An amnesic effect of benzodiazepines in rats?

Effects of benzodiazepine receptor ligands on the performance of an operant delayed matching to position task in rats: opposite effects of FG 7142 and lorazepam

The effects of a series of benzodiazepine (BZ) receptor ligands, ranging from a full agonist through to partial inverse agonists, were examined on short term working memory in the rat. The behavioural paradigm used was a discrete trial, operant delayed matching to position task, as originally described by Dunnett (1985), with delays of 0, 5, 15 and 30 s. The benzodiazepine receptor (BZR) full agonist lorazepam (0.25, 0.375 and 0.5 mg/kg) dose and delay dependently impaired matching accuracy. Lorazepam also increased the latency to respond and decreased the number of nose pokes made into the food tray during the delays. In contrast, the BZR partial agonist ZK 95,962 (1, 3, 10 mg/kg) did not affect matching accuracy, but did increase the speed of responding. The BZR antagonist ZK 93,426 (1.25, 5, 25 mg/kg) had no effects in this paradigm. The BZR weak partial inverse agonists Ro 15-4513 (0.1, 1 and 10 mg/kg) and ZK 90,886 (1, 3 and 10 mg/kg) did not affect accuracy of performance. However, both of these drugs increased the latency to respond and decreased nose poke responses. These motoric effects were particularly strong following 10 mg/kg Ro 15-4513. This shows that the effects of drugs on the accuracy of responding and on the speed of responding can be dissociated. The BZR partial inverse agonist FG 7142 had effects on matching accuracy that were dependent upon dose. The lowest dose of FG 7142 (1 mg/kg) significantly improved accuracy, whereas the highest dose (10 mg/kg) impaired accuracy.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological profile of a potential anxiolytic: AP159, a new benzothieno-pyridine derivative

AP159 [N-cyclohexyl-1,2,3,4-tetrahydrobenzo(b)thieno(2,3c)pyridine]-3- carboamide,hydrochloride) showed clear anti-conflict activity in rats in the absence of effects on muscle relaxation, potentiation of anesthesia (in mice) or anticonvulsant activity (in mice). This anti-conflict effect was antagonized by treatment with Ro15-1788. By contrast with the deficits produced by diazepam, AP159 did not impair passive avoidance. The latter drug also improved scopolamine-induced amnesia in the same task. AP159 did not inhibit 3H-flunitrazepam binding, but potently inhibited 3H-8OH-DPAT binding. This compound increased serotonin and 5HIAA content of the midbrain raphe nuclei and of the amygdala centralis. AP159 has been shown to be a novel non-BZP anxiolytic agent with no side effects in laboratory animals; it could be a clinically effective anxiolytic agent.

Animal model studies of benzodiazepine-induced amnesia

The development of a mouse passive avoidance test as a model for amnesia produced by benzodiazepines is described. The model appropriately classifies the amnesic potential of a wide range of psychoactive drugs as validated by clinical findings. Control experiments indicate that the effect is best described as anterograde amnesia resulting from a failure of consolidation. gamma-Aminobutyric acid (GABA) antagonists had almost no effect on benzodiazepine-induced amnesia, whereas the benzodiazepine-receptor antagonist Ro 15-1788 completely and specifically reversed it. This clinically confirmed finding suggests that benzodiazepine-induced amnesia is mediated through the benzodiazepine-receptor. However, in vivo inhibition of benzodiazepine binding does not correlate well with amnesia in the mouse, and some benzodiazepine-receptor agonists with potent CNS effects in other in vitro models do not produce amnesia. Additional work is needed to clarify what aspects of benzodiazepine receptor occupancy mediate amnesia.

Effects of benzodiazepines on acquisition and performance: a critical assessment

Evidence related to the effects of benzodiazepines on learning and memory is reviewed in the contexts of human verbal learning studies and animal studies using both aversive and non-aversive paradigms. While the impairment of acquisition by benzodiazepines appears to be a robust phenomenon generalizing across species and experimental conditions, the impairment in the performance of an already-learned task by such drugs appears to be more restrictive and highly dependent upon experimental contingencies. Thus far, performance impairment appears to be found mainly in animal studies using non-aversive, food-motivated tasks, with such tasks being particularly well suited for investigating such a phenomenon. At present, there is a noticeable lack of knowledge regarding the neurochemical substrates underlying BDZ-induced impairment. Finally, some issues that may contribute to the presence or absence of a BDZ-induced performance impairment in published studies are briefly considered.

Some evidence for amnesic-like effects of benzodiazepines in animals

In animals, as in humans, benzodiazepines affect memory, inducing almost exclusively an anterograde amnesia. The characteristics of this amnesic-like effect are reviewed in terms of alterations in acquisition, consolidation, recall and/or forgetting processes. Explanations alternative to a true amnesia, i.e., state-dependent learning, cognitive deficits, attenuation of the emotional weight of the conditioning events are examined. Finally, the interference of these putative amnesic effects with experimental procedures devoted to the study of the anxiolytic activities of benzodiazepines are considered.

Anxiolytic drugs and the acquisition of conditioned fear in mice

Previous studies have shown that, in rodents, chlordiazepoxide and other benzodiazepines can interfere with learning in passive avoidance or conditioned suppression procedures. The most consistent effects are observed when the drugs are administered before the acquisition trial and subjects are re-tested in the non-drugged state. It is not clear, however, whether this effect on learning is associated with the behavioural depressant actions of these drugs. In the present study mice were injected with chloridiazepoxide, diazepam, zopiclone, or CGS 9896 and locomotor activity measured in a two-compartment box. The animals were then enclosed in one of the compartments and received a series of footshocks. On a second trial, 24 h after the first, the mice were returned to the box without injection and locomotion and time spent in each compartment were measured. During trial 1 chlordiazepoxide, diazepam, and zopiclone produced dose-related decreases in locomotor activity. The same doses disrupted fear conditioning. CGS 9896 also interfered with the conditioning of fear but did not reduce exploratory activity during the first trial at any of a wide range of doses, showing that learning can be affected without direct behavioural depressant activity. In a further experiment, chlordiazepoxide and CGS 9896 disrupted fear conditioning when injected before trial 1 but not when injected immediately after this trial. Mice drugged with chlordiazepoxide or CGS 9896 before both trials 1 and 2 also showed disrupted conditioning, demonstrating that the drug effects cannot be interpreted in terms of state dependent learning.

The comparative effects of benzodiazepines, progabide and PK 9084 on acquisition of passive avoidance in mice

Acquisition of passive avoidance following aversive conditioning to a dark compartment was measured in mice under the influence of one of seven benzodiazepines, the GABA-mimetic drug progabide or PK 9084, a nonbenzodiazepine ligand on benzodiazepine receptors. The drugs were administered prior to the training trial and retention was measured in the absence of the drug 24 h later. Oral administration (dose in mg/kg in parentheses) of flunitrazepam (0.1), lorazepam (1.0), nitrazepam (3.0), diazepam (10), flurazepam (10) and chlordiazepoxide (30), all prevented retention whereas progabide (100-800) and PPK 9084 (10-100) were ineffective. In comparison to effects on motor capacity none of the benzodiazepines was outstanding in its acquisition interfering effects.

Chlordiazepoxide, go-nogo successive discrimination and brain biogenic amines in cats

Chlordiazepoxide (CDP; 0.4 mg/kg/day, per os) was administered to cats during either the acquisition (CDP 21-22 days) of a go-nogo successive discrimination task (SD) or the performance (CDP 10 days) of the previously learned SD task. Endogenous levels of serotonin, 5-hydroxyindoleacetic acid, noradrenaline and dopamine were assayed in 12 brain areas, in trained as well as in untrained cats. This study has shown that (1) CDP strongly impaired the acquisition but not performance of the SD task, revealing a dissociation of the effects of CDP on these two stages of training; (2) the CDP administration, as well as the SD training, produced regional changes in brain levels of biogenic amines, suggesting the involvement of particular monoaminergic neurons in the behavioral effects of CDP and in operant behavior; and (3) in particular brain areas, interactions were observed between the effects of the SD training and those of the CDP administration on monoamines, indicating that the behavioral state may interfere with the neurochemical effects of CDP.

Amnesia-producing drugs affect hippocampal frequency potentiation

The effects of intravenous injections of lorazepam, scopolamine and propranolol upon hippocampal potentiation produced by commissural stimulation have been investigated in rats anaesthetized with urethane. Administration of 250 micrograms/kg or 500 micrograms/kg lorazepam significantly delayed the onset of secondary potentiation (frequency potentiation) of the population spikes recorded in subfields CA1 and CA3 of the dorsal hippocampus. Scopolamine also delayed the onset of frequency potentiation in CA1, but only at high dose (10 mg/kg). No other measured parameters of frequency potentiation, paired-pulse potentiation or post-tetanic potentiation were affected by any of the drugs. Lorazepam (greater than or equal to 250 micrograms/kg) and propranolol (3 mg/kg) reduced the severity of hippocampal after-discharge. Rhythmic entrainment of after-discharges was occasionally observed. The results are discussed in relation to the possible link between hippocampal potentiation and memory processes.

Benzodiazepine blockade of passive-avoidance task in mice: a state-dependent phenomenon

Four benzodiazepines (diazepam, chlordiazepoxide, halazepam, lorazepam) were tested for their effects on the acquisition of a passive-avoidance task in mice. This was done to determine whether amnesic effects, as reported in humans after diazepam and lorazepam, could be demonstrated by blockade of passive-avoidance responding in mice and, if so, to investigate the possible causes of the blockade by studying the relationships between the blockade and times of drug administration. Each of these benzodiazepines, at doses that did not alter overt behavior, blocked acquisition of the passive-avoidance response when they were administered to mice prior to the training session, but not when they were administered after the training session or prior to testing 24 h later. The block of avoidance responding was reversed, however, when the drugs were administered prior to both training and test sessions. These results suggest that state-dependent learning occurred; i.e., apparent amnesia occurred in the test session with untreated mice that had undergone passive-avoidance learning 24 h earlier under the influence of drug.

A comparative study of the effects of muscimol and diazepam on the recall of noxious events

Muscimol induced in rats a recall deficit which possibly results from a dissociation of learning. In one out of the 2 experimental conditions studied, a cross dissociation of learning was found between diazepam and muscimol.

Alterations in learning performance in the seizure-prone baboon: effects of elicited seizures and chronic treatment with diazepam and phenobarbital

A comparison was made of the effects of chronically administered diazepam and phenobarbital with those of elicited seizures on repeated acquisition learning in 3 prepubertal Papio papio. The learning task required the baboons each day to perform different sequences of lever presses on a three-lever behavior panel. Middle dose levels of both diazepam and phenobarbital were found to improve learning performance relative to base-line control levels, as measured by total errors, efficiency, and time required to complete chains of various lengths to a fixed criterion. The doses were well within therapeutically relevant seizure control and clinical blood level ranges. Higher doses of both drugs generally abolished the performance gains achieved with the lower doses. Seizures elicited twice weekly for 2--3 weeks, or daily for 7 days, induced no overall decrement in performance. Cyclicity in subsequent performance was, however, induced by each individual seizure during the twice weekly seizure period, and learning performance was found to be significantly worse at 42 hr than at 18 hr after each seizure. Implications of these data for acquisition of learning in the epileptic are discussed.

Diazepam maintenance of alcohol preference during alcohol withdrawal

After forced intragastric intubation of alcohol, rats will show a greatly increased tendency to self-administer alcohol in a free-choice situation. Diazepam (Valium) dosage (5 milligrams per kilogram of body weight) during the period ow withdrawal serves to maintain undiminished such alcohol self-administration. Without such diazepam dosage the tendency to self-administer alcohol returns to control levels.