Effects of Ro 15-1788 and CGS 8216 in diazepam-dependent baboons

Comparison of the behavioral effects of bretazenil and flumazenil in triazolam-dependent and non-dependent baboons

Behavioral effects of the benzodiazepine receptor partial agonist bretazenil were compared with those of the benzodiazepine receptor antagonist flumazenil under conditions in which three baboons received continuous intragastric (i.g.) infusion of vehicle and then continuous i.g. infusion of triazolam (1.0 mg/kg/day). In each condition, acute doses of flumazenil (0.01-3.2 mg/kg) and bretazenil (0.01-10.0 mg/kg) were administered every 2 weeks (beginning after 30 days of treatment in the triazolam-dependent condition). Food pellets were available during daily 20-h sessions. Following test injections, 60-min behavioral observations were conducted followed by a fine motor assessment. During chronic vehicle administration, neither drug produced changes in observed behaviors. Bretazenil increased pellets earned and time to complete the fine-motor task (10.0 mg/kg dose). During chronic triazolam dosing, both bretazenil and flumazenil precipitated benzodiazepine withdrawal syndromes, characterized by vomiting, tremors/jerks, and a decrease in pellets earned. Thus, bretazenil can function as an antagonist under conditions of benzodiazepine physical dependence.

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.

Contributions of GABAA receptor subtype selectivity to abuse liability and dependence potential of pharmacological treatments for anxiety and sleep disorders

When benzodiazepines (BZs) supplanted barbiturates as a favored, safer treatment for anxiety and sleep disorders in the 1960s, the abuse liability and dependence potential of these drugs were little understood. Widespread recognition of the difficulty of stopping use of chronically taken BZs emerged through the popular press in the late 1970s, which resulted in reluctance to prescribe these otherwise clinically useful compounds. Evolution of the understanding of the biochemical basis for BZ effects in the 1980s and 1990s, coupled with regulatory emphasis on collection of data used in legal scheduling decisions, made possible a targeted search for drugs that would provide effective treatment for anxiety disorders in the absence of abuse liability or dependence potential. Compounds that have selective efficacy at subtypes of the gamma-aminobutyric acid type A receptor, are active in preclinical anxiolytic screens, but negative in preclinical studies of behavior relevant to evaluation of abuse liability appear to be one promising means for achieving this end.

The influence of midazolam on active avoidance retrieval and acquisition rate in rats

The purpose of the present study was to examine the influence of midazolam on the retrieval and acquisition rate of two-way active avoidance in rats. In the schedule 2 x 100 trials, the effects of midazolam (0.5-5.0 mg/kg), benzodiazepine binding site antagonist flumazenil (2.5-10.0 mg/kg), specific antagonist of GABA(A) receptor, bicuculline (0.5-4.0 mg/kg), and the blocker of GABA(A) receptor containing Cl(-) channels, picrotoxin (1.0-5.0 mg/kg), on the second day retrieval of avoidance performance were investigated, as well as the influence of the used blockers of GABA(A) receptor function on midazolam effects. Furthermore, the effect of midazolam (1.0 mg/kg) on acquisition rate in the 5 x 50 schedule, as well as the effects of third day treatment changing in that paradigm, was examined. Throughout the study, drugs were given intraperitoneally, 30 min before testing. Midazolam at the dose of 1.0 mg/kg facilitated avoidance retrieval, whereas flumazenil and bicuculline did not significantly change behavior. Picrotoxin (5.0 mg/kg) diminished performance. All three kinds of blockers used abolished facilitatory action of midazolam, confirming GABAergic mediation of the effect of benzodiazepine. Midazolam (1.0 mg/kg) increased acquisition rate during five consecutive days relative to saline, but without significant effect on the first day acquisition. In the case of third day changing of treatments, the intersection of regression rate lines was detected. Results from active avoidance paradigm experimentally support the findings from human studies that in certain circumstances, benzodiazepines, potentiating GABAergic neurotransmission, could produce retrieval-enhancing effects in memory tasks.

Principles of drug abuse liability assessment in laboratory animals

This paper describes the rationale for use of preclinical assessments of abuse liability in laboratory animals, and then discusses "cross-cutting" methodological issues that apply to behavioral evaluations intended to contribute to an abuse liability evaluation package. Issues include use of: (1) positive and negative control conditions; (2) full dose-effect evaluations, (3) multiple dependent measures, (4) pharmacokinetic evaluations to guide choice of dose ranges, (5) a species for which good methodological and comparative data are available to aid interpretation of results, and (6) appropriate methods for the group or single-subject experimental design selected. The remainder of the paper describes basic methodology by which three core pieces of behavioral data required by the Food and Drug Administration for its use in the overall abuse liability analysis can be obtained preclinically. Reinforcing effects are assessed in study of drug self-administration; drug discrimination assesses degree of overlap of interoceptive stimulus effects with relevant comparison drugs; physical dependence potential is determined by assessing whether a withdrawal syndrome occurs after chronic drug administration. Background and methodological issues specific to each procedure are discussed. A key consideration for cross-cutting and specific methodological issues is that choices made enable confident interpretation of both positive and negative results.

Zaleplon and triazolam physical dependence assessed across increasing doses under a once-daily dosing regimen in baboons

The ability of the GABA(A)-receptor-subtype-selective hypnotic zaleplon to produce physical dependence was compared to the nonselective benzodiazepine triazolam. Progressively increasing doses of zaleplon and triazolam were given to baboons by intragastric infusion once each day, with doses increasing every 17 days. Next, the highest dose was given for 10-34 additional days by continuous infusion. Both drugs produced increases in food-maintained lever pressing, ataxia, and time to complete a fine motor task. Plasma levels increased dose-dependently; drug was detectable 24 h after higher doses. Flumazenil produced a mild or intermediate precipitated-withdrawal syndrome on day 14 of all dosing conditions. When drug delivery ended after 85-100 days, a benzodiazepine-type withdrawal syndrome occurred. Physical dependence potential of zaleplon and triazolam appear similar.

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.

Tolerance, cross-tolerance and dependence measured by operant responding in rats treated with triazolam via osmotic pumps

Previous research has found that drugs with affinity for omega (benzodiazepine) sites differ in their abilities to produce tolerance and dependence. The present study therefore investigated the effects of ligands of omega (BZ) sites in rats that had been rendered tolerant to a benzodiazepine. Two experiments were carried out in separate groups of rats. Behavioral changes induced by chronic infusion of triazolam (3 mg/kg/day, SC, for 14 days) via osmotic pumps were studied in animals trained on a fixed ratio 10 schedule of food presentation. Control animals were implanted with pumps containing the vehicle. Test drugs were administered IP using cumulative dosing. In one experiment triazolam decreased response rates on days 1, 2 and 3 after implantation of the pumps and tolerance developed to this depressant effect. In the other experiment, vehicle and triazolam treated rats differed in their responding during chronic infusion but differences were not statistically significant on any particular day. Flumazenil (3.0-30 mg/kg) greatly decreased rates of responding on day 11 in triazolam treated rats. This effect may represent a precipitated withdrawal syndrome. However, no withdrawal effects on operant performance were observed upon pump removal. Chronic infusion of triazolam did not affect the sensitivity of rats to alpidem on day 11 (10-100 mg/kg) whereas it abolished the stimulant effect of bretazenil (0.1-1.0 mg/kg). Chronic triazolam treatment produced tolerance to the depressant effects of triazolam (1.0-3.0 mg/kg), lorazepam (0.3-3.0 mg/kg) and zopiclone (10 mg/kg) but no tolerance to those of CL 218,872 (3.0-30 mg/kg) and zolpidem (0.3-3.0 mg/kg) when tested 3-14 days after pump removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Sound vibration, a non-invasive stress: antagonism by diazepam

Rats, subjected to sound-vibration stress, showed an abrupt increase in plasma corticosterone (CS). This stimulation was reliably produced using a Burgess brand "vibro-graver," a standard tool used for engraving. With the tool set at "8" or coarse, the barrel of the tool was placed on the animal's flank and the point held against the side of the metal cage for 15 s. Plasma CS increased to 29.3 +/- 4.7 micrograms/dl at 15 min and 15.7 +/- 1.8 micrograms/dl at 30 min. These levels were significantly higher than animals pretreated with diazepam, 5 mg/kg i.v., 2 h prior to stimulation (9.2 +/- 2.0 and 7.4 +/- 1.5 micrograms/dl, respectively). Animals which were pretreated with CGS-8216 (a mixed agonist/antagonist at the benzodiazepine receptor), 2 mg/kg i.v., 30 min prior to diazepam had the protective effects of diazepam abolished. Sound/vibration produced a significant elevation in plasma CS in animals given CGS-8216 alone; but, this elevation was significantly lower than in vehicle-treated controls. This comparatively lower plasma CS level suggests a partial-agonist, diazepam-like effect by CGS-8216. Experiments were done in conscious unrestrained male Sprague-Dawley rats with chronic i.v. catheters. Except for 15 s stimulation exposure, all animals remained isolated in sound-attenuated one-way vision boxes for the duration of the serial blood sampling. Control stimulation exposure involved similar handling without turning on the engraving tool. These results demonstrate: 1) the usefulness of this tool to provide a repeatable stress stimulus; 2) the ability of diazepam to abolish the stress response; 3) that CGS-8216 can antagonize the action of diazepam; and 4) a demonstration of the partial agonist effects of CGS-8216.

The pharmacology of human anxiety

The human pharmacology of anxiety disorders, including panic disorder, is detailed. The major theories center around the role of benzodiazepine receptor, noradrenergic and serotonergic dysfunction. The contribution that challenge tests with lactate, hyper- and hypocapnia, beta- and alpha-2-adrenoceptor agonists, peptides, pentylenetetrazol, and caffeine make to our understanding of the biological basis of anxiety and these major theories are described and discussed.

The beta-carboline derivatives ZK 93426 and FG 7142 fail to precipitate abstinence signs in diazepam-dependent cats

The aim of the present study was to investigate the ability of different benzodiazepine recognition site antagonists (Ro 15-1788 and ZK 93426) and inverse agonists (Ro 15-4513, FG 7142 and CGS 8216) to induce abstinence signs in diazepam-dependent cats. Different groups of cats were challenged with each of the benzodiazepine recognition site ligands under investigation 24 hours after the last dose of chronic treatment with diazepam (7 mg/kg, IP at 8.00 a.m. and 8.00 p.m. for 21 consecutive days). The benzodiazepine derivatives Ro 15-4513 and Ro 15-1788 precipitated an abstinence syndrome within minutes after IP administration. The pyrazoloquinoline derivative CGS 8216 also induced withdrawal signs that were less severe and had a longer latency than those elicited by Ro 15-4513 and Ro 15-1788. Abstinence signs included tremors, increased muscle tone, irritability, fear, arched-back posture, pupillary dilation and vocalizations. On the other hand, the beta-carboline derivatives ZK 93426 and FG 7142 failed to precipitate abstinence signs in diazepam-dependent cats when given at doses that prevented the acute effects of diazepam. Our results demonstrate that the ability to induce withdrawal signs in diazepam-dependent cats depends on the chemical structure of the challenge drug (i.e., benzodiazepine or pyrazoloquinoline), since beta-carboline antagonists like ZK 93426 and partial inverse agonists like FG 7142 lack this property.