Ro 15-1788-induced seizures in rats continually exposed to diazepam for prolonged periods

Flumazenil-precipitated withdrawal in healthy volunteers following repeated diazepam exposure

RATIONALE

Parametric preclinical studies of the benzodiazepine antagonist flumazenil have contributed to the understanding of the physical dependence associated with chronic benzodiazepine use. However, few parametric studies have been conducted in human participants.

OBJECTIVE

This study was designed to assess the effect of duration of benzodiazepine exposure on the intensity of flumazenil-precipitated withdrawal in healthy volunteers.

METHOD

Participants were randomly assigned to receive either oral diazepam (15 mg/70 kg; n=10) or placebo (n=8) capsules nightly for 28 days. Effects of flumazenil (1 mg/70 kg, intravenously administered) were assessed in challenge sessions conducted before capsule ingestion, and after 1, 7, 14, and 28 days of capsule ingestion.

RESULTS

Flumazenil produced a profile of participant-rated effects consistent with benzodiazepine withdrawal that peaked immediately after completion of the 5-min flumazenil injection and rapidly dissipated thereafter. The magnitude of these effects was comparable after 7, 14, and 28 days of diazepam. Flumazenil also produced modest elevations in blood pressure and decreases in skin temperature in the diazepam group, both of which were sustained throughout the approximate 60-min session.

CONCLUSIONS

These findings support previous human research studies indicating that flumazenil precipitates withdrawal after short chronic exposure to benzodiazepines and suggests that duration of exposure does not influence the intensity of withdrawal beyond the first week of exposure.

Neuroadaptive processes in GABAergic and glutamatergic systems in benzodiazepine dependence

Knowledge of the neural mechanisms underlying the development of benzodiazepine (BZ) dependence remains incomplete. The gamma-aminobutyric acid (GABA(A)) receptor, being the main locus of BZ action, has been the main focus to date in studies performed to elucidate the neuroadaptive processes underlying BZ tolerance and withdrawal in preclinical studies. Despite this intensive effort, however, no clear consensus has been reached on the exact contribution of neuroadaptive processes at the level of the GABA(A) receptor to the development of BZ tolerance and withdrawal. It is likely that changes at the level of this receptor are inadequate in themselves as an explanation of these neuroadaptive processes and that neuroadaptations in other receptor systems are important in the development of BZ dependence. In particular, it has been hypothesised that as part of compensatory mechanisms to diazepam-induced chronic enhancement of GABAergic inhibition, excitatory mechanisms (including the glutamatergic system) become more sensitive [Behav. Pharmacol. 6 (1995) 425], conceivably contributing to BZ tolerance development and/or expression of withdrawal symptoms on cessation of treatment, including increased anxiety and seizure activity. Glutamate is a key candidate for changes in excitatory transmission mechanisms and BZ dependence, (1) since there are defined neuroanatomical relationships between glutamatergic and GABAergic neurons in the CNS and (2) because of the pivotal role of glutamatergic neurotransmission in mediating many forms of synaptic plasticity in the CNS, such as long-term potentiation and kindling events. Thus, it is highly possible that glutamatergic processes are also involved in the neuroadaptive processes in drug dependence, which can conceivably be considered as a form of synaptic plasticity. This review provides an overview of studies investigating changes in the GABAergic and glutamatergic systems in the brain associated with BZ dependence, with particular attention to the possible differential involvement of N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors in these processes.

The effects of diazepam dependence and withdrawal on morphine-induced antinociception and changes in locomotion in male and female rats

Male and female rats were exposed for 3 weeks to diazepam (DZ)-filled or empty capsules (CTR) prior to the daily administration of morphine (MOR, 5 mg/kg, IP) for 5 days. Thereafter, capsules were removed and 48 h later MOR was injected for the next 5 days. The tail-flick latency (TFL) was measured prior to and 15, 30, and 60 min after MOR assessed analgesia. Locomotion (LOC) was determined before and 15 min after injection. Prior to MOR injection (baseline), male rats were more sensitive to the thermal stimulus and were less active than female rats. Daily MOR injections neither affected the baseline TFL nor LOC. Regardless of gender, MOR produced greater analgesia in DZ-dependent and withdrawn rats than in CTR. MOR analgesia was greater in DZ-dependent male than in female rats. Gender differences in MOR analgesia were not of statistical significance in DZ-withdrawn rats. The first dose of MOR produced more depression of LOC in DZ-dependent female than in male rats. Across the time of MOR injections, female DZ-dependent and withdrawn rats were less active than CTR. LOC increased with repeated administration of MOR in all groups of rats. In summary, DZ dependence and withdrawal enhanced MOR analgesia in rats of both sexes. Regardless of chronic treatment, MOR produced more analgesia and less depression of LOC in male than in female rats. It is suggested that a decrease in the function of the GABAergic system plays a role in alteration of MOR analgesia.

Temporal and regional regulation of alpha1, beta2 and beta3, but not alpha2, alpha4, alpha5, alpha6, beta1 or gamma2 GABA(A) receptor subunit messenger RNAs following one-week oral flurazepam administration

The effect of prolonged benzodiazepine administration on GABA(A) receptor subunit (alpha1-6, beta1-3, gamma2) messenger RNAs was investigated in the rat hippocampus and cortex, among other brain areas. Rats were orally administered flurazepam for one week, a protocol which results in benzodiazepine anticonvulsant tolerance in vivo, and in the hippocampus in vitro, in the absence of behavioral signs of withdrawal. Autoradiographs of brain sections, hybridized with [35S]oligoprobes in situ, were examined immediately (day 0) or two days after drug treatment, when rats were tolerant, or seven days after treatment, when tolerance had reversed, and were compared to sections from pair-handled, vehicle-treated controls. Alpha1 subunit messenger RNA level was significantly decreased in CA1 pyramidal cells and dentate granule cells at day 0, an effect which persisted only in CA1 neurons. Decreased "alpha1-specific" silver grain density over a subclass of interneurons at the pyramidal cell border suggested concomitant regulation of interneuron GABA(A) receptors. A reduction in beta3 subunit messenger RNA levels was more widespread among hippocampal cell groups (CA1, CA2, CA3 and dentate gyrus), immediately and two days after treatment, and was also detected in the frontal and parieto-occipital cortices. Changes in beta2 subunit messenger RNA levels in CA1, CA3 and dentate gyrus cells two days after ending flurazepam treatment suggested a concomitant up-regulation of beta2 messenger RNA. There was a trend toward an increased level of alpha5, beta3 and gamma2 subunit messenger RNAs in CA1, CA3 and dentate gyrus cells, which was significant for the beta3 and gamma2 subunit messenger RNAs in the frontal cortex seven days after ending flurazepam treatment. There were no flurazepam treatment-induced changes in any other GABA(A) receptor subunit messenger RNAs. The messenger RNA levels of three (alpha1, beta2 and beta3) of nine GABA(A) receptor subunits were discretely regulated as a function of time after ending one-week flurazepam treatment related to the presence of anticonvulsant tolerance, but not dependence. The findings suggested that a localized switch in the subunit composition of GABA(A) receptor subtypes involving these specific subunits may represent a minimal requirement for the changes in GABA(A) receptor-mediated function recorded previously at hippocampal CA1 GABAergic synapses, associated with benzodiazepine anticonvulsant tolerance.

Does dihydrohonokiol, a potent anxiolytic compound, result in the development of benzodiazepine-like side effects?

The aims of this study were to assess whether dihydrohonokiol, 3'-(2-propenyl)-5-propyl-(1,1'-biphenyl)-2,4'-diol (DHH-B), a potent anxiolytic compound, developed benzodiazepine-like side effects. A 1 mg kg(-1) dose of diazepam, almost equivalent to the minimum dose for the anxiolytic effect, disrupted the traction performance, potentiated hexobarbital-induced sleeping and impaired learning and memory performance. DHH-B, even at a dose of 1 mg kg(-1) (i.e. five times higher than the minimum dose for significant anxiolytic effect) neither developed diazepam-like side effects nor enhanced the side effects of diazepam. Rather, the potentiation by diazepam of hexobarbital-induced sleeping was reduced by 1 mg kg(-1) DHH-B. Furthermore, mice treated with 10 daily administrations of 1 and 5 mg kg(-1) diazepam, but not 0.2-5 mg kg(-1) DHH-B, showed precipitated withdrawal symptoms characterized by hyper-reactivity, tremor and tail-flick reaction when they were challenged with flumazenil (10 mg kg(-1) i.p.). These results suggest that, unlike the benzodiazepine anxiolytic diazepam, DHH-B is less likely to induce motor dysfunction, central depression, amnesia or physical dependence at the effective dose required for the anxiolytic effect.

Induction of partial epileptic seizures by flumazenil

PURPOSE

This study addressed the efficacy of flumazenil (FMZ) to induce or activate interictal or ictal epileptic discharges in patients with medically intractable partial epilepsies.

METHODS

Flumazenil, 1 mg, was injected intravenously in 67 patients undergoing presurgical monitoring for epilepsy surgery, 49 of whom had been treated with benzodiazepines (BZDs) before flumazenil was given. Continuous video electroencephalogram (EEG) monitoring with surface or intracranial electrodes was used to evaluate interictal EEG activity, ictal discharges, and the occurrence and semiology of clinically manifest epileptic seizures.

RESULTS

Interictal epileptiform potentials did not change in frequency or distribution after FMZ. In patients not pretreated with BZDs, epileptic seizures could not be provoked. In eight of the 49 patients pretreated with BZDs, epileptic seizures occurred within 30 min of FMZ application. Seizure semiology and regional EEG onset were identical to seizures recorded without FMZ. Patients operated on according to seizure-onset localization with FMZ had a >75% reduction in seizure frequency or became seizure free.

CONCLUSIONS

Seizure induction by FMZ seems to be a valid method for evaluating seizure semiology and localization of the seizure-onset zone during presurgical monitoring of patients with medically intractable localization-related epilepsies.

Substantia nigra: the involvement of central and peripheral benzodiazepine receptors in physical dependence on diazepam as evidenced by behavioral and EEG effects

Male rats chronically exposed to diazepam (DZ) slowly released from subcutaneously implanted silastic capsules along with empty capsule control rats were focally injected (1 microl) into the substantia nigra (SNR) with the central (CBR) and peripheral (PBR) benzodiazepine receptor antagonists, flumazenil [(FLU) 6.25, 12.5, 25 microg] and PK 11195 [(PK) 3.125, 6.25, 12.5, 25 microg], respectively (weekly intervals; Latin square design). Rats were observed for signs of withdrawal and the EEG was recorded simultaneously from the site of injection (SNR), caudate putamen, thalamus, hippocampus, and frontal cortex. In DZ-dependent rats the Precipitated Abstinence Score (PAS) was significantly related to dose of FLU. The PAS increased with increasing doses of PK (3.125-12.5 microg); however, the highest dose of PK (25 microg) showed less effect. The rapid onset of the PAS was accompanied by a rise in the total power (1-32 Hz) of the EEG (TP(EEG)) in the SNR and other brain areas. The PAS and TP(EEG) had similar time courses. Intranigrally injected FLU and PK did not evoke clonic and tonic-clonic convulsions; however, both antagonists induced dose-related twitches and jerks. Additionally, FLU precipitated a dose-related tachypnea and increases in turning and backing. Chronic DZ treatment altered the spectral content of the EEG, as indicated by a decrease and an increase of the slow and fast frequency bands, respectively. FLU and PK rapidly but transiently reversed the EEG. Data suggest that in the SNR the CBR mediate autonomic and motor signs of DZ withdrawal, while both the CBR and PBR are responsible for twitches and jerks and alteration of the EEG. It is possible that PK also acts on the site linked to a GABA(A)/CBR/ionophore.

Lack of sex differences in anxiety behaviors during precipitated benzodiazepine withdrawal in rats

Nonprecipitated benzodiazepine (BZ) withdrawal has been reported to increase anxiety levels in rats. The present experiment determined if gender or hormonal status would modulate putative changes in anxiety-related behaviors during precipitated BZ withdrawal in rats. Intact and gonadectomized male and female rats were treated for 4 weeks with empty or diazepam (DZ)-filled silastic capsules. Animals were injected with the BZ antagonist flumazenil (RO15-1788; 5 mg/kg, i.p.) or vehicle, and immediately placed on the elevated plus-maze. Following the 10-min behavioral test, rats were decapitated and trunk blood was collected to measure corticosterone and gonadal hormone levels. During precipitated BZ withdrawal rats showed significantly decreased percent open-arm time; however, this finding was confounded by a significant decrease in activity levels (e.g., closed-arm entries and total-arm entries). Precipitated BZ withdrawal did not significantly attenuate percent open-arm entries, which factors out drug-induced changes in activity levels, compared to vehicle control animals. Overall, the results of this experiment suggest that precipitated BZ withdrawal does not significantly increase anxiety levels when compared to control animals.

Diazepam-treated female rats: flumazenil- and PK 11195-induced withdrawal in the hippocampus CA1

Six female rats had a loading dose of 180 mg of diazepam (DZ) contained in two Silastic capsules implanted in their backs. Thereafter, a single 90-mg capsule was implanted weekly for 4 weeks prior to weekly microinjections of 1 microl of flumazenil (6.25, 12.5, or 25 microg) and PK 11195 (3.125, 6.25, or 12.5 microg) or vehicle into the CA1. Three control rats had empty capsules implanted but received only the high dose of flumazenil after 5 weeks. The time of DZ exposure spanned 8 weeks. Mean steady-state plasma levels of DZ were 1.06 +/- 0.11, and the mean total (DZ + metabolites) was 2.46 microg/ml +/- 0.37. Flumazenil elicited a dose-related precipitated withdrawal score (PAS) in DZ-treated rats (but not in controls) characterized by dose-related increases in convulsive (twitches and jerks), motor and autonomic signs, dose-related increases in the percent of total power in the low frequency (1-4 Hz), and decreases in the high-frequency (18-26 Hz) bands of the EEG recorded from the dentate and the amygdala. PK 11195 produced a dose-related increase in the 4-12 Hz band of the EEG recorded from the CA1, whereas the PAS was mild and not dose-related. However, the 6.25 and 12.5-microg doses elicited a significant PAS that tended to increase with dose. These data indicate that chronic DZ produces dependence, and that in the CA1 it involves the participation of central and possibly peripheral benzodiazepine (BZ) receptors located within this structure.

Dorsal raphe and substantia nigra response to flumazenil in diazepam-dependent rats

Flumazenil (FLU; 25 micrograms) and DMSO-vehicle were focally injected (1 microliter) into the substantia nigra (SN) and the dorsal raphe nucleus (DR) in rats chronically implanted with silastic capsules containing diazepam (DZ; 540 mg/week). FLU precipitated an abstinence syndrome in the SN as indicated by a significant abstinence score, several abstinence signs and reduced total power of the fast frequency bands of the electroencephalogram (EEG) in the injections sites frontal cortex, (FC) and hippocampus (H). In contrast, FLU did not produce an abstinence syndrome in the DR, and its effect on the power of the EEG in DR, FC and H was not significantly different from that of the DMSO-vehicle. The data show regional heterogeneity in the response of the SN and the DR to chronic DZ treatment in terms of a focally precipitated abstinence syndrome.

Electrophysiological evidence for agonist properties of flumazenil, a benzodiazepine receptor antagonist, in rat hippocampus slices

The purpose of this study was to determine the ability of the putative benzodiazepine antagonist flumazenil to modulate the excitatory synaptic responses recorded from rat hippocampus slices. The benzodiazepine agonist clonazepam was demonstrated to depress the CA1 population spike. This effect was attributed to an enhancement of GABA efficacy after its electrically-elicited release from local inhibitory circuitry. As an unexpected effect, flumazenil failed to antagonize this depressing effect. Moreover, flumazemil was observed to significantly depress, on its own, the magnitude of the evoked response to the activation of the excitatory afferents. This intrinsic depressant activity of flumazenil suggests that flumazenil acts 'in vitro' as an agonist at the benzodiazepine receptors, and is consistent with some previously reported atypical effects of flumazenil 'in vivo'.

Intrathecally administered flumazenil and PK 11195 precipitate abstinence syndrome in freely moving diazepam dependent rats

The central and peripheral benzodiazepine (BZ) receptor antagonists, flumazenil (FLU) and PK 11195 (PK), administered intrathecally (IT) to diazepam (DZ)-dependent rats produced a precipitated abstinence syndrome. The scores for abstinence increased with increasing dose of FLU but not with increasing dose of PK. Twitches and jerks increased with increased doses of both. Head and body tremors were produced by FLU, but not by PK. Neither FLU nor PK precipitated abstinence in controls. In DZ-dependent rats IT administered FLU and PK did not significantly change the spectral content and the total power of the EEG. The data indicate that an abstinence syndrome is precipitated at the spinal level in DZ-dependent rats and that both central and peripheral BZ receptors are involved.

Flunitrazepam and nordiazepam slowly released from silastic capsules induce physical dependence in rat

The rates of in vitro release of flunitrazepam (FN), nordiazepam (ND) and diazepam (DZ) from silastic capsules were compared and found to be in the following order: DZ > FN > ND. Rats that were implanted subcutaneously with capsules filled with FN or ND for 5 to 7 weeks before administering flumazenil (FLU) (40 mg/kg, i.v.) showed precipitated abstinence as measured by the Precipitated Abstinence Score (PAS) which included a rapid onset of clonic and tonic-clonic convulsions. Rats implanted with DZ also demonstrated significant PAS and seizures. Implantation of similar doses of DZ, FN and ND resulted in different plasma levels of parent benzodiazepines and their metabolites that corresponded with their in vitro release: DZ > FN > ND. These data indicate that, as for DZ, the capsule implantation is an effective method of producing physical dependence on FN and ND in the rat.

Differential expression of benzodiazepine anticonvulsant cross-tolerance according to time following flurazepam or diazepam treatment

In previous studies in which the anti-pentylenetetrazol (PTZ) effect of benzodiazepines was used to measure tolerance, the results depended on the benzodiazepine used for chronic treatment as well as the benzodiazepine given acutely to test for tolerance. In this study, the time course of tolerance reversal was studied in rats given two treatments known to cause anticonvulsant tolerance, 1-week flurazepam (FZP), and 3-week diazepam (DZP). Neither treatment altered convulsive threshold for IV PTZ, but both treatments decreased the convulsive threshold for bicuculline. Withdrawing DZP, but not FZP, treatment resulted in a loss of body weight. Twelve hours after 1-week FZP treatment, all benzodiazepines were significantly less effective, showing tolerance. Forty-eight hours after the 1-week FZP treatment, tolerance was still observed with DZP, FZP, and zolpidem, but was no longer present with clonazepam or bretazenil. After the 3-week DZP treatment, rats were tolerant to all benzodiazepines tested at 12 h of withdrawal, but had lost tolerance to all the drugs except bretazenil by 48 h. The results suggest differences in the way these benzodiazepines interact with their receptors, allowing differential expression of tolerance, and that chronic DZP and FZP treatments affected interactions of the benzodiazepines with their receptors, but not in the same fashion.

Gastrointestinal effects of diazepam-withdrawal are linked to activation of central cholecystokinin-ergic pathways in rats

The influence of flumazenil-precipitated diazepam withdrawal on intestinal myoelectric activity and colonic transit was evaluated, in diazepam-dependent rats. Administered intraperitoneally, flumazenil (15 mg kg-1) induced a strong stimulation of the duodenal spiking activity lasting 197 +/- 20 min, and accelerated colonic transit corresponding to a significantly (P < 0.05) increased value of the geometric centre (3.52 +/- 0.23 vs 2.44 +/- 0.1 for the control). Both devazepide and L365260 administered intracerebroventricularly at a dose of 10 micrograms kg-1 abolished the flumazenil-induced withdrawal effect on the duodenum, whereas at a lower dose (1 microgram kg-1) only L365260 was able to antagonize this effect. In the same way, devazepide, loxiglumide and L365260 suppressed the effect of precipitated withdrawal on colonic transit when administered intracerebroventricularly at a dose of 10 micrograms kg-1, whereas similar blockade was obtained at a dose of 5 micrograms kg-1 with L365260, and 10 ng kg-1 with PD135-158. It is concluded that in rats precipitated diazepam-withdrawal altered intestinal motility and colonic transit and that these effects are mediated by central release of cholecystokinin (CCK) or activation of CCK-ergic neurons.

Different location of benzodiazepine sites involved in gut and behavioral effects of benzodiazepine withdrawal in rats

This work was performed to determine if the alterations in gastric emptying induced by precipitated withdrawal are linked to peripherally or centrally located benzodiazepine sites, in rats treated chronically with diazepam (15 mg/kg/day IP) for 7 days. In sham-capsaicin-treated rats, precipitated withdrawal by flumazenil (15 mg/kg IP) induced an increase of gastric emptying, whereas it had no effect in systemic capsaicin-treated rats. Both groups of animals developed withdrawal syndrome expressed as motor, autonomic, and behavioral signs. On diazepam-dependent rats, central administration of flumazenil (0.15 mg/kg ICV) induced withdrawal syndrome but had no effect on gastric emptying. These preliminary results suggest that benzodiazepine receptors located in the central nervous system are involved in behavioral withdrawal syndrome, whereas benzodiazepine receptors located at the peripheral level are responsible for digestive withdrawal syndrome involving capsaicin-sensitive neurons.

Flumazenil induces seizures and death in mixed cocaine-diazepam intoxications

STUDY HYPOTHESIS

Administration of the benzodiazepine antagonist flumazenil may unmask seizures in mixed cocaine-benzodiazepine intoxication.

DESIGN

Male Sprague-Dawley rats received 100 mg/kg cocaine IP alone, 5 mg/kg diazepam alone, or a combination of diazepam and cocaine. Three minutes later, groups were challenged with vehicle or flumazenil 5 or 10 mg/kg IP. Animal behavior, seizures (time to and incidence), death (time to and incidence), and cortical EEG tracings were recorded.

INTERVENTIONS

Administration of flumazenil to animals after they had received a combination dose of cocaine and diazepam.

RESULTS

In group 1, animals received cocaine followed by vehicle. This resulted in 100% developing seizures and death. Group 2 received diazepam alone followed by vehicle. Animals became somnolent and none died. Group 3 received diazepam followed by 5 mg/kg flumazenil. Animals became somnolent after diazepam and then active after flumazenil administration. In group 4, a combination of cocaine and diazepam was administered simultaneously. This resulted in no overt or EEG-detectable seizures and a 50% incidence of death. Group 5 received a similar combination of cocaine and diazepam, followed later by 5 mg/kg flumazenil. This resulted in an increased incidence of seizures, 90% (P < .01), and death, 100% (P < or = .01), compared with group 4. Group 6 received cocaine and diazepam followed by 10 mg/kg flumazenil. This also resulted in an increased incidence of seizures, 90% (P < or = .01), and death, 90% (P < or = .05), compared with group 4.

CONCLUSION

Flumazenil can unmask seizures and increase the incidence of death in a model of combined cocaine-diazepam intoxications.

Flumazenil induces localised increases in glucose utilization during diazepam withdrawal in rats

The quantitative [14C]2-deoxyglucose autoradiographic technique has been employed to identify the neural circuits involved in diazepam withdrawal. Local cerebral glucose utilization (LCGU) was assessed in parallel groups of rats chronically treated with diazepam (5 mg/kg i.p., daily for 28 days), in rats that were withdrawn from chronic diazepam 24 h previously and in those that received flumazenil (5 mg/kg i.v.) immediately or 24 h after the last dose of diazepam. Two further groups received chronic vehicle or acute flumazenil (5 mg/kg i.v.). Rats withdrawn from diazepam 24 h previously did not produce changes in LCGU in the 51 structures examined compared with both control and chronic diazepam treated groups, suggesting that spontaneous withdrawal from small doses of diazepam does not evoke marked alterations in functional activity. In contrast, flumazenil-precipitated diazepam withdrawal produced a marked increase in glucose use in structures of the Papez circuit of emotion (mammillary body, anterior thalamus, cingulate cortex), together with increases in the septal nucleus, basolateral amygdala and nucleus accumbens. Less widespread increases in glucose use occurred in primary auditory and visual areas and in extrapyramidal areas. This pattern resembles that produced after acute FG-7142 administration (Brain Res., 475 (1988) 218-231). In rats receiving flumazenil 24 h after the last dose of diazepam there was a similar, but more restricted, pattern of change in LCGU. Flumazenil had no effect on LCGU in drug naive rats. Thus, flumazenil could only exert an effect upon LCGU in rats chronically treated with diazepam. These data provide functional neuroanatomical evidence for a withdrawal shift in the inverse agonist direction after chronic diazepam and suggest that flumazenil-precipitated withdrawal changes may merely be a reflection of this phenomenon.

Precipitated abstinence in the diazepam-dependent rat

Physical dependence was produced in the rat by exposure to continuous release of diazepam from silastic capsule implants (recrystallized diazepam) or by dosing through a gastric fistula. The precipitated abstinence syndrome induced by the IV infusion of flumazenil was characterized by clonic and tonic-clonic seizures, retropulsion, digging, rearing, head, limb and body tremors, twitches and jerks of the body, and ear twitches. This abstinence syndrome differed both qualitatively and quantitatively from the milder syndrome induced in previous experiments by the intragastric administration of flumazenil in the diazepam-dependent gastric fistula rat. Capsule-implanted rats had free plasma and extraneuronal brain levels of diazepam, oxazepam, and nordiazepam in the 10(-3) and 10(-4) mg/ml range, and their brain: plasma ratios were not significantly different from 1. The diazepam capsules had a sustained release of over 28 days. These studies show that the capsule implantation technique is an efficacious way of maintaining plasma levels of diazepam and its metabolites, and producing a high level of physical dependence in the rat.

Repeated treatment with alpidem, a new anxiolytic, does not induce tolerance or physical dependence

Alpidem is a new anxiolytic of imidazopyridine structure which has a high affinity for the omega 1 (BZ1) modulatory site of the GABAA receptor. The present study investigated whether tolerance and physical dependence develop after repeated treatment with alpidem, as is observed with benzodiazepines. Mice were given alpidem (100 mg/kg, p.o.) or diazepam (5 mg/kg, p.o.) twice daily for 10 consecutive days. Tolerance was assessed by measuring antagonism of pentylenetetrazole- and isoniazid-induced convulsions and bicuculline-provoked mortality, following repeated drug treatment. Decreases in the latency to isoniazid-induced convulsions and in the minimal convulsant dose of pentylenetetrazole were taken as an index of physical dependence and were evaluated at different times (3, 6, 14, 42, 67, 96 hr) after drug withdrawal or after flumazenil administration. In addition, changes in sensitivity to the convulsant effect of a beta-carboline (beta-CCM) were measured. Repeated treatment with diazepam produced tolerance to its anticonvulsant activities as indicated by shifts of the dose-response curves by a factor of 3-5. After discontinuation of diazepam treatment, spontaneous withdrawal occurred within 24 hr and lasted 67 hr as indicated by decreases in the threshold for convulsions induced by isoniazid and pentylenetetrazole. Flumazenil-induced withdrawal was observed in both isoniazid and pentylenetetrazole-induced convulsion models. Hypersensitivity of mice to the convulsant effect of beta-CCM also occurred. In contrast, repeated treatment with alpidem did not produce tolerance to its anticonvulsant effects and neither spontaneous nor flumazenil-induced withdrawal was observed in the pentylenetetrazole and isoniazid models. Moreover, withdrawal of alpidem did not induce any change in the convulsant activity of beta-CCM. These differences between alpidem and diazepam may be related to the low level of receptor occupancy during repeated treatment with alpidem because of its selectivity for omega 1 (BZ1) sites and to its moderate intrinsic activity.

De novo absence status epilepticus as a benzodiazepine withdrawal syndrome

A 67-year-old woman with a history of psychotropic drug abuse developed confusion. EEG was consistent with absence status epilepticus (AS). Intravenous (i.v.) flumazenil 1 mg, a benzodiazepine antagonist with anticonvulsant properties, increased both confusion and paroxysmal activity. Complete resolution was obtained after diazepam was administered i.v., and the patient then admitted that she had abruptly discontinued long-standing treatment with carpipramine, amitriptyline, bromazepam, and flunitrazepam. The aggravating effect of flumazenil indicates that benzodiazepine withdrawal was probably the elective triggering factor of this de novo absence status epilepticus.

Anticonvulsant activity of flumazenil in rats during ontogenetic development

The influence of flumazenil on seizures induced by pentylenetetrazol (PTZ) was studied in rats aged 7, 12, 18, 25, and 90 days. Flumazenil in doses of 25, 37.5, and 50 mg/kg IP injected 10 min before PTZ exhibited a dose-dependent anticonvulsant action in all age groups studied. It was more effective against generalized tonic-clonic than against minimal clonic seizures at all developmental stages studied. In the two youngest groups, minimal seizures were elicited only rarely under control conditions. Pretreatment with the two lower doses of flumazenil resulted in an increased incidence of this type of seizure for these two groups. The anticonvulsant activity found in all age groups is in agreement with data from other benzodiazepines and speaks against a pure benzodiazepine-antagonistic action of flumazenil.

Behavioral effects of benzodiazepine ligands in non-dependent, diazepam-dependent and diazepam-withdrawn baboons

Acute i.m. injections of benzodiazepine receptor ligands were administered to baboons before 1-h observational sessions. The agonist midazolam produced sedative effects, the antagonist flumazenil produced no behavioral effects, the inverse agonist FG7142 produced tremor and the inverse agonist 3-carboethoxy-beta-carboline hydrochloride (beta CCE) produced tremor, vomiting, jerks and seizures. Co-administration of these drugs (midazolam + beta CCE, midazolam + flumazenil or flumazenil + beta CCE) produced a mutual antagonism of these effects. Compared to the non-dependent condition, in the diazepam-dependent condition (baboons maintained on 20 mg/kg per day diazepam) and withdrawn condition (dependent baboons tested during withdrawal), midazolam produced decreased sedative effects, flumazenil produced increased effects (i.e., tremor, vomiting and jerks), and beta CCE produced increased frequency of seizures. Taken together, these data suggest that (1) benzodiazepine receptor ligands lie on a continuum of behavioral activity, and (2) chronic diazepam administration alters the behavioral effects of these benzodiazepine ligands, producing a shift in the direction of the inverse agonist.

A comparison of the physical dependence inducing properties of flunitrazepam and diazepam

Dogs dosed chronically (4-7 weeks) with oral flunitrazepam (7.6 mg/kg/day) or diazepam (24-36 mg/kg/day) administered in 4 equally divided doses had dose-related flumazenil precipitated benzodiazepine abstinence scale scores (BPAS) of comparable intensities despite the fact that plasma levels of flunitrazepam and its metabolites were much lower than nordiazepam levels in the diazepam-dependent dog. Both groups of dependent dogs had clonic and tonic-clonic seizures after oral and IV flumazenil. Precipitated abstinence signs persisted longer in the diazepam than in the flunitrazepam-dependent dogs. Differences in the pharmacokinetics of the drugs of dependence, their metabolites, and their interactions at receptor sites offer a partial explanation for the high level of dependence seen in the flunitrazepam dog. The finding that the estimated plasma free concentration of flunitrazepam and its metabolites is equal to or greater than that of diazepam and its metabolites together with the fact that flunitrazepam has a higher affinity for the benzodiazepine receptor than either diazepam, nordiazepam or oxazepam can explain why the intensity of the precipitated abstinence syndrome is comparable in flunitrazepam- and diazepam-dependent dogs. Although the flumazenil-induced precipitated abstinence syndromes observed in flunitrazepam- and diazepam-dependent dogs differed qualitatively they did not differ quantitatively. It is therefore concluded from these data that the doses of flunitrazepam and diazepam, chosen for producing comparable degrees of weight loss during dose escalation, did not differ in the degree of physical dependence that they produced in the dog.

Flumazenil: a new benzodiazepine antagonist

Flumazenil is a recently discovered pharmacologic antagonist of the CNS effects of benzodiazepines. It acts by binding CNS benzodiazepine receptors and competitively blocking benzodiazepine activation of inhibitory GABAergic synapses. Animal studies and some human studies appear to demonstrate that flumazenil has weak intrinsic agonist activity; on the other hand, studies are inconclusive in demonstrating any inverse agonist effects of this agent. Evidence available suggests that flumazenil is well tolerated in human beings over a broad range of doses when given either orally or parenterally and does not produce serious adverse effects. In the setting of isolated benzodiazepine overdose, flumazenil is capable of completely reversing coma within one to two minutes, with this effect lasting between one and five hours. Repeat doses can be given safely to reverse recurrent effects of longer-acting benzodiazepines. Flumazenil is undergoing further evaluation by the Food and Drug Administration; should this drug receive approval, it is likely to be used in emergency departments as well as in a variety of other clinical settings. First, it could be used to effect rapid reversal of benzodiazepine-induced sedation that has been administered to facilitate medical, orthopedic, and surgical procedures, particularly in the event of inadvertent respiratory depression. Second, flumazenil might have a therapeutic role in the management of patients who have taken benzodiazepine overdoses. Although most of these patients can be managed successfully with supportive therapy alone, it is possible that the use of flumazenil may obviate the need for intubation and respiratory support in such patients and eliminate the possible adverse effects of even short-term endotracheal intubation. Finally, flumazenil could have both diagnostic and therapeutic value in patients with acute alterations of mental status of unknown etiology, particularly when possible drug overdose is a consideration. Because flumazenil appears to be specific in its antagonism of benzodiazepine-induced respiratory and CNS depression, it could be used empirically to confirm or exclude a role of benzodiazepines in the generation of mental status changes in the setting of overdose or coma of unknown origin. This in turn might obviate the need for further expensive (eg, computed tomography) and sometimes invasive (eg, lumbar puncture) diagnostic modalities. This might be particularly useful because there is nothing about benzodiazepine-induced coma that clearly distinguishes it from other causes of coma; thus, there are no signs or symptoms that may reasonably allow benzodiazepine overdose to be confirmed or eliminated on clinical grounds. Further studies will continue to define the ultimate use of this new agent.

Physical dependence induced in DBA/2J mice by benzodiazepine receptor full agonists, but not by the partial agonist Ro 16-6028

Continuous administration of triazolam, alprazolam or diazepam for a 7-day period by means of minipumps or chronic (17 days) p.o. treatment with alprazolam induced clear physical dependence in DBA/2J mice as assessed by precipitation of a withdrawal syndrome with an i.v. injection of the benzodiazepine receptor partial inverse agonist Ro 15-3505. In contrast, no precipitated withdrawal signs were observed following chronic exposure to high doses of the benzodiazepine receptor partial agonist Ro 16-6028. The use of minipumps and precipitation with a benzodiazepine receptor antagonist permits a simple and rapid evaluation of the physical dependence liability of potent compounds acting at the benzodiazepine receptor. Furthermore, these results support the hypothesis that benzodiazepine receptor partial agonists are less likely to induce physical dependence than full agonists.

Anticonvulsive properties of F1933 (dulozafone) on kindled seizures in the rat

The anticonvulsive properties of a new compound: F1933 (Dulozafone) were investigated in the amygdala kindling model and compared with those of diazepam. Both drugs protected fully kindled rats against generalized seizures but failed to suppress partial ictal events (amygdala afterdischarges and limbic seizures). The anticonvulsive action of F1933, administered at the ED100, was nearly reversed by the specific antagonist of benzodiazepines receptors; R015-1788 (Flumazenil), suggesting that the effect of F1933 is mediated by this receptor. These results also emphasize the usefulness of kindling to test antiepileptic drugs and to confirm their supposed profile of action.

Development of tolerance to clobazam in fully kindled rats: effects of intermittent flumazenil administration

The effects of acute and chronic treatment with the 1,5-benzodiazepine, clobazam, were studied on fully kindled amygdaloid seizures in rats. After acute dosing, clobazam significantly reduced all parameters of kindled seizures (seizure severity, seizure duration, duration of amygdalar afterdischarges) at doses of 7.5 or 10 mg/kg i.p. 'Active' plasma concentrations of clobazam ranged between 300-800 ng/ml. The elimination half-life of clobazam in plasma was about 1 h. Only very low (10-75 ng/ml) levels of the major metabolite, N-desmethylclobazam, were detected in rats. Administration of N-desmethylclobazam indicated that plasma concentrations of at least 300 ng/ml were necessary for anticonvulsant effects. During chronic administration of clobazam, 10 mg/kg 3 times daily, marked tolerance developed to the anticonvulsant and adverse (ataxiogenic and sedative) effects of the benzodiazepine. The experiment was repeated using a different protocol with minimized environmental stimuli and no amygdala stimulation during chronic clobazam administration. The loss of effects on seizure severity and motor function was similar to the first chronic experiment, whereas the loss of effects on seizure and afterdischarge duration was less marked. This indicates that conditioning of 'learned tolerance' is partly involved in clobazam tolerance in kindled rats. Intermittent injection of the benzodiazepine receptor antagonist, flumazenil, 5 mg/kg i.p. every third day, did not alter the loss of pharmacodynamic effects during chronic treatment with clobazam, but seemed to prevent hyperexcitation and other abstinence symptoms in the withdrawal period. The data indicate that periodic injection of a benzodiazepine receptor antagonist does not represent a possible therapeutic approach for preventing the development of tolerance during long-term benzodiazepine exposure.

Physical dependence on diazepam in the dog: precipitation of different abstinence syndromes by the benzodiazepine receptor antagonists Ro 15-1788 and ZK 93426

1. The effects of the benzodiazepine receptor antagonists Ro 15-1788 (flumazenil) and the beta-carboline ZK 93426 were compared in dogs before and after chronic treatment with diazepam. 2. In diazepam-naive dogs, the most prominent behavioural alterations occurring during or after i.v. infusion of Ro 15-1788 up to a dose of 20 mg kg-1 were transient sedation, ataxia, and 'hot foot' behaviour, whereas behavioural alterations observed after ZK 93426 were not different from those observed after i.v. infusion of vehicle alone. This indicates that, in contrast to Ro 15-1788, ZK 93426 did not exert partial agonistic activity at benzodiazepine receptors. 3. In dogs treated 3 times daily with diazepam, 1 mg kg -1 orally, for 1 week, both benzodiazepine antagonists precipitated abstinence symptoms but the number and severity of withdrawal signs induced by Ro 15-1788 were greater than with ZK 93426. 4. In dogs treated 3 times daily with diazepam, 2 mg kg-1 orally, for 2 weeks, severe abstinence symptoms were precipitated in all animals by infusion of either antagonist but differences were found in the type of the symptoms: Ro 15-1788 induced rigid postures or rigid walking with increased muscle tone, tremor, twitches and jerks, whereas ZK 93426 did not alter motility but induced generalized myoclonic jerks and tonic-clonic seizures. A generalized tonic-clonic seizure was also observed in one dog of the trial with infusion of Ro 15-1788. 5. Plasma level determinations during chronic treatment diazepam showed marked accumulation of the major active metabolite desmethyldiazepam, whereas diazepam levels were at least 15 times lower, which might suggest that desmethyldiazepam was responsible for the development of physical dependence on diazepam.