Receptor Antagonist WAY-100635 Research Articles

Evidence for 5-HT1A receptor-mediated antiallodynic and antihyperalgesic effects of apigenin in mice suffering from mononeuropathy.

Neuropathic pain places a devastating health burden, with very few effective therapies. We investigated the potential antiallodynic and antihyperalgesic effects of apigenin, a natural flavonoid with momoamine oxidase (MAO) inhibitory activity, against neuropathic pain and investigated the mechanism(s). The neuropathic pain model was produced by chronic constriction injury of sciatic nerves in male C57BL/6J mice, with pain-related behaviours being assayed by von Frey test and Hargreaves test. In this model the role of 5-HT and 5-HT1A receptor-related mechanisms were investigated in vivo/in vitro. Apigenin repeated treatment (p.o., once per day for 2 weeks), in a dose-related manner (3, 10 and 30 mg·kg-1 ), ameliorated the allodynia and hyperalgesia in chronic nerve constriction injury in mice. These effects seem dependent on neuronal 5-hydroxytryptamine, because (i) the antihyperalgesia and antiallodynia were attenuated by depletion of 5-HT with p-chlorophenylalanine and potentiated by 5-hydroxytryptophan and (ii), apigenin-treated chronic constriction injury mice caused an increased level of spinal 5-HT, associated with diminished MAO activity. In vivo administration, spinally or systematically, of the 5-HT1A antagonist WAY-100635 inhibited the apigenin-induced antiallodynia and antihyperalgesia. In vitro, apigenin acted as a positive allosteric modulator to increase the efficacy (stimulation of [35 S]GTPγS binding) of the 5-HT1A agonist 8-OH-DPAT. Apigenin attenuated neuronal changes caused by chronic constriction of the sciatic nerve in mice, without causing a hypertensive crisis. Apigenin antiallodynic and antihyperalgesic actions against neuropathic pain crucially involve spinal 5-HT1A receptors and indicate it could be used to treat neuropathic pain.

Antidepressant-like effects of dezocine in mice: involvement of 5-HT1A and κ opioid receptors.

Dezocine is an opioid with low efficacy at μ-opioid and κ-opioid receptors. It also inhibits the reuptake of norepinephrine and serotonin. Dezocine is an effective analgesic against various clinical painful conditions and is widely used in many Asian countries. Given the unique pharmacology of dezocine, the drug may also have antidepressant-like properties. However, no published preclinical study has explored this possibility. This study examined the potential antidepressant-like activity of dezocine in mice. Male ICR mice were used in the forced swimming test, the tail suspension test, the warm water tail withdrawal test and locomotor activity test to test the effects of dezocine (0.3-3.0 mg/kg). The 5-HT1A receptor antagonist WAY-100635 (1 mg/kg), the μ-opioid receptor antagonist β-funaltrexamine (2 mg/kg) and the κ-opioid receptor agonist U50488 (1 mg/kg) were also studied in combination with dezocine. Dezocine produced a dose-dependent decrease in the immobility time in the forced swimming test and tail suspension test at doses that did not alter the motoric activity as determined in the locomotion test. WAY-100635 and U50488 but not β-funaltrexamine pretreatment significantly blocked the effects of dezocine. Dezocine dose-dependently increased the latency in the tail withdrawal test which was blocked by WAY-100635 and β-funaltrexamine. Combined, these results suggest that dezocine may have antidepressant-like effects. Considering the well-documented analgesic property of dezocine, it may be useful to treat pain and depression comorbidity.

Ferulic acid alleviates abnormal behaviors in isolation-reared mice via 5-HT1A receptor partial agonist activity.

Preclinical and clinical reports suggest that ferulic acid (FA), a plant-derived phenylpropanoid, is effective against mental health problems such as agitation, anxiety, and irritability in humans, without causing adverse side effects. However, the mechanism of action is unknown. The aim of the study is to investigate the mechanism underlying the ameliorative effects of FA on mental health problems such as agitation, anxiety, and irritability, using in vivo behavioral analysis, in vitro pharmacological analysis, and in silico binding analysis. The effects of FA (10 mg/kg, 50 mg/kg, and 250 mg/kg) on hyperactivity and aggressive behaviors of isolation-reared mice were examined. The effects of FA (50 mg/kg and 250 mg/kg) on extracellular levels of monoamines such as serotonin (5-HT), dopamine, and noradrenaline were analyzed by in vivo microdialysis. The effects of FA (10-13-10-6 M) on 5-HT1A and 5-HT2A receptors were analyzed using a luciferase reporter gene assay. Binding of FA to the mouse 5-HT1A receptor was evaluated by in silico analysis. The behavioral analysis showed that administration of FA (50 mg/kg) 1 h before experiments significantly alleviated hyperactivity and aggressive behaviors in isolation-reared mice. These alleviative effects were abolished by pretreatment with the 5-HT1A receptor antagonist WAY-100635 (1 mg/kg). In vivo microdialysis analysis showed that FA (50 mg/kg) did not change extracellular monoamine levels in the prefrontal cortex of mice. The luciferase reporter gene assay indicated that FA activated 5-HT1A receptors, but not 5-HT2A receptors, in a dose-dependent manner. The maximal response of 5-HT1A receptors to FA was weaker than that to 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT), a 5-HT1A receptor full agonist. In silico binding analysis showed that FA binds to the orthosteric site of 5-HT1A receptors. Taken together, these results suggest that FA ameliorates agitation-, anxiety-, and irritability-like behaviors such as hyperactivity and aggressive behaviors in isolation-reared mice via 5-HT1A receptor partial agonist activity. These findings support the efficacy of FA on mental health problems that have been suggested in preclinical and clinical practice.

Role of 5-HT1A and 5-HT2C receptors of the dorsal periaqueductal gray in the anxiety- and panic-modulating effects of antidepressants in rats

Antidepressant drugs are first-line treatment for panic disorder. Facilitation of 5-HT1A receptor-mediated neurotransmission in the dorsal periaqueductal gray (dPAG), a key panic-associated area, has been implicated in the panicolytic effect of the selective serotonin reuptake inhibitor fluoxetine. However, it is still unknown whether this mechanism accounts for the antipanic effect of other classes of antidepressants drugs (ADs) and whether the 5-HT interaction with 5-HT2C receptors in this midbrain area (which increases anxiety) is implicated in the anxiogenic effect caused by short-term treatment with ADs. The results showed that previous injection of the 5-HT1A receptor antagonist WAY-100635 in the dPAG blocked the panicolytic-like effect caused by chronic systemic administration of the tricyclic AD imipramine in male Wistar rats tested in the elevated T-maze. Neither chronic treatment with imipramine nor fluoxetine changed the expression of 5-HT1A receptors in the dPAG. Treatment with these ADs also failed to significantly change ERK1/2 (extracellular-signal regulated kinase) phosphorylation level in this midbrain area. Blockade of 5-HT2C receptors in the dPAG with the 5-HT2C receptor antagonist SB-242084 did not change the anxiogenic effect caused by a single acute injection of fluoxetine or imipramine in the Vogel conflict test. These results reinforce the view that the facilitation of 5-HT1A receptor-mediated neurotransmission in the dPAG is a common mechanism involved in the panicolytic effect caused by chronic administration of ADs. On the other hand, the anxiogenic effect observed after short-term treatment with these drugs does not depend on 5-HT2C receptors located in the dPAG.

Dual actions of 5-MeO-DIPT at the serotonin transporter and serotonin 5-HT1A receptor in the mouse striatum and prefrontal cortex.

Aims5‐Methoxy‐N,N‐diisopropyltryptamine (5‐MeO‐DIPT) is a synthetic orally active hallucinogenic tryptamine analogue. The present study examined whether the effects of 5‐MeO‐DIPT involve the serotonin transporter (SERT) and serotonin 5‐hydroxytryptamine‐1A (5‐HT1A) receptor in the striatum and prefrontal cortex (PFC).MethodsWe investigated the effects of 5‐MeO‐DIPT on extracellular 5‐HT (5‐HTex) and dopamine (DAex) levels in the striatum and PFC in wildtype and SERT knockout (KO) mice using in vivo microdialysis, and for comparison the effects of the 5‐HT1A receptor antagonist WAY100635 and the 5‐HT1A receptor agonist 8‐OH‐DPAT on 5‐HTex.Results5‐MeO‐DIPT decreased 5‐HTex levels in the striatum, but not PFC. In SERT‐KO mice, 5‐MeO‐DIPT did not affect 5‐HTex levels in the striatum or PFC. In the presence of WAY100635, 5‐MeO‐DIPT substantially increased 5‐HTex levels, suggesting that 5‐MeO‐DIPT acts on SERT and these effects are masked by its 5‐HT1A actions in the absence of WAY100635. 8‐OH‐DPAT decreased 5‐HTex levels in the striatum and PFC in wildtype mice. WAY100635 antagonized the 8‐OH‐DPAT‐induced decrease in 5‐HTex levels. In SERT‐KO mice, 8‐OH‐DPAT did not decrease 5‐HTex levels in the striatum and PFC. 5‐MeO‐DIPT dose‐dependently increased DAex levels in the PFC, but not striatum, in wildtype and SERT‐KO mice. The increase in DAex levels that was induced by 5‐MeO‐DIPT was not antagonized by WAY100635.Conclusion5‐MeO‐DIPT influences both 5‐HTex and DAex levels in the striatum and PFC. 5‐MeO‐DIPT dually acts on SERT and 5‐HT1A receptors so that elevations in 5‐HTex levels produced by reuptake inhibition are limited by actions of the drug on 5‐HT1A receptors.

Cannabidiol induces antidepressant and anxiolytic-like effects in experimental type-1 diabetic animals by multiple sites of action.

Cannabidiol (CBD), a phytocannabinoid compound, presents antidepressant and anxiolytic-like effects in the type-1 diabetes mellitus(DM1) animal model. Although the underlying mechanism remains unknown, the type-1A serotonin receptor (5-HT1A) and cannabinoids type-1 (CB1) and type-2 (CB2) receptors seem to play a central role in mediating the beneficial effects on emotional responses. We aimed to study the involvement of these receptors on an antidepressant- and anxiolytic-like effects of CBD and on some parameters of the diabetic condition itself. After 2 weeks of the DM1 induction in male Wistar rats by streptozotocin (60mg/kg; i.p.), animals were treated continuously for 2-weeks with the 5-HT1A receptor antagonist WAY100635 (0.1mg/kg, i.p.), CB1 antagonist AM251 (1mg/kg i.p.) or CB2 antagonist AM630 (1mg/kg i.p.) before the injection of CBD (30mg/kg, i.p.) or vehicle (VEH, i.p.) and then, they were submitted to the elevated plus-maze and forced swimming tests. Our findings show the continuous treatment with CBD improved all parameters evaluated in these diabetic animals. The previous treatment with the antagonists - 5-HT1A, CB1, or CB2 - blocked the CBD-induced antidepressant-like effect whereas only the blockade of 5-HT1A or CB1 receptors was able to inhibit the CBD-induced anxiolytic-like effect. Regarding glycemic control, only the blockade of CB2 was able to inhibit the beneficial effect of CBD in reducing the glycemia of diabetic animals. These findings indicated a therapeutic potential for CBD in the treatment of depression/anxiety associated with diabetes pointing out a complex intrinsic mechanism in which 5-HT1A, CB1, and/or CB2 receptors are differently recruited.

Role of 5-HT1A receptor-mediated serotonergic transmission in the medial prefrontal cortex in acute restraint stress-induced augmentation of rewarding memory of cocaine in mice

Stress enhances cocaine craving. We recently reported that acute restraint stress increases cocaine conditioned place preference (CPP) in mice; however, the underlying mechanisms remain unclear. This study aimed to examine the role of serotonergic transmission in the medial prefrontal cortex (mPFC) in cocaine CPP enhancement by acute restraint stress, which increases extracellular serotonin (5-HT) levels in the mPFC. Intra-mPFC infusion of the selective serotonin reuptake inhibitor (S)-citalopram prior to the test session significantly increased the cocaine CPP score under non-stressed conditions. This is indicative of the substantial role of increased mPFC 5-HT levels in cocaine CPP enhancement. Moreover, intra-mPFC and systemic administration of the 5-HT1A receptor antagonist WAY100635 immediately before restraint stress exposure significantly attenuated stress-induced cocaine CPP enhancement. Our findings suggest that enhanced serotonergic transmission via 5-HT1A receptors in the mPFC is involved in acute stress-induced augmentation of rewarding memory of cocaine; moreover, the 5-HT1A receptor could be a therapeutic target for stress-induced cocaine craving.

5-HT1A receptor-mediated attenuation of synaptic transmission in rat medial vestibular nucleus impacts on vestibular-related motor function.

Chemogenetic activation of medial vestibular nucleus-projecting 5-HT neurons resulted in deficits in vestibular-mediated tasks, including negative geotaxis, balance beam and rota-rod tests. The 5-HT1A receptor mediates the vestibular-related behavioural effects of 5-HT in the vestibular nucleus. 5-HT1A receptor activation attenuated evoked excitatory postsynaptic currents and evoked inhibitory postsynaptic currents via a presynaptic mechanism in the vestibular nucleus. While the anxiolytic effects of serotonergic neuromodulation are well studied, its role in sensorimotor coordination and postural control is unclear. In this study, we show that an increase of serotonin (5-hydroxytryptamine, 5-HT) at the medial vestibular nucleus (MVN), a brainstem centre for vestibulospinal coordination, by either direct cannula administration or chemogenetic stimulation of MVN-projecting serotonergic neurons, adversely affected performance of rats in vestibular-mediated tasks, including negative geotaxis, balance beam and rota-rod tests. Application of the 5-HT1 and 5-HT7 receptor co-agonist 8-hydroxy-2-(di-n-propylamino) tetralin recapitulated the effect of 5-HT, while co-administration of the specific 5-HT1A receptor antagonist WAY100135 effectively abolished all 5-HT-induced behavioural deficits. This indicated that 5-HT1A receptors mediated the effects of 5-HT in the rat MVN. Using whole-cell patch-clamp recording, we demonstrated that 5-HT1A receptor activation attenuated both evoked excitatory and evoked inhibitory postsynaptic currents through a presynaptic mechanism in the rat MVN. The results thus highlight the 5-HT1A receptor as the gain controller of vestibular-related brainstem circuits for posture and balance.

Aconitine disrupts serotonin neurotransmission via 5-hydroxytryptamine receptor in zebrafish embryo.

Medicinal plants of the genus Aconitum are one of the most commonly used herbs in traditional medicine in East Asia to treat conditions related to the heart, pain, or inflammation. However, these herbs are also dangerous as accidental poisoning due to misuse is a recurring issue. These plants contain a number of diester-diterpenoid alkaloid compounds and aconitine is the most abundant and active one. This study investigated neurotoxicity of aconitine to zebrafish embryos in early development in relation to serotonin regulation. Experimental results showed that aconitine exposure (1, 10, and 100 μM) increased frequency of coiling behavior in zebrafish embryos in a dose-dependent manner and this effect can be triggered by either exposure to 5-hydroxytryptamine 1A (5-HT1A) receptor agonist (±)-8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) or overexpression of serotonin receptor 5-htr1ab. At the same time, coiling behavior caused by aconitine exposure could be rescued by co-exposure to 5-HT1A receptor antagonist WAY-100635 Maleate (WAY100635) and knockdown of 5-htr1ab using morpholino. Exposure to aconitine also significantly increased serotonin receptor 5-htr1ab and 5-htr1bd gene expression at 24 h post fertilization (hpf), but decreased their expression and protein expression of the serotonin receptor at 96 hpf with the high dose. These results suggest that neurotoxicity caused by aconitine is mediated through the 5-HT receptor.

Chemical Composition of Essential Oil from Flower of 'Shanzhizi' (Gardenia jasminoides Ellis) and Involvement of Serotonergic System in Its Anxiolytic Effect.

Gardenia jasminoides Ellis is a famous fragrant flower in China. Previous pharmacological research mainly focuses on its fruit. In this study, the essential oil of the flower of ‘Shanzhizi’, which was a major variety for traditional Chinese medicine use, was extracted by hydro distillation and analyzed by GC-MS. Mouse anxiety models included open field, elevated plus maze (EPM), and light and dark box (LDB), which were used to evaluate its anxiolytic effect via inhalation. The involvement of monoamine system was studied by pretreatment with neurotransmitter receptor antagonists WAY100635, flumazenil and sulpiride. The monoamine neurotransmitters contents in the prefrontal cortex (PFC) and hippocampus after aroma inhalation were also analyzed. The results showed that inhalation of G. jasminoides essential oil could significantly elevated the time and entries into open arms in EPM tests and the time explored in the light chamber in LDB tests with no sedative effect. WAY100635 and sulpiride, but not flumazenil, blocked its anxiolytic effect. Inhalation of G. jasminoides essential oil significantly down-regulated the 5-HIAA/5-HT in the PFC and reduced the 5-HIAA content in hippocampus compared to the control treatment. In conclusion, inhalation of gardenia essential oil showed an anxiolytic effect in mice. Monoamine, especially the serotonergic system, was involved in its anxiolytic effect.

Neferine, a bisbenzylisoquinoline alkaloid of Nelumbo nucifera, inhibits glutamate release in rat cerebrocortical nerve terminals through 5-HT1A receptors

Neferine, a bisbenzylisoquinoline alkaloid present in Nelumbo nucifera, has been reported to exhibit neuroprotective effects. Because reduced glutamatergic transmission through inhibition of glutamate release has been proposed as a mechanism of neuroprotection, we investigated whether and how neferine inhibits glutamate release in the nerve terminals of the cerebral cortex of rats. The results demonstrated that neferine inhibits the glutamate release that is evoked by the potassium channel blocker 4-aminopyridine, doing so in a dose-dependent manner. This effect was prevented by removing extracellular calcium and blocking vesicular transporters or N- and P/Q-type calcium channels but not by blocking glutamate transporters. Neferine decreased the 4-aminopyridine-stimulated elevation in intrasynaptosomal calcium concentration; however, it had no effect on the synaptosomal membrane potential. The inhibition of glutamate release by neferine was also eliminated by the selective 5-hydroxytryptamine 1A (5HT1A) receptor antagonist WAY100635, Gi/o protein inhibitor pertussis toxin, adenylyl cyclase inhibitor MDL12330A, and protein kinase A inhibitor H89. Moreover, immunocytochemical analysis revealed the presence of 5-HT1A receptor proteins in the vesicular transporter of glutamate type 1 positive synaptosomes. The molecular docking study also demonstrated that neferine exhibited the highest binding affinity with 5-HT1A receptors (Autodock scores for 5-HA1A = −11.4 kcal/mol). Collectively, these results suggested that neferine activates 5-HT1A receptors in cortical synaptosomes, which decreases calcium influx and glutamate release through the activation of Gi/o protein and the inhibition of adenylyl cyclase/cAMP/protein kinase A cascade.

Possible Involvement of Serotonergic Mechanism(s) in the Antinociceptive Effects of kaempferol

Background and Objectives: A flavonoid kaempferol (KM) exerts an anti-inflammatory effect and is reportedly capable of preventing metabolic diseases. Nonetheless, a limited number of studies have been carried out on the antinociceptive effects of kaempferol. Objectives: The present study aimed to investigate the involvement of serotonin receptors in the antinociceptive-like activity of KM in male Wistar rats using the tail-flick test. Materials and Methods: The compounds (i.e., KM, morphine, and diclofenac) were intracerebroventricularly administered to rats for the examination of central effects on the thermal pain using the tail-flick test. For the evaluation of the involvement of serotonin receptors in the possible antinociceptive effects of kaempferol, several antagonists (i.e., tropisetron, ketanserin, GR113808, WAY 100635, and penbutolol) were used. Additionally, locomotor activity and motor responses were investigated by the rotarod test after KM treatment. Results: The intracerebroventricular microinjections of KM showed antinociceptive effects using the tail-flick test. The pretreatment with tropisetron as a 5-HT3 receptor antagonist at 1 and 10 mg completely reversed the KM-related antinociception. Furthermore, ketanserin (5-HT2A receptor antagonist) and GR113808 (5-HT4 receptor antagonist) both at 10 mg reduced KM-related antinociception; however, 5-HT1A receptor antagonist WAY 100635 and 5-HT1B antagonist penbutolol did not decrease KM-related antinociception. All KM doses were not observed with a significant effect on locomotor activity or motor reactions. Conclusion: The results of the current study suggested that serotonergic receptors (i.e., 5-HT2A, 5-HT3, and 5-HT4) are effective in the KM antinociceptive activity in male rats.

5-HT1A receptor-mediated attenuation of heat hyperalgesia and mechanical allodynia by chrysin in mice with experimental mononeuropathy

BackgroundPersistent neuropathic pain poses a health problem, for which effective therapy or antidote is in dire need. This work aimed to investigate the pain-relieving effect of chrysin, a natural flavonoid...

Antidepressant-like effect of a selenopropargylic benzamide in mice: involvement of the serotonergic system.

Major depressive disorder is a psychiatric disorder that requires considerable attention, since it dramatically impairs the quality of life of the sufferers. The available treatments do not have the efficacy needed, often presenting several side effects. Organoselenium compounds and benzamides have presented some pharmacological properties, among them an antidepressant-like effect. This study evaluated the antidepressant-like effect of N-(3-(phenylselanyl)prop-2-yn-1-yl)benzamide (SePB), an organoselenium compound containing a benzamide moiety, on the forced swimming test (FST) and the tail suspension test (TST) in mice, as well as the involvement of the serotonergic system in its effect. SePB, tested after different times (15-120min) and doses (1-50mg/kg, intragastrically (i.g.)), reduced immobility of male mice during FST and TST, without changing locomotor activity in the open-field test (OFT), demonstrating its antidepressant-like effect. SePB (10mg/kg) also produced an antidepressant-like effect in female mice in the TST. The preadministration of the serotonin (5-HT) depletor p-chlorophenylalanine (pCPA; 100mg/kg, intraperitoneal route (i.p.) once daily for 4days) prevented the anti-immobility effect of SePB, indicating that the serotonergic system is involved in the SePB antidepressant-like effect. The preadministration of the selective serotonergic receptor antagonists WAY100635 (0.1mg/kg, subcutaneous route (s.c.), a selective 5-HT1A receptor antagonist), ketanserin (1mg/kg, i.p., a 5-HT2A/2C receptor antagonist), and ondansetron (1mg/kg, i.p., a selective 5-HT3 receptor antagonist) also prevented the anti-immobility effect of SePB, demonstrating that these receptors are involved in the antidepressant-like effect of SePB. The search for new antidepressants drugs is a noteworthy goal. This study has described a new compound with an antidepressant-like effect, whose mechanism of action is related to modulation of the serotonergic system.

Antihyperalgesic effects of intrathecal perospirone in a rat model of neuropathic pain

The descending serotonergic pathway, from the brainstem to spinal cord, modulates various aspects of pain processing. The spinal 5-hydroxytryptamine (5-HT)1A and 5-HT2A receptors play pivotal roles in pain modulation. Perospirone is a novel atypical antipsychotic that serves as a 5-hydroxytryptamine (5-HT)1A receptor agonist, a 5-HT2A receptor antagonist, and a dopamine D2 receptor antagonist. Little is known about the effect of perospirone on pain transmission. Here, we explored whether perospirone attenuated neuropathic and inflammatory pain in the spinal cord. A chronic constriction injury to the sciatic nerve was induced in male Sprague-Dawley rats. We evaluated the effects of intrathecal administration of perospirone (10, 20, or 40 μg) on mechanical and cold hyperalgesia using the electronic von Frey and cold plate tests, respectively. Normal rats were assessed in terms of inflammatory nociception using the formalin test and for motor coordination employing the rotarod test. To define the mechanism underlying the action of perospirone, the effects of intrathecal pretreatment with the 5-HT1A receptor antagonist WAY-100635, the 5-HT2A/2C receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-aminopropane (DOI), and the dopamine D2 receptor agonist sumanirole on perospirone action were examined using the electronic von Frey test and cold plate test. Perospirone dose-dependently alleviated mechanical and cold hyperalgesia, but not inflammatory nociception in the spinal cord, and affected motor coordination. WAY-100635 reversed the antihyperalgesic action of perospirone significantly, but neither DOI nor sumanirole exhibited such an effect. We conclude that perospirone attenuates mechanical and cold hyperalgesia principally via 5-HT1A receptor activation in the spinal cord, and the agent is a promising novel candidate for neuropathic pain relief.

Serotonergically dependent antihyperalgesic and antiallodynic effects of isoliquiritin in a mouse model of neuropathic pain

Chronic neuropathic pain poses a significant health problem worldwide, for which effective treatment is lacking. The current work aimed to investigate the potential analgesic effect of isoliquiritin, a flavonoid from Glycyrrhiza uralensis, against neuropathic pain and elucidate mechanisms. Male C57BL/6J mice were subjected to chronic constriction injury (CCI) by loose ligation of their sciatic nerves. Following CCI surgery, the neuropathic mice developed pain-like behaviors, as shown by thermal (heat) hyperalgesia in the Hargreaves test and tactile allodynia in the von Frey test. Repetitive treatment of CCI mice with isoliquiritin (p.o., twice per day for two weeks) ameliorated behavioral hyperalgesia to thermal (heat) stimuli and allodynia to tactile stimuli in a dose-dependent fashion (5, 15 and 45 mg/kg). The isoliquiritin-triggered analgesia seems serotonergically dependent, since its antihyperalgesic and antiallodynic actions were totally abolished by chemical depletion of spinal serotonin by p-chlorophenylalanine, whereas potentiated by 5-HTP (a precursor of 5-HT). Consistently, isoliquiritin-treated neuropathic mice showed escalated levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, isoliquiritin-evoked antihyperalgesia and antiallodynia were preferentially counteracted by the 5-HT1A receptor antagonist WAY-100635 delivered systematically or spinally. Of notable benefit, isoliquiritin was able to correct co-morbid behavioral symptoms of depression and anxiety evoked by neuropathic pain. Collectively, these findings demonstrate, for the first time, the therapeutic efficacy of isoliquiritin on neuropathic hypersensitivity, and this effect is dependent on the spinal serotonergic system and 5-HT1A receptors.

5-HT2A receptor-mediated PKCδ phosphorylation is critical for serotonergic impairments induced by p-chloroamphetamine in mice

p-Chloroamphetamine (PCA), an amphetamine derivative, has been shown to induce serotonergic toxicity. However, the precise mechanism of serotonergic toxicity induced by PCA remains unclear. In this study, PCA treatment (20 mg/kg, i.p.) did not significantly change 5-HT1A receptor gene expression, but significantly increased 5-HT2A receptor gene expression. Furthermore, 5-HT2A receptor antagonist MDL11939, but not 5-HT1A receptor antagonist WAY100635, significantly attenuated PCA-induced serotonergic impairments. We investigated whether PCA activated a specific isoform of protein kinase C (PKC), since previous evidence indicated the involvement of PKC in neurotoxicity induced by amphetamines. We observed that PCA treatment significantly increased the expression levels of PKCδ among all PKC isoforms. MDL11939 treatment significantly attenuated PCA-induced phosphorylation of PKCδ. However, PCA-induced increase in 5-HT2A receptor gene expression was not altered by rottlerin (a pharmacological inhibitor of PKCδ) in mice, suggesting that 5-HT2A receptor is an upstream molecule for the activation of PKCδ. Rottlerin or PKCδ knockout significantly attenuated serotonergic behaviors. However, MDL11939 did not show any additional effects against the attenuation caused by PKCδ knockout in mice, suggesting that PKCδ gene is a molecular target for 5-HT2A receptor-mediated serotonergic effects. Our results suggest that 5-HT2A receptor mediates PCA-induced serotonergic impairments via activation of PKC.δ.

Administration of low doses of the 5-HT1A receptor agonist 8-OH-DPAT attenuates the discriminative signal of amphetamine in the conditioned taste aversion procedure

Several studies have reported that low doses of the 5-HT1A receptor agonist 8-OH-DPAT reduce cocaine-induced locomotor activity. However, it has also been reported that high doses of 8-OH-DPAT do not substitute for or alter the discriminative signal of cocaine (COC) or amphetamine (AMPH). This study aimed to evaluate the effects of low and high doses of the 5-HT1A agonist 8-OH-DPAT on the discriminative signal of AMPH using conditioned taste aversion as a drug discrimination procedure. Additionally, to establish a correlation between the behavioral effects in drug discrimination and changes in dopamine (DA) and gamma-aminobutyric acid (GABA) concentrations, we evaluated the effect of systemic administration of low or high doses of the 5-HT1A receptor agonist 8-OH-DPAT and of the 5-HT1A receptor antagonist WAY100135 on DA and GABA extracellular concentrations in the nucleus accumbens (nAcc) and ventral tegmental area (VTA), respectively, using cerebral microdialysis. The behavioral results showed that low but not high doses of 8-OH-DPAT produced a reduction in the AMPH-induced discriminative signal, while WAY100135 administration prevented such effects. The microdialysis results showed that a low dose of 8-OH-DPAT decreased extracellular DA concentrations in the nAcc and increased GABA concentrations in the VTA. Pretreatment with WAY100135 prevented these effects. These data support the hypothesis that 5-HT1A receptors modulate the behavioral effects of psychostimulant drugs, such as AMPH, through somatodendritic 5-HT1A autoreceptors in the raphe nucleus indicating that 5-HT1A receptors may be an important target for the development of pharmacological treatments for psychostimulant addiction.

Isorhynchophylline Exerts Antinociceptive Effects on Behavioral Hyperalgesia and Allodynia in a Mouse Model of Neuropathic Pain: Evidence of a 5-HT1A Receptor-Mediated Mechanism.

Chronic neuropathic pain poses a significant health problem, for which effective therapy is lacking. The current work aimed to investigate the potential antinociceptive efficacy of isorhynchophylline, an oxindole alkaloid, against neuropathic pain and elucidate mechanisms. Male C57BL/6J mice were subjected to chronic constriction injury (CCI) by loose ligation of their sciatic nerves. Following CCI surgery, the neuropathic mice developed pain-like behaviors, as shown by thermal hyperalgesia in the Hargreaves test and tactile allodynia in the von Frey test. Repetitive treatment of CCI mice with isorhynchophylline (p.o., twice per day for two weeks) ameliorated behavioral hyperalgesia and allodynia in a dose-dependent fashion (5, 15, and 45 mg/kg). The isorhynchophylline-triggered antinociception seems serotonergically dependent, since its antinociceptive actions on neuropathic hyperalgesia and allodynia were totally abolished by chemical depletion of spinal serotonin by PCPA, whereas potentiated by 5-HTP (a precursor of 5-HT). Consistently, isorhynchophylline-treated neuropathic mice showed escalated levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, the isorhynchophylline-evoked antinociception was preferentially counteracted by co-administration of 5-HT1A receptor antagonist WAY-100635. In vitro, isorhynchophylline (0.1-10 nM) increased the Emax (stimulation of [35S] GTPγS binding) of 8-OH-DPAT, a 5-HT1A agonist. Of notable benefit, isorhynchophylline was able to correct co-morbidly behavioral symptoms of depression and anxiety evoked by neuropathic pain. Collectively, these findings confirm, for the first time, the disease-modifying efficacy of isorhynchophylline on neuropathic hypersensitivity, and this effect is dependent on spinal serotonergic system and 5-HT1A receptors.

Purpurin exerted antidepressant-like effects on behavior and stress axis reactivity: evidence of serotonergic engagement.

Major depression represents a significant public health problem worldwide, and effective regimen is lacking. The present study investigated the antidepressant-like effects of purpurin, a natural anthraquinone compound from Rubia tinctorum L., and explored the underlying mechanism(s). Forced swim test (FST) and tail suspension test (TST) were used to assess antidepressant-like effects of purpurin in mice. Effects of purpurin on neuroendocrine responsivity were evaluated at the level of corticosterone and ACTH following acute restraint stress and intracerebroventricular injection of corticotrophin-releasing-factor (CRF). Serotonergic mechanisms underlying purpurin antidepressant effect were explored using biochemical, neurochemical, and pharmacological paradigms. Chronic purpurin treatment exerted in mice dose-dependently antidepressant-like effects on behavior and stress axis reactivity (n = 9-11 per group). The purpurin-triggered antidepressant-like effects are serotonergically dependent, since purpurin-treated mice showed escalated levels of brain serotonin and suppressed monoamine oxidase (MAO) activity (n = 8-11 per group). Consistently, chemical depletion of brain serotonin by p-chlorophenylalanine (PCPA) abolished the antidepressant-like effects of purpurin on behavior and stress axis responsivity (n = 9-10 per group). Moreover, the antidepressant effect by purpurin was preferentially counteracted by 1A-selective 5-HT receptor antagonist WAY-100635, but potentiated by 1A-selective agonist 8-OH-DPAT and sub-effective dose of serotonergic antidepressant fluoxetine (n = 9-11 per group), suggesting a crucial role for 5-HT1A related serotonergic system in mediating such purpurin antidepressant effect. We have revealed the antidepressant-like effects of purpurin on both behavior and stress axis reactivity in mice, with serotonergic system that preferentially couples with 5-HT1A receptors being critically engaged.