Effect of an imidazobenzodiazepine, Ro15-4513, on the incoordination and hypothermia produced by ethanol and pentobarbital

Artemether confers neuroprotection on cerebral ischemic injury through stimulation of the Erk1/2-P90rsk-CREB signaling pathway

Ischemic stroke is one of the leading causes of death and disability among adults. Despite the economic burden of the disease, available treatment options are still very limited. With the exception of anti-thrombolytics and hypothermia, current therapies fail to reduce neuronal injury, neurological deficits and mortality rates, suggesting that the development of novel and more effective therapies against ischemic stroke is urgent. In the present study, we found that artemether, which has been used in the clinic as an anti-malarial drug, was able to improve the neurological deficits, attenuate the infarction volume and the brain water content in a middle cerebral artery occlusion (MCAO) animal model. Furthermore, artemether treatment significantly suppressed cell apoptosis, stimulated cell proliferation and promoted the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), P90^rsk and cAMP responsive element-binding protein (CREB). Artemether protective effect was attenuated by PD98059, an ERK1/2 inhibitor, administration. Similarly, in oxygen-glucose deprivation/reperfusion (OGD/RP) cell models, artemether pre-treatment induced the suppression of the intracellular ROS, the down-regulation of LDH activity, the reduction of caspase 3 activity and of the apoptosis cell rate and reversed the decrease of mitochondrial membrane potential. As with MCAO animal model, artemether promoted the activation of Erk1/2-P90^rsk-CREB signaling pathway. This effect was blocked by the inhibition or knock-down of ERK1/2. The present study provides evidences of the neuroprotective effect of artemether unravelling its potential as a new therapeutic candidate for the prevention and treatment of stroke.

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Artemether conferred neuroprotection in a middle cerebral artery occlusion (MCAO) animal model.

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Artemether conferred neuroprotection on oxygen-glucose deprivation/reperfusion-induced cell injury model.

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Artemether promoted the activation of Erk1/2-P90^rsk-CREB signaling pathway in vitro and in vivo.

Potentiation of Gamma Aminobutyric Acid Receptors (GABAAR) by Ethanol: How Are Inhibitory Receptors Affected?

In recent years there has been an increase in the understanding of ethanol actions on the type A γ-aminobutyric acid chloride channel (GABA_AR), a member of the pentameric ligand gated ion channels (pLGICs). However, the mechanism by which ethanol potentiates the complex is still not fully understood and a number of publications have shown contradictory results. Thus many questions still remain unresolved requiring further studies for a better comprehension of this effect. The present review concentrates on the involvement of GABA_AR in the acute actions of ethanol and specifically focuses on the immediate, direct or indirect, synaptic and extra-synaptic modulatory effects. To elaborate on the immediate, direct modulation of GABA_AR by acute ethanol exposure, electrophysiological studies investigating the importance of different subunits, and data from receptor mutants will be examined. We will also discuss the nature of the putative binding sites for ethanol based on structural data obtained from other members of the pLGICs family. Finally, we will briefly highlight the glycine gated chloride channel (GlyR), another member of the pLGIC family, as a suitable target for the development of new pharmacological tools.

α4-Containing GABA(A) Receptors are Required for Antagonism of Ethanol-Induced Motor Incoordination and Hypnosis by the Imidazobenzodiazepine Ro15-4513

Alcohol (ethanol) is widely consumed for its desirable effects but unfortunately has strong addiction potential. Some imidazobenzodiazepines such as Ro15-4513 are able to antagonize many ethanol-induced behaviors. Controversial biochemical and pharmacological evidence suggest that the effects of these ethanol antagonists and ethanol are mediated specifically via overlapping binding sites on α4/δ-containing GABA_A-Rs. To investigate the requirement of α4-containing GABA_A-Rs in the mechanism of action of Ro15-4513 on behavior, wildtype (WT) and α4 knockout (KO) mice were compared for antagonism of ethanol-induced motor incoordination and hypnosis. Motor effects of ethanol were tested in two different fixed speed rotarod assays. In the first experiment, mice were injected with 2.0 g/kg ethanol followed 5 min later by 10 mg/kg Ro15-4513 (or vehicle) and tested on a rotarod at 8 rpm. In the second experiment, mice received a single injection of 1.5 g/kg ethanol ± 3 mg/kg Ro15-4513 and were tested on a rotarod at 12 rpm. In both experiments, the robust Ro15-4513 antagonism of ethanol-induced motor ataxia that was observed in WT mice was absent in KO mice. A loss of righting reflex (LORR) assay was used to test Ro15-4513 (20 mg/kg) antagonism of ethanol (3.5 g/kg)-induced hypnosis. An effect of sex was observed on the LORR assay, so males and females were analyzed separately. In male mice, Ro15-4513 markedly reduced ethanol-induced LORR in WT controls, but α4 KO mice were insensitive to this effect of Ro15-4513. In contrast, female KO mice did not differ from WT controls in the antagonistic effects of Ro15-4513 on ethanol-induced LORR. We conclude that Ro15-4513 requires α4-containing receptors for antagonism of ethanol-induced LORR (in males) and motor ataxia.

GABAA receptors in the posterior, but not anterior, ventral tegmental area mediate Ro15-4513-induced attenuation of binge-like ethanol consumption in C57BL/6J female mice

GABA(A) receptors have been shown to modulate dopaminergic output from the ventral tegmental area (VTA) in studies of both natural and drug rewards, including alcohol. Ro15-4513, the imidazobenzodiazepine derivative and allosteric modulator at the GABA(A) receptor, reliably antagonizes the behavioral effects of alcohol. Various models of alcohol consumption show a decrease in consummatory behaviors, specific to ethanol, following acute administration of the drug. In the present study, Ro15-4513 was systemically administered, or microinjected into the anterior or posterior VTA, to explore the role of GABA(A) receptors at this region in modulating the high pattern of alcohol consumption by C57BL/6J inbred mice in the Drinking in the Dark (DID) model. Animals had 2h access to ethanol for 6 days prior to drug manipulations. Immediately before the seventh day of access, mice were systemically (I.P.) or site-specifically administered Ro15-4513. Systemic Ro15-4513 (at 10mg/kg) decreased binge-like ethanol intake in the DID paradigm. Additionally, there was a stepwise decrease in consumption following Ro15-4513 microinjection into the posterior VTA, with the highest dose significantly decreasing ethanol intake. There was no effect found following microinjection into the anterior VTA, nor was there an effect of systemic or intra-posterior VTA Ro15-4513 on consumption of a 5% sucrose solution or water. The present findings support a role for Ro15-4513 sensitive VTA-GABA(A) receptors in modulating binge-like ethanol consumption. Moreover, the work here adds to the growing body of literature suggesting regional heterogeneity in the VTA.

Attenuation of the stimulant response to ethanol is associated with enhanced ataxia for a GABA, but not a GABA, receptor agonist

BACKGROUND

The gamma-aminobutyric acid (GABA) system is implicated in the neurobiological actions of ethanol, and pharmacological agents that increase the activity of this system have been proposed as potential treatments for alcohol use disorders. As ethanol has its own GABA mimetic properties, it is critical to determine the mechanism by which GABAergic drugs may reduce the response to ethanol (i.e., via an inhibition or an accentuation of the neurobiological effects of ethanol).

METHODS

In this study, we examined the ability of 3 different types of GABAergic compounds, the GABA reuptake inhibitor NO-711, the GABA(A) receptor agonist muscimol, and the GABA(B) receptor agonist baclofen, to attenuate the locomotor stimulant response to ethanol in FAST mice, which were selectively bred for extreme sensitivity to ethanol-induced locomotor stimulation. To determine whether these compounds produced a specific reduction in stimulation, their effects on ethanol-induced motor incoordination were also examined.

RESULTS

NO-711, muscimol, and baclofen were all found to potently attenuate the locomotor stimulant response to ethanol in FAST mice. However, both NO-711 and muscimol markedly increased ethanol-induced ataxia, whereas baclofen did not accentuate this response.

CONCLUSIONS

These results suggest that pharmacological agents that increase extracellular concentrations of GABA and GABA(A) receptor activity may attenuate the stimulant effects of ethanol by accentuating its intoxicating and sedative properties. However, selective activation of the GABA(B) receptor appears to produce a specific attenuation of ethanol-induced stimulation, suggesting that GABA(B) receptor agonists may hold greater promise as potential pharmacotherapies for alcohol use disorders.

Zolpidem generalization and antagonism in male and female cynomolgus monkeys trained to discriminate 1.0 or 2.0 g/kg ethanol

BACKGROUND

The subtypes of gamma-aminobutyric acid (GABA)(A) receptors mediating the discriminative stimulus effects of ethanol in nonhuman primates are not completely identified. The GABA(A) receptor positive modulator zolpidem has high, intermediate, and low activity at receptors containing alpha(1), alpha(2/3), and alpha(5) subunits, respectively, and partially generalizes from ethanol in several species. The partial inverse agonist Ro15-4513 has the greatest affinity for alpha(4/6)-containing receptors, higher affinity for alpha(5)- and lower, but equal, affinity for alpha(1)- and alpha(2/3)-, containing GABA(A) receptors, and antagonizes the discriminative stimulus effects of ethanol.

METHODS

This study assessed Ro15-4513 antagonism of the generalization of zolpidem from ethanol in male (n = 9) and female (n = 8) cynomolgus monkeys (Macaca fascicularis) trained to discriminate 1.0 g/kg (n = 10) or 2.0 g/kg (n = 7) ethanol (i.g.) from water with a 30-minute pretreatment interval.

RESULTS

Zolpidem (0.017 to 5.6 mg/kg, i.m.) completely generalized from ethanol (>or=80% of total session responses on the ethanol-appropriate lever) for 6/7 monkeys trained to discriminate 2.0 g/kg and 4/10 monkeys trained to discriminate 1.0 g/kg ethanol. Zolpidem partially generalized from 1.0 or 2.0 g/kg ethanol in 6/7 remaining monkeys. Ro15-4513 (0.003 to 0.30 mg/kg, i.m., 5-minute pretreatment) shifted the zolpidem dose-response curve to the right in all monkeys showing generalization. Analysis of apparent pK(B) from antagonism tests suggested that the discriminative stimulus effects of ethanol common with zolpidem are mediated by low-affinity Ro15-4513 binding sites. Main effects of sex and training dose indicated greater potency of Ro15-4513 in males and in monkeys trained to discriminate 1.0 g/kg ethanol.

CONCLUSIONS

Ethanol and zolpidem share similar discriminative stimulus effects most likely through GABA(A) receptors that contain alpha(1) subunits, however, antagonism by Ro15-4513 of zolpidem generalization from the lower training dose of ethanol (1.0 g/kg) may involve additional zolpidem-sensitive GABA(A) receptor subtypes (e.g., alpha(2/3) and alpha(5)).

Physiology and pharmacology of alcohol: the imidazobenzodiazepine alcohol antagonist site on subtypes of GABAA receptors as an opportunity for drug development?

Alcohol (ethanol, EtOH) has pleiotropic actions and induces a number of acute and long-term effects due to direct actions on alcohol targets, and effects of alcohol metabolites and metabolism. Many detrimental health consequences are due to EtOH metabolism and metabolites, in particular acetaldehyde, whose high reactivity leads to nonspecific chemical modifications of proteins and nucleic acids. Like acetaldehyde, alcohol has been widely considered a nonspecific drug, despite rather persuasive evidence implicating inhibitory GABA(A) receptors (GABA(A)Rs) in acute alcohol actions, for example, a GABA(A)R ligand, the imidazobenzodiazepine Ro15-4513 antagonizes many low-to-moderate dose alcohol actions in mammals. It was therefore rather surprising that abundant types of synaptic GABA(A)Rs are generally not responsive to relevant low concentrations of EtOH. In contrast, delta-subunit-containing GABA(A)Rs and extrasynaptic tonic GABA currents mediated by these receptors are sensitive to alcohol concentrations that are reached in blood and tissues during low-to-moderate alcohol consumption. We recently showed that low-dose alcohol enhancement on highly alcohol-sensitive GABA(A)R subtypes is antagonized by Ro15-4513 in an apparently competitive manner, providing a molecular explanation for behavioural Ro15-4513 alcohol antagonism. The identification of a Ro15-4513/EtOH binding site on unique GABA(A)R subtypes opens the possibility to characterize this alcohol site(s) and screen for compounds that modulate the function of EtOH/Ro15-4513-sensitive GABA(A)Rs. The utility of such drugs might range from novel alcohol antagonists that might be useful in the emergency room, to drugs for the treatment of alcoholism, as well as alcohol-mimetic drugs to harness acute positive effects of alcohol.

Tonic for what ails us? high-affinity GABAA receptors and alcohol

Ethanol interactions with gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the brain, play key roles in acute intoxication. However, the exact mechanisms of these ethanol interactions have been the subject of considerable confusion and controversy. Many studies suggest that ethanol potentiates the function of the type A GABA receptor (GABAA-R). However, these findings have not been consistently replicated in experiments that directly examined the effects of ethanol on GABAA-R-mediated ion current. Differences in ethanol sensitivity of different GABAA-R subtypes have been invoked as a potential explanation for the inconsistent findings, and recent work suggests that GABAA-Rs that contain the delta subunit and/or mediate tonic extrasynaptic GABA responses may be especially ethanol sensitive. However, considerable disagreement has arisen over these findings. This special issue of Alcohol contains articles from eight research groups that are examining this issue. The authors present their work, their views on the present state of this area of alcohol research, and their ideas about how to proceed with future studies that may help to address the present confusion and controversy. This editorial provides an introduction to this line of research and the current findings and controversies.

Low dose acute alcohol effects on GABA A receptor subtypes

GABA(A) receptors (GABA(A)Rs) are the main inhibitory neurotransmitter receptors and have long been implicated in mediating at least part of the acute actions of ethanol. For example, ethanol and GABAergic drugs including barbiturates and benzodiazepines share many pharmacological properties. Besides the prototypical synaptic GABA(A)R subtypes, nonsynaptic GABA(A)Rs have recently emerged as important regulators of neuronal excitability. While high doses (> or =100 mM) of ethanol have been reported to enhance activity of most GABA(A)R subtypes, most abundant synaptic GABA(A)Rs are essentially insensitive to ethanol concentrations that occur during social ethanol consumption (< 30 mM). However, extrasynaptic delta and beta3 subunit-containing GABA(A)Rs, associated in the brain with alpha4 or alpha6 subunits, are sensitive to low millimolar ethanol concentrations, as produced by drinking half a glass of wine. Additionally, we found that a mutation in the cerebellar alpha6 subunit (alpha6R100Q), initially reported in rats selectively bred for increased alcohol sensitivity, is sufficient to produce increased alcohol-induced motor impairment and further increases of alcohol sensitivity in recombinant alpha6beta3delta receptors. Furthermore, the behavioral alcohol antagonist Ro15-4513 blocks the low dose alcohol enhancement on alpha4/6/beta3delta receptors, without reducing GABA-induced currents. In binding assays alpha4beta3delta GABA(A)Rs bind [(3)H]Ro15-4513 with high affinity, and this binding is inhibited, in an apparently competitive fashion, by low ethanol concentrations, as well as analogs of Ro15-4513 that are active to antagonize ethanol or Ro15-4513's block of ethanol. We conclude that most low to moderate dose alcohol effects are mediated by alcohol actions on alcohol/Ro15-4513 binding sites on GABA(A)R subtypes.

Low-dose alcohol actions on alpha4beta3delta GABAA receptors are reversed by the behavioral alcohol antagonist Ro15-4513

Although it is now more than two decades since it was first reported that the imidazobenzodiazepine Ro15-4513 reverses behavioral alcohol effects, the molecular target(s) of Ro15-4513 and the mechanism of alcohol antagonism remain elusive. Here, we show that Ro15-4513 blocks the alcohol enhancement on recombinant "extrasynaptic" alpha4/6beta3delta GABA(A) receptors at doses that do not reduce the GABA-induced Cl(-) current. At low ethanol concentrations (< or =30 mM), the Ro15-4513 antagonism is complete. However, at higher ethanol concentrations (> or =100 mM), there is a Ro15-4513-insensitive ethanol enhancement that is abolished in receptors containing a point mutation in the second transmembrane region of the beta3 subunit (beta3N265M). Therefore, alpha4/6beta3delta GABA receptors have two distinct alcohol modulation sites: (i) a low-dose ethanol site present in alpha4/6beta3delta receptors that is antagonized by the behavioral alcohol antagonist Ro15-4513 and (ii) a site activated at high (anesthetic) alcohol doses, defined by mutations in membrane-spanning regions. Receptors composed of alpha4beta3N265Mdelta subunits that lack the high-dose alcohol site show a saturable ethanol dose-response curve with a half-maximal enhancement at 16 mM, close to the legal blood alcohol driving limit in most U.S. states (17.4 mM). Like in behavioral experiments, the alcohol antagonist effect of Ro15-4513 on recombinant alpha4beta3delta receptors is blocked by flumazenil and beta-carboline-ethyl ester (beta-CCE). Our findings suggest that ethanol/Ro15-4513-sensitive GABA(A) receptors are important mediators of behavioral alcohol effects.

The role of GABAergic neuroactive steroids in ethanol action, tolerance and dependence

This article reviews data on ethanol and neurosteroid interactions in the CNS. We discuss how GABAergic neurosteroids, including 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC, produced in response to systemic ethanol administration contribute to several of the effects of ethanol associated with modulation of GABA(A) receptors in rodents. There is an essential correlation between the time course of ethanol-induced 3alpha,5alpha-TH PROG production in the brain and specific behavioral and neural effects of ethanol. Furthermore, the anticonvulsant and inhibitory effects of ethanol on spontaneous neural activity were completely prevented by a key inhibitor of steroid biosynthesis. 3alpha,5alpha-TH PROG influences cognitive processing, spatial learning and memory and alters drinking behaviors in rats. Furthermore, ethanol induction of 3alpha,5alpha-TH PROG is diminished in tolerant and dependent animals. These effects are associated with increases in the sensitivity of GABA(A) receptors to neurosteroids and suggest an important role in ethanol withdrawal. Together, we suggest that 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC contribute to ethanol action and this interaction may represent a new mechanism of ethanol action. The identification of neurosteroid intermediaries involved in ethanol action may lead to important advances in the field and the development of novel therapeutics for alcoholism.

The striatal adenosinergic modulation of ethanol-induced motor incoordination in rats: possible role of chloride flux

Previous studies from our laboratory have provided strong evidence that brain adenosine modulates acute ethanol (i.p.)-induced motor incoordination (MI) through receptor mediated mechanism(s). Recently, we have reported the involvement of the striatum in ethanol-induced MI as well as the striatal adenosinergic modulation of the ethanol-induced motor deficit. The present study was thus designed to further characterize the modulatory effect of striatal adenosine on ethanol-induced MI and to look for its functional correlation with chloride flux within the rat striatum. Intrastriatal microinfusion of adenosine A1 receptor agonist N6-cyclohexyladenosine (CHA) and antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), significantly accentuated and attenuated, respectively, the motor incoordinating effect of ethanol while having no effect on the normal motor coordination in saline-treated control animals. These data confirmed the role of striatal adenosine in ethanol-induced MI. The selectivity of interactions between adenosine A1 agonist and antagonist and ethanol was further confirmed by the study in which neither intrastriatal CHA nor DPCPX significantly altered the MI induced by sodium pentobarbital. Previously, we have shown that intrastriatal Ro15-4513 not only significantly attenuated ethanol-induced MI but also blocked its accentuation by intrastriatal CHA. It is well known that Ro15-4513 antagonizes many, but not all, CNS effects of ethanol by blocking the ethanol potentiation of GABA-stimulated uptake of chloride. Therefore, experiments using striatal microsac preparations were carried out to investigate the possible modulation of chloride conductance by CHA and its relationship to ethanol. High concentrations of CHA (10 and 100 nM) increased the total chloride uptake by the striatal microsacs. Corresponding to the ethanol-adenosine interaction observed behaviorally, a much lower concentration (1 nM) of CHA, being ineffective itself, significantly enhanced the stimulatory action of ethanol on chloride uptake. This effect was blocked by either Ro15-4513 (100 nM) or DPCPX (10 nM). The modulatory effect of GABA and/or ethanol on chloride influx was also evaluated, and the results supported the appropriateness to use striatal microsac preparations in the present study. Overall, the data suggested a functional interaction between ethanol and striatal adenosine and further supported the hypothesis that striatal adenosine might, in part, modulate ethanol-induced MI through its effect on chloride conductance through chloride channels coupled to GABA-benzodiazepine receptor complex.

Central corticotropin-releasing factor and benzodiazepine receptor systems are involved in the social isolation stress-induced decrease in ethanol sleep in mice

Social isolation stress has been demonstrated to decrease the hypnotic activity of ethanol in rodents. In this study, the role of central corticotropin-releasing factor (CRF) and GABA(A)/benzodiazepine (BZD) receptor systems in the social isolation stress-induced decrease in the hypnotic activity of ethanol in mice was investigated by examining the effect of alpha-helical CRF(9-41) (alpha hCRF) and flumazenil, antagonists of CRF and BZD receptors, respectively, on ethanol-induced sleep in group-housed and socially isolated mice. We also tested whether social isolation stress affects the ability of ethanol to enhance the GABA-induced 36Cl- influx into a synaptoneurosomal preparation of mouse forebrain. Social isolation stress significantly decreased both the ethanol (4 g/kg i.p.)-induced and pentobarbital (50 mg/kg i.p.)-induced sleeping times, while this stress had no effect on chloral hydrate (325 mg/kg i.p.)-induced sleep. The i.c.v. injection of alpha hCRF (6.5 nmol) and flumazenil (33 nmol) antagonized the social isolation stress-induced decrease in the ethanol sleep without affecting ethanol sleep in group-housed animals. Social isolation stress significantly attenuated the ability of GABA to stimulate 36Cl- influx but this stress had no effect on the ability of ethanol to enhance GABA-induced 36Cl- influx. These results suggest that the functional changes in central CRF and GABA(A)/BZD receptor systems are involved in the social isolation stress-induced decrease in the hypnotic activity of ethanol in mice.

Ro 15-4513 alteration of pentobarbital dependence

This study investigated the ability of the benzodiazepine inverse agonist, Ro 15-4513, to alter the expression of physical dependence on pentobarbital. Male Sprague-Dawley rats were made physically dependent on pentobarbital by continuous. IP, infusion of escalating doses of pentobarbital for 12 days. In Experiment 1, pentobarbital dependent rats received either vehicle or Ro 15-4513, in doses of 5, 10, or 15 mg/kg, IP, periodically during the pentobarbital abstinence period. As expected, Ro 15-4513 produced a significant, dose-dependent, exacerbation of withdrawal signs in the pentobarbital dependent rats. In Experiment 2, either vehicle or Ro 15-4513, at a dose of 15 mg/ kg, was administered, IP, once daily during the 12 days of continuous pentobarbital infusion. During the subsequent pentobarbital abstinence period it was noted that the withdrawal signs were significantly reduced in the rats receiving the daily administration of Ro 15-4513. It is hypothesized that the benzodiazepine inverse agonist, Ro 15-4513, may inhibit the development of physical dependence on pentobarbital through an opposing action on the GABA-A receptor.

Chronic pentobarbital administration alters gamma-aminobutyric acidA receptor alpha 6-subunit mRNA levels and diazepam-insensitive [3H]Ro15-4513 binding

In order to study the chronic effects of pentobarbital, a positive GABAA receptor modulator, on the inverse agonist binding of the benzodiazepine site, binding of [3H]Ro15-4513 and levels of GABAA receptor alpha 6-subunit mRNA were investigated in the brains of pentobarbital-tolerant/dependent animals, using receptor autoradiography and in situ hybridization histochemistry in consecutive brain sections. Pentobarbital was administered to rats either 60 mg/kg, i.p., once, for acute treatment, or 300 micrograms/10 microliters/h i.c.v. continuously for 6 days via osmotic minipumps to render rats tolerant to pentobarbital. Rats assigned to the dependent group were sacrificed 24 h after discontinuance of pentobarbital infusion, while those assigned to the tolerant group were sacrificed at the end of infusion. The alpha 6 subunit mRNA was increased in the tolerant group only. Diazepam-insensitive [3H]Ro15-4513 binding was increased in the cerebellar granule layer of pentobarbital-tolerant and -dependent rats. No alterations in these parameters were observed in acutely treated animals. These data suggest that chronic pentobarbital treatment induced expression of alpha 6-subunit mRNA. This was in contrast to alpha 1- and gamma 2-subunit mRNA, which in tolerant animals are unchanged, but for which withdrawal triggers a surge in levels. Because the alpha 6-subunit is a major component of the diazepam-insensitive [3H]Ro15-4513 binding site, the increased diazepam-insensitive [3H]Ro15-4513 binding implied de novo synthesis of the receptor subunit protein.

Contribution of "diazepam-insensitive" GABAA receptors to the alcohol antagonist properties of Ro 15-4513 and related imidazobenzodiazepines

Both in vivo and in vitro studies have shown that Ro 15-4513 can antagonize many of the pharmacologic actions of ethanol. In contrast to many benzodiazepine receptor (BzR) ligands, Ro 15-4513 binds with high affinity to a novel GABAA receptor subtype, referred to as "diazepam-insensitive" (DI). This study examined the contribution of DI GABAA receptors to the modulation of ethanol-induced sleep time by Ro 15-4513 and related imidazobenzodiazepines [e.g., Ro 19-4603, Ro 16-6028, and ZG-63 (t-butyl-8-chloro-5,6-dihydro-5-methyl-6-oxo-imidazo[1,5,a] [1,4]benzodiazepine-3-carboxylate)] that possess high affinities for this GABAA receptor subtype. Ro 15-4513 (0.6-5 mg/kg) significantly reduced ethanol (3.5 g/kg, i.p.) sleep time in mice (p < 0.001, analysis of variance). This effect was not blocked by BzR antagonists ZK 93426 (5 mg/kg) and Ro 14-7437 (5 mg/kg), which possess low affinities for DI but bind with high affinities to other "diazepam-sensitive" (DS) GABAA receptor isoforms. Although Ro 19-4603 (2.5 mg/kg) also reduced ethanol sleep time (p < 0.01), this effect was attenuated by coadministration of ZK 93426 (2.5 mg/kg). Ro 16-6028 (2.5 mg/kg) prolonged (p < 0.01) ethanol sleep time. However, in the presence of either Ro 19-7437 (5 mg/kg) or ZK 93426 (2.5 mg/kg) ethanol-induced sleep time was reduced to values approaching those obtained with ethanol in the presence of Ro 15-4513. A low dose (2.5 mg/kg) of ZG-63 did not significantly affect alcohol sleep time. However, in the presence of ZK 93426, ZG-63 increased sleep time (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism by intracerebellar Ro15-4513 of acute ethanol-induced motor incoordination in mice

The possible antiethanol effect of intracerebellarly microinjected Ro15-4513 was investigated using motor incoordination as the test response. The results of this study further confirmed reports from this and other laboratories that this partially negative ligand of benzodiazepine selectively attenuated and nearly reversed the motor impairment of acute ethanol. The attenuation observed after microinjections of doses of 0.05, 0.1, and 0.5 ng was significant and dose related. There was no effect on normal coordination when the highest dose, 0.5 ng, was administered followed by saline instead of a test dose of ethanol. When 0.5 ng of Ro15-4513 alone was microinjected into the cerebellum, no significant change in the locomotor activity was observed. Even a 10-fold higher intracerebellar dose (5 ng) of Ro15-4513 administered alone produced no significant changes in locomotor activity. This suggests that attenuation of ethanol-induced motor incoordination was most likely due to the selective antiethanol effect of Ro15-4513 at the dose range used in the present investigation. The antiethanol effect of intracerebellar Ro15-4513 also reaffirmed the well-known belief that the cerebellum is an important brain region for ethanol's motor-impairing effect. The results also indirectly suggest the inhibition of GABAA-gated chloride ion channel activity as the most likely basis of Ro15-4513's antiethanol effect.

Ro 15-4513 selectively attenuates ethanol, but not sucrose, reinforced responding in a concurrent access procedure; comparison to other drugs

The experiments described in this report used a concurrent access procedure to study ethanol reinforcement. Rats were trained to lever press for a 10% sucrose solution and a 10% ethanol/10% sucrose mixture, and both reinforcers were available on variable-interval 5-s schedules. In baseline and vehicle injection sessions, the animals distributed their responding between both solutions. When injected with the partial inverse benzodiazepine agonist Ro 15-4513 (3, 9, and 18 mg/kg), responding for the ethanol solution decreased while responding for sucrose remained intact. Ethanol injections (0.5 and 1.0 g/kg) engendered a similar profile. Chlordiazepoxide led to an increase in ethanol mix responding at 2 mg/kg and a decrease in ethanol mix responding at higher doses; no dose affected sucrose responding. Morphine (0.5-16 mg/kg) decreased responding for both the ethanol mix and sucrose solutions, more or less simultaneously. Naloxone (0.125-20 mg/kg) selectively reduced ethanol mix responding at low doses, and decreased responding for both reinforcers at high doses. In another group of animals, isocaloric alternatives were concurrently available: 10% ethanol/0.25% saccharin versus 14% sucrose. Injections of Ro 15-4513 and chloridiazepoxide produced similar results as in the first group of rats: an increase in ethanol mix responding with low dose chlordizepoxide, and a decrease in ethanol mix responding with Ro 15-4513. However, naloxone injections did not selectively affect responding for either of the reinforcers when they were isocaloric. These results are discussed in terms of ethanol's neuropharmacological actions.

Radioligands for PET studies of central benzodiazepine receptors and PK (peripheral benzodiazepine) binding sites--current status

The status of the radiochemical development and biological evaluation of radioligands for PET studies of central benzodiazepine (BZ) receptors and the so-called peripheral benzodiazepine binding sites, here discriminated and referred to as PK binding sites, is reviewed against current pharmacological knowledge, indicating those agents with present value and those with future potential. Practical recommendations are given for the preparation of two useful radioligands for PET studies, [N-methyl-11C]flumazenil for central BZ receptors, and [N-methyl-11C]PK 11195 for PK binding sites. Quality assurance and plasma metabolite analysis are also reviewed for these radioligands and practical recommendations are given on methodology for their performance.

Effect of Ro 15-4513 on ethanol-induced conditioned place preference

The benzodiazepine receptor inverse agonist Ro 15-4513 reverses a number of ethanol's effects, including its reinforcing properties as measured through self-administration. The present study examined the effect of this putative ethanol antagonist in a place conditioning design that has been shown to be sensitive to ethanol's rewarding properties in mice. Using an unbiased differential conditioning procedure, DBA/2J mice received, on alternate days, pairings of a distinctive floor stimulus (CS+) with either ethanol (2 g/kg), Ro 15-4513 (3 mg/kg), or a combination of ethanol and Ro 15-4513. On alternate days, a different distinctive floor stimulus (CS-) was paired with vehicle. Under these conditions, ethanol produced a conditioned place preference that was unaffected by Ro 15-4513. Ro 15-4513 alone did not produce either a place preference or aversion. Ro 15-4513 did produce reductions in locomotor activity during conditioning, indicating it was behaviorally active. These results indicate that a dose of Ro 15-4513 that alters general activity does not affect ethanol reward.

Interaction of pregnanolone and pregnenolone sulfate with ethanol and pentobarbital

3-alpha-Hydroxy-5-beta-pregnan-20-one [pregnanolone (PA)] and 3-beta-hydroxy-5-pregnen-20-one 3-sulfate [pregnenolone sulfate (PS)] are steroids that have been shown in biochemical studies to be active at the GABA-benzodiazepine-chloride receptor complex, Pa as a "barbiturate-like" agonist and PS as a "picrotoxin-like" antagonist. Since other compounds that are active at this site interact with the effects of pentobarbital and ethanol, the behavioral effects of these steroids alone and in combination with pentobarbital and ethanol were tested. Pa blocks the convulsions caused by pentylenetetrazole (PTZ) and increases motor activity when given alone in low doses. In combination with either pentobarbital or ethanol, it enhances the depression in motor activity, hypothermia, and hypnosis. In contrast, PS has no effect on PTZ convulsions and depresses motor activity by itself. With pentobarbital, PS enhances the depression in motor activity but has no effect on hypothermia or hypnosis. With ethanol, PS enhances the hypothermia but does not affect motor activity or hypnosis. Therefore, Pa and PS show different but not opposite effects in interacting with compounds active at the GABA-benzodiazepine-chloride receptor complex.

Selective antagonism of acute ethanol-induced motor disturbances by centrally administered Ro 15-4513 in mice

Results of the present investigation demonstrated that Ro 15-4513 when given ICV selectively antagonized ethanol-induced motor disturbances at doses that did not produce motor incoordination and lacked proconvulsant activity. Ro 15-4513 in 10-, 15-, and 22-ng doses antagonized, roughly in a dose-dependent manner, ethanol-induced motor incoordination. The 10-ng dose produced an optimal effect with nearly complete antagonism within 30 min postethanol. The higher, 15 and 22 ng, doses of Ro 15-4513 antagonized, as well as probably reversed, ethanol-induced motor incoordination. The stimulation and inhibition of spontaneous motor activity by 1 and 2 g/kg IP ethanol, respectively, were also selectively antagonized by Ro 15-4513. Neither an alteration in the latency and/or duration of pentylenetetrazol-induced convulsions nor an antagonism to sodium pentobarbital-induced motor incoordination and inhibition of spontaneous motor activity by Ro 15-4513 at dose levels that showed antiethanol effects were observed. Only the 150-ng dose of Ro 15-4513, which exhibited intrinsic activity as proconvulsant, attenuated sodium pentobarbital-induced motor incoordination. When given alone at doses higher than those used in motor coordination experiments, Ro 15-4513 markedly increased spontaneous motor activity dose dependently.

Effects of Ro 15-4513 and ethanol on operant behavior of male and female C57BL/6 mice

Although the partial benzodiazepine receptor inverse agonist, Ro 15-4513, counteracts many ethanol effects, its effect on operant behavior or on ethanol-induced changes in this behavior, remains controversial. In this study, we examined the effects of Ro 15-4513, ethanol, and their interaction on behavior maintained by an FR 20 schedule of food reinforcement. Ro 15-4513 (1.0-4.0 mg/kg) and ethanol (1.5-3.0 g/kg) reduced lever-responding of both male and female mice. The disruptive effect of Ro 15-4513 was of short duration (approximately 10 min), and was greater in male than in female mice. Under equivalent dose and time parameters, ethanol disrupted behavior of both sexes to the same extent. In spite of the disruptive effects of both drugs when given alone, when given after ethanol and prior to testing, Ro 15-4513 attenuated the disruptive effects of ethanol in male mice. The present study extends previous reports by documenting: (1) that the disruptive effect of Ro 15-4513 on mice is of very short duration and occurs at lower doses than previously reported; (2) that, in spite of being disruptive itself, Ro 15-4513 can attenuate the disruptive effects of ethanol on schedule controlled behavior; and (3) that gender is an important consideration in determining the effects of this compound.

Autoradiographic study on [3H]flunitrazepam binding in rat cortex and hippocampus after chronic ethanol treatment

Ethanol alters almost all membrane functions, but it behaves essentially like a benzodiazepine-type GABAergic agonist. The mechanism by which ethanol affects the GABA/benzodiazepine complex is not clear. We studied the possible changes in [3H]flunitrazepam binding induced by chronic ethanol treatment, using light microscopic autoradiography, to try to elucidate the controversy underlying this topic. This technique allows us to measure densities of benzodiazepine receptors in different anatomical brain areas--visual cortex and hippocampus--which seem to constitute the anatomical support for the behavioral and physiological responses affected by ethanol. Autoradiographic studies on the visual cortex and hippocampus from rats chronically treated with ethanol do not show statistically significant differences in the binding of [3H]flunitrazepam with respect to control animals. Furthermore, we did not find either rostro-caudal or medio-lateral differences in benzodiazepine receptor densities in each layer of the visual cortex.

Failure of Ro15-4513 to alter an ethanol-induced taste aversion

The ability of Ro15-4513, an imidazobenzodiazepine inverse benzodiazepine agonist, to attenuate/block the acquisition of an ethanol (ETOH)-induced conditioned taste aversion (CTA) was investigated in two experiments. Experiment 1 examined the effects of Ro15-4513 (3 mg/kg) on rats' consumption of a novel saccharin solution under a traditional CTA paradigm. Experiment 2 examined the effects of Ro15-4513 (3 mg/kg) on rats' consumption of a novel saccharin solution under a preexposure CTA paradigm. Under the preexposure paradigm, rats were given Ro15-4513 immediately before each of five daily consecutive preexposure treatments prior to the initial conditioning day. To obtain maximal preexposure and unconditioned stimulus effects, a 2-g/kg dose of ETOH (20% v/v) was used in the present study. As previously reported, animals given ETOH following 20-min access to a novel saccharin solution established moderate to strong aversions, with the degree of aversion being directly related to the number of conditioning days. Experiment 1 showed that Ro15-4513 failed to alter the CTA induced by ETOH. Experiment 2 further showed that Ro15-4513 failed to block the preexposure effect exerted on the ETOH-mediated CTA. The results confirm previous reports regarding the failure of Ro15-4513 to disrupt an ETOH-induced CTA. These data are in agreement with a number of behavioral studies demonstrating the failure of Ro15-4513 to antagonize certain actions of ETOH. Moreover, the present study along with a previous report suggests that ETOH-induced CTA's do not appear to be mediated via actions at the GABA-BDZ receptor complex.

[11C]Ro 15-4513, a ligand for visualization of benzodiazepine receptor binding. Preparation, autoradiography and positron emission tomography

Ro 15-4513, a partial inverse agonist at the benzodiazepine (BZ) receptor site was labelled with 11C and used for in vitro autoradiography on human post mortem brain sections and for positron emission tomography (PET) on Cynomolgus monkeys. The total radiochemical yield of [11C]Ro 15-4513 was 30-40% with an overall synthesis time of 40 min. The specific radioactivity was about 1000 Ci/mmol at end of synthesis. In vitro autoradiography showed that [11C]Ro 15-4513 bound specifically predominantly in the neocortex of the human brain. Specific binding was also demonstrated in the basal ganglia and the cerebellar cortex. Flumazenil (Ro 15-1788) and clonazepam inhibited the binding in cerebral regions, but a significant proportion in the cerebellum was not inhibited by these agents. This proportion may represent alpha 6-containing BZ receptors. PET examination of [11C]Ro 15-4513 binding in Cynomolgus monkeys demonstrated high uptake of radioactivity in neocortex. The uptake of radioactivity was markedly displaced by high doses of Ro 15-4513 or clonazepam. [11C]Ro 15-4513 should be a useful ligand to examine BZ receptor characteristics in the living human brain by PET.

Alcohol, the chloride ionophore and endogenous ligands for benzodiazepine receptors

Considerable evidence suggests that at least some of the effects of ethanol are mediated by an action on the GABAA receptor chloride channel complex. More speculative is the suggestion that ethanol might interact with endogenous ligands for the benzodiazepine receptor on the complex. This paper considers the evidence for such interactions.

Comparison of the effects of benzodiazepine and beta-carboline inverse agonists on body temperature in mice

The effect of benzodiazepine and beta-carboline inverse agonists on body temperature in mice was investigated using doses shown to be pro-convulsant in other studies. The benzodiazepine partial inverse agonists Ro 15-3505 (0.1-30 mg/kg i.p.), Ro 15-4513 (0.1-10 mg/kg i.p.) and the fuller benzodiazepine inverse agonist Ro 19-4603 (0.03-0.3 mg/kg i.p.) had no effect on rectal temperature. Ro 19-4603 (1 mg/kg i.p.) produced a small hypothermic response. In contrast, the beta-carboline partial and full inverse agonists, FG 7142 (30, 60 mg/kg i.p.) and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (3, 10 mg/kg i.p.), produced large decreases in body temperature. These differential effects of benzodiazepine and beta-carboline inverse agonists on body temperature may provide further evidence for the existence of benzodiazepine receptor subtypes.

RO15-4513 antagonizes the anxiolytic effects of ethanol in a nonshock conflict task at doses devoid of anxiogenic activity

RO15-4513 is a partial benzodiazepine inverse agonist that has been reported to antagonize some of the biochemical and neurobehavioral actions of ethanol. However, whether this antagonistic action of RO15-4513 is dependent on the drug exerting its intrinsic (inverse agonist) properties is unclear at present. The purpose of the present study was to examine whether RO15-4513 was capable of antagonizing the anxiolytic effects of ethanol in a nonshock conflict task at doses that, by themselves, do not reveal the compound's intrinsic anxiogenic properties. The consummatory conflict task employed (negative contrast) involves quantifying how animals respond to an abrupt, unexpected reduction in reward (sucrose solution), and is particularly sensitive to the effects of anxiolytic agents, including ethanol. As previously demonstrated, depressed consummatory behavior engendered by reward reduction was significantly alleviated by ethanol (0.75 g/kg). This anxiolytic effect of ethanol, however, was antagonized dose dependently by RO15-4513 (0.1875-3.0 mg/kg). Only the highest dose of RO15-4513 (3.0 mg/kg) showed evidence of further response suppression. Lower doses of RO15-4513 tested did not exert an anxiogenic effect when given alone. Thus the antagonism of EtOH's anxiolytic (contrast-reducing) effects occurred at doses of RO15-4513 (0.375-1.5 mg/kg) that did not exhibit any intrinsic anxiogenic activity. As such, these results suggest that RO15-4513 interacts with the anxiolytic effects of ethanol in a nonadditive fashion in this test situation.

Central and peripheral benzodiazepine receptors: involvement in an organism's response to physical and psychological stress

The present review discusses the current knowledge of the molecular pharmacology and neuroanatomical and subcellular localization of both the central benzodiazepine/GABA-chloride ionophore receptor complex and the peripheral benzodiazepine receptor. It then reviews all of the literature to date on how these two receptor sites are modulated by environmental stress. The possible role of these sites in learning and memory is also discussed. Finally, a theoretical model is presented which examines the differential, and perhaps complementary, alterations of these two sites in an organism's response to stress.

Effects of Ro 15-4513 on ethanol discrimination in C57BL/6 mice

Ro 15-4513, a partial benzodiazepine receptor inverse agonist, counteracts many of the effects of ethanol, however, its effects on ethanol discrimination in operant paradigms remains unclear. The present study examined the effects of Ro 15-4513 on ethanol discrimination by female C57BL/6 mice in a food-reinforced behavior-operant paradigm. Under the time and dosing conditions used in previous reports, Ro 15-4513 did not alter ethanol discrimination whether given prior to or after ethanol exposure. The drug did, however, attenuate ethanol discrimination for brief periods (less than 8 min) when injected after ethanol and at doses and postinjection times which also disrupted responding. The present study confirmed that Ro 15-4513 attenuated ethanol discrimination, but not to the extent as previously reported. The results indicate that postinjection time is a very critical factor in whether Ro 15-4513 attenuates ethanol discrimination.

Hypothermic effects of a homologous series of short-chain alcohols in rats

The purpose of this study was to assess the utility of the thermoregulatory system as an end point in predicting the toxicity of various short-chain alcohols. Male Fischer rats developed significant hypothermia following acute administration (ip) of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, or 2-butanol. The hypothermic responses to the six alcohols all showed similar segmented responses characterized by a threshold dose below which no change in body temperature occurred, and a suprathreshold regression with increasing dose causing greater hypothermia. Relative potency of the alcohols was assessed using both the threshold dose to cause hypothermia and the dose that would cause body temperature to decrease by 1 degree C. Both measures gave the progression of toxicity from least to most potent of methanol less than ethanol less than 2-propanol less than 1-propanol less than 2-butanol less than 1-butanol. The effective dose of each alcohol was compared to its membrane/buffer partition coefficient (Pm/b), and there was a high inverse correlation between the hypothermic dose of an alcohol and its lipid solubility. That the potency of an alcohol was strongly correlated with its Pm/b suggests that the membrane disordering theory of narcosis may also be used to explain the hypothermic action of alcohols.

Effect of ethanol on memory consolidation in mice: antagonism by the imidazobenzodiazepine Ro 15-4513 and decrement by familiarization with the environment

Three sets of experiments were carried out with CD1 mice tested in a one-trial inhibitory avoidance task. In a first set of experiments the posttraining administration of ethanol (1 or 2 g/kg) impaired, while that of the imidazobenzodiazepine Ro 15-4513 (5 or 10, but not 2.5 mg/kg) improved the retention performance of the animals. In a second set of experiments a by itself ineffective dose of Ro 15-4513 (2.5 mg/kg) antagonized the effect of ethanol (1 and 2 kg/kg). These results are discussed on the basis of the interaction of these drugs with the GABAergic system. In a third set of experiments, in which the performances of mice familiarized with the apparatus were compared with those of non-familiarized mice, ethanol was less effective in impairing memory processes of the experienced subjects. These results are discussed in terms of attenuation of emotionality, resulting in impaired retention, following posttraining ethanol administration.

Are GABAB receptors involved in the pharmacological effects of ethanol?

The interaction of ethanol with GABAB-receptor system and the selectivity of phaclofen for GABA-receptor subtypes were investigated by employing an in vitro model of 36Cl-influx assay in mammalian cultured neurons and also in vivo models of picrotoxin- and NMDA-induced convulsions in rats. Ethanol (20 mM), without having any effect per se, potentiated the effect of GABA on 36Cl-influx, whereas at concentration 50 mM, ethanol activated Cl(-)-channels directly in mice spinal cord cultured neurons. In contrast, (-)baclofen (100 microM) did not modify the effects of GABA or ethanol on 36Cl-influx. Similarly, phaclofen (500 microM), as well as pertussis toxin (140 ng/ml, overnight incubation) did not modify these effects. Interestingly, phaclofen (200 micrograms i.c.v.) reversed the anticonvulsant effect of ethanol, but not that of pentobarbital or diazepam or progabide, against picrotoxin-induced convulsions in rats. However, phaclofen failed to modify the anticonvulsant effect of ethanol against NMDA-induced convulsions. These observations indicate that phaclofen is devoid of GABAA-receptor blockade property, and the anticonvulsant effect of ethanol against picrotoxin may be mediated through the activation of both GABA-receptor subtypes.

The role of bicuculline, aminooxyacetic acid and gabaculine in the modulation of ethanol-induced motor impairment

Ethanol's intoxicating effects may result from ethanol-induced changes in central gamma-aminobutyric acid (GABA) mechanisms. To further test this hypothesis, mice were pretreated with bicuculline (1 mg/kg s.c.), aminooxyacetic acid (15, 20, 25 or 30 mg/kg i.p.) or gabaculine (20 or 40 mg/kg i.p.). Following pretreatment, 20% ethanol (2.25 g/kg i.p.) was administered and rolling roller performance evaluated. All ethanol-treated control animals showed lack of rolling roller performance at 5 min post ethanol but regained rolling roller performance by 35 min. Only 42% of the bicuculline pretreated mice demonstrated lack of rolling roller performance at 5 min post ethanol and all regained rolling roller performance by 15 min. Impairment of rolling roller performance by ethanol was potentiated by aminooxyacetic acid in a dose-dependent manner. Aminooxyacetic acid (25 and 30 mg/kg doses) slowed blood ethanol disappearance although analysis of blood ethanol disappearance and motor impairment curves indicated that aminooxyacetic acid potentiation of ethanol-induced rolling roller performance impairment cannot be attributed solely to aminooxyacetic acid's effect on blood ethanol levels. Gabaculine also potentiated ethanol's impairment of rolling roller performance but was more effective than aminooxyacetic acid in slowing ethanol disappearance, suggesting that in comparison to aminooxyacetic acid, alteration of ethanol metabolism plays a greater role in gabaculine's potentiation of ethanol-induced motor impairment.

Anxiogenic effects of a benzodiazepine receptor partial inverse agonist, RO 19-4603, in a light/dark choice situation

In a light/dark choice procedure, the imidazothienodiazepinone RO 19-4603, given alone, induced a dose-dependent decrease in the time spent by mice in the lit box as well in the number of transitions between the two boxes. These data confirm the anxiogenic intrinsic properties of inverse agonists of the benzodiazepine receptor. Since RO 19-4603 also reversed the anxiolytic effects of ethanol and exhibited proconvulsant properties, it is suggested that the antagonistic action of this drug against ethanol could be due to an additive rather than an interactive process.

Flunitrazepam photoaffinity labeling of the GABA(A) receptor reduces inhibition of [3H]Ro15-4513 binding by GABA

The benzodiazepine drugs modulate gamma-aminobutyric acid (GABA)-mediated synaptic transmission via a high-affinity binding site that is part of the GABA(A) receptor complex, but which is distinct from the GABA binding site. Ro15-4513 is a benzodiazepine negative modulator of GABA action that displays unique anti-ethanol properties both in vivo and in vitro. Ro15-4513 has been reported to photoaffinity label nearly 100% of the benzodiazepine binding sites in rat brain homogenates. In contrast, the benzodiazepine positive modulator flunitrazepam photoaffinity labels only 25% of the sites. Here, we have examined the reversible binding of [3H]Ro15-4513, [3H]flumazenil (Ro15-1788), and [3H]flunitrazepam to embryonic chick brain membranes, and to membranes that have been photoaffinity labeled with nonradioactive flunitrazepam. Photoaffinity labeling with flunitrazepam decreased the subsequent reversible binding of [3H]flunitrazepam and [3H]flumazenil, but increased the binding of [3H]Ro15-4513. The increase in [3H]Ro15-4513 binding after flunitrazepam photoaffinity labeling was due to a decrease in the apparent Kd, with no change in Bmax. Following photoaffinity labeling, negative modulation of [3H]Ro15-4513 binding by GABA was lost, whereas positive modulation of residual [3H]flunitrazepam binding was retained. We conclude that the site photoaffinity labeled by flunitrazepam is distinct from the site responsible for reversible binding of [3H]Ro15-4513.

Differential interactions of Ro 15-4513 with benzodiazepines, ethanol and pentobarbital

The effects of the imidazobenzodiazepine Ro 15-4513 in combination with three CNS depressants (ethanol, benzodiazepine agonists and pentobarbital) were examined in three different experiments. Full antagonism of classical benzodiazepines by Ro 15-4513 was seen in all three situations. Partial antagonism of ethanol occurred in the pull up test of muscle relaxation in rats, but not in the inhibition of ultrasounds produced in rat pups by mild stress. The depressant effect of ethanol on twitching of the urethane-anaesthetised rat suprahyoid muscles was reversed. No attenuation of the effects of pentobarbital was seen in any test.

Do alcoholics have abnormal benzodiazepine receptors?

The behavioral effects of a given amount of ethanol vary greatly between alcoholic and nonalcoholic subjects. A blood alcohol level of more than 150 mg/dL without gross evidence of intoxication is a definitive diagnostic laboratory test for alcoholism (1). In a previous paper, I have proposed that the human body produces a substance similar to caffeine (2). In the present paper, my new concept is used to explain the intriguing ability of alcoholics to tolerate the effects of ethanol. Understanding why alcoholics differ from normal individuals in, their response to ethanol is an important step that will pave the way for the prevention of the transmission of alcoholism to future generations.

Interactions between benzodiazepine antagonists, inverse agonists, and acute behavioral effects of ethanol in mice

The behavioral manifestations of acute ethanol intoxication resemble those of benzodiazepines, barbiturates and general anesthetics. This has led to speculation that these drugs share common mechanisms or sites of actions within the brain. The discovery of a specific benzodiazepine receptor site, and the subsequent development of selective receptor antagonist and inverse agonist drugs, provides a framework to test the involvement of the benzodiazepine receptor complex in mediating ethanol's behavioral effects. The partial inverse agonist Ro15-4513, an analog of the benzodiazepine receptor antagonist Ro15-1788 (flumazenil), has been reported to block or reduce some of ethanol's acute effects in rodents by a benzodiazepine receptor-mediated action. There has been some controversy over whether the "antialcohol" effect of Ro15-4513 is a unique property of this compound or is shared by other benzodiazepine antagonists with inverse agonist activity. We have studied the effects of Ro15-4513 and other benzodiazepine receptor antagonists on acute ethanol intoxication in mice and have obtained evidence that 1) Ro15-4513 differentially affects acute effects of ethanol, 2) an "antialcohol" property is not a general feature of all benzodiazepine antagonists and inverse agonists, and 3) "antialcohol" activity may not be unique to Ro15-4513.

The effects of Ro 15-4513 on ethanol-induced taste aversions

Ro 15-4513 is an imidazobenzodiazepine that has been reported to block a range of behavioral effects of ethanol. In the present experiments, the effects of Ro 15-4513 were assessed on the acquisition of an ethanol-induced conditioned taste aversion. Specifically, rats were given a novel saccharin solution to drink followed by an injection of one of a range of doses of Ro 15-4513 (0.5 and 1.0 mg/kg, Experiment 1A, and 2.0 and 3.0 mg/kg, Experiment 1B) and an injection of ethanol (1.75 g/kg). Ro 15-4513 failed to block the acquisition of the ethanol-induced taste aversion. Possible reasons for this failure were discussed.

Effects of two benzodiazepine inverse agonists, RO 15-4513 and FG 7142, on recovery from pentobarbital and halothane anesthesia in the rat

A new class of drugs, the benzodiazepine inverse agonists, have recently been shown to antagonize some of the behavioral and sedative effects of benzodiazepines, barbiturates, and alcohol. Preliminary studies suggested that at least one of these drugs, RO 15-4513, may also be able to reverse the general anesthetic properties of volatile halogenated agents. Another inverse agonist, FG 7142, exhibits a similar ability to antagonize alcohol or benzodiazepines. However, FG 7142 is less potent than RO 15-4513 and has less affinity for the benzodiazepine receptor (BZR). The present studies were therefore undertaken to compare the analeptic effects and relative potencies of RO 15-4513 and FG 7142 on the anesthetic properties of pentobarbital compared with the general anesthetic agent halothane as measured by the time for recovery of the righting reflex in the rat. Three basic experimental paradigms were employed. Drug (FG or RO) or carrier was administered 5 minutes prior to the induction of pentobarbital anesthesia. Drug or carrier was administered to anesthetized animals 60 minutes after pentobarbital injection. Lastly, drug or carrier was administered 5 minutes prior to 15 minutes of halothane anesthesia. In addition, the selective benzodiazepine antagonist, flumazenil (RO 15-1788), was used to determine if the effects of the benzodiazepine inverse agonists on recovery from barbiturate or halothane anesthesia were due to activity at the BZR. The results revealed that RO was both more potent and more effective than FG at speeding recovery from barbiturate anesthesia in the rat. RO's effects appeared to be primarily due to BZR inverse agonist activity since it could be reversed by the BZR antagonist, flumazenil.(ABSTRACT TRUNCATED AT 250 WORDS)

GABAergic mechanisms in the electrophysiological actions of ethanol on cerebellar neurons

We have found that the partial inverse benzodiazepine agonists Ro 15-4513 and FG 7142 antagonize the depressant electrophysiological effects of locally applied ethanol in the cerebellum. Although absolute tissue concentrations are not known, dose-response curves constructed using pressure-ejection doses as previously described we found that FG 7142 was more efficacious, but less potent than Ro 15-4513. Our observation that ethanol and inverse benzodiazepine agonists have interactions which are not competitive might suggest that these two drugs act through separate, but interactive mechanisms in order to produce the observed ethanol antagonism. If such independent interactions were mediated at different sites on a given macromolecular complex, such as the GABAa/Cl- channel, then one might expect to find allosteric interactions between those sites as well as with the functional response of the complex to GABA activation. Indeed, this hypothesis is consistent with the recent finding of Harris and collaborators that ethanol potentiates the inverse agonist actions of Ro 15-4513 and FG 7142. On the other hand, we were unable to find large ethanol-induced potentiations of GABA effects on all neurons which showed depressant responses to ethanol administration in rat cerebellum. However we did find that the GABAa antagonist, bicuculline, blocks the depressant effects of ethanol on the same neurons. We conclude that the interaction between ethanol and GABA probably does not occur directly at the GABAa receptor site, but that the GABAa mechanism does play a permissive role in the ethanol-induced depressions of cerebellar Purkinje neurons.(ABSTRACT TRUNCATED AT 250 WORDS)