Section Review Central & Peripheral Nervous Systems: Novel anxiolytic agents - 1994 to present

Hibiscus rosa sinensis mediate anxiolytic effect via modulation of ionotropic GABA-A receptors: possible mechanism of action

The current study was designed with the aim to investigate anti-anxiety potential of Hibiscus rosa sinensis roots and its possible mechanism of action. For this purpose hole board test, elevated plus maze test and light/dark exploration test were employed. The ethanol extract of plant was administered orally at two different doses i.e. 100 and 500 mg/kg for consecutive 14 days. The results of present investigation indicate that plant extract significantly (p < 0.05) increased the number of head dips and rearings as compared to control on respective days of observation. The extract increased the time of permanence in open arms and the number of head dips in elevated plus maze. In light/dark test, our study indicate that Hibiscus rosa sinensis significantly (p < 0.05) increased the time spent in light compartment and number of entries as compared to control. In addition the anxiolytic effects of HRS at highest tested dose were blocked by flumazenil, a GABA-A receptor antagonist that indicate that Hibiscus rosa sinensis potentiated the GABAergic actions. The results propose that the ethanol extract of Hibiscus rosa sinensis has prospective anxiolytic effect in mice via inhibition of ionotropic GABA receptors, using different behavioral paradigms.

Evaluation of anxiolytic-like effect of aqueous extract of asparagus stem in mice

There are few studies on the neuropharmacological properties of asparagus, which was applied in Chinese traditional medicine as a tonic and heat-clearing agent. The present study was designed to investigate the anxiolytic-like activity of the aqueous extract of asparagus stem (AEAS) using elevated plus maze (EPM) and Vogel conflict tests (VCT) in mice. AEAS significantly increased the percentage of time spent in open arms in EPM, when compared with control group. In the Vogel conflict drinking test, the numbers of punished licks increased to 177% and 174% by the treatment of AEAS at the doses of 1.5 and 3.0 g/kg (250 and 500 mg sarsasapogenin per kilogram of body weight), compared with control group. The serum cortisol level decreased significantly, at the same time. In conclusion, these findings indicated that the aqueous extract of asparagus stem exhibited a strong anxiolytic-like effect at dose of 1.5 and 3.0 g/kg (250 and 500 mg sarsasapogenin per kilogram of body weight) in experimental models of anxiety and may be considered an alternative approach for the management of anxiety disorder.

Therapeutic applications of compounds in the Magnolia family

The bark and/or seed cones of the Magnolia tree have been used in traditional herbal medicines in Korea, China and Japan. Bioactive ingredients such as magnolol, honokiol, 4-O-methylhonokiol and obovatol have received great attention, judging by the large number of investigators who have studied their pharmacological effects for the treatment of various diseases. Recently, many investigators reported the anti-cancer, anti-stress, anti-anxiety, anti-depressant, anti-oxidant, anti-inflammatory and hepatoprotective effects as well as toxicities and pharmacokinetics data, however, the mechanisms underlying these pharmacological activities are not clear. The aim of this study was to review a variety of experimental and clinical reports and, describe the effectiveness, toxicities and pharmacokinetics, and possible mechanisms of Magnolia and/or its constituents.

Isolation of anxiolytic principle from ethanolic root extract of Cardiospermum halicacabum

Cardiospermum halicacabum roots have been used traditionally for the treatment of epilepsy and anxiety disorders. The purpose of this study was to characterize the putative phytoconstituents present in the ethanolic root extract having anxiolytic activity using an elevated plus-maze (EPM) and light dark transition model. Control mice were orally treated with an equal volume of vehicle (4% gum acacia), and positive control mice were treated with diazepam (1mg/kg). In the EPM test, out of pool of 19 master fractions (MF) only MF-14, 16 and 17 significantly (30mg/kg, p<0.05, p<0.01 and p<0.001) increased the number of entries in the open arm. MF-14, 16 and 17 (10, 20 and 30mg/kg) had also increased the time spent by mice in illuminated part of the box significantly (p<0.05, p<0.01 and p<0.001), as compared to control. However, significant changes (p<0.05, p<0.01 and p<0.001) were recorded in other parameters, e.g., rearing, time spent in the closed arm and dark zone in both the models. These results suggested that C. halicacabum root is an effective anxiolytic agent. The phytoconstituent responsible for the observed central effects was isolated from MF-14 and identified as well-known compound, Cardiospermin, a cyanogenic glucoside.

Anxiolytic-like effects of obovatol isolated from Magnolia obovata: involvement of GABA/benzodiazepine receptors complex

This experiment was performed to investigate whether obovatol isolated from the leaves of Magnolia obovata has anxiolytic-like effects through GABA-benzodiazepine-receptors Cl(-) channel activation. The anxiolytic-like effects of obovatol in mice were examined using the elevated plus-maze and the automatic hole-board apparatus. Oral administration of obovatol (0.2, 0.5 and 1.0 mg/kg) significantly increased the number of open arm entries and the spent time on open arm in the elevated plus-maze test, compared with those of saline. Obovatol (0.2, 0.5 and 1.0 mg/kg) also produced anxiolytic-like effects, as reflected by an increase in head-dipping behaviors. These effects were comparable to those of diazepam (1.0 mg/kg), a well known anxiolytic drug. On the other hand, the anxiolytic-like effects of obovatol and diazepam were reversed by flumazenil, a benzodiazepine receptor antagonist, suggesting that the anxiolytic-like effects of obovatol were involved in GABA-benzodiazepine receptors complex. Obovatol was muscle relaxant by rota-rod test, but its effect was weaker than diazepam. Spontaneous locomotor activity also was inhibited by obovatol. Obovatol selectively increased the GABA(A) receptors alpha(1) subunit expression in amygdala of mouse brain. Obovatol also showed to bind to benzodiazepine receptors competitively in experiments using [(3)H]flunitrazepam in the cerebral cortex of mouse brain. Moreover, obovatol (10, 20 and 50 microM) increased Cl(-) influx and the increased Cl(-) influx was inhibited by flumazenil, in primary cultured neuronal cells and IMR-32 human neuroblastoma cells. These results suggest that obovatol has anxiolytic-like effects, and these pharmacological effects may be mediated by GABA-benzodiazepine receptors-activated Cl(-) channel opening.

Evaluating molecular similarity using reduced representations of the electron density

A model system of four benzodiazepine-like ligands for the central benzodiazepine receptors (CBRs) and peripheral benzodiazepine receptors (PBRs)is examined using a genetic algorithm procedure (GAGS) designed for evaluating molecular similarity. The method is based on the alignment of reduced representations generated from the critical points of the electron density computed at medium crystallographic resolution. The results are further characterized by a comparison with alignments produced by MIMIC, a field-based superimposition method that matches both steric and electrostatic molecular fields. The alignments produced by the two methods are generally seen to be consistent. The relationships of the compounds' binding affinities for both CBRs and PBRs to the alignments determined by GAGS yield a set of structural features required for significant binding to benzodiazepine receptors. Benefits of using reduced representations for evaluating molecular similarities and for constructing pharmacophore models are discussed.

Hydroalcohol extract and fractions ofStachys lavandulifolia vahl: effects on spontaneous motor activity and elevated plus-maze behaviour

The present study aimed to investigate the anxiolytic effects of four fractions of Stachys lavandulifolia Vahl. The aerial parts of the plant were extracted with petroleum ether (PF), ethyl acetate (EF), butanol (BF) and water (AF) and tested for spontaneous motor activity and elevated plus-maze (EPM) behaviour in mice. The hydroalcohol extract (HE) and different fractions of S. lavandulifolia were administered intraperitoneally to male Syrian mice, at various doses, 30 min before the behavioural evaluation. The HE of S. lavandulifolia (at 50 mg/kg) increased the percentage of time spent (39%) and the percentage of arm entries in the open arms (53%). The HE (50 mg/kg), PF (25 and 50 mg/kg), EF (25 and 50 mg/kg) and AF (50 mg/kg) of S. lavandulifolia significantly increased the percentage of time spent and the percentage of arm entries in the open arms. The BF up to a dose of 50 mg/kg had no significant effects on any of the measured parameters in the EPM. The spontaneous locomotor activity was significantly decreased in animals injected with each plant fractions, compared with that of saline. The EF and AF showed the least and the most reduction in the activity, respectively. The anxiolytic effects of EF, PF and AF could be related to their content of flavonoids, phenylpropanoids or terpenoids.

Evaluation of the anxiolytic-like effects of Cecropia glazioui Sneth in mice

Cecropia glazioui Sneth has been used in most Latin American countries as an antihypertensive, cardiotonic, and antiasthmatic folk medicine. In the cardiovascular studies to define its antihypertensive action it was noteworthy that animals treated with the aqueous extract (AE) of C. glazioui were much calmer than control animals. That observation prompted the present study, aimed at an investigation of the effects of AE and of two semipurified fractions on mouse behavior as evaluated in the elevated plus-maze test (EPM). Male adult Swiss mice were treated with AE (0.25-1 g/kg po) acutely (1 h) or repeatedly (24, 7, and 1.5 h before the test). After repeated administration of AE, the frequency of entries in the open arms of EPM was increased threefold. A similar profile of action was observed after treatment with the butanolic fraction (Fbut) but not with the aqueous fraction (Faq). These findings suggest that the AE of C. glazioui promotes an anxiolytic-like effect in mice. The active principles responsible for this action are present in the less polar fraction of the extract, the main constituents of which are flavonoids and terpenes, among other compounds.

New directions in anxiolytic drug research

Agents to treat anxiety have gained in acceptance and importance in the fast pace of life in the second half of this century. The discovery and refinement of the benzodiazepines represented a quantum leap in therapy from early compounds which were essentially sedatives. With the advent of molecular biology, an understanding of the basic mechanism by which the benzodiazepines exert their effects was revealed through the discovery and isolation of the GABAA receptor and its benzodiazepine binding site. This, in turn, has enabled benzodiazepines to be classified into a broad spectrum of pharmacological types ranging from agonist to inverse agonist, thus allowing fine tuning with respect to side-effects. Consequently, newer, more promising agents have emerged which bind at the GABAA BZD site and have reduced side-effects. An example of this is RWJ-51204 (92), a member of a novel structural type which is superior to several marketed benzodiazepines in animals in terms of efficacy and side-effects. The cost-conscious environment of managed health care presents continuing challenges to the discovery and development of safe, highly efficacious, and cost-effective anxiolytic agents.

Potential anxiolytic agents. 3. Novel A-ring modified pyrido[1,2-a]benzimidazoles

A variety of pyrido[1,2-a]benzimidazoles (PBIs) modified on the A-ring were prepared and evaluated for affinity to the benzodiazepine binding site on the GABA-A receptor and in animal models predictive of anxiolytic activity in humans. A-ring benzo-fused derivative 7 exhibited potent activity, as did the 6- and 7-pyrido compounds 3 and 4.

The corticotrophin-releasing factor-binding protein: an act of several parts

Previously the function of hormone binding proteins has been viewed entirely as one of either sequestering ligand activity or of delivering ligand to target tissues. However, some binding proteins have the ability when complexed with ligand to interact directly with target tissues and can undergo considerable post-translational and post-secretional modifications that serve to modify their action. We propose that for the corticotrophin-releasing factor-binding protein (CRF-BP), this adds a further level at which hormonal action may be regulated. This contrasts with previous concepts of a passive role and shows them as important regulators of hormonal action in their own right.