Receptor Antagonist WAY-100635 Research Articles

Presynaptic Inhibitory Effects of Fluvoxamine, a Selective Serotonin Reuptake Inhibitor, on Nociceptive Excitatory Synaptic Transmission in Spinal Superficial Dorsal Horn Neurons of Adult Mice

Fluvoxamine, a selective serotonin (5-HT) reuptake inhibitor, has been shown to exert analgesic effects in humans and laboratory animals. However, its effects on spinal nociceptive synaptic transmission have not been fully characterized. Here, whole-cell recordings were made from dorsal horn neurons in spinal slices with attached dorsal roots from adult mice, and the effects of fluvoxamine on monosynaptic A-fiber- and C-fiber-mediated excitatory postsynaptic currents (EPSCs) evoked in response to electrical stimulation of a dorsal root were studied. Fluvoxamine (10 - 100 μM) concentration-dependently suppressed both monosynaptic A-fiber- and C-fiber-mediated EPSCs, which were attenuated by the selective 5-HT1A receptor antagonist WAY100635. In the presence of the selective 5-HT3 receptor antagonist tropisetron, fluvoxamine hardly suppressed A-fiber-mediated EPSCs, whereas its inhibitory effect on C-fiber-mediated EPSCs was not affected. Although fluvoxamine increased the paired-pulse ratio of A-fiber-mediated EPSCs, it increased the frequency of spontaneous and miniature EPSCs (sEPSCs and mEPSCs). Since sEPSCs and mEPSCs appeared to arise largely from spinal interneurons, we then recorded strontium-evoked asynchronous events occurring after A-fiber stimulation, whose frequency was reduced by fluvoxamine. These results suggest that fluvoxamine reduces excitatory synaptic transmission from primary afferent fibers via presynaptic mechanisms involving 5-HT1A and/or 5-HT3 receptors, which may contribute to its analgesic effects.

Gastrodin attenuates vincristine-induced mechanical hyperalgesia through serotonin 5-HT1A receptors

Gastrodia elata Blume (Orchidaceae) is an old traditional Chinese medicine with demonstrated analgesic efficacy in humans. However, the potential analgesic effect of its active component, gastrodin, has not been systematically studied. This work described the anti-hyperalgesic effect of gastrodin in a mouse model of chemotherapeutic agent vincristine-induced neuropathic pain. Gastrodin (0.05-0.8 mg/kg) dose-dependently reverted the mechanical hyperalgesia in mice. In addition, the anti-hyperalgesic effect of gastrodin was significantly blocked by a selective serotonin 5-HT 1A receptor antagonist WAY100635 (1 mg/kg). In contrast, gastrodin did not significantly alter the general locomotor activity in mice. Taken together, this study demonstrated that gastrodin possesses robust analgesic efficacy in mice and may be a novel analgesic for the management of neuropathic pain. DOI: http://dx.doi.org/10.3329/bjp.v8i4.16836 Bangladesh Journal of Pharmacology Vol.8(4) 2013 414-419

A possible mechanism for the anxiolytic-like effect of gallic acid in the rat elevated plus maze

This work was performed to characterize the possible mechanisms involved in the anxiolytic-like activity of gallic acid (GA) in the rat elevated plus maze (EPM) test. Male Wistar rats were acutely treated with a single dose of GA (10–500mg/kg, i.p.) or diazepam and buspirone, 30min prior to behavioral assessment in the EPM, open-field and rotarod tests. Treatment with GA markedly produced an increase in the time spent and entries in the open arms of EPM at doses of 30 and 300mg/kg, respectively. These effects were comparable to those of the diazepam (1mg/kg, i.p.) and buspirone (1mg/kg, i.p.). Pretreatment with benzodiazepine antagonist flumazenil (3mg/kg, i.p.) partially blocked the anxiolytic-like effect of GA. However, an increase in the time spent and entries in the open arms of EPM observed with GA treatment were significantly inhibited by the 5-HT1A receptor antagonist WAY-100635 (0.5mg/kg, i.p.). In the open-field test, only GA at a dose of 500mg/kg decreased locomotor activity in rats. Moreover, GA (10–300mg/kg, i.p.) or diazepam and buspirone did not alter motor coordination in the rotarod test. These results indicate that GA is an effective anxiolytic agent at low doses, while at the highest dose it has sedative effect. Also this study suggests that the anxiolytic-like activity of GA is primarily mediated by the 5-HT1A but not benzodiazepine receptors.

Chronic curcumin treatment normalizes depression-like behaviors in mice with mononeuropathy: involvement of supraspinal serotonergic system and GABAA receptor

Comorbid depression is commonly observed in individuals who suffer from neuropathic pain, which necessitates improved treatment. Curcumin, a phenolic compound derived from Curcuma longa, possesses both antinociceptive and antidepressant-like activities in animal studies, suggesting its possible usefulness in treating this comorbidity. We investigated the effect of curcumin on depressive-like behaviors in mice with mononeuropathy, and explored the mechanism(s). Chronic constriction injury (CCI) was produced by loosely ligating the sciatic nerves in mice. The nociceptive behaviors were examined using Hargreaves test, and the depressive-like behaviors were determined by forced swim test (FST) and tail suspension test (TST). After CCI injury, the neuropathic mice developed nociceptive and depressive-like behaviors, as shown by thermal hyperalgesia in Hargreaves test and protracted immobility time in FST and TST. Chronic treatment of neuropathic mice with curcumin (45mg/kg, p.o., twice per day for 3weeks) corrected their exacerbated nociceptive and depressive-like behaviors, which was abolished by chemical depletion of brain serotonin rather than noradrenaline. The paralleled antinociceptive and antidepressant-like actions of curcumin seem to be pharmacologically segregated, since intrathecal and intracerebroventricular injection of methysergide, a nonselective 5-HT receptor antagonist, separately counteracted the two actions of curcumin. Further, this antidepression was abrogated by repeated co-treatment with 5-HT1A receptor antagonist WAY-100635 and greatly attenuated by acute co-treatment with GABAA receptor antagonist bicuculline. Curcumin can normalize the depressive-like behaviors of neuropathic mice, which may be independent of the concurrent analgesic action and possibly mediated via the supraspinal serotonergic system and downstream GABAA receptor.

RETRACTED ARTICLE: Auraptenol attenuates vincristine-induced mechanical hyperalgesia through serotonin 5-HT1A receptors

Common chemotherapeutic agents such as vincristine often cause neuropathic pain during cancer treatment in patients. Such neuropathic pain is refractory to common analgesics and represents a challenging clinical issue. Angelicae dahuricae radix is an old traditional Chinese medicine with demonstrated analgesic efficacy in humans. However, the active component(s) that attribute to the analgesic action have not been identified. This work described the anti-hyperalgesic effect of one coumarin component, auraptenol, in a mouse model of chemotherapeutic agent vincristine-induced neuropathic pain. We reported that auraptenol dose-dependently reverted the mechanical hyperalgesia in mice within the dose range of 0.05–0.8 mg/kg. In addition, the anti-hyperalgesic effect of auraptenol was significantly blocked by a selective serotonin 5-HT1A receptor antagonist WAY100635 (1 mg/kg). Within the dose range studied, auraptenol did not significantly alter the general locomotor activity in mice. Taken together, this study for the first time identified an active component from the herbal medicine angelicae dahuricae radix that possesses robust analgesic efficacy in mice. These data support further studies to assess the potential of auraptenol as a novel analgesic for the management of neuropathic pain.

A Role for Peripheral 5-HT2 Receptors in Serotonin-Induced Facilitation of the Expulsion Phase of Ejaculation in Male Rats

The urethrogenital reflex (UGR) is used as a physiological animal model of the autonomic and somatic activity that accompanies ejaculatory-like reflexes (ELRs). Serotonin (5-HT) plays an important role in regulating ejaculation. To examine the effects of intraurethral 5-HT on ELRs and to examine the effects of various 5-HT receptor subtypes on the 5-HT-induced changes in the ELRs. The effects of intraurethral infusion of 5-HT on ELRs were examined by monitoring the urethrogenital reflex in male rats. The effects of various 5-HT receptor-specific antagonists on the 5-HT-induced responses were examined. Main outcome measures were urethral pressure threshold required to elicit the UGR and bulbospongiosus activity or ELRs. Intraurethral infusion of 5-HT (10-1,000 μM) produced a dose-dependent facilitation of the UGR, i.e., decrease in threshold urethral perfusion pressure and an increase in number of ELRs. The 5-HT3 receptor antagonists tropisetron (1 and 3 mg/kg, i.v.) and ramosetron (0.1 and 1 mg/kg, i.v.), the 5-HT7 receptor antagonist SB269970 (3 mg/kg, i.v.), and the 5-HT1 A receptor antagonist WAY-100635 (1 mg/kg, i.v.) all failed to inhibit 5-HT-induced facilitation of the UGR. However, ritanserin (1 mg/kg, i.v.), a nonselective 5-HT2 receptor antagonist, and xylamidine (0.01-1 mg/kg, i.v.), a peripherally restricted nonselective 5-HT2 receptor antagonist, significantly inhibited both the decrease in urethral pressure threshold and the increase in number of ELRs induced by intraurethral infusion of 5-HT. These results suggest that in the male rat urethra, peripheral 5-HT2 receptors are involved in the 5-HT-induced facilitation of the expulsion phase of ejaculation.

Functional expression of 5-HT7 receptor on the substantia gelatinosa neurons of the trigeminal subnucleus caudalis in mice

The substantia gelatinosa (SG) of the trigeminal subnucleus caudalis (Vc; medullary dorsal horn) receives and processes orofacial nociceptive inputs, and serotonergic fibers involved in the descending modulation of nociception are more densely distributed in the superficial laminae of the Vc. This study investigated the direct effects of 5-HT1A/7 receptor agonist 8-OH-DPAT on SG neurons of the Vc to assess functional expression of the 5-HT7 receptor using gramicidin-perforated patch-clamp in postnatal day (PND) 5-84 male mice. Of the 70 SG neurons tested, bath application of 8-OH-DPAT (30μM) induced depolarization (n=33), hyperpolarization (n=16) or no response (n=21). In another 10 SG neurons, 8-OH-DPAT in the presence of 5-HT1A receptor antagonist WAY-100635 (1μM) elicited either depolarization (n=6) or no response (n=4); hyperpolarization was not observed. The 8-OH-DPAT-induced depolarization was significantly blocked by the selective 5-HT7 receptor antagonist SB-269970 (10μM; n=8), but not by WAY-100635 (1μM; n=5). The depolarizing effect of 8-OH-DPAT was maintained in the presence of TTX, CNQX, AP5, picrotoxin, and strychnine, indicating direct postsynaptic action of 8-OH-DPAT on SG neurons (n=6). 5-HT7 receptor mRNA was also detected in five of 21 SG neurons by single-cell RT-PCR. The mean amplitude of 8-OH-DPAT-induced depolarization in PND 5-21 mice (n=21) was significantly larger than that in PND 22-84 mice (n=12), although the proportion of SG neurons responding to 8-OH-DPAT by depolarization did not differ significantly between two age groups of mice. These results indicate that 5-HT7 receptors are functionally expressed in a subpopulation of SG neurons of the Vc and activation of 5-HT7 receptors plays an important role in modulating orofacial nociceptive processing in the SG neurons of the Vc.

Central 5‐HT1A receptor‐mediated modulation of heart rate dynamics and its adjustment by conditioned and unconditioned fear in mice

The beat-by-beat fluctuation (dynamics) of heart rate (HR) depends on centrally mediated control of the autonomic nervous system (ANS) reflecting the physiological state of an organism. 5-HT1A receptors are implicated in affective disorders,associated with ANS dysregulation which increases cardiac risk but their role in autonomic HR regulation under physiological conditions is insufficiently characterized. The effects of subcutaneously administered 5-HT1A receptor ligands on HR dynamics were investigated in C57BL/6 mice during stress-free conditions and emotional challenge (recall of fear conditioned to an auditory stimulus and novelty exposure) using time domain and non-linear HR analyses. Pre-training treatment with of 8-OH-DPAT (0.5 mg·kg(-1) , s.c.) prevented conditioned tachycardia in the retention test indicating impaired fear memory. Pretest 5-HT1A receptor activation by 8-OH-DPAT (0.5 but not 0.1 and 0.02 mg·kg(-1) ) caused bradycardia and increased HR variability. 8-OH-DPAT (0.5 mg·kg(-1) ) lowered the unconditioned and conditioned tachycardia from ∼750 to ∼550 bpm, without changing the conditioned HR response to the sound. 8-OH-DPAT induced profound QT prolongation and bradyarrhythmic episodes. Non-linear analysis indicated a pathological state of HR dynamics after 8-OH-DPAT (0.5 mg·kg(-1) ) with ANS hyperactivation impairing HR adaptability. The 5-HT1A receptor antagonist WAY-100635 (0.03 mg·kg(-1) ) blocked these effects of 8-OH-DPAT. Pre-training 5-HT1A receptor activation by 8-OH-DPAT (0.5 mg·kg(-1) ) impaired memory of conditioned auditory fear based on an attenuated HR increase, whereas pretest administration did not prevent the fear-conditioned HR increase but induced pathological HR dynamics through central ANS dysregulation with cardiac effects similar to acute SSRI overdose.

Effects of a combination of ketanserin and propranolol on inflammatory hyperalgesia in rats

Pain management is still challenging in clinic as current analgesics either are not very effective or produce serious adverse effects. This study aimed to examine if old drugs could display the new use and to develop a novel therapy for inflammatory pain. Injection of carrageenan in hindpaw evoked hyperalgesia detected by noxious heat stimulation. Intraplantar (i.pl.) injection of the 5-HT1A receptor antagonist WAY-100635 increased paw withdrawal latency (PWL) above normal level (hypoalgesia) during the late phase of carrageenan-evoked inflammation. The hypoalgesia was completely abolished by systemic injection of naloxone chloride and naloxone methiodide. Moreover, i.pl. injection of a combination of WAY-100635 and ketanserin, a 5-HT2A receptor antagonist, at their minimal doses attenuated hyperalgesia in the late phase of carrageenan-evoked inflammation. Subcutaneous (s.c.) injection of both ketanserin and propranolol dose-dependently inhibited carrageenan-evoked hyperalgesia. The treatment with a combination of ketanserin and propranolol by s.c. injection abolished carrageenan-evoked hyperalgesia at the doses, at which the drugs failed to alter the hypersensitivity when they were given alone. Furthermore, the combination of ketanserin and propranolol was also effective in relieving arthritic hyperalgesia and muscle pain at a minimal dose. The present study suggests that the activation of 5-HT1A receptors suppressed naloxone-reversible antinociception contributing to the maintenance of inflammatory pain, and that the concomitant blockade of 5-HT1A and 5-HT2A receptors in the periphery produced synergistic effects on inflammatory hyperalgesia. It is proposed that the combination of ketanserin and propranolol injected s.c. could be a promising therapy for relieving inflammatory pain with minimal side effects.

Effects of prolonged selective serotonin reuptake inhibition on the development and expression of l-DOPA-induced dyskinesia in hemi-parkinsonian rats

Dopamine (DA) replacement therapy with l-DOPA is the standard treatment for Parkinson's disease (PD). Unfortunately chronic treatment often leads to the development of abnormal involuntary movements (AIMs) referred to as l-DOPA-induced dyskinesia (LID). Accumulating evidence has shown that compensatory plasticity in serotonin (5-HT) neurons contributes to LID and recent work has indicated that acute 5-HT transporter (SERT) blockade provides anti-dyskinetic protection. However neither the persistence nor the mechanism(s) of these effects have been investigated. Therefore the current endeavor sought to mimic a prolonged regimen of SERT inhibition in l-DOPA-primed and -naïve hemi-parkinsonian rats. Rats received 3 weeks of daily co-treatment of the selective 5-HT reuptake inhibitors (SSRIs) citalopram (0, 3, or 5 mg/kg) or paroxetine (0, 0.5, or 1.25 mg/kg) with l-DOPA (6 mg/kg) during which AIMs and motor performance were monitored. In order to investigate potential mechanisms of action, tissue levels of striatal monoamines were monitored and the 5-HT1A receptor antagonist WAY100635 (0.5 mg/kg) was used. Results revealed that prolonged SSRIs attenuated AIMs expression and development in l-DOPA-primed and -naïve subjects, respectively, without interfering with motor performance. Neurochemical analysis of striatal tissue indicated that a 3 week SERT blockade increased DA levels in l-DOPA-treated rats. Pharmacologically, anti-dyskinetic effects were partially reversed with WAY100635 signifying involvement of the 5-HT1A receptor. Collectively, these findings demonstrate that prolonged SERT inhibition provides enduring anti-dyskinetic effects in part via 5-HT1A receptors while maintaining l-DOPA's anti-parkinsonian efficacy by enhancing striatal DA levels.

5-HT1A receptor antagonists reduce food intake and body weight by reducing total meals with no conditioned taste aversion

Serotonin acts through receptors controlling several physiological functions, including energy homeostasis regulation and food intake. Recent experiments demonstrated that 5-HT1A receptor antagonists reduce food intake. We sought to examine the microstructure of feeding with 5-HT1A receptor antagonists using a food intake monitoring system. We also examined the relationship between food intake, inhibition of binding and pharmacokinetic (PK) profiles of the antagonists. Ex vivo binding revealed that, at doses used in this study to reduce food intake, inhibition of binding of a 5-HT1A agonist by ~40% was reached in diet-induced obese (DIO) mice with a trend for higher binding in DIO vs. lean animals. Additionally, PK analysis detected levels from 2 to 24h post-compound administration. Male DIO mice were administered 5-HT1A receptor antagonists LY439934 (10 or 30mg/kg, p.o.), WAY100635 (3 or 10mg/kg, s.c.), SRA-333 (10 or 30mg/kg, p.o.), or NAD-299 (3 or 10mg/kg, s.c.) for 3days and meal patterns were measured. Analyses revealed that for each antagonist, 24-h food intake was reduced through a specific decrease in the total number of meals. Compared to controls, meal number was decreased 14–35% in the high dose. Average meal size was not changed by any of the compounds. The reduction in food intake reduced body weight 1–4% compared to Vehicle controls. Subsequently, a conditioned taste aversion (CTA) assay was used to determine whether the feeding decrease might be an indicator of aversion, nausea, or visceral illness caused by the antagonists. Using a two bottle preference test, it was found that none of the compounds produced a CTA. The decrease in food intake does not appear to be a response to nausea or malaise. These results indicate that 5-HT1A receptor antagonist suppresses feeding, specifically by decreasing the number of meals, and induce weight loss without an aversive side effect.

The role of 5-HT1A receptors in the anti-aversive effects of cannabidiol on panic attack-like behaviors evoked in the presence of the wild snake Epicrates cenchria crassus (Reptilia, Boidae)

The potential anxiolytic and antipanic properties of cannabidiol have been shown; however, its mechanism of action seems to recruit other receptors than those involved in the endocannabinoid-mediated system. It was recently shown that the model of panic-like behaviors elicited by the encounters between mice and snakes is a good tool to investigate innate fear-related responses, and cannabidiol causes a panicolytic-like effect in this model. The aim of the present study was to investigate the 5-hydroxytryptamine (5-HT) co-participation in the panicolytic-like effects of cannabidiol on the innate fear-related behaviors evoked by a prey versus predator interaction-based paradigm. Male Swiss mice were treated with intraperitoneal (i.p.) administrations of cannabidiol (3 mg/kg, i.p.) and its vehicle and the effects of the peripheral pre-treatment with increasing doses of the 5-HT1A receptor antagonist WAY-100635 (0.1, 0.3 and 0.9 mg/kg, i.p.) on instinctive fear-induced responses evoked by the presence of a wild snake were evaluated. The present results showed that the panicolytic-like effects of cannabidiol were blocked by the pre-treatment with WAY-100635 at different doses. These findings demonstrate that cannabidiol modulates the defensive behaviors evoked by the presence of threatening stimuli, and the effects of cannabidiol are at least partially dependent on the recruitment of 5-HT1A receptors.

Cannabidiol attenuates catalepsy induced by distinct pharmacological mechanisms via 5-HT1A receptor activation in mice

Cannabidiol (CBD) is a non-psychotomimetic compound from Cannabis sativa plant that produces antipsychotic effects in rodents and humans. It also reverses L-dopa-induced psychotic symptoms and improves motor function in Parkinson's patients. This latter effect raised the possibility that CBD could have beneficial effects on motor related striatal disorders. To investigate this possibility we evaluated if CBD would prevent catalepsy induced by drugs with distinct pharmacological mechanisms. The catalepsy test is largely used to investigate impairments of motor function caused by interference on striatal function. Male Swiss mice received acute pretreatment with CBD (5, 15, 30 or 60mg/kg, ip) 30min prior to the D2 receptor antagonist haloperidol (0.6mg/kg), the non-selective nitric oxide synthase (NOS) inhibitor L-nitro-N-arginine (L-NOARG, 80mg/kg) or the CB1 receptor agonist WIN55,212-2 (5mg/kg). The mice were tested 1, 2 or 4h after haloperidol, L-NOARG or WIN55,212-2 injection. These drugs significantly increased catalepsy time and this effect was attenuated dose-dependently by CBD. CBD, by itself, did not induce catalepsy. In a second set of experiments the mechanism of CBD effects was investigated. Thirty minutes before CBD (30mg/kg) the animals received the 5-HT1A receptor antagonist WAY100635 (0.1mg/kg). The anticataleptic effect of CBD was prevented by WAY100635. These findings indicate that CBD can attenuate catalepsy caused by different mechanisms (D2 blockade, NOS inhibition and CB1 agonism) via 5-HT1A receptor activation, suggesting that it could be useful in the treatment of striatal disorders.

Evidence that the anxiolytic-like effects of the beta3 receptor agonist Amibegron involve serotoninergic receptor activity

Anxiety disorders are the most common behavioral disorders, and they exhibit high comorbidity rates. The aim of the present study was to confirm the effects of Amibegron, the first selective beta 3 adrenergic agent, on anxiety and to demonstrate that different serotoninergic receptor subtypes are involved in this effect. We administered the serotonin 5-HT1A receptor antagonist WAY-100635, the serotonin 5-HT2A receptor antagonist Ketanserin and the serotonin 5-HT3 receptor antagonist Ondansetron in mice and evaluated their performance in the elevated plus-maze test. Mice administered with Amibegron (5 and 10mg/kg) showed a dose-dependent prolonged time spent in the open arms and an increase in the number of entries into the open arms during the elevated plus-maze (EPM) test. However, in the control mice, administration of WAY, Ketanserin and Ondansetron demonstrated no effect on the time spent in the open arms and the number of entries into the open arms. In addition, these treatments all significantly reversed the effect of the Amibegron-induced (10mg/kg) increase in the time spent in the open arms. However, only WAY and Ketanserin treatments reversed the Amibegron-induced increase in the number of entries into the open arms. In conclusion, Amibegron exerted a significant anxiolytic effect, which was as effective as Diazepam, in mice during the EPM test. This effect of Amibegron may be mediated by interactions with the serotonin 5-HT1A, 5-HT2A and 5-HT3 receptors.

Anxiolytic-like effect of lavender essential oil inhalation in mice: Participation of serotonergic but not GABAA/benzodiazepine neurotransmission

Ethnopharmacological relevanceLavandula angustifolia (lavender) inhalation has been used in folk medicine for the treatment of anxiety, and clinical and animal studies have corroborated its anxiolytic effect, although its mechanism of action is still not fully understood. Aims of the studyThe objective of the present study was to determine whether the GABAA/benzodiazepine complex or serotonin neurotransmission mediates the anxiolytic-like effect of lavender essential oil. Materials and methodsMale Swiss mice were subjected to the marble-burying test after being exposed to the aroma of lavender essential oil (1–5%), amyl acetate (5%; used as a behaviorally neutral odor), or distilled water for 15min via inhalation. Additionally, the effect of 5% lavender essential oil was also evaluated in mice subjected to the elevated plus maze. GABAA/benzodiazepine mediation was evaluated by pretreating the mice with the GABAA receptor antagonist picrotoxin before the marble burying test and [3H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Serotonergic mediation was studied by pretreating the mice with O-methyl-[3H]-N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY100635), a serotonin 5-HT1A receptor antagonist before the marble burying test. We also evaluated changes in the pharmacologically induced serotonin syndrome and the effects of combined administration of subeffective doses of lavender essential oil and the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). ResultsLavender essential oil (1–5%) decreased the number of marbles buried compared with the control and amyl acetate groups. In the elevated plus maze, 5% lavender essential oil inhalation increased the percentage of time spent on and number of entries into the open arms compared with controls. No effect was seen in the number of closed arm entries or number of beam interruptions in the automated activity chamber. Pretreatment with the GABAA receptor antagonist picrotoxin (0.5mg/kg) did not modify the behavioral effect of 5% lavender essential oil in the marble-burying test. Lavender essential oil also did not alter [3H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Pretreatment with the serotonin 5-HT1A receptor antagonist WAY100635 (3mg/kg) blocked the anxiolytic-like effect of lavender essential oil and the 5-HT1A receptor agonist 8-OH-DPAT (3mg/kg). A combination of ineffective doses of 8-OH-DPAT (0.5mg/kg) and lavender essential oil (0.1%) reduced the number of marbles buried. Finally, 5% lavender essential oil attenuated the serotonin syndrome induced by 40mg/kg fluoxetine plus 80mg/kg 5-hydroxytryptophan. ConclusionsThese results indicate an important role for the serotonergic system in the anxiolytic-like effect of lavender essential oil.

Citrus aurantium L. essential oil exhibits anxiolytic-like activity mediated by 5-HT1A-receptors and reduces cholesterol after repeated oral treatment

BackgroundThe current treatments for anxiety disorders and depression have multiple adverse effects in addition to a delayed onset of action, which has prompted efforts to find new substances with potential activity in these disorders. Citrus aurantium was chosen based on ethnopharmacological data because traditional medicine refers to the Citrus genus as useful in diminishing the symptoms of anxiety or insomnia, and C. aurantium has more recently been proposed as an adjuvant for antidepressants. In the present work, we investigated the biological activity underlying the anxiolytic and antidepressant effects of C. aurantium essential oil (EO), the putative mechanism of the anxiolytic-like effect, and the neurochemical changes in specific brain structures of mice after acute treatment. We also monitored the mice for possible signs of toxicity after a 14-day treatment.MethodsThe anxiolytic-like activity of the EO was investigated in a light/dark box, and the antidepressant activity was investigated in a forced swim test. Flumazenil, a competitive antagonist of benzodiazepine binding, and the selective 5-HT1A receptor antagonist WAY100635 were used in the experimental procedures to determine the mechanism of action of the EO. To exclude false positive results due to motor impairment, the mice were submitted to the rotarod test.ResultsThe data suggest that the anxiolytic-like activity observed in the light/dark box procedure after acute (5 mg/kg) or 14-day repeated (1 mg/kg/day) dosing was mediated by the serotonergic system (5-HT1A receptors). Acute treatment with the EO showed no activity in the forced swim test, which is sensitive to antidepressants. A neurochemical evaluation showed no alterations in neurotransmitter levels in the cortex, the striatum, the pons, and the hypothalamus. Furthermore, no locomotor impairment or signs of toxicity or biochemical changes, except a reduction in cholesterol levels, were observed after treatment with the EO.ConclusionThis work contributes to a better understanding of the biological activity of C. aurantium EO by characterizing the mechanism of action underlying its anxiolytic-like activity.

5-HT depletion, but not 5-HT1A antagonist, prevents the anxiolytic-like effect of citalopram in rat contextual conditioned fear stress model.

Selective serotonin reuptake inhibitors (SSRIs) have been widely used in the treatment of most anxiety disorders. In this study, to clarify the mechanism of the anxiolytic effect, we investigated the mechanism underlying the effect of the SSRI citalopram on rat contextual conditioned fear stress (CFS), an animal model of anxiety. Rats individually received footshocks in a shock chamber. More than 1 day later, they were given citalopram and/or dl-p-chlorophenylalanine (PCPA), various subtype-selective serotonin (5-HT) receptor antagonists: the 5-HT1A receptor antagonist WAY 100635, the 5-HT2A receptor antagonist MDL 100907, the 5-HT2C receptor antagonist SB 242084, the 5-HT3 receptor antagonist tropisetron, the 5-HT4 receptor antagonist GR 125487, the 5-HT6 receptor antagonist SB 258585 or the 5-HT7 receptor antagonist SB 269970. After drug administration, freezing behaviour, which was used as an index of anxiety, was analysed in the same shock chamber without shocks. Citalopram dose dependently reduced conditioned freezing behaviour. The anxiolytic-like effect of citalopram was prevented completely by pretreatment with the 5-HT-depleting agent PCPA, but not by the 5-HT1A receptor antagonist WAY 100635. Furthermore, none of the subtype-selective 5-HT receptor antagonists significantly affected conditioned freezing or affected the anxiolytic-like effect of citalopram. The anxiolytic-like effect of citalopram in contextual CFS model depends on 5-HT availability. In addition, contextual CFS model is suggested to be completely different from conventional anxiety models in neural mechanism or manners of serotonergic involvement. However, further studies are needed to identify the pharmacological mechanisms responsible for the anxiolytic-like effect of citalopram.

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.

Activation of the α7 nicotinic ACh receptor induces anxiogenic effects in rats which is blocked by a 5-HT1a receptor antagonist

The α7 nicotinic acetylcholine receptor (nAChR) is highly expressed in different regions of the brain and is associated with cognitive function as well as anxiety. Agonists and positive allosteric modulators (PAMs) of the α7 subtype of nAChRs have been shown to improve cognition. Previously nicotine, which activates both α7 and non-α7 subtypes of nAChRs, has been shown to have an anxiogenic effect in behavioral tests. In this study, we compared the effects of the α7-selective agonist (PNU-282987) and PAM (PNU-120596) in a variety of behavioral tests in Sprague Dawley rats to look at their effects on learning and memory as well as anxiety. We found that neither PNU-282987 nor PNU-120596 improved spatial-learning or episodic memory by themselves. However when cognitive impairment was induced in the rats with scopolamine (1 mg/kg), both PNU-120596 and PNU-282987 were able to reverse this memory impairment and restore it back to normal levels. While PNU-120596 reversed the scopolamine-induced cognitive impairment, it did not have any adverse effect on anxiety. PNU-282987 on the other hand displayed an increase in anxiety-like behavior at a higher dose (10 mg/kg) that was significantly reduced by the serotonin 5-HT1a receptor antagonist WAY-100135. However the α7 receptor antagonist methyllycaconitine was unable to reverse these anxiety-like effects seen with PNU-282987. These results suggest that α7 nAChR PAMs are pharmacologically advantageous over agonists, and should be considered for further development as therapeutic drugs targeting the α7 receptors.

Cannabidiol administration into the bed nucleus of the stria terminalis alters cardiovascular responses induced by acute restraint stress through 5-HT1A receptor

Systemic administration of cannabidiol (CBD) is able to attenuate cardiovascular responses to acute restraint stress through activation of 5-HT1A receptors. Previous results from our group suggest that the bed nucleus of the stria terminalis (BNST) is involved in the antiaversive effects of the CBD. Moreover, it has been proposed that synapses within the BNST influence restraint-evoked cardiovascular changes, in particular by an inhibitory influence on the tachycardiac response associated to restraint stress. Thus, the present work investigated the effects of CBD injected into the BNST on cardiovascular changes induced by acute restraint stress and if these effects would involve the local activation of 5-HT1A receptors. The exposition to restraint stress increased both blood pressure and heart rate (HR). The microinjection of CBD (30 and 60nmol) into the BNST enhanced the restraint-evoked HR increase, in a dose-dependent manner, without affecting the pressor response. The selective 5-HT1A receptor antagonist WAY100635 by itself did not change the cardiovascular responses to restraint stress, but blocked the effects of CBD. These results showed that CBD microinjected into the BNST enhanced the HR increase associated with acute restraint stress without affecting the blood pressure response. Although these results are not in agreement with those observed after systemic administration of CBD, they are similar to effects observed after reversible inactivation of the BNST. Moreover, similar to the effects observed after systemic administration, CBD effects in the BNST seem to depend on activation of 5-HT1A receptors.