WAY does not affect water or food intake, but increased the SLB duration at all doses. DPAT injections increased feeding, drinking and SLB. All the WAY doses attenuated the DPAT-induced drinking and feeding responses, and the WAY 0.1 and 0.3nmol doses reduced DPAT-induced SLB. DPAT or 5-HT injections decreased the duration of electrographically-determined waking, increased the durations of D and induced the emergence of SWS and REMS states indistinguishable from the hippocampal EEG associated with spontaneous sleep, as judged from visual and spectral analysis. WAY (1nmol) increased SWS and D, and potentiated the 5-HT- and DPAT-induced SWS. These data suggest that 5-HT-induced drinking depends on the activation of presynaptic 5-HT1A receptors, while 5-HT1A autoreceptor activation contributes to the 5-HT-induced sleep. 5-HT-induced drinking and sleep behaviors may thus be provoked by a 5-HT1A-evoked, rebound-like reduction in central 5-HTergic activity. These data also indicate that an ongoing, tonic and inhibitory influence of central 5-HT circuits may participate in the control of feeding, drinking and rest behaviors in pigeons during the wake, nibbling diurnal state. These mechanisms appear to be comparable to those found in mammals, suggesting that they may represent a conserved, plesiomorphic functional trait of the amniotes brain.

The Nonpeptide Oxytocin Receptor Agonist WAY 267,464: Receptor‐Binding Profile, Prosocial Effects and Distribution of c‐Fos Expression in Adolescent Rats

Previous research suggests that the nonpeptide oxytocin receptor (OTR) agonist WAY 267,464 may only partly mimic the effects of oxytocin in rodents. The present study further explored these differences and related them to OTR and vasopressin 1a receptor (V(1a) R) pharmacology and regional patterns of c-Fos expression. Binding data for WAY 267,464 and oxytocin were obtained by displacement binding assays on cellular membranes, while functional receptor data were generated by luciferase reporter assays. For behavioural testing, adolescent rats were tested in a social preference paradigm, the elevated plus-maze (EPM) and for locomotor activity changes following WAY 267,464 (10 and 100 mg/kg, i.p.) or oxytocin (0.1 and 1 mg/kg, i.p.). The higher doses were also examined for their effects on regional c-Fos expression. Results showed that WAY 267,464 had higher affinity (K(i) ) at the V(1a) R than the OTR (113 versus 978 nm). However, it had no functional response at the V(1a) R and only a weak functional effect (EC(50) ) at the OTR (881 nm). This suggests WAY 267,464 is an OTR agonist with weak affinity and a possible V(1a) R antagonist. Oxytocin showed high binding at the OTR (1.0 nm) and V(1a) R (503 nm), with a functional EC(50) of 9.0 and 59.7 nm, respectively, indicating it is a potent OTR agonist and full V(1a) R agonist. WAY 267,464 (100 mg/kg), but not oxytocin, significantly increased the proportion of time spent with a live rat, over a dummy rat, in the social preference test. Neither compound affected EPM behaviour, whereas the higher doses of WAY 267,464 and oxytocin suppressed locomotor activity. WAY 267,464 and oxytocin produced similar c-Fos expression in the paraventricular hypothalamic nucleus, central amygdala, lateral parabrachial nucleus and nucleus of the solitary tract, suggesting a commonality of action at the OTR with the differential doses employed. However, WAY 267,464 caused greater c-Fos expression in the medial amygdala and the supraoptic nucleus than oxytocin, and lesser effects in the locus coeruleus. Overall, our results confirm the differential effects of WAY 267,464 and oxytocin and suggest that this may reflect contrasting actions of WAY 267,464 and oxytocin at the V(1a) R. Antagonism of the V(1a) R by WAY 267,464 could underlie some of the prosocial effects of this drug either through a direct action or through disinhibition of oxytocin circuitry that is subject to vasopressin inhibitory influences.

Serotonin antagonists in the five-choice serial reaction time task and their interactions with nicotine

Much research has implicated the serotonin (5-HT) system in cognitive functioning and psychomotor stimulant abuse, but its role depends on the subtypes of 5-HT receptors involved and the nature of the behavioural task. Here we aimed to extend previous studies by examining the role of 5-HT1A and 5-HT2C receptors in attentional performance. The effects of the selective 5-HT antagonists WAY-100635 and SB-242084 were assessed alone and for interactions with nicotine in the five-choice serial reaction time task in rats. The effects of several doses of WAY-100635 were tested in combination with a fixed dose of nicotine, and then various doses of nicotine were tested in combination with SB-242084. Systemic administration of WAY-100635 and SB-242084 induced opposing effects on speed-related measures in the five-choice serial reaction time task, with antagonism at 5-HT1A receptors increasing omission errors and response latency, and antagonism at 5-HT2C receptors reducing both omissions and latency, and also increasing anticipatory responses; neither drug affected accuracy. Nicotine itself improved all main indices of attention, and there was preliminary evidence that the detrimental effects of WAY-100635 on response latency were weakened by nicotine. Conversely, treatment with SB-242084 enhanced all speed-related indices of performance to above the levels seen under the influence of nicotine alone, thus suggesting that 5-HT2C antagonists might be useful to decrease reaction times if used as an add-on therapy to treat attentional decline.

Potential serotonin 5-HT1A and dopamine D4 receptor modulation of the discriminative stimulus effects of amphetamine in rats

Activation of the dopaminergic system underlies the behavioral effects of (+)-amphetamine, and plays a major role in its discriminative stimulus properties. Although serotonin receptors modulate dopamine levels in the brain, and 5-HT(1A) and 5-HT(2) receptor agonists do not mimic (+)-amphetamine, pretreatment with 5-HT(2A/2C) agonists significantly potentiates the (+)-amphetamine cue. Further, 5-HT(2) antagonists do not modify the discriminative stimulus effect of (+)-amphetamine, but 5-HT(1A) antagonists have never been tested in (+)-amphetamine-trained rats. This study sought to characterize the effects of the 5-HT(1A) antagonist WAY 100635 on (+)-amphetamine-induced discriminative stimulus effects. Male Sprague-Dawley rats were trained in a two-lever, fixed ratio 50, food-reinforced task with (+)-amphetamine sulfate (1.0 mg/kg, i.p., 30 min pretreatment time) as the discriminative stimulus. Substitution and combination tests with WAY 100635 were then performed. WAY 100635 did not produce substitution in amphetamine-trained rats, but significantly increased behavioral disruption. In combination tests 0.4 and 5.4 mg/kg doses of WAY 100635 potentiated the amphetamine cue. We suggest that low doses of WAY 100635 potentiated the (+)-amphetamine cue by blockade of 5-HT(1A) receptors, but stimulation of the dopamine D(4) receptor by higher doses of WAY 100635 may be responsible for potentiation of amphetamine-induced behavioral sensitization. The high percentage of behavioral disruption in substitution tests might suggest that rats trained to discriminate (+)-amphetamine from saline show behavioral sensitization that is not detectable by the drug discrimination assay but may be expressed as hyperactivity and stereotypic behavior that disrupts operant behavior.

WAY 100635 produces discriminative stimulus effects in rats mediated by dopamine D4 receptor activation

In-vitro studies have shown that WAY 100635 is not only a potent 5-HT1A antagonist, but also has high affinity and efficacy at the dopamine D(4) receptor. Nevertheless, the behavioral effects of this compound have not been investigated. This study sought to characterize the discriminative stimulus effects produced by WAY 100635. Male Sprague-Dawley rats were trained in a two-lever, fixed ratio 50, food-reinforced task with WAY 100635 (10 micromol/kg) as a discriminative stimulus. Substitution tests with different doses of WAY 100635 and (-)-pindolol, and combination tests with two 5-HT1A agonists, 8-OH-DPAT and LY 293284; and two dopamine D(4) antagonists, sonepiprazole and A-381393, were performed. Rats trained with a low dose (0.74 micromol/kg) of WAY 100635 could not learn the discrimination task after more than 3 months of sessions. Rats trained to discriminate 10 micromol/kg of WAY 100635 from saline achieved the criterion of accuracy after approximately 35 training sessions. WAY 100635 (2.5-10 micromol/kg) produced a dose-dependent increase in WAY 100635-appropriate responding, with a mean effective dose of 3.44 micromol/kg, whereas saline or pindolol (5-25 micromol/kg) administration resulted in 0% drug lever responding. Pretreatment with the 5-HT(1A) agonists 8-OH-DPAT or LY 293284 did not modify the WAY 100635 curve, but pretreatment with the selective dopamine D(4) antagonists sonepiprazole or A-381393 completely blocked the cue. These results indicate that the discriminative stimulus effect produced by WAY 100635 is mediated by activation of dopamine D(4) receptors.

Antagonist‐induced increase in 5‐HT1A‐receptor expression in adult rat hippocampus and cortex

Many receptor antagonists function as reverse agonists on the signaling transduction pathway, but little is known about the action of these drugs on the regulation of receptor expression. Serotonin 1A (5-HT1A) receptor expression in 5-HT and serum-free fetal hippocampal cultures is increased in the presence of a specific 5-HT1A-receptor antagonist N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl) cyclohexane carboxamide (WAY 100635). To study the plasticity of postsynaptic 5-HT1A receptors in the presence of antagonist in vivo, adult Sprague Dawley rats were injected i.p. either once or twice daily with a dose of WAY 100635 (3 mg/kg) over a period of 3 days. The 5-HT1A receptor expression was detected by immunocytochemistry and light microscopy, and the receptor immunoreactivity (IR) in hippocampus subregions was quantitatively assessed by using a comparative computer-assisted morphometric analysis. Following the daily injections of WAY 100635, a significant increase in 5-HT1A receptor labeling in hippocampal neurons was recorded. This marked increase in 5-HT1A receptor expression, which occurred within 4 h after a single injection of WAY 100635, is evident on the somata membrane and dendritic processes of hippocampal and cortex layer V neurons. By contrast, no increase in 5-HT1A receptor-IR was observed after multiple daily injections at a low dose (1 mg/kg) of WAY 100635. Our study shows that a single or multiple daily injections of WAY 100635 can result in an increase in 5-HT1A receptor-IR. This increase in labeling is consistent with an enhanced expression of the receptor protein. The action of this "inverse agonist" may have clinical importance in disorders such as depression, epilepsy, and Alzheimer's disease in which 5-HT1A receptor levels are deficient.

Role of GABA-ergic and serotonergic systems in the anxiolytic-like mechanism of action of a 5-HT-moduline antagonist in the mouse elevated plus maze

5-HT-moduline is an endogenous tetrapeptide, which acts specifically as an antagonist of 5-HT 1B auto- and heteroreceptors. HG1 is an ethyl arylmethyloxypiperidine acetate and an antagonist of 5-HT-moduline, which has no 5-HT-moduline agonist effect. In a pilot study, HG1 has demonstrated an anxiolytic-like profile in three mouse models of anxiety (elevated plus maze, light/dark, four plates). The aim of our study was to examine the mechanism of the anxiolytic-like effects of HG1 in the mouse elevated plus maze. Male Swiss mice were acutely administered HG1 at active doses in association with GABA antagonists such as flumazenil, bicuculline and picrotoxine, then, with 5-HT 1A (NAN 190, WAY 100635) and 5-HT 1B receptor antagonist (methiothepine). Finally, we tried to potentiate non-active doses of HG1 with 5-HT 1A (8-OHDPAT) and 5-HT 1B receptor agonists (anpirtoline) in the mouse elevated plus maze. Regarding GABA antagonists, only flumazenil antagonised active doses of HG1 in an incomplete manner. Moreover, non-active doses of HG1 were potentiated by low doses of WAY 100635 and by anpirtoline but not by 8-OHDPAT. Finally, the anxiolytic-like effects of HG1 at active doses were antagonised by all serotonergic antagonists (WAY 100635 at higher dose, NAN 190 and methiothepin). HG1 mechanism of action in the mouse elevated plus maze seems to associate a GABA-ergic component exerting a limited regulation of 5-HT neuronal activity and a major serotonergic component, which seems to implicate presynaptic 5-HT 1A and 5-HT 1B receptors.

The Pyridinyl-6 Position of WAY-100635 as a site for radiofluorination—effect on 5-HT 1A receptor radioligand behavior in vivo

Purpose We aimed to evaluate radiofluorination at the pyridinyl-6 position of the selective 5-HT 1A receptor antagonist, WAY-100635 [ N-(2-(1-(4-(2-methoxyphenyl)piperazinyl)ethyl))- N-(2-pyridinyl)cyclohexanecarboxamide)], on 5-HT 1A receptor radioligand behavior in vivo. Procedures The pyridinyl-6 [ 18F]fluoro derivative of WAY-100635 ([ 18F]6FPWAY) was obtained by direct nucleophilic substitution with [ 18F]fluoride ion in a bromo precursor. After intravenous injection of [ 18F]6FPWAY into Cynomolgus monkey, the uptake of radioactivity into brain regions was assessed with positron emission tomography (PET) and blood samples analyzed by high performance liquid chromatography (HPLC) for parent radioligand and radioactive metabolites. The experiment was repeated after pretreatment of the monkey with a dose of WAY-100635 that blocks brain 5-HT 1A receptors. Results After intravenous injection of [ 18F]6FPWAY into Cynomolgus monkey, the uptake of radioactivity into whole brain reached 4.33% of injected dose at 7.5 min. Uptake was highest in 5-HT 1A receptor-rich regions. Pretreatment with WAY-100635 reduced uptake in these regions to near the levels in receptor-devoid cerebellum. [ 18F]6FPWAY was rapidly metabolized in vivo, as evidenced by the rapid appearance of radioactive metabolites in plasma. Conclusion [ 18F]6FPWAY is selective and moderately useful for imaging brain 5-HT 1A receptors in vivo. The pyridinyl-6 position is resistant to defluorination and may be an attractive site for the 18F-labeling of 6FPWAY analogs that resist hydrolysis.

The dorsal raphé nucleus is a crucial structure mediating nicotine's anxiolytic effects and the development of tolerance and withdrawal responses.

Smokers frequently report that they obtain anxiety-reducing (anxiolytic) effects from smoking, and this may be one factor which contributes to nicotine dependence. The aim of this study was to investigate the role of the dorsal raphé nucleus (DRN) in mediating the acute anxiolytic effect of nicotine, the development of tolerance to this effect and the anxiogenic response observed on withdrawal from chronic nicotine. The social interaction test of anxiety was used to investigate the effects of a range of doses of (-)-nicotine (2.5-4000 ng) following DRN infusion, and whether co-administration of the specific 5-HT1A receptor antagonist WAY 100635 could antagonise the anxiolytic action of nicotine. We then examined the effects of intra-DRN nicotine (2.5-7 ng) following six daily injections of subcutaneous (s.c.) (-)-nicotine (0.1 mg/kg). Finally, we examined whether s.c. or intra-DRN (-)-nicotine could antagonise the anxiogenic response seen 72 h after the termination of 7 days of nicotine treatment. Acute nicotine administration into the DRN produced dose-related effects: low doses (2.5-10 ng) induced an anxiolytic effect, intermediate doses were behaviourally silent (100-1000 ng), and an anxiogenic effect was seen following administration of a high dose (4 micrograms). The anxiolytic effect of (-)-nicotine (5 ng) was reversed by co-administration of a behaviourally inactive dose of WAY 100635 (200 ng). Following 6 days of treatment with s.c. 0.1 mg/kg per day (-)-nicotine, tolerance developed to its anxiolytic action in the DRN. Rats withdrawn for 72 h following this chronic treatment showed an anxiogenic response which was reversed by (-)-nicotine injected s.c. (0.1 mg/kg) or into the DRN (5 ng). The present findings therefore suggest that the DRN plays an important role in mediating the acute effects of nicotine on anxiety, as measured in the social interaction test, and that the anxiolytic effect is mediated by activation of somatodendritic 5-HT1A autoreceptors. The DRN is also concerned with mediating the development of tolerance to nicotine's anxiolytic effects and because there is an anxiogenic response 72 h after withdrawal from chronic nicotine, this suggests that an oppositional, compensatory mechanism is mediating the tolerance.

Estimation of apparent p A2 values for WAY 100635 at 5-HT 1A receptors regulating 5-hydroxytryptamine release in anaesthetised rats

5-HT 1A receptor agonists decrease 5-hydroxytryptamine (5-HT) terminal release by activating somatodendritic 5-HT 1A autoreceptors. The selective 5-HT 1A receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N-(2-pyridinyl)cyclohexanecarboxamide (WAY 100635) inhibits these effects of 5-HT 1A receptor agonists. The present study was aimed at estimating apparent p A 2 values for WAY 100635 to antagonise 5-HT 1A receptor agonist-induced decrease in 5-HT release in rat hippocampus. Extracellular concentrations of 5-HT were measured in microdialysis samples after administration of cumulative doses of 5-HT 1A receptor agonists with different intrinsic activity, alone or in the presence of increasing doses of WAY 100635. Administration of cumulative doses of (±)-8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT) (0.01–40 mg/kg), 1[2-(4-fluorobenzoylamino)ethyl]-4-(7-methoxynaphtyl)piperazine (S 14506) (0.00063–2.5 mg/kg), or buspirone (0.16–40 mg/kg), dose-dependently decreased the extracellular concentrations of 5-HT in the ventral hippocampus. Pre-treatment with WAY 100635 (0.01–0.63 mg/kg) shifted the dose–response curve of each agonist to the right in a dose-dependent manner. WAY 100635 antagonised the effects of all three compounds in a competitive manner, with an estimated apparent in vivo p A 2 value of 7.95 (95% confidence limits: 7.66–8.24). Taken together, the results are evidence that buspirone, S 14506 and 8-OH-DPAT, administered in cumulative doses, decreased 5-HT release by activating similar 5-HT 1A receptors, because a common apparent p A 2 value was obtained for WAY 100635. The results also show that orderly microdialysis data can be obtained using cumulative dosing, which enables one to collect dose–response data rapidly, with fewer animals.

The 5-HT 1A antagonist WAY 100635 can block the low-dose locomotor stimulant effects of cocaine

Cocaine treatments of 2.5, 5.0, 10.0 and 15.0 mg/kg induced dose-dependent increases in locomotor behavior. This cocaine-induced increase in locomotion was blocked if the animals were administered the selective 5-HT 1A antagonist, WAY 100635 (0.4 mg/kg) prior to the cocaine treatment. The 0.4-mg/kg dose of WAY 100635 did not affect locomotor behavior or alter cocaine availability in brain.

5-HT 1A receptor antagonists neither potentiate nor inhibit the effects of fluoxetine and befloxatone in the forced swim test in rats

Recent clinical data suggest that coadministration of pindolol with an antidepressant, particularly the 5-hydroxytryptamine (5-HT) reuptake inhibitor fluoxetine, can shorten the time to onset of clinical activity and increase the proportion of responders. We have examined the interaction of antidepressants with 5-HT 1A receptors using the forced swim test in rats using both (±)-pindolol and the selective 5-HT 1A receptor antagonist WAY 100,635 ( N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N-(pyridinyl) cyclohexanecarboxamide trihydrochloride) in combination with either fluoxetine or the selective monoamine oxidase-A inhibitor befloxatone. 8-Hydroxy-dipropylaminotetralin (8-OH-DPAT; 0.125–1 mg/kg s.c.), used as a reference for 5-HT 1A agonist activity, reduced immobility in the forced swim test and this effect was significantly antagonised by WAY 100,635. WAY 100,635 alone (0.01–0.1 mg/kg s.c.) was without effect, although a higher dose, 0.3 mg/kg s.c., had a nonsignificant tendency to increase immobility. In contrast, (±)-pindolol (1–16 mg/kg s.c.) significantly reduced immobility, but to a lesser extent than 8-OH-DPAT. As expected, the antidepressants fluoxetine (10–80 mg/kg p.o.) and befloxatone (0.03–1 mg/kg p.o.) dose-dependently reduced immobility time. When the antidepressants were combined with WAY 100,635 (0.1 mg/kg), WAY 100,635 either had no effect or, at relatively high doses, significantly reduced their activity in this test. Combination of the antidepressants with (±)-pindolol (2 or 4 mg/kg s.c.) failed to reveal a significant interaction. These results demonstrate that the anti-immobility effects of fluoxetine and befloxatone are neither facilitated nor antagonised by doses of WAY 100,635 that completely reverse the effects of 8-OH-DPAT. Furthermore, there was no evidence that coadministration of the antidepressants with (±)-pindolol was able to facilitate their antidepressant-like effects. Thus, whereas direct agonist activity at 5-HT 1A receptors can modulate immobility in the forced swim test, this receptor subtype does not appear to play a major role in the antidepressant-like effects of fluoxetine or befloxatone under the conditions used in this study.

Antiaggresive and Anxiolytic Effects of Gepirone in Mice, and Their Attenuation by WAY 100635

The purpose of the investigation was to ascertain whether (a) the antiaggressive effects of the 5-HT 1A partial agonist, Gepirone, could be mediated via its anxiolytic action; (b) the selective 5-HT 1A antagonist, WAY 100635, reversed these effects, and (c) the modulation of “stress hyperthermia” could be attributed to direct effects of the drugs. Isolated male mice were treated with WAY 100635 (0, 1.5, 2.5, and 5 mg/kg) given 15 min prior to Gepirone (0, 2.5, 5, and 7.5 mg/kg). Rectal temperature was taken before the first injection and again prior to the behavioral tests. In the first session only, subjects were tested for anxiety on the elevated plus-maze before the resident–intruder test. Gepirone reduced aggression in a dose-dependent manner. This effect was counteracted by all doses of WAY 100635. On the elevated plus maze, Gepirone increased open-arm entries and duration and reduced risk assessment. The largest dose of WAY 100635 had a mild direct anxiolytic action, but all doses reduced the anxiolytic action of the largest dose of Gepirone. Body temperature was decreased dose dependently by Gepirone, an effect prevented by WAY 100635. The results justify attributing the involvement of the 5-HT 1A receptors in the modulation of aggression and anxiety.

Combined Effects of Gepirone and (+)WAY 100135 on Territorial Aggression in Mice

LOPEZ-MENDOZA, D., H. AGUILAR-BRAVO AND H. H. SWANSON. Combined effects of Gepirone and (+)WAY 100135 on territorial aggression in mice. PHARMACOL BIOCHEM BEHAV 61(1) 1–8, 1998.—The purpose of this investigation was to elucidate the involvement of the serotonergic 5-HT 1A system in the control of aggression. The paradigm was the response of a resident mouse to an intruder into its territory. Three experiments were performed to assess the action of various doses of Gepirone (a partial agonist) and (+)WAY 100135 (a putative antagonist), separately and in combination, on aggression and on rectal body temperature. The most consistent action of Gepirone was an increase in the latency to attack. After initiation of fighting, rates of attack, chase, and tail rattling were reduced in a dose-dependent manner by IP administration of 2.5, 5, and 10 mg/kg of Gepirone. There was no evidence of sedation or motor impairment, but autogrooming was decreased. When doses of 2.5, 5, and 10 mg/kg of (+)WAY 100135 (WAY) were given, no effects whatsoever on aggressive or other behaviors were observed. In a third experiment, a two-factor design was followed in which injection of WAY (0, 2.5, and 5 mg/kg) was followed 15 min later by injection of Gepirone (0, 2.5, 5, and 10 mg/kg). WAY decreased attack latency, increased attack rate, and attenuated the marked dose-dependent aggression reducing properties of Gepirone. The test procedure resulted in “stress hyperthermia,” which was reduced by Gepirone and increased by WAY. In both behavioral and temperature measures, the larger dose of WAY proved to be less effective than the smaller one. The results support the involvement of the 5-HT 1A system in the modulation of some forms of aggression.

Modulation of the vagal bradycardia evoked by stimulation of upper airway receptors by central 5-HT1 receptors in anaesthetized rabbits.

1. The effects of central application of 5-HT1A and 5-HT1B/1D receptor ligands on the reflex bradycardia, apnoea, renal sympathoexcitation and pressor response evoked by stimulating upper airway receptors with smoke in atenolol-pretreated anaesthetized rabbits were studied. 2. Intracisternal administration of the 5-HT1A receptor antagonists WAY-100635 (100 microg kg(-1)) and (-)pindolol (100 microg kg(-1)) significantly reduced the smoke-induced bradycardia, attenuated the pressor response and in the case of (-)pindolol, sympathetic nerve activity. The same dose of WAY-100635 i.v. was without effect. 3. Buspirone (200 microg kg(-1), i.c.) potentiated the reflex bradycardia. This action was prevented if the animals were pretreated with WAY-100635 (100 Hg kg(-1), i.v.) 4. (+)8-OH-DPAT (25 microg kg(-1), i.c.) attenuated the evoked bradycardia, pressor response, apnoea and renal sympathoexcitation. The attenuation of the apnoea and renal sympathoexcitation, but not the bradycardia or pressor response was prevented in animals pretreated with WAY-100635 (100 microg kg(-1), i.v.). The attenuation of the reflex bradycardia and the reduction in the renal sympathoexcitation were reduced by pretreatment with the 5-HT1B/1D receptor antagonist GR127935 (100 microg kg(-1), i.v.). 5. In WAY-100635 (100 microg kg(-1), i.v.) pretreated animals, sumatriptan (a 5-HT1B/1D receptor agonist) reduced the reflex bradycardia and the pressor response. The 5-HT1B/1D receptor antagonist GR127935 (20 microg kg(-1), i.c. or 100 microg kg(-1), i.v.) had no effect on the reflex responses. 6. In conclusion, the present data are consistent with the hypothesis that activation of central 5-HT1A receptors potentiate whilst activation of 5-HT1B/1D receptors attenuate the reflex activation of cardiac preganglionic vagal motoneurones evoked by stimulation of upper airway receptors with smoke in rabbits.