RO 15-1788 produces naloxone-reversible analgesia in the rat

Intraperitoneal and intracerebroventricular administration of the benzodiazepine antagonist RO 15-1788 produced analgesia to both thermal and mechanical pain. This effect was reversed by pretreatment with the opioid antagonist naloxone but was unaffected by pretreatment with the benzodiazepine agonist midazolam. Furthermore, administration of the benzodiazepine antagonist RO 15-3505 was without analgesic effect. It is, therefore, proposed that the intrinsic action induced by RO 15-1788 is exerted via the indirect activation of endogenous opioid systems and that the observed effect is not due to the action of the antagonist on the benzodiazepine receptor.     

Effects of repeated RO 15-1788 administration in benzodiazepine-dependent baboons

Administration of the benzodiazepine antagonist, RO 15-1788, to baboons that were chronically exposed to diazepam or triazolam precipitated withdrawal signs. When RO 15-1788 was administered repeatedly at one or three day intervals, precipitated withdrawal signs were attenuated. However, these baboons remained tolerant to the sedative effects of the high doses of benzodiazepines to which they were continuously exposed. While tolerance to agonist effects of drugs and development of physical dependence are often thought to be functionally interrelated phenomena, the present results suggest that these may be separable properties of the benzodiazepines. The present results clearly indicate that certain actions of benzodiazepine agonists and antagonists can be independently regulated.     

Dose-dependent reversal of chlordiazepoxide-induced discrimination impairment by Ro 15-1788

Chlordiazepoxide (10 mg/kg), administered on eight successive acquisition sessions, impaired a light-cued, successive discrimination in male Sprague-Dawley rats by increasing the number of incorrect responses. The benzodiazepine receptor antagonist Ro 15-1788 (5 and 10 mg/kg) reversed the discrimination impairment and reduced the number of incorrect responses in a generally dose-dependent manner when co-administered with chlordiazepoxide. These findings suggest that the impairment of successive discrimination by chlordiazepoxide is mediated by central benzodiazepine receptor sites. When administered alone, however, the 10 mg/kg dose of Ro 15-1788 (but not the 5 mg/kg dose) produced a mild benzodiazepine-like impairment in discrimination, which was accompanied by a small but significant increase in incorrect responses. These findings suggest that Ro 15-1788 may also have some intrinsic action of its own, which needs to be assessed independently of its use as a mediational research tool.Portions of these data were presented at the Annual Meeting of the Psychonomic Society, Seattle, Washington, 1987     

Specific benzodiazepine antagonist RO15-1788 and thirst-induced drinking in the rat

Midazolam, a new water-soluble benzodiazepine, increased the water intake of water deprived rats. The effect was abolished by concurrent treatment with the benzodiazepine antagonist, RO15-1788. The lack of effect of RO15-1788 on phenobarbitone-induced hyperdipsia confirmed the specificity of the antagonist action. Alone RO15-1788 (0.3-30 mg . kg-1) had no effect on thirst-induced drinking. Thus, it was not necessary to posit the action of an endogenous benzodiazepine ligand in thirst-induced drinking.     

Reversal of chlordiazepoxide-induced impairment in successive discrimination performance by RO 15-1788

The effects of chiordiazepoxide (CDP) alone and in combination with Ro 15-1788 on the performance of a previously learned go-no go successive discrimination were studied in male Sprague-Dawley rats. CDP 10 mg/kg impaired discrimination performance in six sucessive sessions, with animals showing recovery in two post-drug sessions. The impairment in disrcimination performance was due to an increase in responding during no go (waiting) periods of the task. The benzodizepine (BDZ) receptor antagonist Ro 15-778 (5 and 10 mg/kg) reversed the impairment in discrimination performance in sessions 2-6 (but not 1) when co-administered with CDP. While the effectiveness of Ro 15-1788 was not dose-dependent, the reversal in discrimination impairment was due to a reduction in responding during no go periods of the task. These findings suggest that the impairment in discrimination performance produced by CDP is mediated by central BDZ receptor sites. When administered alone, Ro 15-1788 10 mg/kg (but not 5mg/kg) produced a mild BDZ-like impairment in discrimination performance and increase in a no go period responding. These findings suggest that Ro 15-1788 is not a neutral antagonist but has some intrinsic action of its own.     

Behavioural effects of pentylenetetrazole reversed by chlordiazepoxide and enhanced by RO 15-1788

Summary The effects of low doses of pentylenetetrazole (PTZ) on exploratory behaviour and locomotor activity in the rat, were measured in the holeboard apparatus. PTZ (30 mg/kg) significantly reduced exploratory head-dipping, an effect that was significantly reversed by chlordiazepoxide (5 mg/kg) and enhanced by RO 15-1788 (20 mg/kg). RO 15-1788 (20 mg/kg) also significantly enhanced the reduction in locomotor activity produced by PTZ (30 mg/kg); although this reduction was not reversed by chlordiazepoxide (5 mg/kg) the reduction in locomotor activity with the drug combination was no greater than that with either drug alone. The results are discussed with respect to a coupling between the benzodiazepine receptors and the site at which PTZ acts.     

RO 15-1788 does not influence postpartum aggression in lactating female rats

Recently, Hansen et al. (1985) suggested behavioural similarities between lactating rats and non-maternal rats treated with benzodiazepines (BDZ), indicating that lactation may be associated with an increased activity state at the GABA/BDZ receptor complex similar to BDZ treatment. A logical prediction of this hypothesis is that BDZ antagonists should decrease typical maternal behaviours involved, such as aggression.We tested this hypothesis by measuring the behavioural effects of the BDZ antagonist RO 15-1788 (1.25–10 mg/kg IP) on aggressive behaviour of lactating female rats confronted with male intruders. We could not support the hypothesis; no consistent behavioural effects of RO 15-1788 on aggression were found. The implications of this finding for the proposed hypothesis are discussed.     

Changes in benzodiazepine receptors by acute stress: different effect of chronic diazepam or RO 15-1788 treatment

In rats submitted to acute stress by forced swimming there was an immediate sharp decline in the binding of [3H]flunitrazepam and of [3H]ethyl-beta-carboline-3-carboxylate in synaptosomal membranes of the cerebral cortex and hippocampus. This was followed by a rebound increase in benzodiazepine receptors after 60 min, specially in the hippocampal formation. These two changes were blocked by chronic treatment with diazepam for 14 days (4 mg/kg/day). On the other hand, long-term treatment with the antagonist RO 15-1788 did not modify the changes caused by the acute stress. These findings are discussed in relation to the possible regulation of benzodiazepine receptors by agonists and antagonists.     

Specific proconvulsant action of an imidazobenzodiazepine (RO 15-1788) on isoniazid convulsions

The imidazobenzodiazepine RO 15-1788 is a specific proconvulsant against isoniazid induced convulsions when given intravenously at 10 to 50 mg/kg i.v. The compound fails to change the brain content of GABA or the decrease of this parameter elicited by isoniazid. It is possible that its action depends on the agonistic effects on the benzodiazepine receptor. This possibility is supported by its lack of action on picrotoxin convulsions which are due to an action on the Cl^? ion gate.     

Amnestic effects of lormetazepam and their reversal by the benzodiazepine antagonist Ro 15-1788

A combined visual (pictures) and auditory (word lists) memory test developed to trace the course of information processing under pharmacological or other influences was validated in a group of 20 subjects (control group) and then applied to determine the amnesic effects of lormetazepam and the reversal of these effects by the benzodiazepine antagonist Ro 15-1788. Three groups of n=10 subjects received either 0.02 mg/kg IV lormetazepam (groups B and C) or placebo (group A) followed 14 min later by 0.03 mg/kg IV Ro 15-1788 (groups A and C) or placebo (group B). The time course of memory performance in the three groups was investigated and compared across three consecutive 14-min phases: before (phase 1) and after (phase 2) the first intravenous administration, and after the second treatment (phase 3). Results were also compared with those of 20 subjects from a drug-free control group in order to verify the memory test. Lormetazepam clearly impaired immediate and delayed free recall as well as recognition in both visual and auditory tasks. These effects were completely reversed by Ro 15-1788, which alone had no clear effect on memory performance in this study. Psychometric scales indicated concomitant sedation and impaired concentration after lormetazepam alone. Interestingly, lormetazepam retrogradely enhanced performance in the visual test of delayed free recall. The impaired acquisition of new information after the administration of lormetazepam may be associated with an improvement of the consolidation process of information acquired before drug treatment.This article is part of the doctoral thesis of Dagmar Berenberg     

Reversal of antinociceptive effect of cholecystokinin by benzodiazepines and a benzodiazepine antagonist, Ro 15-1788

Intraperitoneally administered benzodiazepines, chlordiazepoxide (2-5 mg/kg), diazepam (1 mg/kg), flurazepam (1 mg/kg) and a benzodiazepine antagonist, Ro 15-1788 (0.5 mg/kg), reversed the antinociceptive effect in mice which was induced by intracisternal administration of 1 microgram of sulfated cholecystokinin octapeptide. The antinociceptive effect of cholecystokinin was reversed by naloxone, suggesting that the antinociceptive action involves endogenous opioid peptides in its production. On the other hand, morphine-induced analgesia was not reversed by diazepam and Ro 15-1788. These facts rule out opioid receptors as the site of the antagonism between the benzodiazepines or Ro 15-1788 and cholecystokinin on the antinociceptive effect. Benzodiazepines and Ro 15-1788 seem to inhibit the release of opioid peptides induced by cholecystokinin.     

The anxiogenic action of RO 5-4864 in the social interaction test: effect of chlordiazepoxide,RO 15-1788 and CGS 8216

Summary RO 5-4864 (20 mg/kg), a benzodiazepine with high affinity for peripheral-type benzodiazepine binding sites in rat kidney and brain, but not for the classical CNS sites, reduced the time spent by pairs of rats in active social interaction, without reducing locomotor activity, possibly reflecting an anxiogenic action. This anxiogenic effect was not reversed by chlordiazepoxide (5 or 10 mg/kg) given acutely, but was reversed by chlordiazepoxide (5 mg/kg) given for 5 days prior to testing. RO 15-1788 (10 mg/kg), a drug that antagonises several effects of benzodiazepines but has little affinity for peripheral-type sites, had no action on the reduction in social interaction induced by RO 5-4864. However, CGS 8216 (10 mg/kg) which also antagonises the effects of benzodiazepines and has little affinity for RO 5-4864 recognition sites, significantly enhanced the reduction in social interaction caused by RO 5-4864, and the combination produced a significant decrease in locomotor activity. These results are discussed in terms of possible sites of action of RO 5-4864 on the GABA-benzodiazepine receptor complex.     

Beneficial actions of RO 15-1788, a benzodiazepine receptor antagonist, in hemorrhagic shock

We studied RO 15-1788, a new benzodiazepine receptor antagonist, [ethyl 8-fluoro-5, 6-dihydro-5-methyl-6-oxo-4H-imidazo (1, 5a) (1, 4) benzodiazepine-3-carboxylate] to determine its effects in a murine model of hemorrhagic shock. Hemorrhaged rats treated with RO 15-1788 maintained post-reinfusion mean arterial blood pressure (MABP) at significantly higher values compared to rats receiving only the vehicle (final MABP 114 +/- 4 vs 82 +/- 4 mmHg, p less than 0.001). Moreover, RO 15-1788 decreased the release of the lysosomal hydrolase, cathepsin D (p less than 0.02) into the circulation and blunted the plasma accumulation of free amino-nitrogen groups (p less than 0.01). Furthermore, the plasma activity of a myocardial depressant factor (MDF) was significantly lower in RO 15-1788 treated rats subjected to hemorrhagic shock than in those given the vehicle (18 +/- 2 vs 42 +/- 4 U/ml, p less than 0.01). Additionally, in vitro analysis indicated that RO 15-1788 antagonizes PAF induced coronary vasoconstriction and cardiac depression observed in perfused rat hearts, as well as inhibiting PAF induced platelet aggregation in cat platelet rich plasma. Our results suggest that antagonism of PAF actions can contribute significantly to the beneficial effects of RO 15-1788 in hemorrhagic shock.     

RO 15-1788 antagonises the central effects of diazepam in man without altering diazepam bioavailability

1 In a double-blind, placebo controlled study, the efficacy of Ro 15-1788, a new benzodiazepine antagonist, in blocking the cognitive, psychomotor and subjective effects of diazepam, was investigated in a group of six healthy male volunteers. 2 The central effects of orally administered diazepam (40 mg) were most pronounced 1 h after dosing and persisted for 9 h with decreasing severity. 3 Concurrent oral administration of Ro 15-1788 (200 mg) completely prevented the impairment in cognitive and psychomotor function observed after diazepam alone. 4 The duration of action of Ro 15-1788 was shorter than that of diazepam. 5 Plasma diazepam levels after administration of the diazepam/antagonist combination were very similar to those observed following diazepam alone.     

Disruption of schedule-controlled behavior by Ro 15-1788 one day after acute treatment with benzodiazepines

The behavioral effects of the benzodiazepine antagonist Ro 15-1788 were studied in squirrel monkeys after acute injections of benzodiazepines. Monkeys responded under a multiple schedule of food presentation with alternating fixed-interval (FI) and fixed-ratio (FR) components. Chlordiazepoxide (10 mg/kg) increased FI responding and had little effect on FR responding 1 h after it was administered; FI responding was still elevated during the session on the following day. When Ro 15-1788 (0.1–3 mg/kg) was administered 1 h after chlordiazepoxide, it antagonized the effects of chlordiazepoxide in a dose-related manner. When Ro 15-1788 was administered 1 day after chlordiazepoxide, however, doses of 1 or 3 mg/kg suppressed both FI and FR responding. Suppression of schedule-controlled responding was also observed when Ro 15-1788 (3 mg/kg) was administered 1 day after diazepam (3 or 5.6 mg/kg) or N-desmethyldiazepam (5.6 mg/kg). The results show that Ro 15-1788 can precipitate disruption of schedule-controlled behavior 1 day after acute treatment with benzodiazepines.Animals used in this study were maintained in accordance with the guidelines of the Committee on Animals of the Harvard Medical School and of the Committee on Care and Use of Laboratory Animals of the Institute of Laboratory Animal Resources, National Research Council; DHEW publication (NIH) 78-23, revised 1978     

Behavioural evidence for partial agonist properties of RO 15-1788, a benzodiazepine receptor antagonist

Rats trained to discriminate pentylenetetrazol from saline had this cue antagonized by the benzodiazepine, clorazepate. Ro 15-1788 reversed the antagonism of the pentylenetetrazol cue produced by clorazepate. Similarly, Ro 15-1788 blocked the anti-conflict effect of clorazepate. Rats trained to discriminate clorazepate from saline, however, generalized this cue to Ro 15-1788. These results demonstrate that Ro 15-1788 is not a pure benzodiazepine antagonist, but has partial agonist properties.     

Specific antagonism by RO 15-1788 of benzodiazepine-induced increases in food intake in rhesus monkeys

Food intake of rhesus monkeys was limited to a single daily 2 hr session of banana flavored pellet availability, seven days a week. Following stabilization of intake, the effects of intragastric bromazepam, diazepam and pentobarbital, when given alone, were determined by delivering a dose twice weekly, 60 min before the session. Dose-dependent increases in food intake were observed with the following descending order of potencies: bromazepam, diazepam and pentobarbital. RO 15-1788 (0.5-1.0 mg/kg, IM), when given alone, five min before the session had no effect on food intake. When given in combination with bromazepam and diazepam, RO 15-1788 completely blocked the increases in food intake observed when the benzodiazepines were given alone. The specificity of this antagonism was shown by the failure of RO 15-1788 to alter the food intake increases induced by pentobarbital. These results confirm and extend previous reports of the specific antagonism of benzodiazepine behavioral effects by RO 15-1788 to an additional species and another behavioral effect of benzodiazepines.     

Benzodiazepine antagonist RO 15-1788 partly reverses some anxiolytic effects of ethanol in the mouse

The effects of the benzodiazepine (BZD) receptor antagonist RO 15-1788 (3 mg/kg) on the anxiolytic properties of ethanol in mice confronted with a light/dark choice procedure and with the staircase test were investigated. RO 15-1788 reversed the effects of ethanol on some of the behavioural parameters without eliciting intrinsic effects when given alone. These data closely resemble those we previously obtained with several BZD receptor inverse agonists such as RO 15-3505, RO 15-4513 or -CCM. Since anxiogenic-like properties of low doses of RO 15-1788 have been identified by other authors, it is suggested that the antagonistic action of this drug against some of the behavioural effects of ethanol could be due to its being a partial BZD inverse agonist.     

Chronic RO 15-1788 treatment increases the number of benzodiazepine receptors in rat cerebral cortex and hippocampus

Administration of 4 mg/kg per day of diazepam in the drinking water for 14 days produced a small, but not significant decrease of benzodiazepine binding sites for [3H]flunitrazepam and [3H]ethyl-beta-carboline-3-carboxylate. Similar treatment with the benzodiazepine antagonist RO 15-1788 resulted in a marked increase in the density of sites for both ligands in the synaptosomal membranes of cerebral cortex and hippocampal formation.     

Effects of RO 15-1788 on a running response rewarded on continuous or partial reinforcement schedules

Two experiments were run in which rats were rewarded with food for running in a straight alley at one trial a day, followed by extinction of the running response. During acquisition of the response, reward was delivered either on a continuous reinforcement (CRF) or on a quasirandom 50% partial reinforcement (PRF) schedule. The groups given PRF were more resistant to extinction than those given CRF, the well-known partial reinforcement extinction effect. In Experiment 1 different groups of rats were injected during acquisition only with 1, 5 or 10 mg/kg of the benzodiazepine antagonist, RO 15-1788, or with placebo. In Experiment 2, 5 mg/kg RO 15-1788 or placebo were administered in a full cross-over design during acquisition, extinction or both. At the end of Experiment 2 only [³H]-flunitrazepam binding was measured in either the presence or absence of added -aminobutyrate (GABA) in homogenates of hippocampi dissected from the animals that had received behavioural training. The drug affected running speeds during both acquisition and extinction in different ways depending upon the schedule of reinforcement (CRF or PRF) and also gave rise to enhanced GABA stimulation of [³H]-flunitrazepam binding. The results are discussed in relation to the hypothesis that the neurochemical pathways by which reinforcement schedules modify behaviour include a step influenced by benzodiazepine receptors.