Involvement Of 5-HT1A Receptors Research Articles

Involvement of 5-HT1A receptors of the thalamic descending pathway in the analgesic effect of intramuscular heating-needle stimulation in a rat model of lumbar disc herniation.

Intramuscular (IM) heating-needle therapy, a non-painful thermal therapy, has been found to exert an analgesic effect via the thalamic ventromedial (VM) nucleus, solely by reducing the triggering threshold for descending inhibition; this could be modulated by intracephalic 5-hydroxytryptamine-1A (5-HT1A) receptors, rather than via the regular analgesia pathway. In this study, the effect and the potential serotonergic mechanism of IM heating-needle stimulation at 43°C were explored in the case of the pathological state of lumbar disc herniation (LDH). A modified classic rat model of LDH, induced via autologous nucleus pulposus implantation, was utilized. IM inner heating-needles were applied at the attachment point of skeletal muscle on both sides of the L4 and L5 spinous processes. WAY-100635 and 8-OH-DAPT, 5-HT1A receptor antagonist and agonist, were separately injected into the bilateral thalamic mediodorsal (MD) and VM nucleus via an intrathalamic catheter. Nociception was assessed by bilateral paw withdrawal reflexes elicited by noxious mechanical and heat stimulation. IM heating-needle stimulation at a temperature of 43°C for 30 or 45 min significantly relieved both mechanical and heat hyperalgesia in the rat model of LDH (P < 0.05). Heat hyperalgesia was found to be significantly enhanced by administration of WAY-100635 into the thalamic VM nucleus, blocking the effect of heating-needle stimulation in a dose-dependent manner (P < 0.05), while no effects were detected after injection into the thalamic MD nucleus (P > 0.05). Injection of 8-OH-DAPT into the thalamic MD nucleus exerted no modulating effects on either mechanical or heat hyperalgesia (P > 0.05). IM heating-needle stimulation at 43°C for 30 min may activate 5-HT1A mechanisms, via the thalamic VM nucleus, to attenuate hyperalgesia in a rat model of LDH. This innocuous form of thermal stimulation is speculated to selectively activate the descending inhibition mediated by the thalamic VM nucleus, exerting an analgesic effect, without the involvement of descending facilitation of the thalamic MD nucleus.

Beneficial effects of atypical antipsychotics on object recognition deficits after adolescent toluene exposure in mice: involvement of 5-HT1A receptors

ABSTRACT Background: Inhalant (e.g. toluene) misuse by adolescents has been linked to psychosis and persistent cognitive deficits. Identifying effective strategies to improve cognitive deficits following chronic toluene misuse is critical. 5-HT1A receptor has been proposed as a target for the treatment of cognitive deficits. Objectives: We compared the effects of antipsychotics on recognition deficits after adolescent toluene exposure in mice and elucidated the role of 5-HT1A receptors in the cognition-improving effects of antipsychotics. Methods: Male NMRI mice (n = 279) received one injection per day of either toluene (750 mg/kg) or corn oil at postnatal days 35–39 and 42–46. Thereafter, the acute and subchronic effects of haloperidol, aripiprazole, or clozapine on toluene-induced recognition deficits were evaluated by novel object recognition test. Results: Acute administration of aripiprazole (p < .05) and clozapine (p < .01), but not haloperidol, significantly attenuated the toluene-induced recognition deficits. Pretreatment with 5-HT1A receptor antagonist WAY -100,635 (p < .05) blocked their beneficial effects. Moreover, 5-HT1A receptor agonist buspirone (p < .01) ameliorated the toluene-induced recognition deficits, which was reversed by WAY -100,635 (p < .001). Finally, after repeated treatment with clozapine, aripiprazole, and buspirone daily for 14 days, the impaired object recognition in toluene-exposed mice was significantly improved (p < .05) and the beneficial effects lasted for at least 2 weeks (p < .05). Conclusions: The results indicate that clozapine and aripiprazole, which display 5-HT1A agonist properties, restored cognitive deficits in mice induced by adolescent toluene exposure. These findings suggest that these antipsychotics should be further explored as a potential treatment option for cognitive deficits in patients with psychosis associated with toluene exposure.

Dissecting the contribution of 5-HT1A auto- and heteroreceptors in sucrose overconsumption in mice

The rise in obesity prevalence has been linked to overconsumption of high-sugar containing food and beverages. Recent evidence suggests that chronic sucrose consumption leads to changes in serotonergic neuroplasticity within the neural circuits involved in feeding control. Although there is a relationship between serotonin signalling in the brain and diet-induced obesity, the specific serotonin (5-HT) receptors or pathways involved remain unknown. The 5-HT1A receptor subtype plays a role in regulating mood, anxiety, and appetite, and has been associated with reversing addiction to substances of abuse. However, the respective role of 5-HT1A auto- vs heteroreceptors in sucrose consumption has not been examined. Mice were given controlled access to either 5%, 10% or 25% w/v sucrose, or water as a control, for 12 weeks using the well-established “drinking in the dark” protocol (n = 6–8 mice per group). Ligands selectively targeting 5-HT1A auto- and/or heteroreceptors (NLX-112, unbiased 5-HT1A receptor agonist; NLX-101, preferential heteroreceptor agonist; F13714, preferential autoreceptor agonist) were administered i.p. acutely after 6 and 12 weeks of sucrose consumption. The specific involvement of 5-HT1A receptors in these effects was verified by blockade with the selective 5-HT1A receptors antagonist WAY-100,635. The specific subpopulation of 5-HT1A receptors involved in sucrose consumption was dependent on the concentration of sucrose solution and the duration of exposure to sucrose (6 weeks vs 12 weeks). Long-term sucrose consumption leads to accentuated 5-HT1A autoreceptor function. Thus, targeting 5-HT1A autoreceptors might represent an effective therapeutic strategy to combat the rise in obesity resulting from the overconsumption of high-sugar diet.

Central involvement of 5-HT1A receptors in antinociception induced by photobiomodulation in animal model of neuropathic pain.

This study aimed to investigate the central involvement of 5-HT1A receptors in the nociceptive behavior of mice submitted to the chronic constriction injury (CCI) of sciatic nerve and the subsequent application of photobiomodulation (PBM). Male mice (Swiss-albino) were submitted to CCI and subsequently received an infusion of WAY100635 (5-HT1A receptor antagonist) or intracerebroventricular saline (ICV), followed by infrared laser irradiation (808nm), in continuous mode, with the power of 100mW and a dose of 0J/cm2 (control group) or 50J/cm2. The thermal hyperalgesia was evaluated by hot plate test, while mechanical allodynia was evaluated by von Frey filaments. After CCI, animals showed a reduction in the nociceptive threshold (p<0.001) when compared to the sham group. In von Frey test, the CCI + saline + PBM 50J/cm2 group showed an increase in nociceptive threshold (p<0.001) in all measurement moments in comparison with groups CCI + SALINE + PBM 0J/cm2, CCI + WAY100635 + PBM 50J/cm2, and CCI + WAY100635 + PBM 0J/cm2. Similarly, in hot plate test, CCI + SALINE + PBM 50J/cm2 group showed an increase in nociceptive threshold after application of PBM at 120 and 180min. Because of the results found, it can be suggested the involvement of 5-HT1A receptors in the central nervous system, since WAY100635 was able to reverse the antinociceptive effect provided by PBM in animals submitted to CCI.

Anxiolytic and antidepressant-like effects of essential oil from the fruits of Piper nigrum Linn. (Black pepper) in mice: involvement of serotonergic but not GABAergic transmission system

In this study, the anxiolytic activity of Piper nigrum essential oil (PNEO) was evaluated in the elevated plus maze (EPM) and the antidepressant-like effect was evaluated through tail suspension test (TST) in mice. Flumazenil, a competitive inhibitor of GABAA receptor in the benzodiazepine site and WAY-100635 maleate salt, a 5-HT1A receptor antagonist were used to find out the possible mechanism(s) of action of PNEO. To exclude the false-positive results due to the enhancement of the locomotor activity, the animals were submitted to open field test (OFT). We also measured monoamines levels of the mice brain after acute PNEO treatment. The data obtained from the study suggest that the anxiolytics and antidepressant-like effect of PNEO have observed in EPM and TST respectively in a dose-dependent manner after oral acute and repetitive treatment. WAY-100635, but not flumazenil was able to reverse the effect of PNEO in EPM and TST both, indicating the possible involvement of 5-HT1A receptor. The neurochemical analysis showed no alteration in monoamine levels in mice brains. Furthermore, no locomotor impairment or sign of toxicity or changes in body weight or abnormalities in the biochemical parameters, except for a significant decrease in total cholesterol level was observed after treatment with PNEO. The findings suggest that Piper nigrum EO possesses a dual anxiolytic and antidepressant-like effect through the possible involvement of serotonergic transmission.

Taurine-mediated aggression is abolished via 5-HT1A antagonism and serotonin depletion in zebrafish

Taurine is one of the most abundant amino acids in vertebrates involved in important physiological functions, including osmoregulation, membrane stability, and neuronal activity. The pleiotropic effects of taurine support the existence of different mechanisms of action (e.g., modulation of GABAA, strychnine-sensitive glycine, and NMDA receptors), which can play a role in aggressive-related responses. However, the mechanisms underlying the effects of taurine on aggression are still poorly understood. Because aggression has been associated with diverse central mechanisms, especially serotonergic activity, we aimed to investigate the involvement of this system in taurine-induced aggression in zebrafish. We treated adult zebrafish with ρ-chlorophenylalanine (ρCPA), an inhibitor of the serotonin synthesis, as well as 5-HT1A receptor antagonist and agonist (WAY100135 and buspirone, respectively). Taurine effects were tested individually at three concentrations (42, 150, and 400 mg/L) for 60 min. We further analyzed the effects on aggression and locomotion using the mirror-induced aggression test. Taurine concentration that changed behavioral responses was selected to the succeeding pharmacological experiments using ρCPA, WAY100135, and buspirone. We found that buspirone did not alter the aggression. Yet, 42 mg/L taurine increased aggression, which was abolished by ρCPA and WAY100135, indicating the involvement of 5-HT1A receptors in taurine-mediated aggression. These set of data support an indirect mechanism mediating taurine-induced aggression via serotonin release and activation of 5-HT1A receptors in zebrafish. While the exact mechanisms underlying aggression are still unclear, our novel findings reveal a key role of the serotonergic system in the effects of taurine, supporting the use of zebrafish models to understand the neural basis of aggression in vertebrates.

Galanin (1–15)-fluoxetine interaction in the novel object recognition test. Involvement of 5-HT1A receptors in the prefrontal cortex of the rats

Galanin (1-15) [GAL(1–15)] participates in mood regulation and depression. GAL(1–15) is also able to enhance the antidepressant effects induced by Fluoxetine (FLX) in the forced swimming test through interaction between GALR1-GALR2 and 5-HT1A receptors that induced changes in the binding characteristics and mRNA of the 5-HT1AR in the hippocampus.Since the medial prefrontal cortex (mPFC) is a core region for the interaction between emotional processing and cognition with a high density of 5-HT1AR and GALR1 and GALR2, we have analyzed the binding characteristics and mRNA levels of 5-HT1AR in the mPFC after GAL(1–15)-FLX administration in the rats. GAL(1–15) increased the Kd and the Bmax of the 5HT1AR agonist binding in the mPFC as well as the mRNA levels of 5-HT1AR in mPFC. Moreover, GAL(1–15) reversed the effects of memory impairment induced by FLX(10 mg/kg) in the Novel Object Recognition task. GALR2 was involved in these effects, since the specific GALR2 antagonist M871 blocked GAL(1–15) mediated actions at behavioral level. On the contrary GAL(1–15) did not reverse the effect of FLX in the Object Location Memory task.In conclusion, our results describe an interactions between GAL(1–15) and FLX in the mPFC involving interactions at the 5-HT1AR receptor level in the plasma membrane with changes at the transcriptional level with implications also at functional level. The GALR1-GALR2-5-HT1A heteroreceptor could be postulated to be used to reverse some of the adverse effects of FLX on memory processes.

Antidepressant-like effects of a novel curcumin derivative J147: Involvement of 5-HT1A receptor

Depression is a dysthymia disorder characterized by a pervasive or persistent mental disorder that causes mood, cognitive and memory deficits. J147, a curcumin analogue, increases brain derived neurotrophic factor (BDNF) levels and facilitates memory in animals. Because curcumin has the antidepressant-like activity, the present study investigated the potential antidepressant-like effects of J147 in the forced swimming test (FST) and tail suspension tests (TST) and the involvement of 5-HT receptors related to cAMP signaling. The results suggested that acute treatment of J147 at doses of 5 and 10 mg/kg via gavage markedly reduced the duration of immobility in both TST and FST, either 1 h or 3 h after treatment, respectively. It did not alter locomotor activity but influence the immobile response. The molecular biological assays showed that 5-HT1A receptor expression was significantly increased at 1 h after treatment with J147 at a dose of 10 mg/kg. In addition, pre-treatment of mice with WAY-100635 blocked the J147's effect in the FST. 5-HT1B receptor expression was not significantly increased with increasing doses of J147. The 5-HT1B receptors antagonist isamoltan partially prevented J147's effect in the FST. The levels of downstream molecular targets, cAMP, PKA, pCREB and BDNF were significantly increased 1 h after treatment with J147 at doses of 5 and 10 mg/kg. The up-regulated pCREB and BDNF levels lasted for 3 h after 10 mg/kg of J147. These findings demonstrated that J147 has antidepressant-like effects that are mediated, at least in part, by activating the 5-HT1A/cAMP/PKA/CREB/BDNF-signaling pathway.

The antipsychotic drug brexpiprazole reverses phencyclidine-induced disruptions of thalamocortical networks

Brexpiprazole (BREX), a recently approved antipsychotic drug in the US and Canada, improves cognitive dysfunction in animal models, by still largely unknown mechanisms. BREX is a partial agonist at 5‐HT1A and D2 receptors and antagonist at α1B- and α2C-adrenergic and 5-HT2A receptors all with a similar potency. The NMDA receptor antagonist phencyclidine (PCP), used as pharmacological model of schizophrenia, activates thalamocortical networks and decreases low frequency oscillations (LFO; <4 Hz). These effects are reversed by antipsychotics. Here we assessed the ability of BREX to reverse PCP-induced hyperactivity of thalamocortical circuits, and the involvement of 5-HT1A receptors in its therapeutic action. BREX reversed PCP-induced neuronal activation at a lower dose in centromedial/mediodorsal thalamic nuclei (CM/MD; 0.5mg/kg) than in pyramidal medial prefrontal cortex neurons (mPFC, 2mg/kg), perhaps due to antagonism at α1B-adrenoceptors, abundantly expressed in the thalamus. Conversely, a cumulative 0.5 mg/kg dose reversed a PCP-induced LFO decrease in mPFC but not in CM/MD. BREX reduced LFO in both areas, yet with a different dose-response, and moderately excited mPFC neurons. The latter effect was reversed by the 5-HT1A receptor antagonist WAY-100635. Thus, BREX partly antagonizes PCP-induced thalamocortical hyperactivity, differentially in mPFC versus CM/MD. This regional selectivity may be related to the differential expression of α1B-, α2C-adrenergic and 5-HT2A receptors in both regions and/or different neuronal types. Furthermore, the pro-cognitive properties of BREX may be related to the 5-HT1A receptor-mediated increase in mPFC pyramidal neuron activity. Overall, the present data provide new insight on the brain elements involved in BREX's therapeutic actions.

A serotonergic deficit in the dorsal periaqueductal gray matter may underpin enhanced panic-like behavior in diabetic rats.

It is known that diabetic (DBT) animals present dysregulation on the serotonergic system in several brain areas associated with anxiety-like responses. The aim of this study was to investigate the involvement of 5-HT1A receptors on dorsal periaqueductal gray (dPAG) in the behavioral response related to panic disorder in type-1 DBT animals. For this, the escape response by electric stimulation (ES) of dPAG in DBT and normoglycemic (NGL) animals was assessed. Both NGL and DBT animals were exposed to an open-field test (OFT) 28 days after DBT confirmation. The current threshold to induce escape behavior in DBT animals was reduced compared with NGL animals. No impairment in locomotor activity was observed when DBT animals were compared with NGL animals. An intra-dPAG injection of the 5-HT1A receptor agonist (±)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) increased the [INCREMENT] threshold in both DBT and NGL, suggesting a panicolytic-like effect. DBT animals presented a more pronounced panicolytic-like response compared with NGL as a higher [INCREMENT] threshold was observed after 8-OH-DPAT treatment, which could be a consequence of the increased expression of the 5-HT1A receptor in the dPAG from DBT animals. Our results are in line with the proposal that a deficiency in serotonergic modulation of the dPAG is involved in triggering the panic attack and the 5-HT1A receptors might be essential for the panicolytic-like response.

5-HT1a activation in PO/AH area induces therapeutic hypothermia in a rat model of intracerebral hemorrhage.

Therapeutic hypothermia is widely applied as a neuroprotective measure on intracerebral hemorrhage (ICH). However, several clinical trials regarding physical hypothermia encountered successive failures because of its side-effects in recent years. Increasing evidences indicate that chemical hypothermia that targets hypothalamic 5-HT1a has potential to down-regulate temperature set point without major side-effects. Thus, this study examined the efficacy and safety of 5-HT1a stimulation in PO/AH area for treating ICH rats. First, the relationship between head temperature and clinical outcomes was investigated in ICH patients and rat models, respectively. Second, the expression and distribution of 5-HT1a receptor in PO/AH area was explored by using whole-cell patch and confocal microscopy. In the meantime, the whole-cell patch was subsequently applied to investigate the involvement of 5-HT1a receptors in temperature regulation. Third, we compared the efficacy between traditional PH and 5-HT1a activation-induced hypothermia for ICH rats. Our data showed that more severe perihematomal edema (PHE) and neurological deficits was associated with increased head temperature following ICH. 5-HT1a receptor was located on warm-sensitive neurons in PO/AH area and 8-OH-DPAT (5-HT1a receptor agonist) significantly enhanced the firing rate of warm-sensitive neurons. 8-OH-DPAT treatment provided a steadier reduction in brain temperature without a withdrawal rebound, which also exhibited a superior neuroprotective effect on ICH-induced neurological dysfunction, white matter injury and BBB damage compared with physical hypothermia. These findings suggest that chemical hypothermia targeting 5-HT1a receptor in PO/AH area could act as a novel therapeutic manner against ICH, which may provide a breakthrough for therapeutic hypothermia.

Panicolytic-like effect of tramadol is mediated by opioid receptors in the dorsal periaqueductal grey

Tramadol is a synthetic opioid prescribed for the treatment of moderate to severe pain, acting as agonist of μ-opioid receptors and serotonin (5-HT) and noradrenaline (NE) reuptake inhibitor. This study evaluated the effects of tramadol in rats submitted to the elevated T-maze (ETM), an animal model that evaluates behavioural parameters such as anxiety and panic. Male Wistar rats were intraperitoneally (i.p.) treated acutely with tramadol (16 and 32mg/kg) and were submitted to the ETM. Tramadol (32mg/kg) promoted a panicolytic-like effect. Considering that dorsal periaqueductal grey (dPAG) is the main brain structure related to the pathophysiology of panic disorder (PD), this study also evaluated the participation of 5-HT and opioid receptors located in the dPAG in the panicolytic-like effect of tramadol. Seven days after stereotaxic surgery for implantation of a cannula in the dPAG, the animals were submitted to the test. To assess the involvement of 5-HT1A receptors on the effect of tramadol, we combined the 5-HT1A receptor antagonist, WAY100635 (0.37nmol), microinjected intra-dPAG, 10min prior to the administration of tramadol (32mg/kg, i.p.). WAY100635 did not block the panicolytic-like effect of tramadol. We also associated the non-selective opioid receptor antagonist, naloxone, systemically (1mg/kg, i.p.) or intra-dPAG (0.5nmol) administered 10min prior to tramadol (32mg/kg, i.p.). Naloxone blocked the panicolytic-like effect of tramadol in both routes of administrations, showing that tramadol modulates acute panic defensive behaviours through its interaction with opioid receptors located in the dPAG.

Blunted 5-HT1A receptor-mediated responses and antidepressant-like behavior in mice lacking the GABAB1a but not GABAB1b subunit isoforms.

There is accumulating evidence for a role of GABAB receptors in depression. GABAB receptors are heterodimers of GABAB1 and GABAB2 receptor subunits. The predominant GABAB1 subunit isoforms are GABAB1a and GABAB1b. GABAB1 isoforms in mice differentially influence cognition, conditioned fear, and susceptibility to stress, yet their influence in tests of antidepressant-like activity has not been fully investigated. Given the interactions between GABAB receptors and the serotonergic system and the involvement of 5-HT1A receptors (5-HT1AR) in antidepressant action, we sought to evaluate 5-HT1AR function in GABAB1a-/- and GABAB1b-/- mice. GABAB1a-/- and GABAB1b-/- mice were assessed in the forced swim test (FST), and body temperature and hypothalamic-pituitary-adrenal (HPA) responses to the 5-HT1AR agonist 8-OH-DPAT were determined. Brain 5-HT1AR expression was assessed by [3H]-MPPF and [3H]-8-OH-DPAT autoradiography and 5-HT1AR G-protein coupling by [35S]GTP-γ-S autoradiography. As previously described, GABAB1a-/- mice showed an antidepressant-like profile in the FST. GABAB1a-/- mice also demonstrated profoundly blunted hypothermic and motoric responses to 8-OH-DPAT. Furthermore, 8-OH-DPAT-induced corticosterone and adrenocorticotropic hormone (ACTH) release were both attenuated in GABAB1a-/- mice. Interestingly, [3H]-MPPF and [3H]-8-OH-DPAT binding was largely unaffected by genotype. [35S]GTP-γ-S autoradiography suggested that altered 5-HT1AR G-protein coupling only partially contributes to the functional presynaptic 5-HT1AR desensitization, and not at all to the blunted postsynaptic 5-HT1AR-mediated responses, seen in GABAB1a-/- mice. These data demonstrate distinct functional links between 5-HT1ARs and the GABAB1a subunit isoform and suggest that the GABAB1a isoform may be implicated in the antidepressant-like effects of GABAB receptor antagonists and in neurobiological mechanisms underlying depression.

5-HT1A receptor: Role in the regulation of different types of behavior

Serotonin, a brain neurotransmitter, acting via 14 types of serotonin (5-HT) receptors regulates different forms of both normal and pathological behavior. All 5-HT receptors (except for 5-HT3 representing an ion channel (ionotropic receptor)) belong to a superfamily of metabotropic receptors coupled with G-proteins. Each receptoris characterized by a unique gene, spectrum of affinity to different agonists and antagonists, specific distribution in the brain, and a set of controlled functions. Among this diversity of 5-HT receptors, the evolutionarily most ancient 5-HT1A receptor is of a special interest since it plays a key role in autoregulating of the brain 5-HT system. This role of 5-HT1A receptors is caused by the peculiarities of their localization (pre- or postsynaptically on 5-HT neurons), depending on which they can exert the opposite effect on the functional activity of the 5-HT system. The review is devoted to the data of the literature and the results obtained by the authors about the factors regulating the expression and functional activity of 5-HT1A receptors and their influence on behavior. The structure of the 5-HT1A receptor gene was described; and the latest data on the posttranslational regulation of the activity of 5-HT1A receptors and interaction of 5-HT receptors were given. Special attention was paid to the role of the 5-HT1A receptor’s heterodimerization with the 5-HT7 serotonin receptor and the functional inactivation of the 5-HT1A receptor. The involvement of 5-HT1A receptors in regulation of aggressive behavior, catalepsy, anxiety, depression, and unique natural adaptation (hibernation) was demonstrated. Special attention was paid to the involvement of these receptors in regulation of (1)—fear-induced defensive aggression the base of thedomestication process; (2) intermale aggression resulting in the establishment of a dominant–subordinant relationship in the animal community and underlying human asocial behavior; and (3) the mechanisms of depression and the effect of clinically efficient antidepressants of the serotonin reuptake inhibitors group. The role of 5-HT1A/5-HT7 heterodimerization in the mechanism of the antidepressants effect was hypothesized.

Neurochemical and behavioral studies on the 5-HT1A-dependent antipsychotic action of the mGlu4 receptor agonist LSP4-2022

LSP4-2022 is a novel, orthosteric agonist of mGlu4 receptor that induces antipsychotic-like activity in animal studies. In the present study, the involvement of 5-HT1A receptors in LSP4-2022-induced antipsychotic actions and the neurochemical background of that interaction were investigated. In several behavioral tests the actions of effective doses of the compound (0.5–2 mg/kg) were antagonized via the administration of the 5-HT1A antagonist WAY100635 (0.1 mg/kg). The co-administration of sub-effective dose of the 5-HT1A agonist (R)-(S)-8-OH-DPAT (0.01 mg/kg) intensified the activity of ineffective doses of LSP4-2022, having no influence on the efficacy of the active doses. The co-administration of effective doses of both compounds did not intensify each other's action.In the microdialysis in vivo tests, MK-801 (0.6 mg/kg) induced an enhancement of the release of dopamine, serotonin, glutamate and GABA in the prefrontal cortex. Administration of LSP4-2022 (2 mg/kg) abolished this MK-801-induced effect on neurotransmitter release. Co-administration with WAY100635 (0.1 mg/kg), a 5-HT1A antagonist, completely (dopamine, serotonin) or partially (glutamate, GABA) counteracted this LSP4-2022-induced effect. Subsequently, the patch-clamp recordings of spontaneous EPSCs were performed. sEPSCs were evoked in slices from the mouse prefrontal cortex by DOI (10 μM). LSP4-2022 (2.5; 5 and 10 μm) reversed DOI-induced changes in both the frequency and amplitude of the sEPSCs, but the more robust effect on the frequency was observed. The administration of WAY100635 had no effect on the LSP4-2022-induced effects on sEPSCs, indicating that the mGlu4-5-HT1A interaction does not occur via single-neuron signaling but involves neuronal circuits that regulate neurotransmitter release.This article is part of the Special Issue entitled ‘Metabotropic Glutamate Receptors, 5 years on’.

Nucleus incertus contributes to an anxiogenic effect of buspirone in rats: Involvement of 5-HT1A receptors

The nucleus incertus (NI), a brainstem structure with diverse anatomical connections, is implicated in anxiety, arousal, hippocampal theta modulation, and stress responses. It expresses a variety of neurotransmitters, neuropeptides and receptors such as 5-HT1A, D2 and CRF1 receptors. We hypothesized that the NI may play a role in the neuropharmacology of buspirone, a clinical anxiolytic which is a 5-HT1A receptor partial agonist and a D2 receptor antagonist. Several preclinical studies have reported a biphasic anxiety-modulating effect of buspirone but the precise mechanism and structures underlying this effect are not well-understood. The present study implicates the NI in the anxiogenic effects of a high dose of buspirone. Systemic buspirone (3 mg/kg) induced anxiogenic effects in elevated plus maze, light-dark box and open field exploration paradigms in rats and strongly activated the NI, as reflected by c-Fos expression. This anxiogenic effect was reproduced by direct infusion of buspirone (5 μg) into the NI, but was abolished in NI-CRF-saporin-lesioned rats, indicating that the NI is present in neural circuits driving anxiogenic behaviour. Pharmacological studies with NAD 299, a selective 5-HT1A antagonist, or quinpirole, a D2/D3 agonist, were conducted to examine the receptor system in the NI involved in this anxiogenic effect. Opposing the 5-HT1A agonism but not the D2 antagonism of buspirone in the NI attenuated the anxiogenic effects of systemic buspirone. In conclusion, 5-HT1A receptors in the NI contribute to the anxiogenic effect of an acute high dose of buspirone in rats and may be functionally relevant to physiological anxiety.

Oleanolic acid acrylate elicits antidepressant-like effect mediated by 5-HT1A receptor.

The development of new drugs for the treatment of depression is strategic to achieving clinical needs of patients. This study evaluates antidepressant-like effect and neural mechanisms of four oleanolic acid derivatives i.e. acrylate (D1), methacrylate (D2), methyl fumarate (D3) and ethyl fumarate (D4). All derivatives were obtained by simple one-step esterification of oleanolic acid prior to pharmacological screening in the forced swimming (FS) and open field (OF) tests. Pharmacological tools like α-methyl-p-tyrosine (AMPT, catecholamine depletor), p-chlorophenylalanine (serotonin depletor), prazosin (PRAZ, selective α1-receptor antagonist), WAY-100635 (selective serotonin 5-HT1A receptor antagonist) as well as monoamine oxidase (MAO) and functional binding assays were conducted to investigate possible neural mechanisms. In the FS test, D1 showed the most promising antidepressant-like effect without eliciting locomotor incoordination. Unlike group of mice pretreated with AMPT 100 mg/kg, PCPA 100 mg/kg or PRAZ 1 mg/kg, the effect of D1 was attenuated by WAY-100635 0.3 mg/kg pretreatment. D1 demonstrated moderate inhibition of MAO-A (IC50 = 48.848 ± 1.935 μM), potency (pEC50 = 6.1 ± 0.1) and intrinsic activity (Emax = 26 ± 2.0%) on 5-HT1A receptor. In conclusion, our findings showed antidepressant-like effect of D1 and possible involvement of 5-HT1A receptor.

Antidepressant-like effect of Tabernaemontana catharinensis hydroalcoholic extract in mice: Evidence of the involvement of 5-HT1A receptors.

The Tabernaemontana catharinensis shrub belongs to the Apocynaceae family and has been shown to present several pharmacological effects in studies that used ethanolic or aqueous extracts of the plant. The present study investigated the possible antidepressant activity of Tabernaemontana catharinensis hydroalcoholic extract in the forced swim test in mice. The mechanisms involved in this antidepressant-like effect were also assessed. Tabernaemontana catharinensis extract (1,000 mg/kg, p.o.) decreased immobility time in the forced swim test after acute and chronic treatment. The antiimmobility effect of Tabernaemontana catharinensis extract was not prevented by pretreatment with the 2-adrenoceptor antagonist yohimbine (1 mg/kg, i.p.) or dopamine D1 receptor antagonist SCH 23390 (0.05 mg/kg, s.c.). Conversely, pretreatment with the serotonin 5-hydroxytryptamine-1A (5-HT1A) receptor antagonist NAN-190 (.5 mg/kg, i.p.) completely blocked the antidepressant-like effect of Tabernaemontana catharinensis in the forced swim test. These effects may depend on flavonones, flavononols, xanthones, flavones, and tannins in Tabernaemontana catharinensis .W e hypothesize that these compounds are responsible for the antidepressant-like action of this plant, with involvement of the monoaminergic system. In conclusion, Tabernaemontana catharinensis produces an antidepressant-like effect in the forced swim test.

Asenapine Effects On Peroxidation and Calcium Movements in HL-1 Cells

Introduction Bipolar patients are at higher risk for cardiovascular morbidity and mortality than their counterparts in the general population. In a recent in vitro study, Asenapine, a new antipsychotic for the treatment of mania/mixed mania, was found to keep physiological endothelial function by activation of eNOS-related NO release and to protect endothelial cells against peroxidation by interference with mitochondria, apoptosis and cell survival. Objective To examine the cardiac protective effects elicited by Asenapine against peroxidation and on the Ca2+ movements. Methods In HL-1 that had undergone oxidative stress by 20 min hydrogen peroxide the effects of 30 min pre-treatment with Asenapine on survival and proliferation will be examined. In Fura-2AM loaded HL-1 we will next analyze the effects of Asenapine on Ca2+ movements and the related involvement of cAMP/PKA and PLC pathways, CaMKII, L and T type Ca2+ channels and 5HT1A receptors. The role of ‘capacitative” Ca2+ entry, plasma-membrane Ca2+ pump inhibitor (PMCA) and Na+/Ca2+ exchanger will be analyzed. Changes of membrane potential caused by interference with K+ channels will be examined, as well. Results We expect to find a proliferative and anti-peroxidative effect of Asenapine in HL-1 cells. Asenapine could also affect Ca2+ movements through cAMP/PKA and PLC-dependent signalling and the involvement of 5HT1A receptors. The effects of Asenapine could also be related to changes of plasma membrane by interference with K+ channels and the modulation of PMCA activity and Na+/Ca2+ exchanger. Conclusions We expect to further confirm the protective effect of Asenapine against peroxidative injuries. Implications will be discussed

P.1.g.049 Disruption of MEK–ERK activation in brain during midazolam-induced sleep in mice

Excessive activation of non-NMDA receptors, AMPA and kainate, contributes to neuronal degeneration in acute and progressive pathologies, possibly including schizophrenia. Because 5-HT1A receptor agonists have neuroprotective properties (e.g., against NMDA-induced neurotoxicity), we compared the effects of the antipsychotics, clozapine, ziprasidone and aripiprazole, that are partial agonists at 5-HT1A receptor, with those of haloperidol, which is devoid of 5-HT1A agonist properties, on kainic acid (KA)-induced striatal lesion volumes, in C57Bl/6N mice. The involvement of 5-HT1A receptors was determined by antagonist studies with WAY100635, and data were compared with those obtained using the potent and high efficacy 5-HT1A receptor agonist, F13714. Intra-striatal KA lesioning and measurement of lesion volumes using cresyl violet staining were carried out at 48 h after surgery. F13714, antipsychotics or vehicle were administered ip twice, 30 min before and 3 1/2 h after KA injection. WAY100635 (0.63 mg/kg) or vehicle were given sc 30 min before each drug injection. Clozapine (2 × 10 mg/kg), ziprasidone (2 × 20 mg/kg) and aripiprazole (2 × 10 mg/kg) decreased lesion volume by 61%, 59% and 73%, respectively. WAY100635 antagonized the effect of ziprasidone and of aripiprazole but only slightly attenuated that of clozapine. In contrast, haloperidol (2 × 0.16 mg/kg) did not affect KA-induced lesion volume. F13714 dose-dependently decreased lesion volume. The 61% decrease of lesion volume obtained with F13714 (2 × 0.63 mg/kg) was antagonized by WAY100635. WAY100635 alone did not affect lesion volume. These results show that 5-HT1A receptor activation protects against KA-induced striatal lesions and indicate that some atypical antipsychotic agents with 5-HT1A agonist properties may protect against excitotoxic injury, in vivo.