The value of genetic and pharmacological approaches to understanding the complexities of GABAA receptor subtype functions: The anxiolytic effects of benzodiazepines

Anxiolytic-like Effects and Quantitative EEG Profile of Palmitone Induces Responses Like Buspirone Rather Than Diazepam as Clinical Drugs

Anxiety is a mental disorder with a growing worldwide incidence due to the SARS-CoV-2 virus pandemic. Pharmacological therapy includes drugs such as benzodiazepines (BDZs) or azapirones like buspirone (BUSP) or analogs, which unfortunately produce severe adverse effects or no immediate response, respectively. Medicinal plants or their bioactive metabolites are a shared global alternative to treat anxiety. Palmitone is one active compound isolated from Annona species due to its tranquilizing activity. However, its influence on neural activity and possible mechanism of action are unknown. In this study, an electroencephalographic (EEG) spectral power analysis was used to corroborate its depressant activity in comparison with the anxiolytic-like effects of reference drugs such as diazepam (DZP, 1 mg/kg) and BUSP (4 mg/kg) or 8-OH-DPAT (1 mg/kg), alone or in the presence of the GABA_A (picrotoxin, PTX, 1 mg/kg) or serotonin 5-HT_1A receptor antagonists (WAY100634, WAY, 1 mg/kg). The anxiolytic-like activity was assayed using the behavioral response of mice employing open-field, hole-board, and plus-maze tests. EEG activity was registered in both the frontal and parietal cortex, performing a 10 min baseline and 30 min recording after the treatments. As a result, anxiety-like behavior was significantly decreased in mice administered with palmitone, DZP, BUSP, or 8-OH-DPAT. The effect of palmitone was equivalent to that produced by 5-HT_1A receptor agonists but 50% less effective than DZP. The presence of PTX and WAY prevented the anxiolytic-like response of DZP and 8-OH-DPAT, respectively. Whereas only the antagonist of the 5-HT_1A receptor (WAY) inhibited the palmitone effects. Palmitone and BUSP exhibited similar changes in the relative power bands after the spectral power analysis. This response was different to the changes induced by DZP. In conclusion, brain electrical activity was associated with the anxiolytic-like effects of palmitone implying a serotoninergic rather than a GABAergic mechanism of action.

Modification of brain waves and sleep parameters by Citrus reticulata Blanco. cv. Sai-Nam-Phueng essential oil

Background

Citrus essential oil (EO) has been used for mood elevation and sedative hypnotic purposes. However, scientific proofs of its central nervous system (CNS) action remained largely unexplored. This study investigated chemotypes, electrical brain waves and sleep-wake effects of the essential oil from Citrus reticulata in rat model.

Methods

Chemical contents of citrus EO were analyzed using gas chromatography-mass spectrometry (GC–MS). Male Wistar rats implanted with electrodes on the frontal and parietal skulls were used for electroencephalographic (EEG) recording while inhaling the citrus EO (200 μl on cotton wool). Diazepam (10 mg/kg, p.o.) was used as a standard anxiolytic drug. EEG frequency analyses were performed by using Fast Fourier transform. All data were statistical analyzed using One-way ANOVA followed by Tukey's test.

Results

GC–MS analysis revealed d-limonene (95.7%) as a major constituent of citrus EO. The EEG results showed that overall EEG patterns of citrus EO effects were relatively similar to that of diazepam. However, significant differences between treatments were seen from sleep-wake analyses. Diazepam significantly increased episode numbers of awake and non-rapid eye movement (REM) sleep and reduced averaged episode duration. On the other hand, the citrus EO significantly decreased REM sleep latency and increased total time and episode numbers of REM sleep.

Conclusion

These findings demonstrated unique CNS effects of C. reticulata EO with EEG fingerprints and sleep-wake profiles. The data might be useful for citrus essential oil sub-classification and clinical application.

The leaves of Crataeva nurvala Buch-Ham. modulate locomotor and anxiety behaviors possibly through GABAergic system

Background

Crataeva nurvala Buch-Hum is an indigenous herb, extensively used in traditional medicines of the South Asian countries to treat inflammation, rheumatic fever, gastric irritation, and constipation. Despite this wide range of uses, very little information is known regarding its effects on the central nervous system (CNS). Therefore, this study evaluated the neuropharmacological properties of methanolic extract of Crataeva nurvala leaves (MECN) using a number of behavioral models in animals. This study also identified potentially active phytochemicals in MECN.

Methods

Following MECN administration (at 50, 100 and 200 mg/kg; b.w.) the animals (male Swiss albino mice) were employed in hole-cross test (HCT), open field test (OFT), and rota-rod test (RRT) to evaluate sedative properties, where anxiolytic activities were investigated using elevated plus maze (EPM), light dark box (LDB), and marble burying test (MBT). The involvement of GABAergic system was evaluated using thiopental sodium (TS)-induced sleeping time determination test. Moreover, colorimetric phytochemical tests as well as GC/MS-MS were also conducted to define the phytochemical constituents of MECN.

Results

MECN possesses sedative properties indicated through the dose-dependent inhibition of locomotor activities of the animals in HCT and OFT and motor coordination in RRT. MECN also exhibited prominent anxiolytic properties through decreased burying behavior in MBT, increased time spent and transitions in open arm of EPM, and increased time spent in light compartment of LDB. In addition, the treatments potentiated TS-mediated hypnosis indicating a possible participation of GABAergic system in the observed sedative and anxiolytic activities. Phytochemical screening of MECN revealed 48 different compounds in it. We reviewed and conceive that the sedative and anxiolytic effects could be due to the presence of neuroactive compounds such as phytol, D-allose, and α-Tocopherol in MECN.

Conclusion

The present study showed that MECN possesses sedative and anxiolytic potential which could be beneficial in treatment of anxiety and insomnia associated with different psychological disorders.

Psychopharmacology of combined activation of the serotonin1A and σ1 receptors

The selective serotonin (5-HT) reuptake inhibitors (SSRIs) are generally used for the treatment of major depressive disorders, and the 5-HT1A and σ1 receptors are considered to be targets for treatment of psychiatric disorders. Some SSRIs such as fluvoxamine have agonistic activity towards for the σ1 receptor, but it is not known whether the effect on the receptor plays a key role in the pharmacological effects. We have recently demonstrated that fluvoxamine shows an anti-anhedonic effect in picrotoxin-induced model of anxiety/depression, while the SSRI paroxetine, which have little affinity for the σ1 receptor, does not. We also suggest that the anti-anhedonic effect of fluvoxamine is mediated by combined activation of the 5-HT1A and σ1 receptors and it is associated with activation of prefrontal dopaminergic system. In these studies, picrotoxin-treated mice and adrenalectomized/castrated mice were used as decreased GABAA receptor function and neurosteroid-deficient models, respectively. These findings suggest that the functional interaction between the 5-HT1A and σ1 receptors activates prefrontal dopaminergic system under the conditions of decreased brain GABAA receptor function and the neurochemical effect is linked to the behavioral effect. This review summarizes the pharmacological role of the 5-HT1A and σ1 receptors, focusing on the functional interaction between these receptors, and the role of prefrontal dopaminergic system in depressive-like behaviors.

Anti-anhedonic effect of selective serotonin reuptake inhibitors with affinity for sigma-1 receptors in picrotoxin-treated mice

BACKGROUND AND PURPOSE

Prefrontal dopamine release by the combined activation of 5-HT1A and sigma-1 (σ1 ) receptors is enhanced by the GABAA receptor antagonist picrotoxin in mice. Here, we examined whether this neurochemical event was accompanied by behavioural changes.

EXPERIMENTAL APPROACH

Male mice were treated with picrotoxin to decrease GABAA receptor function. Their anhedonic behaviour was measured using the female encounter test. The expression of c-Fos was determined immunohistochemically.

KEY RESULTS

Picrotoxin caused an anxiogenic effect on three behavioural tests, but it did not affect the immobility time in the forced swim test. Picrotoxin decreased female preference in the female encounter test and attenuated the female encounter-induced increase in c-Fos expression in the nucleus accumbens. Picrotoxin-induced anhedonia was ameliorated by fluvoxamine and S-(+)-fluoxetine, selective serotonin reuptake inhibitors with high affinity for the σ1 receptor. The effect of fluvoxamine was blocked by a 5-HT1A or a σ1 receptor antagonist, and co-administration of the σ1 receptor agonist (+)-SKF-10047 and the 5-HT1A receptor agonist osemozotan mimicked the effect of fluvoxamine. By contrast, desipramine, duloxetine and paroxetine, which have little affinity for the σ1 receptor, did not affect picrotoxin-induced anhedonia. The effect of fluvoxamine was blocked by a dopamine D2/3 receptor antagonist. Methylphenidate, an activator of the prefrontal dopamine system, ameliorated picrotoxin-induced anhedonia.

CONCLUSION AND IMPLICATIONS

Picrotoxin-treated mice show anhedonic behaviour that is ameliorated by simultaneous activation of 5-HT1A and σ1 receptors. These findings suggest that the increased prefrontal dopamine release is associated with the anti-anhedonic effect observed in picrotoxin-treated mice.

New knockout model confirms a role for androgen receptors in regulating anxiety-like behaviors and HPA response in mice

Men are less likely than women to suffer from anxiety disorders. Because gonadal hormones play a crucial role in many behavioral sex differences, they may underlie sex differences in human anxiety. In rodents, testosterone (T) exerts anxiolytic effects via the androgen receptor (AR): we found that male mice with a naturally-occurring mutation rendering the AR dysfunctional, referred to as spontaneous testicular feminization mutation (sTfm), showed more anxiety-like behaviors than wildtype (WT) males. Here, we used Cre-lox recombination technology to create another dysfunctional allele for AR. These induced Tfm (iTfm) animals also displayed more anxiety-like behaviors than WTs. We further found that AR-modulation of these behaviors interacts with circadian phase. When tested in the resting phase, iTfms appeared more anxious than WTs in the open field, novel object and elevated plus maze tests, but not the light/dark box. However, when tested during the active phase (lights off), iTfms showed more anxiety-related behavior than WTs in all four tests. Finally, we confirmed a role of T acting via AR in regulating HPA axis activity, as WT males with T showed a lower baseline and overall corticosterone response, and a faster return to baseline following mild stress than did WT males without T or iTfms. These findings demonstrate that this recombined AR allele is a valuable model for studying androgenic modulation of anxiety, that the anxiolytic effects of AR in mice are more prominent in the active phase, and that HPA axis modulation by T is AR dependent.

Clobazam therapeutic drug monitoring: a comprehensive review of the literature with proposals to improve future studies

BACKGROUND

Clobazam was recently approved for Lennox-Gastaut syndrome in the United States. There is no published review article focused on clobazam therapeutic drug monitoring (TDM) in English.

METHODS

More than 200 clobazam articles identified by a PubMed search were carefully reviewed for information on clobazam pharmacokinetics. Clobazam is mainly metabolized by a cytochrome P450 (CYP) isoenzyme, CYP3A4, to its active metabolite, N-desmethylclobazam. Then, N-desmethylclobazam is mainly metabolized by CYP2C19 unless the individual has no CYP2C19 activity [poor metabolizer (PM)].

RESULTS

Using a mechanistic approach to reinterpret the published findings of steady-state TDM and single-dosing pharmacokinetic studies, 4 different serum clobazam concentration ratios were studied. The available limited steady-state TDM data suggest that the serum N-desmethylclobazam/clobazam ratio can be useful for clinicians, including identifying CYP2C19 PMs (ratio >25 in the absence of inhibitors). There are 3 possible concentration/dose (C/D) ratios. The clobazam C/D ratio has the potential to measure the contribution of CYP3A4 activity to the clearance of clobazam from the body. The N-desmethylclobazam C/D ratio does not seem to be a good measure of clobazam clearance and should be substituted with the total (clobazam + N-desmethylclobazam) C/D ratio.

CONCLUSIONS

Future clobazam TDM studies need to use trough concentrations after steady state has been reached (>3 weeks in normal individuals and several months in CYP2C19 PMs). These future studies need to explore the potential of clobazam and total C/D ratios. Better studies on the relative potency of N-desmethylclobazam compared with the parent compound are needed to provide weighted total serum concentrations that correct for the possible lower N-desmethylclobazam pharmacodynamic activity. Standardization and more studies of C/D ratios from clobazam and other drugs can be helpful to move TDM forward.

Comparison of the effects of the GABAB receptor positive modulator BHF177 and the GABAB receptor agonist baclofen on anxiety-like behavior, learning, and memory in mice

γ-Aminobutyric acid B (GABAB) receptor activation is a potential therapeutic approach for the treatment of drug addiction, pain, anxiety, and depression. However, full agonists of this receptor induce side-effects, such as sedation, muscle relaxation, tolerance, and cognitive disruption. Positive allosteric modulators (PAMs) of the GABAB receptor may have similar therapeutic effects as agonists with superior side-effect profiles. The present study behaviorally characterized N-([1R,2R,4S]-bicyclo[2.2.1]hept-2-yl)-2-methyl-5-(4-[trifluoromethyl]phenyl)-4-pyrimidinamine (BHF177), a GABAB receptor PAM, in mouse models of anxiety-like behavior, learning and memory. In addition, the effects of BHF177 were compared with the agonist baclofen. Unlike the anxiolytic chlordiazepoxide, baclofen (0.5, 1.5, and 2.5 mg/kg, intraperitoneally) and BHF177 (10, 20, and 40 mg/kg, orally) had no effect on anxiety-like behavior in the elevated plus maze, light/dark box, or Vogel conflict test. Baclofen increased punished drinking in the Vogel conflict test, but this effect may be attributable to the analgesic actions of baclofen. At the highest dose tested (2.5 mg/kg), baclofen-treated mice exhibited sedation-like effects (i.e., reduced locomotor activity) across many of the tests, whereas BHF177-treated mice exhibited no sedation-like effects. BHF177 exhibited pro-convulsion properties only in mice, but not in rats, indicating that this effect may be species-specific. At doses that were not sedative or pro-convulsant, baclofen and BHF177 had no selective effects on fear memory retrieval in contextual and cued fear conditioning or spatial learning and memory in the Barnes maze. These data suggest that BHF177 has little sedative activity, no anxiolytic-like profile, and minimal impairment of learning and memory in mice.

Synthesis of novel cognition enhancers with pyrazolo[5,1-c][1,2,4]benzotriazine core acting at γ-aminobutyric acid type A (GABA(A)) receptor

Memory dysfunction associated with aging, neurodegenerative and psychiatric disorders represents an increasing medical need. Advances in research exploring the biological mechanisms underlying learning and memory have opened new potential approaches for development of memory-enhancing therapies addressed to selective neuronal targets. In this work, we synthesized some derivatives with a pyrazolo[5,1-c][1,2,4]benzotriazine core to identify ligands on GABAA receptors subtype (benzodiazepine site on GABAA-receptor) endowed with the potential of enhancing cognition activity without the side effects usually associated with non-selective GABAA modulators. In fact, there is much evidence that GABAA-R (γ-aminobutyric acid, type A receptor) subtype ligands have relevance in learning and memory. In vitro and in vivo tests have been performed. Pharmacological data indicate that compounds 7, 13, 14 and 22 act as dual functional modulators of GABAA-Rs (promnemonic and anxiolytic agents) while only compounds 3 and 10 stand out as selectively displaying good antiamnesic and procognitive activity (1 and 3 mg/kg, respectively).

The GABAergic system contributes to the anxiolytic-like effect of essential oil from Cymbopogon citratus (lemongrass)

ETHNOPHARMACOLOGICAL RELEVANCE

The essential oil (EO) from Cymbopogon citratus (DC) Stapf is reported to have a wide range of biological activities and is widely used in traditional medicine as an infusion or decoction. However, despite this widely use, there are few controlled studies confirming its biological activity in central nervous system.

MATERIALS AND METHODS

The anxiolytic-like activity of the EO was investigated in light/dark box (LDB) and marble-burying test (MBT) and the antidepressant activity was investigated in forced-swimming test (FST) in mice. Flumazenil, a competitive antagonist of benzodiazepine binding and the selective 5-HT(1A) receptor antagonist WAY100635 was used in experimental procedures to determine the action mechanism of EO. To exclude any false positive results in experimental procedures, mice were submitted to the rota-rod test. We also quantified some neurotransmitters at specific brain regions after EO oral acute treatment.

RESULTS

The present work found anxiolytic-like activity of the EO at the dose of 10mg/kg in a LDB. Flumazenil, but not WAY100635, was able to reverse the effect of the EO in the LDB, indicating that the EO activity occurs via the GABA(A) receptor-benzodiazepine complex. Only at higher doses did the EO potentiate diethyl-ether-induced sleeping time in mice. In the FST and MBT, EO showed no effect. Finally, the increase in time spent in the light chamber, demonstrated by concomitant treatment with ineffective doses of diazepam (DZP) and the EO, revealed a synergistic effect of the two compounds. The lack of activity after long-term treatment in the LDB test might be related to tolerance induction, even in the DZP-treated group. Furthermore, there were no significant differences between groups after either acute or repeated treatments with the EO in the rota-rod test. Neurochemical evaluation showed no amendments in neurotransmitter levels evaluated in cortex, striatum, pons, and hypothalamus.

CONCLUSIONS

The results corroborate the use of Cymbopogon citratus in folk medicine and suggest that the anxiolytic-like effect of its EO is mediated by the GABA(A) receptor-benzodiazepine complex.

1,4-Benzodiazepin-2-ones in medicinal chemistry

1,4-Benzodiazepin-2-ones have applications in many areas of medicinal chemistry that are not restricted to 'classical' CNS treatments such as sedatives, epilepsy and muscle relaxants. We will describe selected examples of 1,4-benzodiazepin-2-ones in other areas of medicinal chemistry including uses as G-protein-coupled receptor antagonists, enzyme inhibitors and anticancer agents. Examples from our group will mainly show the use of palladacycle complexes of 1,4-benzodiazepin-2-ones as anticancer agents.

Decreased GABAA and GABAB receptor functional activity in cannabinoid CB1 receptor knockout mice

The interaction between brain GABAergic and endocannabinoid systems was evaluated by examining the quantitative and functional status of GABAergic receptors in cannabinoid CB(1) receptor knockout (CB(1)(-/-)) mice. To this aim, GABA(A) ([(3)H]-Muscimol binding assay), GABA(B) (baclofen-stimulated [(35)S]-GTPγS binding assay), GABA(A)α(1), GABA(A)α(2) and GABA(A)γ(2) receptors gene expression (real-time reverse transcriptase polymerase chain reaction [PCR]) were carried out in CB(1)(-/-) and wild-type mice (CB(1)(+/+)). [(3)H]-Muscimol binding assays revealed significant reduction in the density of GABA(A) receptors in CA2 (30%) and DG (28%) of the hippocampus, thalamus (40%), cingulate (28%) and motor cortex (35%) of CB(1)(-/-) mice. Functional activity of metabotropic GABA(B) receptors was measured by evaluating the ability of GABA(B) agonist baclofen to stimulate [(35)S]-GTPγS binding. The results showed significant reduced [(35)S]-GTPγS binding in CA1 (61%), CA3 (51%) and DG (60%) of CB(1)(-/-) mice compared with CB(1)(+/+) mice. Real-time reverse transcriptase PCR was carried out for evaluating gene expression of α(1), α(2) and γ(2) subunits of GABA(A) receptor in the amygdala. The results showed significant reduced GABA(A)α(1) (50%) and GABA(A)α(2) (40%) receptor subunits gene expression in the amygdala of CB(1)(-/-) mice. No difference was observed in GABA(A)γ(2) receptor subunit gene expression. This study provides strong evidence of the involvement of CB(1) receptors in the control of GABAergic responses mediated by GABA(A) and GABA(B) receptors, and suggests a possible role of the endocannabinoid system in the regulation of anxiety-related disorders.

Orofacial movements in phospholipase C-related catalytically inactive protein-1/2 double knockout mice: Effect of the GABAergic agent diazepam and the D(1) dopamine receptor agonist SKF 83959

Orofacial movements are regulated by D(1)-like dopamine receptors interacting with additional mechanisms. Phospholipase C-related catalytically inactive protein (PRIP) regulates cell surface expression of GABA(A) receptors containing a gamma2 subunit. Mutant mice with double knockout of PRIP-1 and PRIP-2 were used to investigate aspects of GABAergic regulation of orofacial movements and interactions with D(1) mechanisms. Vertical jaw movements, tongue protrusions and movements of the head and vibrissae were reduced in PRIP-1/2 double knockouts. The GABA(A)ergic agent diazepam reduced movements of the head and vibrissae; these effects were unaltered in PRIP-1/2 double knockouts. The D(1)-like agonist SKF 83959 induced vertical jaw movements, incisor chattering, and movements of the head and vibrissae that were unaltered in PRIP-1/2 double knockouts. However, SKF 83959-induced tongue protrusions were reduced in PRIP-1/2 double knockouts. PRIP-mediated regulation of GABA(A)ergic receptor mechanisms influences topographically distinct aspects of orofacial movement and interacts with D(1) receptor systems.

In vitro and whole animal evidence that methylmercury disrupts GABAergic systems in discrete brain regions in captive mink

The effects of mercury (Hg) on key components of the GABAergic system were evaluated in discrete brain regions of captive juvenile male American mink (Neovison vison) using in vitro and in vivo (whole animal) experimental approaches. In vitro studies on cortical brain tissues revealed that inorganic Hg (HgCl(2); IC50=0.5+/-0.2microM) and methyl Hg (MeHgCl; IC50=1.6+/-0.2microM) inhibited glutamic acid decarboxylase (GAD; EC 4.1.1.15) activity. There were no Hg-related effects on [(3)H]-muscimol binding to GABA(A) receptors (IC50s>100microM). HgCl(2) (IC50=0.8+/-0.3microM) but not MeHgCl (IC50>100microM) inhibited GABA-transaminase (GABA-T; EC 2.6.1.19) activity. In a whole animal study, neurochemical indicators of GABAergic function were measured in brain regions (occipital cortex, cerebellum, brain stem, and basal ganglia) of captive mink fed relevant levels of MeHgCl (0 to 2microg/g feed, ppm) daily for 89d. No effects on GAD activity were measured. Concentration-dependent decreases in [(3)H]-muscimol binding to GABA(A) receptors and GABA-T activity were found in several brain regions, with reductions as great as 94% (for GABA(A) receptor levels) and 71% (for GABA-T activity) measured in the brain stem and basal ganglia. These results show that chronic exposure to environmentally relevant levels of MeHg disrupts GABAergic signaling. Given that GABA is the main inhibitory neurotransmitter in the mammalian nervous system, prolonged disruptions of its function may underlie the sub-clinical impacts of MeHg at relevant levels to animal health.

Allosteric modulation by benzodiazepines of GABA-gated chloride channels of an identified insect motor neurone

The actions of benzodiazepines were studied on the responses to GABA of the fast coxal depressor (D(f)) motor neurone of the cockroach, Periplaneta americana. Ro5-4864, diazepam and clonazepam were investigated. Responses to GABA receptors were enhanced by both Ro5-4864 and diazepam, whereas clonazepam, a potent-positive allosteric modulator of human GABA(A) receptors, was ineffective on the native insect GABA receptors of the D(f) motor neurone. Thus, clear pharmacological differences exist between insect and mammalian native GABA-gated chloride channels with respect to the actions of benzodiazepines. The results enhance our understanding of invertebrate GABA-gated chloride channels which have recently proved important in (a) comparative studies aimed at identifying human allosteric drug-binding sites and (b) understanding the actions of compounds used to control ectoparasites and insect crop pests.