RO 15-4513 induces seizures in DBA/2 mice undergoing alcohol withdrawal

Modulation of ion channels in clinical psychopharmacology: adults and younger people

This review focuses on the use of Na(+), Ca(2+) and Cl(-) channel modulators in psychiatric disease. Drugs that modulate ion channels have been used in psychiatry for more than a century, and in this review we critically evaluate clinical research that reports the therapeutic effects of drugs acting on GABA(A), voltage-gated Na(+) and voltage-gated Ca(2+) channels in pediatric and adult patients. As in other fields, the evidence underpinning the use of medicines in younger people is far less robust than for adults. In addition, we discuss some current developments and highlight clinical disorders in which current molecules could be further tested. Notable success stories, such as benzodiazepines (in sleep and anxiety disorders) and antiepileptics (in bipolar disorder), have been the result of serendipitous discoveries or refinements of serendipitous discoveries, as in all other major treatments in psychiatry. Genomic, high-throughput screening and molecular pharmacology discoveries may, however, guide further developments in the future. This could include increased research in promising targets that have been perceived as commercially risky, such as selective α-subunit GABA(A) receptors.

GABA(A) receptor subtypes as targets for neuropsychiatric drug development

The main inhibitory neurotransmitter system in the brain, the gamma-aminobutyric acid (GABA) system, is the target for many clinically used drugs to treat, for example, anxiety disorders and epilepsy and to induce sedation and anesthesia. These drugs facilitate the function of pentameric A-type GABA (GABA(A)) receptors that are extremely widespread in the brain and composed from the repertoire of 19 subunit variants. Modern genetic studies have found associations of various subunit gene polymorphisms with neuropsychiatric disorders, including alcoholism, schizophrenia, anxiety, and bipolar affective disorder, but these studies are still at their early phase because they still have failed to lead to validated drug development targets. Recent neurobiological studies on new animal models and receptor subunit mutations have revealed novel aspects of the GABA(A) receptors, which might allow selective targeting of the drug action in receptor subtype-selective fashion, either on the synaptic or extrasynaptic receptor populations. More precisely, the greatest advances have occurred in the clarification of the molecular and behavioral mechanisms of action of the GABA(A) receptor agonists already in the clinical use, such as benzodiazepines and anesthetics, rather than in the introduction of novel compounds to clinical practice. It is likely that these new developments will help to overcome the present problems of the chronic treatment with nonselective GABA(A) agonists, that is, the development of tolerance and dependence, and to focus the drug action on the neurobiologically and neuropathologically relevant substrates.

A role for GABA mechanisms in the motivational effects of alcohol

Low doses of ethanol have been hypothesized to act directly via proteins that form ligand-gated receptor channels, such as the gamma-aminobutyric acid (GABA) receptor complex, to allosterically alter function, particularly in specific brain areas such as those hypothesized to be involved in ethanol reinforcement. At the pharmacological level, one can antagonize the effects of ethanol with GABA antagonists, particularly its sedative, anxiolytic-like and acute reinforcing actions. Brain sites involved in the GABAergic component of ethanol reinforcement include the ventral tegmental area, elements of the extended amygdala (including the central nucleus of the amygdala), and the globus pallidus. Chronic administration of ethanol sufficient to produce dependence and increased ethanol intake are associated with increased GABA release in the amygdala and increased sensitivity to GABA agonists. A hypothesis is proposed that GABAergic interactions with the brain stress neurotransmitter corticotropin-releasing factor in specific elements of the extended amygdala may be an important component for the motivation for excessive drinking associated with the transition from social drinking to addiction.

Similar effects of cocaine and immobilization stress on the levels of heat-shock proteins and stress-activated protein kinases in the rat hippocampus, and on swimming behaviors: the contribution of dopamine and benzodiazepine receptors

Cocaine (COC) has been reported to cause effects similar to physiological stressors in the brain neuroendocrinal system, including heat-shock protein (HSP) expression, although these effects have not been elucidated in detail. In the present study, we examined the effects of repeated (4 days) treatments with cocaine hydrochloride (35 mg/kg, i.p.) and 10 min immobilization stress (IM) on the distribution of HSP (HSP27, HSP60, HSP70, HSC70) and stress-activated protein kinase (SAPK) (SAPKalpha, SAPKbeta, SAPKgamma) immunoreactive nerve cells (positive cells) in the rat hippocampus. The swimming behaviors of the rats in the forced swimming test were also examined. In both COC and IM groups, an early enhancement (5 h time point) of hippocampal HSP (HSP27, HSP60, HSP70, HSC70) and SAPK (SAPKbeta, SAPKgamma) positive cells was observed, whereas a recovery (SAPKs) or attenuation (HSP60 and HSC70) was observed at the 24 h time point. In both groups, a depression of the swimming behaviors (attenuation in the activity counts and time until immobility) below the control level was observed at the 5 h point, but a recovery was observed at the 24 h time point. At the 48 h time point, all parameters returned to the control level. These alterations in the levels of HSPs and SAPKs, and the swimming behaviors were similar to those observed in the stress (IM) group, and were characteristic in that all of these alterations were attenuated by the benzodiazepine inverse agonist, Ro 15-4513 (5 mg/kg, i.p.), and the dopamine D1 receptor antagonist, SCH23390 (0.5 mg/kg, i.p.), which was not observed in the groups treated with another stressor-like drug (bicuculline).

Increased mRNA expression for the alpha(1) subunit of the GABA(A) receptor following nitrous oxide exposure in mice

The mechanisms by which nitrous oxide (N(2)O) produces physical dependence and withdrawal seizures are not well understood, but both N(2)O and ethanol exert some of their effects via the GABA(A) receptor and several lines of evidence indicate that withdrawal from N(2)O and ethanol may be produced through similar mechanisms. Expression levels of mRNA transcripts encoding several GABA(A) receptor subunits change with chronic ethanol exposure and, therefore, we hypothesized that N(2)O exposure would produce changes in mRNA expression for the alpha(1) subunit. Male, Swiss--Webster mice, 10--12 weeks of age, were exposed for 48 h to either room air or a 75%:25% N(2)O:O(2) environment. Brains were sectioned and mRNA for the alpha(1) subunit was detected by in situ hybridization using an 35S-labelled cRNA probe. N(2)O exposure produced a significant increase in expression levels of the alpha(1) subunit mRNA in the cingulate cortex, the CA1/2 region of the hippocampus, the dentate gyrus, the subiculum, the medial septum, and the ventral tegmental area. These results lend support to the hypothesis that N(2)O effects are produced, at least in part, through the GABA(A) receptor and that N(2)O produces these effects through actions in the cingulate cortex, hippocampus, ventral tegmental area and medial septum. These results are also further evidence that ethanol and N(2)O produce dependence and withdrawal through common mechanisms.

Ethanol and neurotransmitter interactions--from molecular to integrative effects

There is extensive evidence that ethanol interacts with a variety of neurotransmitters. Considerable research indicates that the major actions of ethanol involve enhancement of the effects of gamma-aminobutyric acid (GABA) at GABAA receptors and blockade of the NMDA subtype of excitatory amino acid (EAA) receptor. Ethanol increases GABAA receptor-mediated inhibition, but this does not occur in all brain regions, all cell types in the same region, nor at all GABAA receptor sites on the same neuron, nor across species in the same brain region. The molecular basis for the selectivity of the action of ethanol on GaBAA receptors has been proposed to involve a combination of benzodiazepine subtype, beta 2 subunit, and a splice variant of the gamma 2 subunit, but substantial controversy on this issue currently remains. Chronic ethanol administration results in tolerance, dependence, and an ethanol withdrawal (ETX) syndrome, which are mediated, in part, by desensitization and/or down-regulation of GABAA receptors. This decrease in ethanol action may involve changes in subunit expression in selected brain areas, but these data are complex and somewhat contradictory at present. The sensitivity of NMDA receptors to ethanol block is proposed to involve the NMDAR2B subunit in certain brain regions, but this subunit does not appear to be the sole determinant of this interaction. Tolerance to ethanol results in enhanced EAA neurotransmission and NMDA receptor upregulation, which appears to involve selective increases in NMDAR2B subunit levels and other molecular changes in specific brain loci. During ETX a variety of symptoms are seen, including susceptibility to seizures. In rodents these seizures are readily triggered by sound (audiogenic seizures). The neuronal network required for these seizures is contained primarily in certain brain stem structures. Specific nuclei appear to play a hierarchical role in generating each stereotypical behavioral phases of the convulsion. Thus, the inferior colliculus acts to initiate these seizures, and a decrease in effectiveness of GABA-mediated inhibition in these neurons is a major initiation mechanism. The deep layers of superior colliculus are implicated in generation of the wild running behavior. The pontine reticular formation, substantia nigra and periaqueductal gray are implicated in generation of the tonic-clonic seizure behavior. The mechanisms involved in the recruitment of neurons within each network nucleus into the seizure circuit have been proposed to require activation of a critical mass of neurons. Achievement of critical mass may involve excess EAA-mediated synaptic neurotransmission due, in part, to upregulation as well as other phenomena, including volume (non-synaptic diffusion) neurotransmission. Effects of ETX on receptors observed in vitro may undergo amplification in vivo to allow the excess EAA action to be magnified sufficiently to produce synchronization of neuronal firing, allowing participation of the nucleus in seizure generation. GABA-mediated inhibition, which normally acts to limit excitation, is diminished in effectiveness during ETX, and further intensifies this excitation.

Alcohol, GABAA-benzodiazepine receptor complex, and aggression

Neurobiological investigations have become productive since experimental protocols were developed that engender large increases in aggressive behavior after acute alcohol challenges in individual experimental animals. Recent developments extended the heightened aggressive behavior to rats that self-administered alcohol shortly before the social confrontation. Quantitative ethological analysis revealed that alcohol prolongs "bursts" of aggressive acts and displays and disrupts communication between the aggressive animal and the opponent who defends, submits, or flees. Pharmacological modulation of the GABAA receptor with benzodiazepine agonists and neuroactive steroids results in dose-dependent biphasic changes in aggressive behavior that mimic the dose-effect function of alcohol; benzodiazepines potentiate the aggression-heightening effects of alcohol as well as the behaviorally suppressive effects; and antagonists at benzodiazepine receptors prevented the aggression-heightening effects of alcohol. The maturational and experiential origins for potentially distinctive GABAA receptor characteristics in individuals who exhibit heightened aggressive behavior await identification.

Alcohol, the reward system and dependence

Evidence is presented to show that multiple neurotransmitter systems of the brain reward systems including GABA, glutamate, dopamine, serotonin and opioid peptides are involved in alcohol reinforcement. Dependence is associated with changes in many of these same systems, but also with changes in other neurotransmitters, such as brain corticotropin releasing factor. A midbrain forebrain circuitry that involves parts of the nucleus accumbens and amygdala is hypothesized to be the focus for the neuropharmacology of alcohol reinforcement.

Neural mechanisms of drug reinforcement

The brain substrates involved in the effect of cocaine on brain stimulation reward, in the psychomotor activation associated with cocaine, and in cocaine self-administration appear to be focused on the medial forebrain bundle and its connections with the basal forebrain, notably the nucleus accumbens. Chronic access to cocaine produces a withdrawal state as reflected in increases in brain stimulation reward thresholds, and this change in reward threshold appears to be opposite to the actions of the drug administered acutely. These effects are thought to reflect a change in the activity of reward elements in the medial forebrain bundle and may be responsible for the negative reinforcing state associated with the anhedonia of cocaine withdrawal. Opiate receptors particularly sensitive to the reinforcing effects of heroin also appear to be located in the region of the nucleus accumbens and the ventral tegmental area. There is good evidence for both dopamine-dependent and dopamine-independent opioid interactions in the ventral tegmental-nucleus accumbens connection. In addition, the opiate receptors in the region of the nucleus accumbens may become sensitized during the course of opiate withdrawal and thus become responsible for the aversive stimulus effects of opiate dependence. Reliable measures of the acute reinforcing effects of ethanol have been established in rat models, and substantial evidence exists to show that non-deprived rats will orally self-administer pharmacologically relevant amounts of ethanol in lever-press choice situations. Neuropharmacological studies of ethanol reinforcement in non-dependent rats suggest important roles for serotonin, GABA and dopamine. A role for opioid peptides in ethanol reinforcement may reflect more general actions of opioid peptides in consummatory behavior. Studies of ethanol dependence have implicated brain GABAergic and CRF systems in the more motivational aspects of withdrawal. Future studies will need to focus on the common neurobiologic changes associated with all these drugs, particularly regarding their hedonic and motivational properties.

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.

Neuropharmacology of Cocaine and Ethanol Dependence

Drug addiction includes two important characteristics, chronic compulsive or uncontrollable drug use and a withdrawal syndrome when use of the drug is stopped. Animal models for the motivational components of drug dependence have been developed allowing a systematic exploration of the neurobiological mechanisms of drug dependence. The reinforcing actions of acute cocaine as measured by intravenous cocaine self-administration appear to be mediated by the presynaptic release of dopamine in the region of the nucleus accumbens and may preferentially involve the dopamine D-1 receptor subtype. The nucleus accumbens circuitry involved in the reinforcing actions of cocaine may include the ventral pallidum and may be modulated by serotonin. Chronic cocaine produces increases in brain reward thresholds that may reflect the "dysphoria" and anhedonia associated with cocaine dependence and suggests a dysregulation of brain reward systems possibly involving dopamine. Reliable measures for the acute reinforcing effects of ethanol in nondependent animals have been established in the rat using a lever press operant and a taste habituation procedure. Important roles have been established for serotonin, GABA, dopamine, and opioids in the acute reinforcing properties of ethanol, perhaps acting on some of the same neural circuitry subsuming the reinforcing actions of other drugs of abuse. Studies of the motivational aspects of ethanol dependence have suggested a functional role for brain corticotropin-releasing factor. These results suggest that the neurobiology of drug dependence involves not only neurotransmitters that mediate the acute reinforcing properties of drugs, but also the aversive motivational and emotional aspects of drug withdrawal. Advances in our understanding of brain changes associated with the switch from acute effects to chronic actions may provide a key to our understanding of not only drug dependence, but also psychopathology such as, anxiety, and affective disorders.

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.

Neuroadaptive responses to chronic ethanol

Cellular responses of neuronal tissue to chronic ethanol exposure are reviewed. Evidence for adaptive responses to the acute actions of ethanol is available for five systems: GABA-activated chloride channels, voltage-sensitive calcium channels, NMDA-activated cation channels, receptors coupled through stimulatory guanine nucleotide binding proteins, and membrane lipid order. We suggest that at least some of these adaptive responses occur because of ethanol actions at the level of gene expression.

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.

Modulation of benzodiazepine agonist and inverse-agonist receptor binding by GABA during ethanol withdrawal

1. The present study examined the capacity of GABA to modulate flunitrazepam and Ro15-4513 binding to putative GABAA receptors. Binding was measured in distinct brain regions both before and during selected periods of withdrawal from ethanol. 2. Rats were fed a nutritionally complete liquid ethanol (4.5% w/v) diet for 4 days and at various times after the last dose of ethanol (0, 12, 24, & 72 hr), rats were sacrificed and extensively washed brain membrane fractions were prepared. 3. Competitive inhibition of 3H-flunitrazepam binding by either flunitrazepam or Ro15-4513 (10(-10)M to 10(-7)M) was performed in the absence and presence of GABA (10(-5)M). In the presence of GABA, the apparent affinity for flunitrazepam was increased approximately 1.7 fold and the apparent affinity for Ro15-4513 was decreased by 1.7 fold. 4. No alteration in the capacity of GABA to modulate flunitrazepam or Ro15-4513 affinity (e.g. GABA-shift) was observed in cortical membrane preparations either 12 or 72 hr following ethanol cessation. 5. Further, no changes in GABA-modulation of flunitrazepam binding was evident 0, 12, 24, or 72 hr after the last ethanol dose in membranes prepared from cortex, hippocampus or cerebellum. 6. Therefore, results from the present study indicate that the capacity of GABA to modulate receptor affinity for benzodiazepine agonists and inverse-agonists in rat cortex, hippocampus or cerebellum is not altered during withdrawal from chronic ethanol.

Overexcitement and disinhibition. Dynamic neurotransmitter interactions in alcohol withdrawal

In alcohol withdrawal, abnormalities occur in a number of neurotransmitter systems: there is reduced inhibitory function, and increased activity of excitatory systems. The former, indicated by reduced GABA and alpha-2-adrenoceptor activity, acts in conjunction with, and is exacerbated by, the latter, which itself may be due to the potentiation of NMDA activity by depletion of magnesium, and overactivity of catecholaminergic and CRF neurones. These dysfunctions produce immediate effects and may also contribute to the long-term changes in brain excitability by a kindling-like process. It is possible that early and active treatment may oppose this process. Present strategies for treatment of alcohol withdrawal enhance GABA and alpha-2 inhibitory, or reduce excitatory, mechanisms. Future possibilities include the use of CRF and/or NMDA antagonists.

Alcoholism and panic disorder: is the comorbidity more than coincidence?

Studies on alcoholic patients have found a higher than expected prevalence of panic disorder, and suggest a positive correlation between the level of alcohol consumption and severity of anxiety. Conversely, there is an increased prevalence of alcoholism among patients with panic disorder and their blood relatives. A comparison of symptoms, physiological and neurochemical changes known to occur in both alcohol withdrawal and panic disorder reveals a degree of similarity between the 2 conditions. Based on the data, we propose that the chemical and cognitive changes occurring as the result of repeated alcohol withdrawals may kindle and condition coincidence of panic attacks in susceptible individuals. Implications of our postulates for treatment of alcohol withdrawal and panic disorder in alcoholics and for future studies are discussed.

Neuropharmacological and clinical aspects of alcohol withdrawal

Abnormalities in the function or activity of several neurotransmitter systems have been demonstrated after acute and chronic, exposure to alcohol, and in alcohol withdrawal. The changes can be divided into alterations in function of inhibitory and excitatory systems. Inhibitory dysfunction is indicated by reduced gamma-aminobutyric acid and alpha-2-adrenoceptor activity. In conjunction with, and exacerbating this, is increased activity of excitatory systems, perhaps the most significant of which is the probable potentiation of N-methyl-D-aspartate activity by depletion of magnesium. There is additional, and possibly secondary, overactivity of catecholamine and corticotropin releasing factor neuronal systems. Other, less specific changes include increased numbers of calcium channels, which would increase neuronal excitability. The evidence for these changes is presented, and the implications for new treatment regimes for alcohol withdrawal are discussed.

The effects of ethanol and Ro 15-4513 on elevated plus-maze and rotarod performance in long-sleep and short-sleep mice

The effects of ethanol and diazepam were examined in long-sleep (LS) and short-sleep (SS) mice using the elevated plus-maze. Ethanol had more pronounced effects in SS mice than in LS mice. In contrast, LS mice were more sensitive to the effects of diazepam on the elevated plus-maze. The ataxic effects of ethanol were measured by rotarod performance. SS mice were more resistant to the ataxic effects of a 2.0 g/kg dose of ethanol than LS mice. Ro 15-4513 reversed ethanol's ataxic effects when administered after ethanol in both LS mice and SS mice. Pentobarbital-induced ataxia was unaffected by treatment with Ro 15-4513. Studies of competition of Ro 15-4513 on 3H-flunitrazepam binding indicated that LS and SS mice did not differ in this measure in cortex, cerebellum or hippocampus.

Chronic ethanol treatment alters the behavioral effects of Ro 15-4513, a partially negative ligand for benzodiazepine binding sites

Pentylenetetrazol (PTZ)-induced convulsion were studied in control, chronic ethanol-maintained, and ethanol-withdrawal rats. The convulsive doses of PTZ varied among the different groups of rats. Ethanol-maintained rats required higher doses of PTZ to produce convulsions, compared to control and ethanol-withdrawal rats. The partially negative ligands for benzodiazepine binding sites, Ro 15-4513 (2 mg/kg, i.p.) and FG 7142 (20 mg/kg, i.p.) produced proconvulsant effect in saline (control) and ethanol-withdrawal rats as they potentiated the effect of subconvulsive dose of PTZ. A higher dose of Ro 15-4513 (4 mg/kg, i.p.), but not FG 7142 (up to 80 mg/kg, i.p.), also produced proconvulsant effect in ethanol-maintained rats. Furthermore, Ro 15-4513 (5, 10 mg/kg, i.p.), but not FG 7142 (up to 80 mg/kg, i.p.), produced clonic-tonic seizures of short duration in ethanol-withdrawal rats. These effects of Ro 15-4513 and FG 7142 were reversed by diazepam (2 mg/kg, i.p.), as well as by the GABA-neutral Ro 15-1788 (10 mg/kg, i.p.), thereby, indicating the involvement of central benzodiazepine receptors in the action of Ro 15-4513 and FG 7142. These observations suggest that chronic ethanol treatment selectively alters the receptor sensitivity to Ro 15-4513, an ethanol antagonist and partially negative ligand for BZ sites, and this observation supports the notion that ethanol effects are more susceptible to reversal by the imidazobenzodiazepine as compared to other negative ligand for BZ binding sites.

Effects of ethanol and imidazobenzodiazepine Ro 15-4513 on spontaneous saccades of the pigmented rat

The present study was aimed at investigating the alterations of the spontaneous saccadic eye movements of pigmented rats following ethanol administration. In addition we have studied the efficacy of the imidazobenzodiazepine Ro 15-4513 in reversing the effects of alcohol on saccades. The horizontal component of spontaneous eye movements was recorded by means of the magnetic field search coil technique on 11 head-restrained, pigmented rats. After the intraperitoneal injection of ethanol (1 g/kg) spontaneous saccades showed: i) a backward post-saccadic drift, with an exponential-like time course (time constant 100-150 ms); ii) a remarkable reduction of mean saccadic amplitude, up to 37% of control; iii) a significant decrease of peak velocity, which was reduced to about 80% of control. All these effects appeared and developed within a few minutes after the administration and were still present one hour later. When Ro 15-4513 (5 mg/kg) was injected i.p., 15 min after ethanol, the post-saccadic drift amplitude was immediately reduced and the drift was completely abolished within about 30 min. Mean saccadic amplitude returned to control values within a few minutes and was then steadily maintained for the following period examined (30 min). On the contrary, peak velocity showed only a slight tendency to recover which never was significant. When the same dose of Ro 15-4513 was injected alone there was no post-saccadic drift. However, mean saccadic amplitude increased, almost immediately, up to 160% of control. Its value showed a slight constant decrease in the following 30 min. Peak velocity was only slightly increased (up to 106% of control), but never was significantly different from control. Our results show that ethanol induces a remarkable impairment in the performance of spontaneous saccades. The imidazobenzodiazepine Ro 15-4513 is able to reverse completely only some of the alcohol-induced alterations, i.e. the post-saccadic drift and the reduction of saccadic amplitude, while it fails to counter efficiently the reduction of peak velocity. Ro 15-4513 exerts an intrinsic action, which is opposite to that of ethanol, on some of the saccadic parameters we have examined.

Ethanol and the benzodiazepine-GABA receptor-ionophore complex

Ethanol has a pharmacological profile similar to that of classes of drugs like benzodiazepines and barbiturates, which enhance GABAergic transmission in the mammalian CNS. Several lines of behavioral, electrophysiological and biochemical studies suggest that ethanol may bring about most of its effects by enhancing GABAergic transmission. Recently, ethanol at relevant pharmacological concentrations has been shown to enhance GABA-induced 36Cl-fluxes in cultured spinal cord neurons, synaptoneurosomes and microsacs. These enhancing effects of ethanol were blocked by GABA antagonists. Ro15-4513, an azido analogue of classical BZ antagonist Ro15-1788, reversed most of the behavioral effects of ethanol and other effects involving 36Cl-flux studies. The studies summarized below indicate that most of the pharmacological effects of ethanol can be related to its effects on GABAergic transmission.

A new alcohol antagonist: phaclofen

The ability of the GABA(B) receptor antagonist, phaclofen to alter behavioral effects of ethanol was evaluated by loss of righting reflex (sleep time), motor incoordination (bar holding), spontaneous locomotion (open field activity) and hypothermia. Pretreatment with phaclofen significantly decreased the effects of ethanol on motor incoordination, locomotor activity and hypothermia. However, phaclofen had no effect on either pentobarbitalor diazepam-induced motor incoordination. Phaclofen slightly increased the ED50 for loss of the righting reflex but did not alter either the duration of reflex loss produced by ethanol or blood ethanol levels at awakening. Our results suggest phaclofen is rapidly inactivated resulting in difficulty in observing antagonism of long duration ethanol effects. These findings suggest that the GABA(B) system may play a role in mediating several important actions of ethanol.

Attenuation of ethanol intoxication by alpha-2 adrenoceptor antagonists

The interaction of a highly potent and selective alpha-2 adrenoceptor antagonist, atipamezole with ethanol was investigated in tests assessing a number of ethanol's behavioral effects. Atipamezole antagonized ethanol's effects on directed exploration in a holeboard test, reduced observer-rated intoxication and also reduced the duration of loss of righting reflex caused by ethanol. Similar effects were produced by another alpha-2 adrenoceptor antagonist idazoxan. The magnitude of the effects was comparable to that produced in the same animal models by the imidazodiazepine Ro 15-4513, which antagonizes ethanol by an action at central benzodiazepine receptors. Whereas Ro 15-4513 possesses marked behavioral effects on its own, atipamezole is comparatively inactive in all paradigms so far tested. The data suggest that alpha-2 adrenoceptors can play an important role in modulating the intoxicating effects of ethanol.

Benzodiazepines in the treatment of alcoholism

This chapter comprises three sections that cover the main aspects of benzodiazepines and alcohol: (1) the basic pharmacology of benzodiazepines; (2) use of benzodiazepines in the treatment of withdrawal; and (3) the use of benzodiazepines in treating alcoholics. The basic studies suggest that a major site of action of alcohol may be the GABA/benzodiazepine receptor complex and that compensatory alterations in this complex may underly withdrawal. In the section on alcohol withdrawal, interactions between the GABA/benzodiazepine receptor complex, sympathetic nervous system, and hypothalamic-pituitary-adrenal axis are discussed. Use of benzodiazepines in the treatment of the alcohol withdrawal syndrome are reviewed, including the possibility that the benzodiazepines may prevent withdrawal-induced "kindling." Lastly, we review indications for, and efficacy of, benzodiazepines in long-term treatment of patients with alcoholism. Benzodiazepines are not indicated for the treatment of alcoholism. Furthermore, they have very few indications in alcoholics and their dependency-producing potency has to be appreciated when they are used in patients with alcoholism.

RO15-4513 but not FG-7142 reverses anticonvulsant effects of ethanol against bicuculline- and picrotoxin-induced convulsions in rats

The reversal of anticonvulsant effect of ethanol against chemoconvulsions by RO15-4513 was investigated in rats as this novel imidazobenzodiazepine (ethyl-8 azido-5, 6-dihydro-5-methyl-6-Oxo-4H-imidazo [1,5a] [1,4] benzodiazepine-3-carboxylate) is reported to antagonize the acute behavioral and biochemical effects of ethanol in animals. Reversal of ethanol effects on onset of myoclonic jerks, tonic extensor phase, mortality time and percent protection against mortality were compared with not only other anticonvulsant pentobarbital but also with another inverse agonist FG-7142. Pretreatment with RO15-4513 (4 mg/kg) reversed the protective effect of ethanol against bicuculline-induced tonic extensor phase and mortality (87%). This response was sensitive to reversal by RO15-1788 (10 mg/kg). However, onset of myoclonic jerks and duration of clonus were not significantly altered. It also reversed the effect against picrotoxin but the reversal against mortality was up to 50%. As compared to ethanol, RO15-4513 reversed partially the protective effect of pentobarbital against bicuculline- and picrotoxin-induced convulsions. FG-7142 failed to reverse the protective effect of ethanol and pentobarbital against bicuculline-induced tonic extensor phase although it reversed the effect against onset and mortality. It had no effect on the protective effect against picrotoxin-induced convulsions. Both RO15-4513 and FG-7142 possessed proconvulsant effects against bicuculline but not against picrotoxin. These observations suggest that RO15-4513 has a more preferential action against ethanol effects as compared to the other inverse agonist.

The benzodiazepine receptor inverse agonist RO15-4513 exacerbates, but does not precipitate, ethanol withdrawal in mice

RO15-4513, an imidazobenzodiazepine that has been reported to antagonize several behavioral and biochemical actions of ethanol, was given to C3H mice at various times during withdrawal from chronic (72 hours) continuous exposure to ethanol vapor. When administered immediately following chronic ethanol exposure, RO15-4513 (6 or 12 mg/kg) did not influence the withdrawal response. However, when given at subsequent times (3, 5, and 8 hours postethanol withdrawal), RO15-4513 significantly increased the severity of the withdrawal response in ethanol-exposed mice. Moreover, this exacerbation was completely reversed by pretreatment with the benzodiazepine receptor antagonist RO15-1788. Thus, these data indicate that the benzodiazepine inverse agonist, RO15-4513, is capable of exacerbating, but not precipitating, ethanol withdrawal.

Antagonizing the anticonvulsant effect of ethanol using drugs acting at the benzodiazepine/GABA receptor complex

The ability of various benzodiazepine receptor ligands to antagonize the anticonvulsant action of ethanol was investigated using intravenous infusion of the GABA antagonist bicuculline. The partial inverse agonists FG 7142, RO 15-4513 and RO 15-3505 produced dose-related reductions in seizure threshold. These compounds also partially reversed the anticonvulsant action of ethanol. However, the magnitude of the effects in each case was only equivalent to the reduction in seizure threshold caused by each compound when administered alone. This is the proconvulsant effect of each compound merely subtracted from the anticonvulsant effect of ethanol. ZK 93426, a benzodiazepine receptor antagonist which alone failed to alter seizure threshold, did not affect the anticonvulsant action of ethanol. Both RO 15-4513 and RO 15-3505 also lowered the seizure threshold of barbiturate-treated mice, again in a subtractive fashion. The ability of RO 15-4513 and other inverse agonists to antagonize the anticonvulsant effect of ethanol appears to result from their intrinsic proconvulsant properties.

Molecular interactions of ethanol with GABAergic system and potential of RO15-4513 as an ethanol antagonist

The behavioral and biochemical effects of ethanol in man and animals have been investigated for a long time. A role of catecholamines in the central stimulatory action and during withdrawal has been envisaged, but more recent observations have revealed the involvement of inhibitory synaptic transmitter, GABA, in the actions of ethanol. Ethanol-induced motor incoordination, hypnosedation, antianxiety, and anticonvulsant actions are reported to be GABA-mediated. Involvement of the GABA system has been implicated in ethanol withdrawal-induced seizures in animals. More direct evidences using Cl- influx studies in synaptoneurosomes and spinal neuronal culture studies confirm such a mode of action of ethanol, probably influencing the chloride channel modulation at the GABA-benzodiazepine receptor ionophore complex. RO15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-Oxo-4H-imidazo [1,5-alpha], [1,4] benzodiazepine-3-carboxylate), a novel imidazobenzodiazepine, an analogue of the classical benzodiazepine antagonist is reported to possess alcohol antagonistic properties. RO15-4513 reverses both the behavioral and biochemical effects of ethanol, including the action of GABA-induced Cl- fluxes. But its potential clinical application may be restricted due to its inverse agonistic property. The present review focuses on the GABA-linked behavioral and biochemical actions of ethanol and discusses the potential of RO15-4513 as an alcohol antagonist.

Ro 15-4513 does not antagonize the discriminative stimulus- or rate-depressant effects of ethanol in rats

Female rats, trained to discriminate between IP administered 1.2 g/kg ethanol (ETOH) and the saline vehicle (12 ml/kg), did not press the nondrug associated lever in tests with ETOH (0.9 and 1.2 g/kg) plus the purported amethystic imidazo benzodiazepine Ro 15-4513 (3 and 10 mg/kg) as examined at two intervals after ETOH administrations viz. 7.5 and 15 min. The two doses of Ro 15-4513 were administered 5 min prior to ETOH. Response times were increased in tests with the combination. ETOH in expired air was not different in the two drug conditions, i.e., ETOH singly and together with Ro 15-4513, irrespective of the dose combinations examined. Rats trained to press a bar (FR-10 operant behavior) for sweetened water disclosed increases in the time used to obtain the reinforcer after treatments with ETOH and Ro 15-4513. Thus, Ro 15-4513 did not seem to reverse any of the behaviors examined in this study.