Changes in GABA(A) receptor gene expression induced by withdrawal of, but not by long-term exposure to, zaleplon or zolpidem

Zolpidem use and risk of suicide: A systematic review and meta-analysis

INTRODUCTION

Zolpidem is one of the most commonly prescribed nonbenzodiazepine hypnotic drugs for insomnia. Published epidemiological studies linked zolpidem with the risk of suicide. However, to date, no meta-analysis investigated this association. Hence, we systematically reviewed and meta-analysed the current evidence from real-world studies reporting the risk of suicide with the use of zolpidem.

METHODS

Medline (Ovid), Embase (Ovid), and PsycINFO databases were searched from inception till June 2021 for real-world evidence studies reporting the risk of suicide with the use of zolpidem. The quality assessment of included studies was assessed using the New-Castle Ottawa Scale (NOS). Random-effect meta-analysis was performed using a generic inverse variance method.

RESULTS

This meta-analysis was based on four studies with 344,753 participants, of which 42,279 were zolpidem users. The methodological quality of all the included studies was of high quality. A significantly increased risk of suicide or suicide attempt was found in zolpidem users compared to non-users, with a pooled relative risk of 1.88 (95% CI: 1.54 - 2.30). Furthermore, an increased risk of suicidal death was observed in zolpidem users compared to non-users, with a pooled relative risk of 1.82 (95% CI: 1.43 - 2.30). Dose-response analysis also revealed a significantly increased risk of suicide in patients receiving ≥ 180cDDD (cumulative defined daily doses) of zolpidem (124 times), followed by 90-179cDDD (113 times) and <90cDDD (93 times) of zolpidem compared to non-users.

CONCLUSION

In conclusion, zolpidem use was associated with an increased risk of suicide or suicide attempt and suicidal death. Therefore, careful prescribing practices must be followed by considering the risk-benefit profile.

GABAA receptor subtypes and benzodiazepine use, misuse, and abuse

Benzodiazepines have been in use for over half a century. While they remain highly prescribed, their unfavorable side-effect profile and abuse liability motivated a search for alternatives. Most of these efforts focused on the development of benzodiazepine-like drugs that are selective for specific GABA_A receptor subtypes. While there is ample evidence that subtype-selective GABA_A receptor ligands have great potential for providing symptom relief without typical benzodiazepine side-effects, it is less clear whether subtype-selective targeting strategies can also reduce misuse and abuse potential. This review focuses on the three benzodiazepine properties that are relevant to the DSM-5-TR criteria for Sedative, Hypnotic, or Anxiolytic Use Disorder, namely, reinforcing properties of benzodiazepines, maladaptive behaviors related to benzodiazepine use, and benzodiazepine tolerance and dependence. We review existing evidence regarding the involvement of different GABA_A receptor subtypes in each of these areas. The reviewed studies suggest that α1-containing GABA_A receptors play an integral role in benzodiazepine-induced plasticity in reward-related brain areas and might be involved in the development of tolerance and dependence to benzodiazepines. However, a systematic comparison of the contributions of all benzodiazepine-sensitive GABA_A receptors to these processes, a mechanistic understanding of how the positive modulation of each receptor subtype might contribute to the brain mechanisms underlying each of these processes, and a definitive answer to the question of whether specific chronic modulation of any given subtype would result in some or all of the benzodiazepine effects are currently lacking from the literature. Moreover, how non-selective benzodiazepines might lead to the maladaptive behaviors listed in DSM and how different GABA_A receptor subtypes might be involved in the development of these behaviors remains unexplored. Considering the increasing burden of benzodiazepine abuse, the common practice of benzodiazepine misuse that leads to severe dependence, and the current efforts to generate side-effect free benzodiazepine alternatives, there is an urgent need for systematic, mechanistic research that provides a better understanding of the brain mechanisms of benzodiazepine misuse and abuse, including the involvement of specific GABA_A receptor subtypes in these processes, to establish an informed foundation for preclinical and clinical efforts.

Eszopiclone for insomnia

BACKGROUND

Insomnia is a major public health issue affecting between 6% to 10% of the adult population in Western countries. Eszopiclone is a hypnotic drug belonging to a newer group of hypnotic agents, known as new generation hypnotics, which was marketed as being just as effective as benzodiazepines for this condition, while being safer and having a lower risk for abuse and dependence. It is the aim of the review to integrate evidence from randomised controlled trials and to draw conclusions on eszopiclone's efficacy and safety profile, while taking methodological features and bias risks into consideration.

OBJECTIVES

To assess the efficacy and safety of eszopiclone for the treatment of insomnia compared to placebo or active control.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled trials (CENTRAL), MEDLINE, Embase, PsycINFO, PSYNDEX and registry databases (WHO trials portal, ClinicalTrials.gov) with results incorporated from searches to 10 February 2016. To identify trials not registered in electronic databases, we contacted key informants and searched reference lists of identified studies. We ran an update search (21 February 2018) and have placed studies of interest in awaiting classification/ongoing studies. These will be incorporated into the next version of the review, as appropriate.

SELECTION CRITERIA

Parallel group randomised controlled trials (RCTs) comparing eszopiclone with either placebo or active control were included in the review. Participants were adults with insomnia, as diagnosed with a standardised diagnostic system, including primary insomnia and comorbid insomnia.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted outcome data; one reviewer assessed trial quality and the second author cross-checked it.

MAIN RESULTS

A total of 14 RCTs, with 4732 participants, were included in this review covering short-term (≤ 4 weeks; 6 studies), medium-term (> 4 weeks ≤ 6 months; 6 studies) and long-term treatment (> 6 months; 2 studies) with eszopiclone. Most RCTs included in the review included participants aged between 18 and 64 years, three RCTs only included elderly participants (64 to 85 years) and one RCT included participants with a broader age range (35 to 85 years). Seven studies considered primary insomnia; the remaining studies considered secondary insomnia comorbid with depression (2), generalised anxiety (1), back pain (1), Parkinson's disease (1), rheumatoid arthritis (1) and menopausal transition (1).Meta-analytic integrations of participant-reported data on sleep efficacy outcomes demonstrated better results for eszopiclone compared to placebo: a 12-minute decrease of sleep onset latency (mean difference (MD) -11.94 min, 95% confidence interval (CI) -16.03 to -7.86; 9 studies, 2890 participants, moderate quality evidence), a 17-minute decrease of wake time after sleep onset (MD -17.02 min, 95% CI -24.89 to -9.15; 8 studies, 2295 participants, moderate quality evidence) and a 28-minute increase of total sleep time (MD 27.70 min, 95% CI 20.30 to 35.09; 10 studies, 2965 participants, moderate quality evidence). There were no significant changes from baseline to the first three nights after drug discontinuation for sleep onset latency (MD 17.00 min, 95% CI -4.29 to 38.29; 1 study, 291 participants, low quality evidence) and wake time after sleep onset (MD -6.71 min, 95% CI -21.25 to 7.83; 1 study, 291 participants, low quality evidence). Adverse events during treatment that were documented more frequently under eszopiclone compared to placebo included unpleasant taste (risk difference (RD) 0.18, 95% CI 0.14 to 0.21; 9 studies, 3787 participants), dry mouth (RD 0.04, 95% CI 0.02 to 0.06; 6 studies, 2802 participants), somnolence (RD 0.04, 95% CI 0.02 to 0.06; 8 studies, 3532 participants) and dizziness (RD 0.03, 95% CI 0.01 to 0.05; 7 studies, 2933 participants). According to the GRADE criteria, evidence was rated as being of moderate quality for sleep efficacy outcomes and adverse events and of low quality for rebound effects and next-day functioning.

AUTHORS' CONCLUSIONS

Eszopiclone appears to be an efficient drug with moderate effects on sleep onset and maintenance. There was no or little evidence of harm if taken as recommended. However, as certain patient subgroups were underrepresented in RCTs included in the review, findings might not have displayed the entire spectrum of possible adverse events. Further, increased caution is required in elderly individuals with cognitive and motor impairments and individuals who are at increased risk of using eszopiclone in a non-recommended way.

Potential role for histone deacetylation in chronic diazepam-induced downregulation of α1-GABAA receptor subunit expression

Corroborating evidence indicate that the downregulation of GABAA receptor subunit expression may underlie tolerance to the anticonvulsant and anxiolytic actions of benzodiazepine (BZ) ligands that act as full allosteric modulators (FAMs) of GABA actions at a variety of GABAA receptor subtypes. We and others have shown that 10-14 days treatment with increasing doses of diazepam (a FAM) resulted in anticonvulsant tolerance and decreased the expression of the α1 GABAA receptor subunit mRNA and protein in frontal cortex. In addition, we have also shown that long-term treatment with imidazenil, a partial allosteric modulator of GABA action at selective GABAA receptor subtypes, fail to change the expression of the α1 subunit mRNA or induce tolerance to its anticonvulsant or anxiolytic action. However, little is known regarding the potential role of epigenetic mechanisms on long-term BZ-induced downregulation of GABAA receptor subunit. Therefore, we examined the role of histone acetylation and DNA methylation mechanisms on long-term diazepam-induced downregulation of the α1 subunit mRNA expression in rat frontal cortex. We found that 10 days treatment with increasing doses of diazepam but not imidazenil decreased the expression of the α1 GABAA receptor subunit mRNA and promoter acetylation in frontal cortex. In addition, we also found that 10 days treatment with diazepam but not imidazenil increased the expression of histone deacetylase (HDAC) 1 and 2 in frontal cortex. Thus, the increased expression of HDAC1 and HDAC2 (class 1 HDACs) and consequently increased histone deacetylation mechanism of this class 1 HDACs, may underlie long-term diazepam-induced decreased expression of the α1 GABAA receptor subunit mRNA in frontal cortex.

GABA withdrawal syndrome: GABAA receptor, synapse, neurobiological implications and analogies with other abstinences

The sudden interruption of the increase of the concentration of the gamma-aminobutyric acid (GABA), determines an increase in neuronal activity. GABA withdrawal (GW) is a heuristic analogy, with withdrawal symptoms developed by other GABA receptor-agonists such as alcohol, benzodiazepines, and neurosteroids. GW comprises a model of neuronal excitability validated by electroencephalogram (EEG) in which high-frequency and high-amplitude spike-wave complexes appear. In brain slices, GW was identified by increased firing synchronization of pyramidal neurons and by changes in the active properties of the neuronal membrane. GW induces pre- and postsynaptic changes: a decrease in GABA synthesis/release, and the decrease in the expression and composition of GABAA receptors associated with increased calcium entry into the cell. GW is an excellent bioassay for studying partial epilepsy, epilepsy refractory to drug treatment, and a model to reverse or prevent the generation of abstinences from different drugs.

Targeting the modulation of neural circuitry for the treatment of anxiety disorders

Anxiety disorders are a major public health concern. Here, we examine the familiar area of anxiolysis in the context of a systems-level understanding that will hopefully lead to revealing an underlying pharmacological connectome. The introduction of benzodiazepines nearly half a century ago markedly improved the treatment of anxiety disorders. These agents reduce anxiety rapidly by allosterically enhancing the postsynaptic actions of GABA at inhibitory type A GABA receptors but side effects limit their use in chronic anxiety disorders. Selective serotonin reuptake inhibitors and serotonin/norepinephrine reuptake inhibitors have emerged as an effective first-line alternative treatment of such anxiety disorders. However, many individuals are not responsive and side effects can be limiting. Research into a relatively new class of agents known as neurosteroids has revealed novel modulatory sites and mechanisms of action that are providing insights into the pathophysiology of certain anxiety disorders, potentially bridging the gap between the GABAergic and serotonergic circuits underlying anxiety. However, translating the pharmacological activity of compounds targeted to specific receptor subtypes in rodent models of anxiety to effective therapeutics in human anxiety has not been entirely successful. Since modulating any one of several broad classes of receptor targets can produce anxiolysis, we posit that a systems-level discovery platform combined with an individualized medicine approach based on noninvasive brain imaging would substantially advance the development of more effective therapeutics.

Neonatal finasteride administration alters hippocampal α4 and δ GABAAR subunits expression and behavioural responses to progesterone in adult rats

Allopregnanolone is a neurosteroid that has been reported to fluctuate during early developmental stages. Previous experiments reported the importance of neonatal endogenous allopregnanolone levels for the maturation of the central nervous system and particularly for the hippocampus. Changes in neonatal allopregnanolone levels have been related to altered adult behaviour and with psychopathological susceptibility, including anxiety disorders, schizophrenia and drug abuse. However, the mechanism underlying these changes remains to be elucidated. In the present study we assessed changes in hippocampal expression of α4 and δ GABAA receptor (GABAAR) subunits as a consequence of neonatal finasteride (a 5-α reductase inhibitor) administration during early development (PD6 to PD15) in male rats. We observed that the treatment altered the temporal window of the natural peak in the expression of these subunits during development. Additionally, the level of these subunits were higher than in non-handled and control animals in the adult hippocampus. We observed that in adulthood, neonatal finasteride-treated animals presented an anxiogenic-like profile in response to progesterone administration which was absent in the rest of the groups. In conclusion, these results corroborate the relevance of neonatal maintenance of neurosteroid levels for behavioural anxiety responses in the adult, and point to some of the mechanisms involved in this alterations.

The effects of zolpidem treatment on GABA(A) receptors in cultured cerebellar granule cells: changes in functional coupling

AIMS

Hypnotic zolpidem is a positive allosteric modulator of γ-aminobutyric acid (GABA) action, with preferential although not exclusive binding for α1 subunit-containing GABA(A) receptors. The pharmacological profile of this drug is different from that of classical benzodiazepines, although it acts through benzodiazepine binding sites at GABA(A) receptors. The aim of this study was to further explore the molecular mechanisms of GABA(A) receptor induction by zolpidem.

MAIN METHODS

In the present study, we explored the effects of two-day zolpidem (10 μM) treatment on GABA(A) receptors on the membranes of rat cerebellar granule cells (CGCs) using [(3)H]flunitrazepam binding and semi-quantitative PCR analysis.

KEY FINDINGS

Two-day zolpidem treatment of CGCs did not significantly affect the maximum number (B(max)) of [(3)H]flunitrazepam binding sites or the expression of α1 subunit mRNA. However, as shown by decreased GABA [(3)H]flunitrazepam binding, two-day exposure of CGCs to zolpidem caused functional uncoupling of GABA and benzodiazepine binding sites at GABA(A) receptor complexes.

SIGNIFICANCE

If functional uncoupling of GABA and benzodiazepine binding sites at GABA(A) receptors is the mechanism responsible for the development of tolerance following long-term administration of classical benzodiazepines, chronic zolpidem treatment may induce tolerance.

Zolpidem for insomnia

INTRODUCTION

The imidazopyridine derivative zolpidem , which acts as a benzodiazepine (BZ) receptor agonist, is the most widely prescribed hypnotic drug in the US.

AREAS COVERED

This review addresses the neuroreceptor properties of zolpidem; clinical pharmacokinetics, pharmacodynamics and drug interactions; efficacy as a hypnotic; adverse effects; tolerance, dependence and withdrawal; relation to motor vehicle accidents and complex sleep behaviors; and new dosage forms.

EXPERT OPINION

Approved doses of zolpidem (10 mg for adults, 5 mg for the elderly) are consistently effective in reducing sleep latency and consequently increasing sleep duration in patients with insomnia. However, favorable effects on sleep maintenance are observed less consistently. Residual daytime effects are unlikely with recommended doses, and provided that at least 8 h elapse prior to arising. Hypnotic efficacy is maintained with repeated nightly use, and the risk of rebound insomnia is low. Dependence and abuse of zolpidem are no more likely to occur than with typical benzodiazepines. Newly available novel dosage forms of zolpidem have increased therapeutic options for patients with insomnia variants such as sleep maintenance insomnia and middle-of-the-night awakening.

The effects of zolpidem treatment and withdrawal on the in vitro expression of recombinant alpha1beta2gamma2s GABA(A) receptors expressed in HEK 293 cells

Zolpidem, a widely used hypnotic drug which acts through benzodiazepine binding sites, is a positive allosteric modulator of gamma-aminobutyric acid (GABA) action with preferential affinity for GABA(A) receptors containing alpha1 subunit. The pharmacological profile of zolpidem is different from that of classical benzodiazepines. The aim of this study was to find out whether zolpidem treatment triggers adaptive changes in the recombinant alpha1 subunit-containing GABA(A) receptors other than those observed following treatment with classical benzodiazepine-diazepam. Radioligand binding studies showed that 2-day exposure of human embryonic kidney (HEK) 293 cells stably expressing recombinant alpha1beta2gamma2s GABA(A) receptors to zolpidem (10 muM) up-regulated the maximum number (B (max)) of [(3)H]flunitrazepam, [(3)H]muscimol, and [(3)H]t-butylbicycloorthobenzoate ([(3)H]TBOB) binding sites without changing their affinity (K (d)), suggesting an increase in total GABA(A) receptor number. Semi-quantitative RT-PCR analysis demonstrated increased levels of alpha1 subunit mRNA, while Western blot demonstrated up-regulated gamma2 subunit proteins, suggesting that zolpidem induced de novo synthesis of receptors proteins, at both the transcriptional and translational levels. GABA-induced potentiation of [(3)H]flunitrazepam binding to membranes obtained from zolpidem-treated cells was markedly reduced, indicating allosteric uncoupling between GABA and benzodiazepine binding sites. The number of benzodiazepine and convulsant binding sites as well as the functional coupling between GABA and benzodiazepine binding sites normalized in 24 h following discontinuation of zolpidem treatment. The results of our in vitro studies suggest that a 2-day exposure of recombinant alpha1 subunit-containing GABA(A) receptors stably transfected in HEK 293 cells to zolpidem induces adaptive changes in this selective GABA(A) receptor subtype, which are not substantially different from those obtained after prolonged exposure of cells to high concentrations of diazepam.

Regulation of GABA(A) receptor subunit expression by pharmacological agents

The gamma-aminobutyric acid (GABA) type A receptor system, the main fast-acting inhibitory neurotransmitter system in the brain, is the pharmacological target for many drugs used clinically to treat, for example, anxiety disorders and epilepsy, and to induce and maintain sedation, sleep, and anesthesia. These drugs facilitate the function of pentameric GABA(A) receptors that exhibit widespread expression in all brain regions and large structural and pharmacological heterogeneity as a result of composition from a repertoire of 19 subunit variants. One of the main problems in clinical use of GABA(A) receptor agonists is the development of tolerance. Most drugs, in long-term use and during withdrawal, have been associated with important modulations of the receptor subunit expression in brain-region-specific manner, participating in the mechanisms of tolerance and dependence. In most cases, the molecular mechanisms of regulation of subunit expression are poorly known, partly as a result of neurobiological adaptation to altered neuronal function. More knowledge has been obtained on the mechanisms of GABA(A) receptor trafficking and cell surface expression and the processes that may contribute to tolerance, although their possible pharmacological regulation is not known. Drug development for neuropsychiatric disorders, including epilepsy, alcoholism, schizophrenia, and anxiety, has been ongoing for several years. One key step to extend drug development related to GABA(A) receptors is likely to require deeper understanding of the adaptational mechanisms of neurons, receptors themselves with interacting proteins, and finally receptor subunits during drug action and in neuropsychiatric disease processes.

Plasticity of the alpha4betadelta GABAA receptor

The GABAR [GABA(A) (gamma-aminobutyric acid type A) receptor], which mediates most inhibition in the brain, is regulated homoeostatically to maintain an optimal level of neuronal excitability. In particular, the alpha(4)betadelta subtype of the GABAR plays a pivotal role in this regulation. This receptor, which is expressed extrasynaptically on the dendrites, normally has low expression in the brain, but displays a remarkable degree of plasticity. It can also be a sensitive target for endogenous neurosteroids such as THP (3alpha-hydroxy-5[alpha]beta-pregnan-20-one (allo-pregnanolone); a neurosteroid and positive modulator of the GABAR), which is released during stress, although the effect of the steroid is polarity-dependent, such that it increases inward current, but decreases outward current, at alpha(4)beta(2)delta GABAR. Expression of alpha(4)beta(2)delta GABAR in CA1 hippocampus is also tightly regulated by fluctuating levels of neurosteroids, as seen at the onset of puberty. Declining levels of inhibition resulting from the decrease in THP at puberty are compensated for by an increase in alpha(4)betadelta GABAR along the apical dendrites of CA1 hippocampal pyramidal cells, which reduces neuronal excitability by decreasing the input resistance. However, excessive decrease of neuronal function is averted when THP levels rise, as would occur during stress, because this steroid decreases the outward GABAergic tonic current via inhibition of alpha(4)beta(2)delta GABAR, thereby restoring measures of neuronal excitability to pre-pubertal levels. Thus the homoeostatic regulation of alpha(4)betadelta GABAR expression plays an important role in maintaining ambient levels of neuronal excitability at puberty.

Puberty, steroids and GABA(A) receptor plasticity

GABA(A) receptors (GABAR) mediate most inhibition in the CNS and are also a target for neuroactive steroids such as 3alpha,5[alpha]beta-THP (3alphaOH-5[alpha]beta-OH-pregnan-20-one or [allo]pregnanolone). Although these steroids robustly enhance current gated by alpha1beta2delta GABAR, we have shown that 3alpha,5[alpha]beta-THP effects at recombinant alpha4beta2delta GABAR depend on the direction of Cl(-) flux, where the steroid increases outward flux, but decreases inward flux through the receptor. This polarity-dependent inhibition of alpha4beta2delta GABAR resulted from an increase in the rate and extent of rapid desensitization of the receptor, recorded from recombinant receptors expressed in HEK-293 cells with whole cell voltage clamp techniques. This inhibitory effect of 3alpha,5[alpha]beta-THP was not observed at other receptor subtypes, suggesting it was selective for alpha4beta2delta GABAR. Furthermore, it was prevented by a selective mutation of basic residue arginine 353 in the intracellular loop of the receptor, suggesting that this might be a putative chloride modulatory site. Expression of alpha4betadelta GABAR increases markedly at extrasynaptic sites at the onset of puberty in female mice. At this time, 3alpha,5[alpha]beta-THP decreased the inhibitory tonic current, recorded with perforated patch techniques to maintain the physiological Cl(-) gradient. By decreasing this shunting inhibition, 3alpha,5[alpha]beta-THP increased the excitability of CA1 hippocampal pyramidal cells at puberty. These effects of the steroid were opposite to those observed before puberty when 3alpha,5[alpha]beta-THP reduced neuronal excitability as a pre-synaptic effect. Behaviorally, the excitatory effect of 3alpha,5[alpha]beta-THP was reflected as an increase in anxiety at the onset of puberty in female mice. Taken together, these findings suggest that the emergence of alpha4beta2delta GABAR at the onset of puberty reverses the effect of a stress steroid. These findings may be relevant for the mood swings and increased response to stressful events reported in adolescence.

Methanol extract of Longanae Arillus augments pentobarbital-induced sleep behaviors through the modification of GABAergic systems

This experiment was performed to investigate whether methanol extract of Longanae Arillus (MELA) has hypnotic effects and/or enhances pentobarbital-induced sleep behaviors through the GABAergic systems. MELA prolonged sleep time and reduced sleep latency induced by pentobarbital similar to muscimol, a GABAA receptors agonist. MELA also increased sleep rate and sleep time in the combined administration with pentobarbital at the sub-hypnotic dosage and showed synergic effects with muscimol in potentiating sleep onset and enhancing sleep time induced by pentobarbital. However, MELA itself did not induce sleep at higher dose which was used in this experiment. In addition, both of MELA and pentobarbital increased chloride influx in primary cultured cerebellar granule cells. MELA increased GABAA receptors gamma-subunit expression and had no effect on the expression of alpha- and beta-subunits, and glutamic acid decarboxylase (GAD) in primary cultured cerebellar granule cells, showing different expression of subunits from pentobarbital. In conclusion, MELA itself does not induce sleep, but it augments pentobarbital-induced sleep behaviors through the modification of GABAergic systems.

Cyclopeptide alkaloid fraction from Zizyphi Spinosi Semen enhances pentobarbital-induced sleeping behaviors

This study aimed to investigate effects of cyclopeptide alkaloid fraction of ZSS (CAFZ) on pentobarbital-induced sleeping behaviors and to determine whether these effects were mediated by gamma-aminobutyric acid (GABA) receptors Cl(-) channel activation, using a Western blot technique and Cl(-) sensitive fluorescence probe. GABA receptors subunits expression and Cl(-) influx were investigated in cultured cerebellar granule cells. CAFZ shortened sleeping onset and prolonged sleeping time induced by pentobarbital (42 mg/kg). It also significantly increased the falling asleep rate and duration of sleeping time at a sub-hypnotic dosage of pentobarbital (28 mg/kg). In addition, CAFZ in combination with GABA A receptors agonist, muscimol, synergistically prolonged pentobarbital-induced sleeping time. Both of CAFZ and pentobarbital treatment decreased GABA A receptors alpha-subunit expression, but did not change beta- and gamma-subunit expression. However, we found CAFZ and pentobarbital increased Cl(-) influx, CAFZ showed similar effects with muscimol in potentiating Cl(-) influx inducing effects of low-dose pentobarbital. In conclusion, it is suggested that the enhancement of Cl(-) influx by CAFZ may play an important role in the potentiation of pentobarbital-induced sleeping behaviors.

Stress, ethanol, and neuroactive steroids

Neurosteroids play a crucial role in stress, alcohol dependence and withdrawal, and other physiological and pharmacological actions by potentiating or inhibiting neurotransmitter action. This review article focuses on data showing that the interaction among stress, ethanol, and neuroactive steroids may result in plastic molecular and functional changes of GABAergic inhibitory neurotransmission. The molecular mechanisms by which stress-ethanol-neuroactive steroids interactions can produce plastic changes in GABA(A) receptors have been studied using different experimental models in vivo and in vitro in order to provide useful evidence and new insights into the mechanisms through which acute and chronic ethanol and stress exposure modulate the activity of GABAergic synapses. We show detailed data on a) the effect of acute and chronic stress on peripheral and brain neurosteroid levels and GABA(A) receptor gene expression and function; b) ethanol-stimulated brain steroidogenesis; c) plasticity of GABA(A) receptor after acute and chronic ethanol exposure. The implications of these new mechanistic insights to our understanding of the effects of ethanol during stress are also discussed. The understanding of these neurochemical and molecular mechanisms may shed new light on the physiopathology of diseases, such as anxiety, in which GABAergic transmission plays a pivotal role. These data may also lead to the need for new anxiolytic, hypnotic and anticonvulsant selective drugs devoid of side effects.

Neurosteroid regulation of GABA(A) receptors: Focus on the alpha4 and delta subunits

Neurosteroids, such as the progesterone metabolite 3alpha-OH-5alpha[beta]-pregnan-20-one (THP or [allo]pregnanolone), function as potent positive modulators of the GABA(A) receptor (GABAR) when acutely administered. However, fluctuations in the circulating levels of this steroid at puberty, across endogenous ovarian cycles, during pregnancy or following chronic stress produce periods of prolonged exposure and withdrawal, where changes in GABAR subunit composition may occur as compensatory responses to sustained levels of inhibition. A number of laboratories have demonstrated that both chronic administration of THP as well as its withdrawal transiently increase expression of the alpha4 subunit of the GABAR in several areas of the central nervous system (CNS) as well as in in vitro neuronal systems. Receptors containing this subunit are insensitive to benzodiazepine (BDZ) modulation and display faster deactivation kinetics, which studies suggest underlie hyperexcitability states. Similar increases in alpha4 expression are triggered by withdrawal from other GABA-modulatory compounds, such as ethanol and BDZ, suggesting a common mechanism. Other studies have reported puberty or estrous cycle-associated increases in delta-GABAR, the most sensitive target of these steroids which underlies a tonic inhibitory current. In the studies reported here, the effect of steroids on inhibition, which influence anxiety state and seizure susceptibility, depend not only on the subunit composition of the receptor but also on the direction of Cl(-) current generated by these target receptors. The effect of neurosteroids on GABAR function thus results in behavioral outcomes relevant for pubertal mood swings, premenstrual dysphoric disorder and catamenial epilepsy, which are due to fluctuations in endogenous steroids.

Flumazenil selectively prevents the increase in alpha(4)-subunit gene expression and an associated change in GABA(A) receptor function induced by ethanol withdrawal

The actions of ethanol on gamma-aminobutyric acid type A (GABA(A)) receptors are still highly controversial issues but it appears that some of its pharmacological effects may depend on receptor subunit composition. Prolonged ethanol exposure produces tolerance and dependence and its withdrawal alters GABA(A) receptor subunit gene expression and function. Whereas benzodiazepines are clinically effective in ameliorating ethanol withdrawal symptoms, work in our laboratory showed that benzodiazepines also prevent, in vitro, some of the ethanol withdrawal-induced molecular and functional changes of the GABA(A) receptors. In the present work, we investigated the effects, on such changes, of the benzodiazepine receptor antagonist flumazenil that can positively modulate alpha(4)-containing receptors. We here report that flumazenil prevented both the ethanol withdrawal-induced up-regulation of the alpha(4)-subunit and the increase in its own modulatory action. In contrast, flumazenil did not inhibit ethanol withdrawal-induced decrease in alpha(1)- and delta-subunit expression as well as the corresponding decrease in the modulatory action on GABA(A) receptor function of both the alpha(1)-selective ligand zaleplon and the delta-containing receptor preferentially acting steroid allopregnanolone. These observations are the first molecular and functional evidence that show a selective inhibition by flumazenil of the up-regulation of alpha(4)-subunit expression elicited by ethanol withdrawal.

Neurosteroids, GABAA receptors, and ethanol dependence

RATIONALE

Changes in the expression of type A receptors for gamma-aminobutyric acid (GABA) represent one of the mechanisms implicated in the development of tolerance to and dependence on ethanol. The impact of such changes on the function and pharmacological sensitivity of GABAA receptors (GABAARs) has remained unclear, however. Certain behavioral and electrophysiological actions of ethanol are mediated by an increase in the concentration of neuroactive steroids in the brain that results from stimulation of the hypothalamic-pituitary-adrenal (HPA) axis. Such steroids include potent modulators of GABAAR function.

OBJECTIVES

We have investigated the effect of ethanol exposure and withdrawal on subunit expression and receptor function evaluated by subunit selective compounds, as well as the effects of short-term exposure to ethanol on both neurosteroid synthesis and GABAAR function, in isolated neurons and brain tissue.

RESULTS

Chronic treatment with and subsequent withdrawal from ethanol alter the expression of genes for specific GABAAR subunits in cultured rat neurons, and these changes are associated with alterations in receptor function and pharmacological sensitivity to neurosteroids, zaleplon, and flumazenil. Acute ethanol exposure increases the amount of 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in hippocampal slices by a local action independent of the activity of the HPA axis. This effect of ethanol was associated with an increased amplitude of GABAAR-mediated miniature inhibitory postsynaptic currents recorded from CA1 pyramidal neurons in such slices.

CONCLUSIONS

Chronic ethanol exposure elicits changes in the subunit composition of GABAARs, which, in turn, likely contribute to changes in receptor function associated with the altered pharmacological and behavioral sensitivity characteristic of ethanol tolerance and dependence. Ethanol may also modulate GABAAR function by increasing the de novo synthesis of neurosteroids in the brain in a manner independent of the HPA axis. This latter mechanism may play an important role in the central effects of ethanol.

Novel oral drug administration in an animal model of neuroleptic therapy

A novel method of oral drug administration was used in a neuroleptic animal study. Seventy male Sprague-Dawley rats were randomly subdivided into four groups, which were treated with clozapine, haloperidol, diazepam or a vehicle solution (5% sucrose solution). Oral drug treatment was achieved by training the rats to drink the drug of choice mixed with five percent sucrose or vehicle solution from a syringe. Within 3-4 weeks the haloperidol group developed vacuous chewing movement, which did not disappear with discontinuation of the drug. Significant weight gain was observed for all drug groups in relation to the control group, whereas only the diazepam group showed a significant increase in response latency on the disengage test of sensorimotor function, which disappeared with drug withdrawal. A novel means of testing the motivational status showed that all drug-treated groups engaged in eating chocolate before grooming (t=11.69, p<0.001), whereas the control group showed no specific tendency towards either task. Furthermore, there was a significant delay in grooming for the haloperidol group compared to the other drug groups and controls. In conclusion, a novel method of oral drug administration with minimum stress was introduced that was sufficient to cause the described changes in behavioural parameters. Additionally, the combination of tests used provided an efficient discrimination between the behavioural effects of clozapine, haloperidol and diazepam in rodents.

Long-term effects of diazepam and phenobarbital treatment during development on GABA receptors, transporters and glutamic acid decarboxylase

Diazepam (DZ) and phenobarbital (PH) are commonly used to treat early-life seizures and act on GABAA receptors (GABAR). The developing GABAergic system is highly plastic, and the long-term effects of postnatal treatment with these drugs on the GABAergic system has not been extensively examined. In the present study, we investigated the effects of prolonged DZ and PH treatment during postnatal development and then discontinuation on expression of a variety of genes involved in GABAergic neurotransmission during adulthood. Rat pups were treated with DZ, PH or vehicle from postnatal day (P) 10-P40 and then the dose was tapered for 2 weeks and terminated at P55. Expression of GABAR subunits, GABAB receptor subunits, GABA transporters (GAT) and GABA synthesizing enzymes (glutamic acid decarboxylase: GAD) mRNAs in hippocampal dentate granule neurons (DGNs) were analyzed using antisense RNA amplification at P90. Protein levels for the alpha1 subunit of GABAR, GAD67, GAT1 and 3 were also assessed using Western blotting. At P90, mRNA expression for GAT-1, 3, 4, GABAR subunits alpha4, alpha6, beta3, delta and theta and GABAB receptor subunit R1 was increased and mRNA expression for GAD65, GAD67 and GABAR subunits alpha1 and alpha3 were decreased in DGNs of rats treated with DZ and PH. The current data suggest that prolonged DZ and PH treatment during postnatal development causes permanent alterations in the expression of hippocampal GABA receptor subunits, GATs and GAD long after therapy has ended.

[Dependence on zolpidem: a report of two cases]

Zolpidem is a sedative and hypnotic drug belonging to imidazopyridine family. Zolpidem facilitates GABAA function more selectively than benzodiazepines, and produces a selective hypnotic effect. In comparison with benzodiazepines this mechanism could be reduce liability to induce dependence. Recently, some cases of zolpidem abuse and dependence have been published. The Authors report 2 cases of addiction to high dose of zolpidem and compare them with others described in the literature. Both patients had been reknown drug addicts before their first prescription of zolpidem and a borderline personality disorder was diagnosed. The patients rapidly developed over consumption and dependence of the molecule, when taking doses as high as 240 and 400 mg daily. To get zolpidem, one patient falsifies prescriptions. They don't suffer from the sedative effects while searching for anxiolytic and stimulating effects. They were also dysarthric, confused, high energy for mental and physical activity. The cases of zolpidem abuse and dependence in the literature describe these symptoms and others such as losing sense of orientation in time and space, amnesia and visual hallucinations. The most typical withdrawal symptom is high levels of anxiety. Moreover, one patient presents an epileptic seizure whereas the other display a severe psychiatric complication such a psychosis. In the literature, withdrawal was accompanied by confusion, suicidal ideas, nausea, vomiting, sweat, tremors, tachycardia and insomnia rebound. The epileptic seizures are described but acute psychosis complication is rare. Pharmacological hypotheses are described. The effects of zolpidem on GABAA receptor gene expression are consistent with the reduced tolerance liability of this drug as well as with other ability to induce both physical dependence and withdrawal syndrome. Through the review of the literature, the Authors noted that 50% of the cases of dependence on zolpidem are drug addicts, therefore concluding that drug addicts are more likely to become dependent on zolpidem.

Comparative pharmacokinetics and pharmacodynamics of short-acting hypnosedatives: zaleplon, zolpidem and zopiclone

Benzodiazepines have historically been the mainstay of treatment for sleeping disorders, yet they have many shortcomings. A new group of sedative hypnotic agents has been developed for this purpose. Similar to the benzodiazepines, zaleplon, zolpidem and zopiclone have activity at the GABA receptor complex, yet they appear to have more selectivity for certain subunits of the GABA receptor. This produces a clinical profile that is more efficacious with fewer side effects. Zaleplon, zolpidem and zopiclone are structurally distinct. Due to variation in binding to the GABA receptor subunits, these three compounds show subtle differences in their effect on sleep stages, and as antiepileptics, anxiolytics and amnestics. The duration of action of zaleplon, zolpidem and zopiclone can be related to their individual pharmacokinetic profile, which subsequently determines the time course of drug effect. Each of these compounds has a unique pharmacokinetic profile with different bioavailability, volume of distribution and elimination half-lives. Zaleplon has a rapid elimination so there are fewer residual side effects after taking a single dose at bedtime. By comparison, zolpidem and zopiclone have a more delayed elimination so there may be a prolonged drug effect. This can result in residual sedation and side effects but may be useful for sustained treatment of insomnia with less waking during the night. There are also differences in potency based on plasma concentrations suggesting that there are differences in binding to the GABA receptor complex. Although zaleplon has a much lower bioavailability (30%), the treatment dose is similar to zolpidem and zopiclone (bioavilaibility of 70%) because of the increased potency of zaleplon. The pharmacokinetics and pharmacodynamics of zaleplon, zolpidem and zopiclone are significantly different from benzodiazepines. The new drugs are sufficiently unique from each other to allow customisation of treatment for various types of insomnia. While zaleplon may be best indicated for the delayed onset of sleep, zolpidem and zopiclone may be better indicated for maintaining a complete night's sleep. Only the patient's symptoms and response to treatment will dictate the best course of treatment.

Inhibition by miltirone of up-regulation of GABAA receptor α4 subunit mRNA by ethanol withdrawal in hippocampal neurons

Miltirone, a tanshinone isolated from the root of Salvia miltiorrhiza, has been characterized as a low-affinity ligand for central benzodiazepine receptors. We have now shown that this compound bound with low affinity (micromolar range) to central benzodiazepine recognition sites but did not interact with peripheral benzodiazepine receptors. It failed to potentiate Cl(-) currents induced by gamma-aminobutyric acid (GABA) both in Xenopus oocytes expressing recombinant human GABA(A) receptors and in cultured rat hippocampal pyramidal cells, but it inhibited the ability of diazepam to potentiate the effect of GABA in these systems. Miltirone (1-10 microM) also partially inhibited the increase in the abundance of the mRNA for the alpha(4) subunit of the GABA(A) receptor induced by ethanol withdrawal in cultured hippocampal neurons. These results suggest that miltirone might ameliorate the symptoms associated with discontinuation of long-term administration of ethanol or of other positive modulators of the GABA(A) receptor.

Detoxification from High-Dose Zolpidem Using Diazepam

OBJECTIVE

To report a rare case of physical and psychological addiction to an excessive dose of zolpidem and subsequent completed detoxification using diazepam.

CASE SUMMARY

A 46-year-old white man with a history of polysubstance abuse received a prescription for zolpidem 2 years prior to his hospital detoxification. During that time, he gradually escalated the total dosage to an amount of 400 mg/day in divided doses. Upon hospitalization, he was detoxified using a standard benzodiazepine 7-day diazepam tapering regimen.

DISCUSSION

Zolpidem is a nonbenzodiazepine medication approved for the short-term treatment of insomnia. Its mechanism is a selective benzodiazepine type 1 receptor agonist. The selectivity of the drug for the type 1 receptor may not be absolute and is inversely dose dependent. Compared with the benzodiazepines, zolpidem addiction is rare. However, at higher than recommended doses for extended periods of time, its addictive potential may be similar to that of the benzodiazepines.

CONCLUSIONS

Given the similarities in receptor binding and pharmacologic activities of zolpidem and the benzodiazepines, we chose to use a standard benzodiazepine detoxification protocol to treat zolpidem withdrawal. Confirmation of this has been evidenced by successful zolpidem detoxification using a standard 7-day benzodiazepine/diazepam taper regimen.

Encapsulation and release of the hypnotic agent zolpidem from biodegradable polymer microparticles containing hydroxypropyl-beta-cyclodextrin

The goal of this study was to design a prolonged release system of the hypnotic agent zolpidem (ZP) useful for the treatment of insomnia. In this work, ZP alone or in the presence of HP-beta-CD was encapsulated in microparticles constituted by poly(DL-lactide) (PDLLA) and poly(DL-lactide-co-glycolide) (PLGA) and the drug release from these systems was evaluated. ZP alone-loaded microparticles were prepared by the classical O/W emulsion-solvent evaporation method. Conversely, ZP/HP-beta-CD containing microparticles were prepared by the W/O/W emulsion-solvent evaporation method following two different procedures (i.e. A and B). Following procedure A, the previously produced ZP/HP-beta-CD solid complex was added to the water phase of primary emulsion. In the procedure B, HP-beta-CD was added to the aqueous phase and ZP to the organic phase. The resulting microparticles were characterized about morphology, size, encapsulation efficiency and release rates. FT-IR, X-ray, and DSC results suggest the drug is in an essentially amorphous state within the microparticles. The release profiles of ZP from microparticles were in general biphasic, being characterized by an initial burst effect and a subsequent slow ZP release. It resulted that co-encapsulating ZP with or without HP-beta-CD in PDLLA and PLGA the drug release from the corresponding microparticles was protracted. Moreover, in a preliminary pharmacological screening, the ataxic activity in rats was investigated and it was found that intragastric administration of the ZP/HP-beta-CD/PLGA microparticles prepared according to procedure B produced the same ataxic induction time as the one induced by the currently used formulation Stilnox. Interestingly moreover, there was a longer ataxic lasting and a lower intensity of ataxia produced by the ZP/HP-beta-CD/PLGA-B-formulation already after 60 min following the administration. However, a need for further pharmacokinetic and pharmacodynamic studies resulted to fully evaluate the utility of this last formulation for the sustained delivery of ZP.

Changes in GABA(A) receptor gene expression associated with selective alterations in receptor function and pharmacology after ethanol withdrawal

Changes in the expression of subunits of the GABA type A (GABA(A)) receptor are implicated in the development of ethanol tolerance and dependence as well as in the central hyperexcitability associated with ethanol withdrawal. The impact of such changes on GABA(A) receptor function and pharmacological sensitivity was investigated with cultured rat hippocampal neurons exposed to ethanol for 5 d and then subjected to ethanol withdrawal. Both ethanol treatment and withdrawal were associated with a marked decrease in the maximal density of GABA-evoked Cl- currents, whereas the potency of GABA was unaffected. Ethanol exposure also reduced the modulatory efficacy of the benzodiazepine receptor agonists lorazepam, zolpidem, and zaleplon as well as that of the inverse agonists Ro 15-4513 and FG 7142, effects that were associated with a reduced abundance of mRNAs encoding the receptor subunits alpha1, alpha3, gamma2L, and gamma2S. Ethanol withdrawal restored the efficacy of lorazepam, but not that of low concentrations of zolpidem or zaleplon, to control values. Flumazenil, which was ineffective in control neurons, and Ro 15-4513 each potentiated the GABA response after ethanol withdrawal. These effects of withdrawal were accompanied by upregulation of the alpha2, alpha3, and alpha4 subunit mRNAs as well as of the alpha4 protein. Diazepam or gamma-hydroxybutyrate, but not baclofen, prevented the changes in both GABA(A) receptor pharmacology and subunit mRNA levels induced by ethanol withdrawal. Changes in GABA(A) receptor gene expression induced by prolonged exposure to and withdrawal of ethanol are thus associated with altered GABA(A) receptor function and pharmacological sensitivity.

Ethanol withdrawal-induced up-regulation of the α2 subunit of the GABAA receptor and its prevention by diazepam or γ-hydroxybutyric acid

The gamma-aminobutyric acid type A (GABA(A)) receptor is an important pharmacological target of ethanol. The effect of ethanol withdrawal on the expression of the alpha(2) subunit of this receptor was examined with rat cerebellar granule cells in primary culture. Long-term exposure of these cells to ethanol (100 mM, 5 days) did not affect the abundance of the mRNA for the alpha(2) subunit, as revealed by an RNase protection assay. In contrast, subsequent ethanol withdrawal for 3 h induced a marked increase in the amount of this mRNA (2.6-fold) as well as in that of the encoded polypeptide (2.2-fold), the latter revealed by immunoblot analysis. Exposure of the cells to gamma-hydroxybutyric acid (100 mM) during ethanol withdrawal prevented the increase in the amounts of both the alpha(2) mRNA and polypeptide, whereas similar treatment with diazepam (10 microM) blocked the increase in the abundance of the alpha(2) polypeptide but not that in the amount of the alpha(2) mRNA. The effect of gamma-hydroxybutyric acid was not blocked by the competitive GABA(B) receptor antagonist SCH 50911(10 microM). Given that the alpha(2) subunit of the GABA(A) receptor mediates the anxiolytic action of benzodiazepines, its up-regulation during discontinuation of long-term ethanol exposure might be relevant to the therapeutic efficacy of these drugs in the treatment of anxiety associated with ethanol withdrawal.

Molecular mechanisms of tolerance to and withdrawal of GABA(A) receptor modulators

Here, we summarize recent data pertaining to the effects of GABA(A) receptor modulators on the receptor gene expression in order to elucidate the molecular mechanisms behind tolerance and dependence induced by these drugs. Drug selectivity and intrinsic activity seems to be important to evidence at the molecular level the GABA(A) receptor tolerance. On the contrary, we suggested that all drug tested are equally potentially prone to induce dependence. Our results demonstrate that long-lasting exposure of GABA(A) receptors to endogenous steroids, benzodiazepines and ethanol, as well as their withdrawal, induce marked effects on receptor structure and function. These results suggest the possible synergic action between endogenous steroids and these drugs in modulating the functional activity of specific neuronal populations. We report here that endogenous steroids may play a crucial role in the action of ethanol on dopaminergic neurons.

A Novel Clinical Pattern of Visual Hallucination After Zolpidem Use

BACKGROUND

Zolpidem is a new hypnotic that is supposed to have fewer side effects than traditional benzodiazepines. Some psychotic reactions, such as visual or hypnagogic hallucinations, have been reported to be associated with zolpidem use.

CASE REPORT

A young female experienced three episodes of hallucination associated with the use of zolpidem. The visual or hypnagogic hallucination happened after she had stopped zolpidem and then restarted it 2 days later.

CONCLUSION

We postulate that hypnagogic or visual hallucinations associated with zolpidem use may be related to rapid withdrawal and restarting of zolpidem. The possible mechanism may be associated with the changes in the GABAA receptor. Avoiding "as needed" use of zolpidem and using the lowest effective dose may prevent these adverse effects.

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.

Anxiogenic effects of neurosteroid exposure: sex differences and altered GABAA receptor pharmacology in adult rats

Acute exposure to progesterone or its neurosteroid derivative allopregnanolone (3alpha,5alpha-THP) is anxiolytic, consistent with the GABA modulatory effects of 3alpha,5alpha-THP at the GABA(A) receptor. However, continuous exposure to progesterone increases anxiety in association with increased expression of the benzodiazepine-insensitive GABA(A) receptor alpha4 subunit. Furthermore, negative mood symptoms and altered GABA(A) receptor pharmacology in patients with premenstrual dysphoric disorder occur in the early luteal phase in association with peak circulating levels of progesterone and 3alpha,5alpha-THP. Because sex differences have been reported in steroid-regulated anxiety responses, the present study investigated the role of sex and development in the regulation of anxiety after short-term exposure to 3alpha,5alpha-THP. To this end, we compared the effects of hormone administration in adult male, adult female, and juvenile female rats. Increased anxiety in the elevated plus maze was evident in all groups after 48-h exposure to either 3alpha,5alpha-THP or progesterone. At this time point, alterations in the anxiolytic profile of benzodiazepine agonists and antagonists were also observed in both adult males and females in the elevated plus maze. However, sex differences in the acoustic startle response were observed after short-term hormone treatment such that only female rats displayed an increased response indicative of higher anxiety levels. These results suggest that although neurosteroid exposure may influence both the pharmacological properties of the GABA(A) receptor and the manifestation of anxiety in both sexes, the effects of neurosteroids may be modulated in a sex- and task-specific manner.

Gamma-hydroxybutyric acid and diazepam antagonize a rapid increase in GABA(A) receptors alpha(4) subunit mRNA abundance induced by ethanol withdrawal in cerebellar granule cells

Both benzodiazepines and gamma-hydroxybutyric acid (GHB) are used to treat alcohol withdrawal syndrome. The molecular basis for this therapeutic efficacy was investigated with primary cultures of rat cerebellar granule cells. Long-term exposure of these cells to ethanol (100 mM, 5 days) reduced the abundance of mRNAs encoding the gamma(2)L and gamma(2)S subunits of the GABA type A receptor (-32 and -23%, respectively) but failed to affect that of alpha(1), alpha(4), or alpha(6) subunit mRNAs. Subsequent ethanol withdrawal resulted in decreases in the amounts of alpha(1) (-29%), alpha(6) (-27%), gamma(2)L (-64%), and gamma(2)S (-76%),subunit mRNAs that were maximal after 6 to 12 h. In contrast, 3 h after ethanol withdrawal, the abundance of the alpha(4) subunit mRNA was increased by 46%. Ethanol withdrawal did not affect neuronal morphology but reduced cellular metabolic activity. The increase in alpha(4) subunit was confirmed by functional studies showing a positive action of flumazenil in patch clamp recordings of GABA-stimulated currents after ethanol withdrawal. Diazepam (10 microM) or GHB (100 mM) prevented the increase in the amount of the alpha(4) subunit mRNA, the metabolic impairment, and the positive action of flumazenil induced by ethanol withdrawal but failed to restore the expression of the alpha(1) and gamma(2) subunits. The antagonism by GHB seems not to be mediated by a direct action at GABA(A)R because GHB failed to potentiate the effects of GABA or diazepam on Cl(-) currents mediated by GABA type A receptor.

Changes in GABA(A) receptor gene expression induced by withdrawal of, but not by long-term exposure to, ganaxolone in cultured rat cerebellar granule cells

The effects of ganaxolone, a synthetic analog of the endogenous neuroactive steroid allopregnanolone, on the function and expression of GABA(A) receptors were determined. Electrophysiological recordings demonstrated that ganaxolone potentiated with a potency and efficacy similar to those of allopregnanolone the Cl- currents evoked by GABA at recombinant human GABA(A) receptors (comprising alpha1beta2gamma2L or alpha2beta2gamma2L subunit assemblies) expressed in Xenopus oocytes. Exposure of cultured rat cerebellar granule cells to 1 microM ganaxolone for 5 days had no effect on the abundance of mRNAs encoding the alpha1, alpha2, alpha3, alpha4, alpha5, gamma2L, or gamma2S subunits of the GABA(A) receptor. Withdrawal of ganaxolone after such long-term treatment, however, induced an increase in the abundance of alpha2, alpha4, and alpha5 subunit mRNAs and a decrease in the amounts of alpha1, gamma2L, and gamma2S subunit mRNAs. These changes were maximal 3 to 6 h after drug withdrawal and were reversible, being no longer apparent after 24 h. These results suggest that long-term exposure of cerebellar granule cells to ganaxolone does not affect the sensitivity of the GABA(A) receptor to several positive modulators. Nevertheless, the reduction in the amounts of the alpha1 and gamma2 subunit mRNAs together with the increase in the abundance of the alpha4 subunit mRNA induced by abrupt discontinuation of long-term treatment with ganaxolone suggest that withdrawal of this drug might result in a reduced response to classic benzodiazepines.

Comparison of the effects of zaleplon, zolpidem, and triazolam at various GABA(A) receptor subtypes

The pyrazolopyrimidine zaleplon is a hypnotic agent that acts at the benzodiazepine recognition site of GABA(A) receptors. Zaleplon, like the hypnotic agent zolpidem but unlike classical benzodiazepines, exhibits preferential affinity for type I benzodiazepine (BZ(1)/omega(1)) receptors in binding assays. The modulatory action of zaleplon at GABA(A) receptors has now been compared with those of zolpidem and the triazolobenzodiazepine triazolam. Zaleplon potentiated GABA-evoked Cl(-) currents in Xenopus oocytes expressing human GABA(A) receptor subunits with a potency that was higher at alpha1beta2gamma2 receptors than at alpha2- or alpha3-containing receptors. Zolpidem, but not triazolam, also exhibited selectivity for alpha1-containing receptors. However, the potency of zaleplon at these various receptors was one-third to one-half that of zolpidem. Zaleplon and zolpidem also differed in their actions at receptors containing the alpha5 or gamma3 subunit. Zaleplon, zolpidem, and triazolam exhibited similar patterns of efficacy among the different receptor subtypes. The affinities of zaleplon for [(3)H]flunitrazepam or t-[(35)S]butylbicyclophosphorothionate ([(35)S]TBPS) binding sites in rat brain membranes were lower than those of zolpidem or triazolam. Furthermore, zaleplon, unlike zolpidem, exhibited virtually no affinity for the peripheral type of benzodiazepine receptor.

Progesterone withdrawal increases the alpha4 subunit of the GABA(A) receptor in male rats in association with anxiety and altered pharmacology - a comparison with female rats

Withdrawal from the neurosteroid 3alpha,5alpha-allopregnanolone after chronic administration of progesterone increases anxiety in female rats and up-regulates the alpha4 subunit of the GABA(A) receptor (GABA(A)-R) in the hippocampus. We investigated if these phenomena would also occur in male rats. Progesterone withdrawal (PWD) induced higher alpha4 subunit expression in the hippocampus of both male and female rats, in association with increased anxiety (assessed in the elevated plus maze) comparable to effects previously reported. Because alpha4-containing GABA(A)-R are insensitive to the benzodiazepine (BDZ) lorazepam (LZM), and are positively modulated by flumazenil (FLU, a BDZ antagonist), we therefore tested the effects of these compounds following PWD. Using whole-cell patch clamp techniques, LZM-potentiation of GABA ((EC20))-gated current was markedly reduced in CA1 pyramidal cells of male rats undergoing PWD compared to controls, whereas FLU had no effect on GABA-gated current in control animals but increased it in PWD animals. Behaviorally, both male and female rats were significantly less sensitive to the anxiolytic effects of LZM. In contrast, FLU demonstrated significant anxiolytic effects following PWD. These data suggest that neurosteroid regulation of the alpha4 GABA(A)-R subunit may be a relevant mechanism underlying anxiety disorders, and that this phenomenon is not sex-specific.