Comparison of the pharmacological properties of classical and novel BZ-omega receptor ligands

Concordance and incongruence in preclinical anxiety models: Systematic review and meta-analyses

Rodent defense behavior assays have been widely used as preclinical models of anxiety to study possibly therapeutic anxiety-reducing interventions. However, some proposed anxiety-modulating factors - genes, drugs and stressors - have had discordant effects across different studies. To reconcile the effect sizes of purported anxiety factors, we conducted systematic review and meta-analyses of the literature on ten anxiety-linked interventions, as examined in the elevated plus maze, open field and light-dark box assays. Diazepam, 5-HT1A receptor gene knockout and overexpression, SERT gene knockout and overexpression, pain, restraint, social isolation, corticotropin-releasing hormone and Crhr1 were selected for review. Eight interventions had statistically significant effects on rodent anxiety, while Htr1a overexpression and Crh knockout did not. Evidence for publication bias was found in the diazepam, Htt knockout, and social isolation literatures. The Htr1a and Crhr1 results indicate a disconnect between preclinical science and clinical research. Furthermore, the meta-analytic data confirmed that genetic SERT anxiety effects were paradoxical in the context of the clinical use of SERT inhibitors to reduce anxiety.

Ethopharmacological evaluation of the rat exposure test: a prey-predator interaction test

The rat exposure test (RET) is a prey (mouse)-predator (rat) situation that activates brain defensive areas and elicits hormonal and defensive behavior in the mouse. Here, we investigated possible correlations between the spatiotemporal [time spent in protected (home chamber and tunnel) and unprotected (surface) compartments and frequency of entries into the three compartments] and ethological [e.g., duration of protected and unprotected stretched-attend postures (SAP), duration of contact with the rat's compartment] measures (Experiment 1). Secondly, we investigated the effects of systemic treatment with pro- or anti-aversive drugs on the behavior that emerged from the factor analysis (Experiment 2). The effects of chronic (21 days) imipramine and fluoxetine on defensive behavior were also investigated (Experiment 3). Exp. 1 revealed that the time in the protected compartment, protected SAP and rat contacts loaded on factor 1 (defensive behavior), while the total entries and unprotected SAP loaded on factor 2 (locomotor activity). Exp. 2 showed that alprazolam (but not diazepam) selectively changed the defensive factor. Caffeine produced a mild proaversive-like effect, whereas yohimbine only decreased locomotor activity (total entries). Fluoxetine (but not imipramine) produced a weak proaversive-like effect. 5-HT(1A)/5-HT(2) receptor ligands did not change any behavioral measure. In Exp. 3, chronic fluoxetine (but not imipramine) attenuated the defensive behavior factor without changing locomotion. Given that the defensive factor was sensitive to drugs known to attenuate (alprazolam and chronic fluoxetine) and induce (caffeine) panic attack, we suggest the RET as a useful test to assess the effects of panicolytic and panicogenic drugs.

Stabilization study on a wet-granule tableting method for a compression-sensitive benzodiazepine receptor agonist

SX-3228, 6-benzyl-3-(5-methoxy-1,3,4-oxadiazol-2-yl)-5,6,7,8-tetrahydro-1,6-naphthyridin-2(1H)-one, is a newly-synthesized benzodiazepine receptor agonist intended to be developed as a tablet preparation. This compound, however, becomes chemically unstable due to decreased crystallinity when it undergoes mechanical treatments such as grinding and compression. A wet-granule tableting method, where wet granules are compressed before being dried, was therefore investigated as it has the advantage of producing tablets of sufficient hardness at quite low compression pressures. The results of the stability testing showed that the drug substance was chemically considerably more stable in wet-granule compression tablets compared to conventional tablets. Furthermore, the drug substance was found to be relatively chemically stable in wet-granule compression tablets even when high compression pressure was used and the effect of this pressure was small. After investigating the reason for this excellent stability, it became evident that near-isotropic pressure was exerted on the crystals of the drug substance because almost all the empty spaces in the tablets were occupied with water during the wet-granule compression process. Decreases in crystallinity of the drug substance were thus small, making the drug substance chemically stable in the wet-granule compression tablets. We believe that this novel approach could be useful for many other compounds that are destabilized by mechanical treatments.

Effects of compression and grinding on chemical stability of a benzodiazepine receptor agonist

SX-3228, 6-benzyl-3-(5-methoxy-1,3,4-oxadiazol-2-yl)-5,6,7,8-tetrahydro-1,6-naphthyridin-2(1H)-one, is a newly synthesized benzodiazepine receptor agonist intended to be developed as a tablet preparation. However, it was found that the drug substance was remarkably chemically unstable in tablet form compared to the powder mixture for tableting. Chemical destabilization due to compression also occurred in the drug substance alone. After investigating the cause of the destabilization, powder X-ray diffraction analysis showed that the crystallinity of the drug substance decreased depending on the extent of mechanical treatments such as compression and grinding. In thermal analysis it became evident that the exothermic peaks due to degradation clearly broadened and shifted toward lower temperatures by these mechanical treatments. It was then revealed that the degradation temperature decreased and the amount of degradation products after storage increased with decreasing crystallinity, even though there was little change in the amount of degradation products shortly after mechanical treatments. These results demonstrated that the drug substance became chemically unstable with decreasing crystallinity. It was proved that chemical instability of the drug substance in the tablet preparation was due to decreasing crystallinity caused by compression. It would therefore be difficult to produce chemically stable tablets containing this compound using a conventional manufacturing process. Tablets for this compound should be prepared without mechanical treatments such as compression and grinding.

Inhibition of the NMDA receptor/Nitric Oxide pathway in the dorsolateral periaqueductal gray causes anxiolytic-like effects in rats submitted to the Vogel conflict test

Background

Several studies had demonstrated the involvement of the dorsolateral portion of periaqueductal grey matter (dlPAG) in defensive responses. This region contains a significant number of neurons containing the enzyme nitric oxide synthase (NOS) and previous studies showed that non-selective NOS inhibition or glutamate NMDA-receptor antagonism in the dlPAG caused anxiolytic-like effects in the elevated plus maze.

Methods

In the present study we verified if the NMDA/NO pathway in the dlPAG would also involve in the behavioral suppression observed in rats submitted to the Vogel conflict test. In addition, the involvement of this pathway was investigated by using a selective nNOS inhibitor, Nω-propyl-L-arginine (N-Propyl, 0.08 nmol/200 nL), a NO scavenger, carboxy-PTIO (c-PTIO, 2 nmol/200 nL) and a specific NMDA receptor antagonist, LY235959 (4 nmol/200 nL).

Results

Intra-dlPAG microinjection of these drugs increased the number of punished licks without changing the number of unpunished licks or nociceptive threshold, as measure by the tail flick test.

Conclusion

The results indicate that activation of NMDA receptors and increased production of NO in the dlPAG are involved in the anxiety behavior displayed by rats in the VCT.

Contribution of alpha1 subunit-containing gamma-aminobutyric acidA (GABAA) receptors to motor-impairing effects of benzodiazepines in squirrel monkeys

RATIONALE

Benzodiazepines (BZs) are effective anxiolytics and hypnotics, but their use is limited by unwanted side effects, such as motor impairment.

OBJECTIVES

To assess the contribution of alpha1 subunit-containing gamma-aminobutyric acid(A) (GABA(A)) receptor subtypes to the motor-impairing effects of BZs, the present study evaluated two observable measures of motor coordination (balance on a pole, resistance to hind-limb flexion) engendered by nonselective and selective BZ-site agonists in squirrel monkeys.

MATERIALS AND METHODS

Multiple doses of nonselective BZs (triazolam, alprazolam, diazepam, and chlordiazepoxide) and alpha1 subunit-preferring agonists (zolpidem and zaleplon) were administered to adult male squirrel monkeys (N = 4-6), and experimenters rated the monkey's ability to balance on a horizontal pole ("ataxic-like effects"), as well as the degree of resistance to hind-limb flexion ("myorelaxant-like effects").

RESULTS

Administration of all BZ-type drugs resulted in ataxic-like and myorelaxant-like effects. Pretreatment with the alpha1 subunit-preferring antagonist beta-carboline-3-carboxylate-t-butyl ester (betaCCT) attenuated the ataxic-like effects engendered by both types of drugs. However, betaCCT was largely ineffective at blocking the ability of both BZs and non-BZs to induce myorelaxant-like effects.

CONCLUSIONS

These experiments demonstrate dose-dependent motor impairment in squirrel monkeys using quantitative behavioral observation techniques. Altogether, these findings suggest a lack of a prominent role for alpha1 subunit-containing receptors in the alteration of hind-limb flexion, a putative measure of myorelaxation, induced by BZ-type drugs in monkeys.

Hypnosedative-induced complex behaviours : incidence, mechanisms and management

A number of news items and case reports describing complex behaviours (e.g. sleep driving, sleep cooking, sleep eating, sleep conversations, sleep sex) associated with the use of hypnosedative medications have recently received considerable attention. Regulatory agencies examining these reports have subsequently issued warnings regarding the potential of hypnosedative agents to produce complex behaviours. Despite these warnings, little is known about the likelihood, presentation, treatment or prevention of hypnosedative-induced complex behaviours. The purpose of this review is to evaluate the published evidence regarding the clinical presentation, incidence, mechanism and management of sleep-related behaviours induced by nonbenzodiazepine receptor agonists (NBRAs).Review of the literature identified ten published case reports of NBRA-induced complex behaviours involving 17 unique patients. Fifteen of the 17 patients described in the case reports had taken zolpidem, one had taken zaleplon and one had taken zopiclone. The complex behaviours most commonly reported were sleep eating, sleepwalking with object manipulation, sleep conversations, sleep driving, sleep sex and sleep shopping. Elevated serum concentrations resulting from increased medication dose or drug-drug interactions appeared to play a role in some but not all cases. Sex, age, previous medication exposure and concomitant disease states were not consistently found to be related to the risk of experiencing a medication-induced complex behaviour.From a pharmacological standpoint, enhancement of GABA activity at GABAA receptors (particularly alpha1-GABAA receptors) is a possible mechanism for hypnosedative complex behaviours and amnesia. Evidence suggests that complex behaviour risk may increase with both dose and binding affinity at alpha1-GABAA receptors. The amnesia that accompanies complex behaviours is possibly due to inhibition of consolidation of short- to long-term memory, suggesting that the risk may extend to non-GABAergic hypnosedatives. While amnesia and GABA-related receptor actions are the most frequently discussed mechanisms for complex behaviours in the literature, they do not fully explain such behaviours, suggesting that other mechanisms and factors probably play a role.A number of potential strategies are available to manage or prevent hypnosedative-induced complex behaviours. These include lowering the dose of, or stopping, the offending hypnosedative, switching to a different hypnosedative, treating patients with other classes of medications, using nonpharmacological treatment strategies for patients with sleep disorders, examining drug regimens for potential drug interactions that may predispose patients to experiencing complex behaviours, administering hypnosedative medications appropriately and selecting patients more carefully for treatment in terms of their likelihood of experiencing medication adverse effects.

NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile], a unique subtype-selective GABAA receptor positive allosteric modulator: in vitro actions, pharmacokinetic properties and in vivo anxiolytic efficacy

The novel positive allosteric modulator NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile] possesses a functional selectivity profile at GABA(A) receptors of alpha(5) > alpha(3) > alpha(2) > alpha(1) based on oocyte electrophysiology with human GABA(A) receptors. Compared with other subtype-selective ligands, NS11394 is unique in having superior efficacy at GABA(A)-alpha(3) receptors while maintaining low efficacy at GABA(A)-alpha(1) receptors. NS11394 has an excellent pharmacokinetic profile, which correlates with pharmacodynamic endpoints (CNS receptor occupancy), yielding a high level of confidence in deriving in vivo conclusions anchored to an in vitro selectivity profile and allowing for translation to higher species. Specifically, we show that NS11394 is potent and highly effective in rodent anxiety models. The anxiolytic efficacy of NS11394 is most probably mediated through its high efficacy at GABA(A)-alpha(3) receptors, although a contributory role of GABA(A)-alpha(2) receptors cannot be excluded. Compared with benzodiazepines, NS11394 has a significantly reduced side effect profile in rat (sedation, ataxia, and ethanol interaction) and mouse (sedation), even at full CNS receptor occupancy. We attribute this benign side effect profile to very low efficacy of NS11394 at GABA(A)-alpha(1) receptors and an overall partial agonist profile across receptor subtypes. However, NS11394 impairs memory in both rats and mice, which is possibly attributable to its efficacy at GABA(A)-alpha(5) receptors, albeit activity at this receptor might be relevant to its antinociceptive effects (J Pharmacol Exp Ther 327:doi;10.1124/jpet.108.144, 2008). In conclusion, NS11394 has a unique subtype-selective GABA(A) receptor profile and represents an excellent pharmacological tool to further our understanding on the relative contributions of GABA(A) receptor subtypes in various therapeutic areas.

Activation of cannabinoid CB1 receptors in the dorsolateral periaqueductal gray induces anxiolytic effects in rats submitted to the Vogel conflict test

There are contradictory results concerning the effects of systemic injections of cannabinoid agonists in anxiety-induced behavioral changes. Direct drug administration into brain structures related to defensive responses could help to clarify the role of cannabinoids in these changes. Activation of cannabinoid CB(1) receptors in the dorsolateral periaqueductal gray induces anxiolytic-like effects in the elevated plus maze. The aim of this work was to verify if facilitation of endocannabinoid-mediated neurotransmission in this region would also produce anxiolytic-like effects in another model of anxiety, the Vogel conflict test. Male Wistar rats (n=5-9/group) with cannulae aimed at the dorsolateral periaqueductal gray were water deprived for 24 h and pre-exposed to the apparatus where they were allowed to drink for 3 min. After another 24 h-period of water deprivation, they received the microinjections and, 10 min later, were placed into the experimental box. In this box an electrical shock (0.5 mA, 2 s) was delivered in the spout of a drinking bottle at every twenty licks. The animals received a first microinjection of vehicle (0.2 microl) or AM251 (a cannabinoid CB(1) receptor antagonist; 100 pmol) followed, 5 min later, by a second microinjection of vehicle, anandamide (an endocannabinoid, 5 pmol), AM404 (an inhibitor of anandamide uptake, 50 pmol) or URB597 (an inhibitor of Fatty Acid Amide Hydrolase, 0.01 or 0.1 nmol). Anandamide, AM404 and URB597 (0.01 nmol) increased the total number of punished licks. These effects were prevented by AM251. The results give further support to the proposal that facilitation of CB(1) receptor-mediated endocannabinoid neurotransmission in the dorsolateral periaqueductal gray modulates defensive responses.

Comparison of short- and long-acting benzodiazepine-receptor agonists with different receptor selectivity on motor coordination and muscle relaxation following thiopental-induced anesthesia in mice

In this study, we compared the effects of Type I benzodiazepine receptor-selective agonists (zolpidem, quazepam) and Type I/II non-selective agonists (zopiclone, triazolam, nitrazepam) with either an ultra-short action (zolpidem, zopiclone, triazolam) or long action (quazepam, nitrazepam) on motor coordination (rota-rod test) and muscle relaxation (traction test) following the recovery from thiopental-induced anesthesia (20 mg/kg) in ddY mice. Zolpidem (3 mg/kg), zopiclone (6 mg/kg), and triazolam (0.3 mg/kg) similarly caused an approximately 2-fold prolongation of the thiopental-induced anesthesia. Nitrazepam (1 mg/kg) and quazepam (3 mg/kg) showed a 6- or 10-fold prolongation of the anesthesia, respectively. Zolpidem and zopiclone had no effect on the rota-rod and traction test. Moreover, zolpidem did not affect motor coordination and caused no muscle relaxation following the recovery from the thiopental-induced anesthesia. However, zopiclone significantly impaired the motor coordination at the beginning of the recovery. Triazolam significantly impaired the motor coordination and muscle relaxant activity by itself, and these impairments were markedly exacerbated after the recovery from anesthesia. Nitrazepam and quazepam significantly impaired motor coordination, and the impairments were exacerbated after the recovery. These results suggest that the profile of recovery of motor coordination and muscle flaccidity after co-administration of benzodiazepine-receptor agonists and thiopental is related to the half-life and selectivity for the benzodiazepine-receptor subtypes.

Comparative effects of nonselective and subtype-selective gamma-aminobutyric acidA receptor positive modulators in the rat-conditioned emotional response test

Benzodiazepine receptor anxiolytics show no selectivity between gamma-aminobutyric acid-A receptors containing alpha1, alpha2, alpha3 or alpha5 subunits. Pharmacological studies and data emerging from transgenic mouse models, however, predict that compounds with selective affinity and/or efficacy for gamma-aminobutyric acid-A receptor subtypes would have novel pharmacological profiles. Thus, the gamma-aminobutyric acid-A-alpha1 'affinity selective' drug zolpidem has a sedative-hypnotic profile, whereas L838,417, which has 'selective efficacy' for gamma-aminobutyric acid-A-alpha2, alpha3 and alpha5 receptors, has an anxiolytic-like profile. Here, we compare the nonselective benzodiazepine-site-positive modulators diazepam, lorazepam, midazolam, alprazolam and zopiclone with (i) gamma-aminobutyric acid-AA-alpha1 affinity selective compounds zolpidem and CL218,872 and (ii) L838,417, in the rat-conditioned emotional response test after systemic administration. Given the role of the basolateral amygdala in anxiety and the expression of alpha1, alpha2 and alpha3 subunits in this region, we also assessed the effects of bilateral infusion of L838,417 and midazolam directly into basolateral amygdala in the conditioned emotional response test. Nonselective modulators at low-moderate doses produced anxiolytic effects and sedation at higher doses. Zolpidem was inactive as an anxiolytic and engendered severe sedation, whereas CL218,872 produced an anxiolytic-like profile with minimal sedation. L838,417 produced an anxiolytic-like profile with no sedation, albeit producing behavioural disturbance at high doses. Infusion of midazolam and L838,417 into basolateral amygdala engendered anxiolytic-like effects, although both compounds were more effective after systemic injections, implicating additional brain sites in their anxiolytic-like actions after systemic administration. In conclusion, the diversity of effects of the compounds studied implicates both intrinsic efficacy and/or subtype selectivity as important determinants of anxiolytic-like effects in the rat-conditioned emotional response test.

Neuroprotective effects of the β-carboline abecarnil studied in cultured cortical neurons and organotypic retinal cultures

Presently there is no neuroprotective pharmacological treatment of proven clinical safety and efficacy available. The purpose of this study was to investigate whether the beta-carboline, abecarnil (Abe), which has already passed clinical phase III trials in patients with anxiety disorders, is neuroprotective in in vitro models of cerebral ischemia or excitotoxicity. Abe (100 nM) protected cultured cortical neurons when applied 20 min before or 20 min after combined oxygen glucose deprivation (OGD). Furthermore, cultured cortical neurons were protected from NMDA excitotoxicity when Abe (100 nM) was administered 20 min before or concurrent with 100 microM NMDA. In contrast, in adult rat organotypic retinal cultures, Abe failed to protect retinal ganglion cells (RGCs) against glutamate (Glu) excitotoxicity. Thus, although our data demonstrate that Abe is a potential neuroprotectant in cultured neurons, the lack of effect in an organotypical model of Glu toxicity indicates that further study is required before Abe might be considered for human neuroprotection trials.

Anxiolytic-like effect of cannabidiol in the rat Vogel conflict test

Cannabidiol (CBD) is a major constituent of the Cannabis sativa plant. It inhibits the anxiogenic activity of high doses of Delta9-tetrahydrocannabinol and induces anxiolytic-like effects. However, the mechanisms underlying the actions of CBD are unknown. Therefore, the aim of the present study was to test the effects of CBD in the Vogel test, a widely used animal model of anxiety. In addition, it was verified if these effects would depend on benzodiazepine-receptor activation. After 24 h of water deprivation, male Wistar rats were subjected to an initial 3-min non-punished (pre-test) drinking session. This was followed by an additional 24-h period of water deprivation followed by a 3-min punished-licking session (test). Diazepam (3 mg/kg) or CBD (2.5, 5 or 10 mg/kg) were intraperitoneally injected 30 min before the test session. CBD (10 mg/kg) and diazepam had similar anticonflict effects, increasing the number of punished licks. The effect of diazepam, but not of CBD, was prevented by the benzodiazepine-receptor antagonist flumazenil (10 mg/kg). To exclude that the anticonflict effects were reflecting non-specific drug effects, we checked the effects of CBD on water consumption and nociceptive response. The drug did not interfere on the former variable in a non-punished test session. Moreover, contrary to morphine (5 mg/kg), CBD was ineffective in the tail-flick test. In conclusion, CBD induced an anticonflict effect not mediated by benzodiazepine receptors or by non-specific drug interference on nociceptive threshold or water consumption. These results reinforce the hypothesis that this cannabinoid has anxiolytic properties.

A comparison of chlordiazepoxide, bretazenil, L838,417 and zolpidem in a validated mouse Vogel conflict test

RATIONALE

GABAA receptors containing an alpha2 subunit are proposed to mediate the anxiolytic effect of benzodiazepines (BZ) based on studies in transgenic mice using unconditioned models of anxiety. Conditioned models of anxiety were not assessed and are rarely encountered in phenotyping of genetically modified animals. The novel benzodiazepine site ligand L838,417 is a partial agonist at GABAA receptors containing an alpha2, alpha3 or alpha5 subunit and an antagonist at alpha1 receptors, giving an anxiolytic profile devoid of sedation. However, this compound has not previously been assessed in mice.

OBJECTIVES

(1) Establish the Vogel conflict test (VCT) in C57BL/6J mice and validate it with a range of pharmacological tools and (2) compare the full and partial GABAA receptor positive modulators chlordiazepoxide (CDP) and bretazenil (BRZ), respectively, with the subtype selective ligands zolpidem (ZOL; alpha1 selective) and L838,417.

RESULTS

(1) enhanced thirst (water deprivation or isoproterenol administration), analgesia (lamotrigine) or cognitive impairment (MK-801) did not generate false positives in the VCT; (2) CDP and BRZ engendered linear dose-related anti-conflict effects and also increased unpunished drinking; (3) L838,417 engendered a bell-shaped anti-conflict effect and did not increase unpunished drinking; (4) the anti-conflict effect of CDP and L838,417 were antagonised by flumazenil, whereas BRZ's effect was insensitive to this antagonist; and (5) ZOL induced motoric deficits and no anti-conflict effect.

CONCLUSION

We have established the VCT in C57BL/6J mice and validated this test behaviourally, physiologically and pharmacologically. The novel GABAA receptor ligand L838,417 was anxiolytic in this mouse model, and unlike the non-selective compounds, had no effect on unpunished drinking.

TPA023 [7-(1,1-dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine], an agonist selective for alpha2- and alpha3-containing GABAA receptors, is a nonsedating anxiolytic in rodents and primates

7-(1,1-Dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine (TPA023) is a triazolopyridazine that binds with equivalent high (subnanomolar) affinity to the benzodiazepine binding site of recombinant human GABA(A) receptors containing an alpha1, alpha2, alpha3, or alpha5 subunit but has partial agonist efficacy at the alpha2 and alpha3 subtypes and essentially antagonist efficacy at the alpha1 and alpha5 subtypes. In rats, TPA023 gave time- and dose-dependent occupancy after oral dosing, with 50% occupancy corresponding to a dose of 0.42 mg/kg. It has anxiolytic-like activity in unconditioned (elevated plus maze) and conditioned (fear-potentiated startle and conditioned suppression of drinking) rat models of anxiety with minimum effective doses (MED; 1-3 mg/kg) corresponding to 70 to 88% occupancy. However, there was no appreciable sedation in a response sensitivity (chain-pulling) assay at a dose of 30 mg/kg, resulting in 99% occupancy. Similarly, TPA023 was robustly anxiolytic in the squirrel monkey conditioned emotional response assay, with a MED of 0.3 mg/kg, but did not produce any sedation in a lever-pressing test of sedation even at 10 mg/kg. TPA023 produced no impairment in performance in the mouse Rotarod assay, and there was only a mild interaction with ethanol. In addition to anxiolytic-like efficacy, TPA023 had anticonvulsant activity in a mouse pentylenetetrazole seizure model. Finally, TPA023 did not cause precipitated withdrawal in mice treated for 7 days with the nonselective agonist triazolam, nor did N-methyl-beta-carboline-3-carboxamide (FG 7142) precipitate withdrawal in mice treated for 7 days with TPA023. In summary, the novel alpha2/alpha3-selective efficacy profile of TPA023 translates into a nonsedating anxiolytic profile that is distinct from nonselective agonists.

Differential effects of infralimbic vs. ventromedial orbital PFC lidocaine infusions in CD-1 mice on defensive responding in the mouse defense test battery and rat exposure test

The ventromedial prefrontal cortex (vmPFC) is extremely sensitive to a variety of stressful situations and threatening events, and has been suggested to be an associative cortical brain system processing the integration of anxiety-related cognitive, affective and motivated behavior in rodents, primates and humans. In addition, recent evidence suggests that (a) anxiety-related affective processing appears to be lateralized to the right hemisphere vmPFC; and (b) there appears to be functional heterogeneity within the rodent vmPFC. The present study evaluated the possibility that distinct sub-areas of the right hemisphere ventral PFC might differentially influence anxiety-like defensive responding in two different predator stress situations following transient inactivation of the ventromedial orbital (vMO) or infralimbic (IL) vmPFC in CD-1 mice. In week 1, IL vmPFC lidocaine infusions reduced anxiety-like defensive responding in mice (enhanced approach and contact) confronted with a hand-held anesthetized rat stimulus in the mouse defense test battery (vMO inactivation exerted minimal effects). In week 2, vMO lidocaine infusions enhanced anxiety-like defensive responding (enhanced avoidance and protected risk assessment) toward a barricaded live rat in the rat exposure test (IL inactivation exerted minimal effects). Although it is unclear whether week 1 mouse defense test battery testing influenced week 2 rat exposure test results, these preliminary data suggest functional differences within the mouse right hemisphere ventral PFC related to cautious evaluation of predator threat. Given the dense unilateral reciprocal connectivity between the IL and vMO subregions of the PFC, both associative ventromedial cortical areas may exert complimentary yet dissociable roles in the processing of threat stimuli. This suggests that while the IL vmPFC may mediate cautious evaluation of threat situations (risk assessment), the vMO PFC may inhibit prepotent avoidance responses to facilitate such IL-mediated adaptive behavioral responses.

Anxioselective anxiolytics: can less be more?

Benzodiazepines remain widely used for the treatment of anxiety disorders despite a side-effect profile that includes sedation, myorelaxation, amnesia, and ataxia, and the potential for abuse. gamma-Aminobutyric acid(A) (GABA(A)) receptor partial agonists, subtype-selective agents, and compounds combining both of these features are being developed in an attempt to achieve benzodiazepine-like efficacy without these potentially limiting side effects. This article reviews the nonclinical and clinical studies of "anxioselective" anxiolytics that target GABA(A) receptors and discusses potential mechanisms subserving an anxioselective profile.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

SL651498, a GABAA receptor agonist with subtype-selective efficacy, as a potential treatment for generalized anxiety disorder and muscle spasms

SL651498 (6-fluoro-9-methyl-2-phenyl-4-(pyrrolidin-1-yl-carbonyl)-2,9-dihydro-1H-pyrido[3,4-b]indol-1-one) was identified as a drug development candidate from a research program designed to discover subtype-selective GABA(A) receptor agonists for the treatment of generalized anxiety disorder and muscle spasms. The drug displays high affinity for rat native GABA(A) receptors containing alpha(1) (K(i) = 6.8 nM) and alpha(2) (K(i) = 12.3 nM) subunits, and weaker affinity for alpha5-containing GABA(A) receptors (K(i) = 117 nM). Studies on recombinant rat GABA(A) receptors confirm these findings and indicate intermediate affinity for the alpha(3)beta(2)gamma(2) subtype. SL651498 behaves as a full agonist at recombinant rat GABA(A) receptors containing alpha(2) and alpha(3) subunits, and as a partial agonist at recombinant GABA(A) receptors expressing alpha(1) and alpha(5) subunits. SL651498 produced anxiolytic-like and skeletal muscle relaxant effects qualitatively similar to those of benzodiazepines (BZs) [minimal effective dose (MED): 1 to 10 mg/kg, i.p. and 3 to 10 mg/kg, p.o.]. However, unlike these latter drugs, SL651498 induced muscle weakness, ataxia or sedation at doses much higher than those having anxiolytic-like activity (MED: 30 to 100 mg/kg, i.p. or p.o.). Moreover, in contrast to BZs, SL651498 did not produce tolerance to its anticonvulsant activity or physical dependence. It was much less active than BZs in potentiating the depressant effects of ethanol or impairing cognitive processes in rodents. The differential profile of SL651498 as compared to BZs may be related to its selective efficacy at the alpha(2)- and alpha(3)-containing GABA(A) receptors. This suggests that selectively targeting GABA(A) receptor subtypes can lead to drugs with increased clinical specificity. SL651498 represents a promising alternative to agents currently used for the treatment of anxiety disorders and muscle spasms without the major side effects seen with classical BZs.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

A new three-carbon synthon for efficient synthesis of benzannelated and 1-(2-arylethenyl) heterocycles

The novel three-carbon synthon 1-(1H-1,2, 3-benzotriazol-1-yl)-3-chloroacetone for the synthesis of benzothiazoles, pyrido[1,2-a]indoles, and styryl-substituted indolizines and imidazo[1,2-a]pyridines is reported. The proposed routes are a general and efficient approach for heterocyclizations followed by benzannelations or attachment of arylethenyl pharmacophores.

Pharmacological studies on synthetic flavonoids: comparison with diazepam

The present experiments compared the central BZ-omega binding characteristics and pharmacological profiles of two synthetic flavonoids (6-bromoflavone and 6-bromo-3'-nitroflavone) with those of the benzodiazepine (BZ) diazepam. In vitro experiments showed that while diazepam displaced [3H]flumazenil binding to the GABA(A) receptor in membranes from rat cerebellum and spinal cord, two brain areas enriched in the BZ-omega1 and BZ-omega2 receptor subtypes, with nearly equivalent half maximally effective concentrations, 6-bromo-3'-nitroflavone was somewhat more potent in displacing [3H]flumazenil binding to membranes from rat cerebellum (IC50 = 31 nM) than from spinal cord (IC50 = 120 nM), indicating selectivity for the BZ-omega1 receptor subtype. 6-Bromoflavone displayed weak (IC50 = 970 nM) affinity for the BZ-omega1 and no affinity for the BZ-omega2 (IC50 > 1000 nM) receptor subtypes. Diazepam, but not the synthetic flavonoids increased the latency to clonic seizures produced by isoniazid, thereby indicating that neither 6-bromoflavone nor 6-bromo-3'-nitroflavone display detectable intrinsic activity at GABA(A) receptors in vivo. Results from two conflict tests in rats showed that 6-bromoflavone (3-10 mg/kg) and 6-bromo-3'-nitroflavone (0.3-1 mg/kg) elicited anxiolytic-like activity in the punished drinking test, while both drugs were inactive in the punished lever pressing test. The positive effects displayed by the synthetic flavonoids in the punished drinking procedure were smaller than that of diazepam and were not antagonized by the BZ receptor antagonist flumazenil. In two models of exploratory activity, 6-bromoflavone (3-30 mg/kg) and 6-bromo-3'-nitroflavone (0.3-1 mg/kg) produced anxiolytic-like effects in the rat elevated plus-maze test, whereas both compounds failed to modify the behavior of mice in the light/dark test over a wide dose-range. The effects in the elevated plus-maze were antagonized by flumazenil. In the mouse defense test battery, where mice were confronted with a natural threat (a rat), 6-bromoflavone and 6-bromo-3'-nitroflavone failed to decrease flight reactions after the rat was introduced into the test area and risk assessment behavior displayed when subjects were constrained in a straight alley, and only weakly affected risk assessment of mice chased by the rat and defensive biting upon forced contact with the threat stimulus. In a drug discrimination experiment 6-bromoflavone and 6-bromo-3'-nitroflavone up to 30 and 3 mg/kg, respectively, did not substitute for the BZ chlordiazepoxide. Taken together, these results failed to demonstrate that the synthetic flavonoids 6-bromoflavone and 6-bromo-3'-nitroflavone possess anxiolytic-like properties similar or superior to that of diazepam, as was suggested previously. Furthermore, they question the contribution of BZ-omega receptors to the behavioral effects of 6-bromoflavone and 6-bromo-3'-nitroflavone.