Selective activation of metabotropic G-protein-coupled glutamate 7 receptor elicits anxiolytic-like effects in mice by modulating GABAergic neurotransmission

We describe the anxiolytic-like effects of the first, selective metabotropic G-protein-coupled glutamate 7 (mGlu7) receptor agonist, N,N'-dibenzyhydryl-ethane-1,2-diamine dihydrochloride (AMN082), as measured in the modified stress-induced hyperthermia (SIH) and the four-plate tests. Administration of AMN082 (3-6 mg/kg intraperitoneally) to Swiss mice produced anxiolytic-like effects in the modified SIH and four-plate tests. Moreover, it was ineffective as an anxiolytic in the SIH test in mGlu7 receptor knockout mice as compared with wild-type C57BL/6J littermate controls. In contrast, diazepam (1.25-5 mg/kg) significantly reduced SIH in both the wild-type and knockout animals. The anxiolytic-like effect of AMN082 in the SIH paradigm was abolished by pretreatment with flumazenil (10 mg/kg intraperitoneally). This indicates an involvement of gamma-aminobutyric acid-ergic neurotransmission in AMN's anxiolytic actions. The results indicate that activation of the mGlu7 receptor produces anxiolytic-like effects via the modulation of the gamma-aminobutyric acid system.     

GABAA-benzodiazepine receptor complex ligands and stress-induced hyperthermia in singly housed mice

Stress-induced hyperthermia (SIH) in singly housed mice, in which the rectal temperature of a mouse is measured twice with a 10-min interval, enables to study the effects of a drug on the basal (T1) and on the stress-enhanced temperature (T2), 10 min later, using the rectal procedure as stressor. SIH (T2-T1) reflects a stress-induced phenomenon sensitive to stress- or anxiety-modifying effects of drugs. Several benzodiazepine agonists (diazepam, chlordiazepoxide, oxazepam and alprazolam) dose-dependently antagonized SIH either in NMRI mice from two different breeders or in BALB/c mice. No major differences in the sensitivity for any of the drugs tested were found between strains or between substrains from different breeders. The selective BZ1 receptor agonists alpidem and zolpidem only at relatively high doses antagonized SIH, whereas flumazenil, FG7142, pentylenetetrazol and phenobarbital did not affect SIH. Alcohol antagonized SIH, and the effects of diazepam could be antagonized by flumazenil. The findings that full BZ receptor agonists have anxiolytic-like effects in the singly housed SIH paradigm are comparable to those previously found in the group-housed version. The singly housed SIH is proposed as a simple and reliable screen for detecting anxiety-like properties of drugs that is valid in every mouse strain tested so far.     

Anxiolytic-Like Effect of baicalin and its additivity with other anxiolytics

Baicalin, a naturally occurring flavonoid, was previously reported to exert anxiolytic-like effects in the Vogel conflict test. In the present study, the anxiolytic effects of baicalin alone and in combination with other anxiolytics were tested in mice using the elevated plus-maze (EPM). Baicalin treatment (7.5 - 30 mg/kg) significantly increased entries into and time spent in open arms, indicative of an anxiolytic-like effect. Motor-depressive and myorelaxant side effects commonly associated with anxiolytics were not observed with baicalin at effective anxiolytic doses in the hole-board and horizontal wire tests, respectively. Co-administration of baicalin (3.75 mg/kg) with dl-tetrahydropalmatine ( dl-THP; 0.25 mg/kg), an anxiolytic-hypnotic alkaloid, both at sub-effective doses, induced an additive effect resulting in considerable anxiolysis. Similarly, an additive anxiolytic-like effect was observed with baicalin (3.75 mg/kg) and diazepam (DZ; 0.5 mg/kg). Results obtained from this study demonstrate the potential of baicalin as a candidate anxiolytic and its possible application in multidrug therapy. Abbreviations. BZS:benzodiazepine-binding site EPM:elevated plus-maze DZ:diazepam GABA (A):type A gamma-aminobutyric acid dl-THP: dl-tetrahydropalmatine.     

Behavioural phenotypic characterization of CD-1 mice lacking the neuropeptide S receptor

Neuropeptide S (NPS) is the endogenous ligand of a previously orphan receptor now named NPSR. In the brain NPS regulates several biological functions including anxiety, arousal, locomotion, food intake, learning and memory, pain and drug abuse. Mice lacking the NPSR gene (NPSR(-/-)) represent an useful tool to investigate the neurobiology of the NPS/NPSR system. NPSR(-/-) mice have been generated in a 129S6/SvEv genetic background. In the present study we generated CD-1 congenic NPSR(+/+) and NPSR(-/-) mice and investigated their phenotype and sensitivity to NPS in various behavioural assays. The phenotype analysis revealed no locomotor differences between NPSR(+/+) and NPSR(-/-) mice. The behaviour of NPSR(+/+) and NPSR(-/-) mice in the righting reflex test was superimposable. No differences were recorded between the two genotypes in the elevated plus maze, open field and stress-induced hyperthermia tests, with the exception of rearing behaviour that was reduced in knockout animals. Moreover the behaviour of NPSR(+/+) and NPSR(-/-) mice in the forced swimming, novel object recognition and formalin assays was similar. The stimulatory effects of NPS in the locomotor activity test and its anxiolytic-like actions in the elevated plus maze and open field assays were evident in NPSR(+/+) but not NPSR(-/-) animals. In conclusion, the present study indicates that the NPS/NPSR system does not tonically control locomotion, sensitivity to diazepam, anxiety, depressive-like behaviours, memory and pain transmission in mice. Furthermore our results clearly show that the product of the NPSR gene represents the mandatory protein for all the NPS biological effects so far described.     

Behavioral effects of saredutant, a tachykinin NK2 receptor antagonist, in experimental models of mood disorders under basal and stress-related conditions

The present study was made to investigate the role of tachykinin NK2 receptors in the expression of stress-related behaviors in animals. Under basal conditions, intraperitoneal (i.p.) administration of the selective tachykinin NK2 receptor antagonist, saredutant (1 and 3 mg/kg) or diazepam (1 mg/kg) exerted anxiolytic-like effects in rodents, as they reduced grooming score of Wistar male rats tested in the novelty-induced grooming sampling test (NGT) and increased percentage of time and entries in open arms of Swiss male mice tested in the elevated plus maze (EPM) test. After previous exposure to stress-related conditions, as induced by a 2-min forced swim made 5 min prior to the EPM test, saredutant but not diazepam, exhibited anxiolytic-like effects in mice. To study the antidepressant-like activity of tachykinin NK2 receptor antagonist under basal conditions, different groups of rats were injected i.p. with saredutant (2.5, 5 and 10 mg/kg) or the tricyclic antidepressant, clomipramine (50 mg/kg) and tested in the forced swim test (FST), a widely used antidepressant-responsive test. The influence of stress-related conditions was studied in rats subjected to electric foot-shocks (1 mA, 1 s) 24, 5 and 1 h prior to FST, after drugs injection. In the FST, clomipramine decreased the immobility time only under basal conditions, but not after application of acute foot-shocks. To the contrary, saredutant-treated rats also exhibited more active behavior in FST after previous exposure to stressors. These results give further support to the hypothesis that tachykinin NK2 receptors may be a therapeutic target for pharmacological treatment of stress-related diseases, such as anxiety and depression.     

Anxiolytic-like activity of the mGLU2/3 receptor agonist LY354740 in the elevated plus maze test is disrupted in metabotropic glutamate receptor 2 and 3 knock-out mice

Rationale (1S,2S,5R,6S)-2-Aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY354740) is a potent and selective agonist for group II metabotropic glutamate (mGlu2 and mGlu3) receptors, with anxiolytic-like activity in animal and human models, and efficacy in anxiety patients. However, the lack of mGlu2 or mGlu3 receptor specific agonists has prevented in vivo characterization of individual functions of these two receptors in mediating the anxiolytic-like effects of LY354740.Objective To utilize mGlu2 receptor and mGlu3 receptor knockout animals and the mGlu2/3 selective antagonist (2S,1S,2S)-2-(9-xanthylmethyl)-2-(2-carboxycyclopropyl)glycine (LY341495) to further investigate the roles of mGlu2 and mGlu3 receptors in mediating the anxiolytic-like actions of LY354740 in a mouse model of anxiety [elevated plus maze (EPM) test].Methods To confirm that mGlu2/3 receptors are responsible for anxiolytic-like activity in the EPM under these test conditions, mice were pretreated with LY341495 at 30 min prior to s.c. administered LY354740. Subsequently, saline vehicle or LY354740 was administered (s.c.) 30 min before the EPM testing in wild-type, mGlu2 receptor knockout, and mGlu3 receptor knockout mice.Results LY354740 reduced in a dose-dependent manner anxiety-related behavior on the EPM in wild-type mice with a maximally effective dose of 10–20 mg/kg s.c. Pretreatment with LY341495 potently prevented the anxiolytic-like effects of LY354740 (20 mg/kg, s.c.) in mice. Although the mGlu2 receptor knockout and mGlu3 receptor knockout mice were grossly normal, the anxiolytic-like activity of LY354740 (20 mg/kg, s.c.) was not evident in either mGlu2 or mGlu3 receptor knockout mice, when compared to their wild-type controls.Conclusions The activation of both mGlu2 and mGlu3 receptors by LY354740 appears to be required for anxiolytic-like activity in the EPM test in mice. These studies serve as a foundation for additional studies on underlying circuits, brain structures, and receptor subtypes involved in the anxiolytic-like actions of mGlu receptor active agents, and the design of future drugs for anxiety disorders in humans.     

Effects of rolipram on the elevated plus-maze test in rats: a preliminary study.

The objective of the present study was to assess the behavioural effects of rolipram, a specific cAMP phosphodiesterase (PDE4) inhibitor, in the elevated plus-maze (EPM) test in rats. Results showed that rolipram at the highest dose tested (0.1 mg/kg) increased the percentage of both time spent and entries into open arms, although a decrease of locomotor activity in the EPM test was also observed. In contrast, diazepam (3.0 mg/kg) exhibited the typical profile of an anxiolytic in the EPM test, increasing the percentage of time spent and entries into open arms as well as locomotor activity. A posterior statistical analysis, however, established that the effects of both rolipram and diazepam on parameters denoting anxiolytic-like activity were statistically independent from those reflecting locomotor activity reduction. Furthermore, the effects of both rolipram and diazepam were shown to be distinct from those exhibited by tricyclic antidepressant imipramine which did not show any anxiolytic-like effects in the EPM test, although a reduction of locomotor activity was also detected. Although these preliminary results suggest that rolipram may have some anxiolytic-like properties on the EPM test in rats, such an interpretation should be taken cautiously due to the observed effects on locomotor activity, which could complicate the interpretation of results from rolipram and other PDE4 inhibitors in the current test and in other anxiety animal models.     

Factors triggering abolishment of benzodiazepines effects in the Four-Plate Test--retest in mice.

Abolishment of anxiolytic-like effects of diazepam occurs during re-exposure to some animal tests of anxiety. We investigated the loss of anxiolytic-like effects of diazepam during Trial 2 on previously undrugged mice, namely one-trial tolerance (OTT). Swiss mice were subjected to 1) Four-Plate Test (FPT) without punishments in Trial 1 or 2) FPT without punishments in both Trials or 3) FPT with spatial modifications in Trial 1 or 4) Elevated Plus Maze (EPM), then 24 h later to FPT, with saline, diazepam (1 mg/kg) or DOI (1 mg/kg). Removing punishments in Trial 1 does not counteract the effect reduction of diazepam in Trial 2, but spatial modifications of the aversive environment. Previous exposure to EPM does not trigger a loss of efficacy of diazepam in FPT. Electric punishments do not trigger OTT to benzodiazepines; whilst knowledge of the environment seems to be responsible for this phenomenon. FPT may be useful to study OTT because punishments potentate OTT in this model of anxiety.     

The neurokinin NK2 antagonist, saredutant, ameliorates stress-induced conditions without impairing cognition

The current work extends our previous findings in stress-related disorders, but also addresses the impact of a neurokinin-2 (NK2) antagonist on cognition. Besides efficacy in mood disorders, an NK2 antagonist may have the potential to lack the disinhibitory components and adverse side effects associated with existing clinical treatments. Saredutant (3-30 mg/kg, per os, p.o.) was tested for anxiolytic-like potential in three mouse models: holeboard, stress-induced hyperthermia (SIH) and four-plate. In the holeboard model saredutant (30 mg/kg) showed a trend to increase head dipping without affecting general activity. In the SIH model, saredutant demonstrated a significant reduction in stress-induced temperature at 30 mg/kg, while the number of punished crossings in the four-plate was increased at all doses tested (3-30 mg/kg). While chlordiazepoxide (CDP) demonstrated anxiolytic-like effects in these models, the adverse side effects of benzodiazepines, such as sedation, disinhibition and cognitive deficits are well-documented. Saredutant produced no detrimental effect in three models of cognition: Morris Water Maze (MWM) in rats, spontaneous alternation in a Y-maze in mice and novel objection recognition in mice. In contrast, the benzodiazepine, diazepam (DZM), produced cognitive impairments. NK2 receptor antagonists like saredutant may therefore yield beneficial effects for mood disorders without the adverse effects of current treatments.     

Pharmacology of neuropeptide S in mice: therapeutic relevance to anxiety disorders

Rationale Neuropeptide S (NPS) and its receptor (NPSR) comprise a recently deorphaned G protein-coupled receptor system. Recent reports implicate NPS in the mediation of anxiolytic-like activity in rodents. Objectives To extend the characterization of NPS, the present studies examined the in vitro pharmacology of mouse NPSR and the in vivo pharmacology of NPS in three preclinical mouse models predictive of anxiolytic action: the four-plate test (FPT), elevated zero maze (EZM), and stress-induced hyperthermia (SIH). The ability of NPS to produce antidepressant-like effects in the tail suspension test (TST) was also investigated. Results In vitro, mouse NPS_1–20 (mNPS_1–20) and the C-terminal glutamine-truncated mouse NPS_1–19 bound mNPSR with high affinity (K _i  = 0.203 ± 0.060, 0.635 ± 0.141 nM, respectively) and potently activated intracellular calcium release (EC₅₀ = 3.73 ± 1.08, 4.10 ± 1.25 nM). NPS produced effects in vivo consistent with anxiolytic-like activity. In FPT, NPS increased punished crossings (minimal effective dose [MED]: mNPS_1–20 = 0.2 μg, mNPS_1–19 = 0.02 μg), similar to the reference anxiolytic, alprazolam (MED 0.5 μg). NPS increased the percentage of time spent in the open quadrants of EZM (MED: mNPS_1–20 = 0.1 μg, mNPS_1–19 = 1.0 μg), like the reference anxiolytic, chlordiazepoxide (MED 56 μg). In SIH, NPS attenuated stress-induced increases in body temperature similar to alprazolam but with a large potency difference between the NPS peptides (MED: mNPS_1–20 = 2.0 μg, mNPS_1–19 = 0.0002 μg) and mNPS_1–20 increased baseline temperature. Unlike fluoxetine, NPS did not effect immobility time in TST, indicating a lack of antidepressant-like activity. Conclusions These data provide an important confirmation and expansion of the anxiolytic-like effects of NPS and implicate the NPS system as a novel target for anxiolytic drug discovery.     

Anxiolytic-like effects of Gastrodia elata and its phenolic constituents in mice

The purpose of this study was to characterize the putative anxiolytic-like effects of the aqueous extract of the rhizome of Gastrodia elata along with its phenolic constituents, 4-hydroxybenzyl alcohol (HA) and 4-hyroxybenzaldehyde (HD), using an elevated plus maze (EPM) in mice. The mice were administered either the aqueous G. elata extract orally or received an intraperitoneal injection of the phenolic constituents, 1 h before the behavioral evaluation in the EPM. A single treatment of the aqueous G. elata extract significantly increased the percentage of time spent and arm entries into the open arms of the EPM versus the saline controls. Among the phenolic constituents of G. elata, HA and HD significantly increased the percentage of time spent and arm entries into the open arms of the EPM versus saline controls (p<0.05). Moreover, there were no changes in the locomotor activity and myorelaxant effects in any group compared with the saline controls. In addition, the anxiolytic-like effects of G. elata extract were blocked by both WAY 100635 (0.3 mg/kg, i.p.), a 5-HT(1A) receptor antagonist, and flumazenil (10 mg/kg, i.p.), a GABA(A) receptor antagonist. The anxiolytic-like effects of HA were inhibited by WAY 100635 and the effects of HD were antagonized by flumazenil. These results indicate that G. elata is an effective anxiolytic agent, and suggests that the anxiolytic-like effects of G. elata via the serotonergic nervous system depends on HA and those effects of G. elata via the GABAergic nervous system depends on HD.     

Antagonism of AMPA receptors produces anxiolytic-like behavior in rodents: Effects of GYKI 52466 and its novel analogues

Rationale Although emerging number of data supports the role of glutamate receptors and the potential of their antagonists in anxiety disorders, the involvement of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors in anxiety is less well characterized. Objective To evaluate the anxiolytic potential of 2,3-benzodiazepine (2,3BDZ) type AMPA receptor antagonists in various models of anxiety. Materials and methods Whole-cell currents, hippocampal field potentials, elevated plus maze (EPM), meta-chlorophenylpiperazine (mCPP)-induced anxiety model, Vogel test in rats and light–dark test (LD) in mice were used to determine AMPA/kainite receptor properties and anxiolytic-like activity of a series of 2,3BDZ-type compounds. Results The reference compound GYKI 52466 was proved active in two anxiety models in non-sedative doses: minimal effective dose (MED) was especially low in EPM (0.01 mg/kg) GYKI 53405 and GYKI 53655 showed anxiolytic-like activity in two tests (EPM and mCPP). EGIS-8332 was active in EPM and LD while EGIS-9637 showed anxiolytic-like potency in EPM, mCPP and Vogel model. EGIS-10608 was the most effective compound among 2,3BDZs tested in EPM and Vogel models (MEDs are 0.01 and 2.5 mg/kg, respectively). 2,3BDZs were active in anxiety models at doses lower than those produced sedative effects. NBQX showed anxiolytic-like activity in EPM only (3 mg/kg). Conclusions The results show that non-competitive AMPA receptor antagonists can profoundly block anxiety-like behavior in rodents independently from their motor depressant activity. However, the sedative properties at higher doses might limit their therapeutic utility as new anxiolytic drugs.     

Central nervous system activity of acute administration of isopulegol in mice

Isopulegol is a monoterpene alcohol intermediate in the preparation of (-)-menthol and it is present in the essential oils of various plants. This work presents behavioral effects of isopulegol in animal models of open field, elevated plus maze (EPM), rota rod, hole board, barbiturate-induced sleeping time, tail suspension and forced swimming tests in mice. Isopulegol was administered intraperitoneally to male mice at single doses of 25 and 50 mg/kg, while diazepam 1 or 2 mg/kg and imipramine 10 or 30 mg/kg were used as standard drugs. The results showed that, similar to diazepam (1 mg/kg), both doses of isopulegol significantly modified all the observed parameters in the EPM test, without alter the general motor activity in the open field test. In the same way, both doses of isopulegol increased the number of head dips in the hole-board test. Forced swimming and tail suspension tests showed that isopulegol (25 and 50 mg/kg) was able to induce a significant increase in the immobility time, in opposite to imipramine, a recognized antidepressant drug. There was a decrease in the sleep latency time and prolongation of the pentobarbital-induced sleeping time with both doses of Isopulegol. Different from diazepam (2 mg/kg), isopulegol (25 e 50 mg/kg) had no effect on the motor coordination of animals in the rota rod test. These results showed that isopulegol presented depressant- and anxiolytic-like effects.     

The selective serotonin (5-HT)1A receptor ligand, S15535, displays anxiolytic-like effects in the social interaction and Vogel models and suppresses dialysate levels of 5-HT in the dorsal hippocampus of freely-moving rats

RATIONALE: The benzodioxane, S15535, possesses low intrinsic activity and marked selectivity at 5-HT1A receptors, hippocampal populations of which are implicated in anxious states. OBJECTIVE: Herein, we examined its potential anxiolytic actions in relation to its influence upon extracellular levels of 5-HT in the dorsal hippocampus of freely-moving rats. Its effects were compared with those of other anxiolytic agents: the 5-HT1A agonists, buspirone and 8-hydroxy-2-(di-n-propylamino)-tetralin HBr (8-OH-DPAT), the 5-HT2C antagonist, SB206,553 and the benzodiazepine, diazepam. METHODS: Potential anxiolytic actions were evaluated in the Vogel conflict paradigm (increase in punished responses) and the social interaction (SI) test (increase in active SI) in rats. Extracellular levels of 5-HT were determined by microdialysis. RESULTS: In analogy to diazepam. S15535 increased punished responses in the Vogel test. This action was dose dependently expressed over a broad (16-fold) dose range. Buspirone and 8-OH-DPAT were likewise active, but yielded highly biphasic dose-response curves. SB206,553 was dose dependently active in this model. In the SI test, S15535 similarly mimicked the anxiolytic-like effect of diazepam and was active over a broad dose range. Buspirone and 8-OH-DPAT again showed biphasic dose-response curves, as did SB206,553. In both the Vogel and SI tests, the anxiolytic-like effects of S15535 were abolished by the selective 5-HT1A receptor antagonist, WAY100,635, which was inactive alone. S15535 exerted its anxiolytic-like effects with a more pronounced separation to motor-disruptive doses than the other drugs. Finally, S15535 suppressed dialysate levels of 5-HT in the dorsal hippocampus, an action abolished by WAY100,635. Buspirone, 8-OH-DPAT and diazepam, but not SB206,553, also reduced 5-HT levels. CONCLUSION: Likely reflecting its distinctive ability to selectively and preferentially activate pre- versus postsynaptic 5-HT1A receptors, S15535 suppresses hippocampal 5-HT release and displays marked anxiolytic-like effects over a broad dose range in the relative absence of motor perturbation.     

Anxiolytic-Like Effects of Chrysanthemum indicum Aqueous Extract in Mice: Possible Involvement of GABAA Receptors and 5-HT1A Receptors

Chrysanthemum indicum Linne is an ancient herbal medicine used to treat bone and muscle deterioration, ocular infl ammation, headache, and anxiety in Korea, China, and Japan. Furthermore, tea derived from Chrysanthemum indicum Linne has been used to treat anxiety by facilitating relaxation and curing insomnia. However, no reports exist on the anxiolytic-like effects of Chrysanthemum indicum Linne water extract (CWE) in mice. In the present study, we investigated the anxiolytic-like effects of CWE using the elevated plus-maze (EPM) test in mice. CWE, at a dose of 500 mg/kg (p.o.), signifi cantly increased the time spent in the open arms of the EPM compared to a vehicle-injected control group. Moreover, the effect of CWE (500 mg/kg) was blocked by bicuculline (a selective GABA_A receptor antagonist) and WAY 100635 (a selective 5-HT_1A receptor antagonist). Taken together, these fi ndings suggest that the anxiolytic-like effects of CWE might be mediated by the GABA_A receptor and the 5-HT_1A receptor.     

Neuropeptide S: A transmitter system in the brain regulating fear and anxiety

The recently discovered Neuropeptide S (NPS) and its cognate receptor represent a highly interesting system of neuromodulation with unique physiological effects. On one hand, NPS increases wakefulness and arousal. On the other, NPS produces anxiolytic-like effects by acutely reducing fear responses as well as modulating long-term aspects of fear memory, such as attenuation of contextual fear or enhancement of fear extinction. The main sources of NPS in the brain are a few clusters of NPS-producing neurons in the brainstem. NPS binds to a G-protein-coupled receptor that is highly conserved among vertebrates and stimulates mobilization of intracellular Ca²⁺ as well as activation of protein kinases. In synaptic circuits within the amygdala, which are important for processing of acute fear as well as formation and expression of fear memories, NPS causes increased release of the excitatory transmitter glutamate, especially in synaptic contacts to a subset of GABAergic interneurons. Polymorphisms in the human NPS receptor gene have been associated with altered sleep behavior and panic disorder. In conclusion, the NPS system displays a unique physiological profile with respect to the specificity and time course of its actions. These functions could provide interesting opportunities for both basic research and clinical applications.     

Neuropeptide S Enhances Memory During the Consolidation Phase and Interacts with Noradrenergic Systems in the Brain

Neuropeptide S (NPS) has been shown to promote arousal and anxiolytic-like effects, as well as facilitation of fear extinction. In rodents, NPS receptors (NPSR) are prominently expressed in brain structures involved in learning and memory. Here, we investigate whether exogenous or endogenous NPS signaling can modulate acquisition, consolidation, or recall of emotional, spatial, and contextual memory traces, using two common behavioral paradigms, inhibitory avoidance (IA) and novel object recognition. In the IA paradigm, immediate and delayed post-training central NPS administration dose dependently enhanced memory retention in mice, indicating that NPS may act during the consolidation phase to enhance long-term memory. In contrast, pre-training or pre-test NPS injections were ineffective, suggesting that NPS had no effect on IA memory acquisition or recall. Peripheral administration of a synthetic NPSR antagonist attenuated NPS-induced IA memory enhancement, showing pharmacological specificity. NPS also enhanced hippocampal-dependent non-aversive memory in the novel object recognition task. In contrast, NPSR knockout mice displayed deficits in IA memory, novel object recognition, and novel place or context recognition, suggesting that activity of the endogenous NPS system is required for memory formation. Blockade of adrenergic signaling by propranolol attenuated NPS-induced memory enhancement in the IA task, indicating involvement of central noradrenergic systems. These results provide evidence for a facilitatory role of NPS in long-term memory, independent of memory content, possibly by acting as a salience signal or as an arousal-promoting factor.     

Anxiolytic-like effects of MTEP, a potent and selective mGlu5 receptor agonist does not involve GABA(A) signaling

Several lines of evidence suggest a crucial involvement of glutamate in the mechanism of action of anxiolytic drugs including the involvement of group I metabotropic glutamate (mGlu) receptors. Given the recent discovery of a selective and brain penetrable mGlu5 receptor antagonists, the effect of 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-pyridine (MTEP), i.e. the most potent mGlu5 antagonist, was evaluated in established models of anxiety after single or repeated administration. We also studied if the anxiolytic effect of MTEP is mediated by mechanism involving the GABA-benzodiazepine (BZD) receptor complex. Experiments were performed on male Wistar rats or male Albino Swiss mice. The anxiolytic-like effects of MTEP were tested in the conflict drinking test and the elevated plus-maze test in rats as well as in the four-plate test in mice. MTEP (0.3-3.0 mg/kg) induced anxiolytic-like effects in the conflict drinking test (after single and repeated administration) and in the elevated plus-maze test in rats. In the four-plate test in mice, it exerted anxiolytic activity at a dose of 20 mg/kg. MTEP had no effect on the locomotor activity of animals. The anxiolytic-like effect of MTEP was not changed by BZD antagonist flumazenil. Moreover, a synergistic interaction between non-effective doses of MTEP and diazepam was observed in the conflict drinking test. These data suggest that selective mGlu5 receptor antagonists mediated anxiolysis is not dependent on GABA-ergic system and that these agents may play a role in the therapy of anxiety.     

Characterization of (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one as a positive allosteric modulator of GABAB receptors

BACKGROUND AND PURPOSE: As baclofen is active in patients with anxiety disorders, GABAB receptors have been implicated in the modulation of anxiety. To avoid the side effects of baclofen, allosteric enhancers of GABAB receptors have been studied to provide an alternative therapeutic avenue for modulation of GABAB receptors. The aim of this study was to characterize derivatives of (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one (rac-BHFF) as enhancers of GABAB receptors. EXPERIMENTAL APPROACH: Enhancing properties of rac-BHFF were assessed in the Chinese hamster ovary (CHO)-Galpha16-hGABA(B1a,2a) cells by Fluorometric Imaging Plate Reader and GTPgamma[35S]-binding assays, and in rat hippocampal slices by population spike (PS) recordings. In vivo activities of rac-BHFF were assessed using the loss of righting reflex (LRR) and stress-induced hyperthermia (SIH) models. KEY RESULTS: In GTPgamma[35S]-binding assays, 0.3 microM rac-BHFF or its pure enantiomer (+)-BHFF shifted the GABA concentration-response curve to the left, an effect that resulted in a large increase in both GABA potency (by 15.3- and 87.3-fold) and efficacy (149% and 181%), respectively. In hippocampal slices, rac-BHFF enhanced baclofen-induced inhibition of PS of CA1 pyramidal cells. In an in vivo mechanism-based model in mice, rac-BHFF increased dose-dependently the LRR induced by baclofen with a minimum effective dose of 3 mg kg(-1) p.o. rac-BHFF (100 mg kg(-1) p.o.) tested alone had no effect on LRR nor on spontaneous locomotor activity, but exhibited anxiolytic-like activity in the SIH model in mice.Conclusions and implications:rac-BHFF derivatives may serve as valuable pharmacological tools to elucidate the pathophysiological roles played by GABAB receptors in the central and peripheral nervous systems.     

Neuropeptide S attenuates neuropathological, neurochemical and behavioral changes induced by the NMDA receptor antagonist MK-801

Neuropeptide S (NPS) and its cognate receptor were reported to mediate anxiolytic-like and arousal effects. NPS receptors are predominantly expressed in the brain, especially in limbic structures, including amygdala, olfactory nucleus, subiculum and retrosplenial cortex. In contrast, the NPS precursor is expressed in only a few brainstem nuclei where it is co-expressed with various excitatory transmitters, including glutamate. The current study investigates interactions of the NPS system with glutamatergic neurotransmission. It has been suggested that dysfunctions in glutamatergic neurotransmission via N-methyl-d-aspartate (NMDA) receptors might be involved in the pathophysiology of schizophrenia since NMDA receptor antagonists, such as MK-801, have been shown to induce psychotic-like behavior in humans and animal models. Also, MK-801 is known to produce histological changes such as cytoplasmic vacuoles in retrosplenial cortex neurons where NPS receptors are highly expressed. In this study we show that NPS is able to alleviate neuropathological, neurochemical and behavioral changes produced by NMDA receptor antagonists. NPS treatment attenuated MK-801-induced vacuolization in the rat retrosplenial cortex in a dose-dependent manner that can be blocked by an NPS receptor-selective antagonist. NPS also suppressed MK-801-induced increases of extracellular acetylcholine levels in the retrosplenial cortex. In the prepulse inhibition (PPI) assay, animals pretreated with NPS recovered significantly from MK-801-induced disruption of PPI. Our study suggests that NPS may have protective effects against the neurotoxic and behavioral changes produced by NMDA receptor antagonists and that NPS receptor agonists may elicit antipsychotic effects.