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

The Zebrafish Neurophenome Database (ZND): a dynamic open-access resource for zebrafish neurophenotypic data

Zebrafish (Danio rerio) are widely used in neuroscience research, where their utility as a model organism is rapidly expanding. Low cost, ease of experimental manipulations, and sufficient behavioral complexity make zebrafish a valuable tool for high-throughput studies in biomedicine. To complement the available repositories for zebrafish genetic information, there is a growing need for the collection of zebrafish neurobehavioral and neurological phenotypes. For this, we are establishing the Zebrafish Neurophenome Database (ZND; www.tulane.edu/∼znpindex/search ) as a new dynamic online open-access data repository for behavioral and related physiological data. ZND, currently focusing on adult zebrafish, combines zebrafish neurophenotypic data with a simple, easily searchable user interface, which allow scientists to view and compare results obtained by other laboratories using various treatments in different testing paradigms. As a developing community effort, ZND is expected to foster innovative research using zebrafish by federating the growing body of zebrafish neurophenotypic data.

Social approach-avoidance behavior of a high-anxiety strain of rats: effects of benzodiazepine receptor ligands

RATIONALE

To better understand anxiety disorders with social impairments as well as to identify new treatments, it is important to develop preclinical procedures involving social components of anxiety. Recently, a novel procedure was reported: the rat Social Approach-Avoidance (SAA) test. In this test, the time spent by a test rat in a large social compartment containing an unfamiliar stimulus rat reflects the anxiety state of the animal. It was shown that pre-stressing the test rat increased the avoidance of the social compartment as characterized by an increase in the time spent in the nonsocial compartment.

OBJECTIVE

(1) To use a high-anxiety strain, F-344 rats, instead of pre-stressed animals, (2) to automate the test by using video tracking to measure time spent in both compartments and their subdivisions, and (3) to validate this modified test with known benzodiazepine receptor ligands.

MATERIALS AND METHODS

F-344 rats were treated with either chlordiazepoxide or diazepam (benzodiazepine receptor agonists), or RO 19-4603 or FG 7142 (benzodiazepine receptor inverse agonists).

RESULTS

The agonists produced anxiolytic-like effects, whereas the inverse agonists produced anxiogenic-like effects. These effects were most marked in the two extreme zones in terms of distance to the stimulus rat.

CONCLUSIONS

F-344 rats display spontaneous avoidance behavior in the modified SAA procedure, and approach-avoidance behavior in these rats is sensitive to benzodiazepine agonists and inverse agonists in a bidirectional manner. The finding that the assessment of time spent into two virtual zones in each of the compartments markedly increased the sensitivity to both anxiolytics and anxiogenics will be discussed using the concept of physical defensive distance.

The Mouse Defense Test Battery: pharmacological and behavioral assays for anxiety and panic

The Mouse Defense Test Battery was developed from tests of defensive behaviors in rats, reflecting earlier studies of both acute and chronic responses of laboratory and wild rodents to threatening stimuli and situations. It measures flight, freezing, defensive threat and attack, and risk assessment in response to an unconditioned predator stimulus, as well as pretest activity and postthreat (conditioned) defensiveness to the test context. Factor analyses of these indicate four factors relating to cognitive and emotional aspects of defense, flight, and defensiveness to the test context. In the Mouse Defense Test Battery, GABA(A)-benzodiazepine anxiolytics produce consistent reductions in defensive threat/attack and risk assessment, while panicolytic and panicogenic drugs selectively reduce and enhance, respectively, flight. Effects of GABA(A)-benzodiazepine, serotonin, and neuropeptide ligands in the Mouse Defense Test Battery are reviewed. This review suggests that the Mouse Defense Test Battery is a sensitive and appropriate tool for preclinical evaluation of drugs potentially effective against defense-related disorders such as anxiety and panic.

Predator-elicited flight responses in Swiss-Webster mice: an experimental model of panic attacks

1. The nosological status of panic disorder is still a matter of debate. Nevertheless, evidence is emerging that panic attacks have a different pattern of drug responsiveness from other forms of anxiety. 2. Several experimental animal models of panic attacks have been developed. These vary in the extent to which they meet criteria for face validity, predictive validity and construct validity, normally applied to such models. 3. In the present review, the authors examine the possibility that predator-elicited flight responses in Swiss-Webster mice might serve as an experimental model for the screening of panic-modulating drugs. 4. Drug effects on flight responses clearly indicate that this model has good predictive validity as panic-promoting agents increase flight reactions, while panicolytic drug challenge induces opposite effects. In addition, drugs devoid of any effect on panic attack, also do not alter flight behavior. 5. These findings strongly suggest that the model of predator-elicited flight responses in Swiss-Webster mice is useful for the investigation of panic-modulating drugs.

Benzodiazepine receptor ligands modulate ethanol drinking in alcohol-preferring rats

The effects of benzodiazepine receptor ligands with different intrinsic activity profiles were studied on voluntary ethanol consumption in the selectively bred alcohol-preferring AA (Alko, Alcohol) rat line, and compared to those of an opiate antagonist, naloxone, and a serotonin uptake inhibitor, citalopram. The rats were first allowed to develop a strong preference for 10% (v/v) ethanol solution in tap water over plain water until their ethanol consumption stabilized. Thereafter, the period when ethanol solution was available for the rats was gradually reduced to 4 h, 3 times a week, every second working day. The acute effects of positive allosteric modulators (agonists) of the gamma-aminobutyric acid type A (GABAA)/benzodiazepine receptor [midazolam, abecarnil, ethyl 5-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate (ZK 91296), bretazenil, and 2,5-dihydro-2-(4-methylphenyl)-3H-pyrazolo[4,3-C]quinolin-3(5H)-on e (CGS 9895)] and of negative allosteric modulators [inverse agonists, ethyl 8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5- a][1,4]benzodiazepine-3-carboxylate (Ro 15-4513) and t-butyl 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a]thieno[2,3- f][1,4]diazepine-3-carboxylate (Ro 19-4603)] were tested after i.p. injections of three different drug doses using saline injections as a control treatment. The benzodiazepine agonists had rather modest effects on ethanol intake, measured 1 and 4 h after the injections, whereas the inverse agonists and naloxone strongly decreased ethanol consumption. Acute citalopram had no clear effect on ethanol drinking, but it slightly decreased the consumption of novel food during the 4-h session, as did all other benzodiazepine agonists except bretazenil. Neither the inverse agonists nor naloxone had any significant effect on food intake.(ABSTRACT TRUNCATED AT 250 WORDS)

The benzodiazepine inverse agonist RO19-4603 exerts prolonged and selective suppression of ethanol intake in alcohol-preferring (P) rats

The time course of the benzodiazepine (BDZ) inverse agonist RO19-4603 in antagonizing ethanol (EtOH) intake was investigated in alcohol-preferring (P) rats (n = 7) maintained on 24-h continuous free-choice access to EtOH (10% v/v), water, and food. After fluid intakes had stabilized over several weeks, animals were injected with Tween-80 vehicle solution or RO19-4603 (0.075, 0.150, and 0.30 mg/kg). EtOH and water intakes were determined at 8- and 24-h intervals. RO19-4603 caused a marked attenuation of EtOH drinking with each of the doses tested. EtOH intake during the 8-h following 0.075, 0.150, and 0.30 mg/kg RO19-4603 was decreased by approximately 36, 74, and 57%, respectively. Intakes during the 24-h interval were similar to the vehicle control condition. However, 32 h post-drug administration, EtOH intakes were reduced to approximately 27, 31, and 29% following the 0.075, 0.150 and 0.30 mg/kg doses, respectively. To further confirm the reliability of the RO19-4603 dose-response effect, and its selectivity for EtOH, the highest dose condition (0.30 mg/kg) was tested twice. The second 0.30 mg/kg dose condition exerted a profile of effects similar to the initial treatment; 8 h following administration, intake was decreased to 60% of the control level, and 32 h post-drug administration intake was decreased to approximately 46% of the controls. These decreases were evidently selective in comparison with water, since water drinking showed compensatory increases which paralleled the decreased EtOH consumption. Dose-response comparisons indicated that 0.150 mg/kg approaches the maximum effective dose, since the 0.30 mg/kg dose of RO19-4603 did not produce an additional decrease in EtOH intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of benzodiazepine receptor inverse agonists on locomotor activity and exploration in mice

This study investigates the effects of benzodiazepine receptor inverse agonists on the locomotor and exploratory behaviour of mice when tested in a familiar environment. The weak partial inverse agonist Ro 15-3505 (0.3, 1, 3 mg/kg i.p.) significantly increased locomotion and hole-dipping in habituated mice. However, the more efficacious partial inverse agonists Ro 15-4513 (0.3, 1, 3 mg/kg i.p.) and Ro 19-4603 (0.03, 0.1, 0.3 mg/kg i.p.) had no effect on these parameters. The benzodiazepine receptor antagonist flumazenil (3, 10, 20 mg/kg i.p.) also increased locomotion and hole-dipping in habituated mice, although like Ro 15-3505, these effects were of short duration occurring largely in the first 15 min following injection. Opposite effects were obtained with the partial benzodiazepine agonist Ro 17-1812 (1, 3, 10 mg/kg i.p.) which produced a longer-lasting significant decrease in hole-dipping behaviour in habituated mice without altering locomotion. Finally, in contrast to its effects in habituated animals, Ro 15-3505 (0.3, 1, 3 mg/kg i.p.) did not modify either locomotion or exploration in mice which were tested in a novel environment, showing that the effects of the inverse agonist were state-dependent. This demonstration that, under certain conditions, the weak benzodiazepine receptor inverse agonist Ro 15-3505 and the antagonist flumazenil, produce behavioural activation is in accordance with the work of others suggesting that these classes of compound may increase arousal and may therefore be of some value in treatment of memory disorders.

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

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

Electroencephalogram effect measures and relationships between pharmacokinetics and pharmacodynamics of centrally acting drugs

Electroencephalogram (EEG) effect parameters may be useful in pharmacokinetic-pharmacodynamic modelling studies of drug effects on the central nervous system (CNS). Effect parameters derived from a quantitative analysis of the EEG appear to be perfectly suited to characterise the relationships between pharmacokinetics and pharmacodynamics of benzodiazepines and intravenous anaesthetics. EEG parameters represent many of the characteristics of ideal pharmacodynamic measures, being continuous, objective, sensitive and reproducible. These features provide the opportunity to derive concentration-effect relationships for these drugs in individuals, which yield important quantitative information on the potency and intrinsic efficacy of these drugs. The EEG techniques presented can be used to study the influences of factors such as age, disease, chronic drug use and drug interactions on the concentration-effect relationships of psychotropic drugs. An important issue is the choice of the EEG parameter to characterise the CNS effects of the compounds. More attention must be paid to evaluating the relevance of EEG parameters to the pharmacological effects of the drugs. Knowledge of the relationship between EEG effect parameters and clinical effects of drugs under different physiological and pathophysiological conditions is crucial to determining the value of EEG parameters in drug effect monitoring. Pharmacodynamic parameters derived from the concentration-EEG effect relationship may be correlated to pharmacodynamic parameters obtained from other in vitro and in vivo effect measurements. These comparisons revealed that changes in the amplitudes in the beta frequency band of EEG signals is a relevant measure of pharmacological effect intensity of benzodiazepines, which reflects their affinity and intrinsic efficacy at the central gamma-aminobutyric acid (GABA) benzodiazepine receptor complex. The exact EEG correlates of the anxiolytic, anticonvulsant, sedative and hypnotic actions of benzodiazepines have not yet clearly been elucidated. For intravenous anaesthetics, close correlations between the potency determined with EEG measurements and clinical measures of anaesthetic depth have been established, suggesting that, in principle, EEG parameters can adequately reflect depth of anaesthesia. However, more study is required to further substantiate these findings.

Differences in intrinsic efficacy of benzodiazepines are reflected in their concentration-EEG effect relationship

1. The relevance of EEG effect parameters as a measure of the central nervous system effects of benzodiazepines was evaluated. The concentration-EEG effect relationships of the benzodiazepine agonist midazolam, partial agonist bretazenil, antagonist flumazenil and inverse agonist Ro 19-4603 were quantified and compared with the intrinsic efficacy and affinity of these compounds at the gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex. 2. The pharmacokinetics and pharmacodynamics of the compounds were determined after a single intravenous bolus administration of 5 mg kg-1 midazolam, 2.5 mg kg-1 bretazenil, 10 mg kg-1 flumazenil or 2.5 mg kg-1 Ro 19-4603 to male Wistar derived rats. In a separate experiment the distribution between blood, cerebrospinal fluid and brain concentrations of these compounds was determined. A sensitive assay was developed to measure bretazenil and Ro 19-4603 concentrations in small samples of biological fluids. 3. The benzodiazepine-induced changes in amplitudes in the 11.5-30 Hz frequency band, as determined by aperiodic analysis, was used as EEG effect measure. Concentration-EEG effect relationships were derived by a pharmacokinetic-pharmacodynamic modelling procedure and in the case of midazolam, bretazenil and Ro 19-4603 successfully quantified by the sigmoidal Emax model. Large differences in maximal effect of midazolam (Emax = 73 +/- 2 microVs-1), bretazenil (Emax = 19 +/- 1 microVs-1) and Ro 19-4603 (Emax = -6.5 +/- 0.4 microVs-1) were observed, reflecting their differences in intrinsic efficacy. A close correlation was found between the EC50 values based on free drug concentration and receptor affinity as determined by displacement of [3H]-flumazenil in a washed brain homogenate at 37 degrees C. In the concentration range of receptor saturation flumazenil did not produce any changes in the EEG effect measure.4. The study demonstrated that the change in amplitudes in the 11.5-30 Hz frequency band of the EEG is a relevant measure of the pharmacological effect intensity of benzodiazepines, because it seems to reflect their affinity and intrinsic efficacy at the central GABA-benzodiazepine receptor complex.

Effects of the benzodiazepine receptor inverse agonist, DMCM, on the behaviour of mice: an ethopharmacological study

Ethopharmacological procedures and a two-compartment black and white test box were used to examine behavioural effects produced by the benzodiazepine receptor inverse agonist, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), when given by intraperitoneal injection (0.4 and 1.0 mg/kg) to pair-housed adult CD1 male mice. Control mice received injections of the solvent. Behaviour in the light-dark box was examined at 30 min after the injection and behaviour during encounters with an untreated group-housed male, in a neutral cage, was then assessed by ethological procedures. In dominant mice, aggressive behaviour was significantly reduced and the ratio of flight, relative to aggression received, was significantly increased by DMCM at 0.4 mg/kg. At 1 mg/kg but not 0.4 mg/kg, DMCM decreased time spent by dominant mice in the light compartment of the test box. In both dominant and subordinate mice, flight was increased by DMCM at 1 mg/kg to a level close to statistical significance. Treatment with DMCM had no other detectable effect on the behaviour of subordinate animals. It is suggested that anxiogenic activity of this compound might induce a shift of agonistic behaviour from aggression to "fear-induced flight".