Drug effects on a discrete conditioned avoidance response in dogs, rhesus monkeys and rats

The conditioned avoidance response test re-evaluated: is it a sensitive test for the detection of potentially atypical antipsychotics?

The present review discusses the history and paradigm of the conditioned avoidance response (CAR) in rats for the detection of potential antipsychotic activity of drugs. In addition, the role of dopamine (DA) D2, serotonin (5-HT)2A/2C, alpha1, 5-HT1A, DA D4, muscarinic and glutamate receptors in the suppression of CAR induced by various classes of drugs is evaluated. Finally, data investigating brain sites of action for the mediation of CAR behavior is discussed. It is concluded that the CAR test, originally found to be sensitive for the detection of antipsychotic drugs with high affinity as antagonists for brain dopamine receptors, is also sensitive for the detection of potentially antipsychotic compounds acting primarily via neurotransmitter receptors other than the DA D2 receptor. Furthermore, the review confirms the importance of the nucleus accumbens(shell) in the mediation of effects on CAR produced by traditional, as well as atypical antipsychotic drugs.

Effect of various psychotropic drugs on the performance of avoidance and escape behaviors in rats

The effect of different doses of nine psychotropic drugs upon conditioned avoidance responses (CARs) developed on a stable basis, after appropriate training, was investigated in rats and compared with their capacity to disrupt escape responses (ERs). Haloperidol (HAL), chlorpromazine (CPZ), morphine (MOR), pentobarbital (PENT), chlordiazepoxide (CDP), meprobamate (MPB), and amphetamine (AMPH) dose dependently inhibited both behaviors. Imipramine also disrupted CARs dose dependently, but did not affect ERs at maximal tolerated doses. Significant differences in the minimal effective doses, effective dose range, and time of onset and duration of action, as well as in potency, were observed. The quantitative determination of the level of selectivity, based upon the ratio ED50 escape failure/ED50 avoidance failure, indicated that all CNS depressants tested caused a selective inhibition of avoidance behavior. HAL was found to be the most specific, followed, in order, by CDP, MOR, CPZ, MPB, and PENT, whose ratio values were not significantly different. AMPH produced a nearly parallel impairment of both behaviors and quipazine only affected CARs at toxic doses. It is concluded that both neuroleptic and nonneuroleptic CNS depressant drugs have selective inhibitory effects on avoidance behavior. Data revealed differences that were more quantitative than qualitative.

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.

The effects of clozapine on shuttle-box avoidance responding in rats: comparisons with haloperidol and chlordiazepoxide

Previous studies have shown that clozapine produces effects different from those of other antipsychotic drugs on positively reinforced responding but may give rise to similar disruptions of avoidance behavior. To investigate the actions of clozapine on avoidance responding in more detail the effects of this drug were compared with those of haloperidol and chlordiazepoxide in rats trained to avoid shock in a shuttle-box. Acute administration of all three drugs reduced avoidance responses and increased escape failures although clozapine produced this latter effect only at a high dose. With repeated administration of each drug over 4 days tolerance developed rapidly to the effect of clozapine, the effect of haloperidol increased and there was no systematic change in the action of chlordiazepoxide. Disrupted avoidance responding after acute administration of clozapine does not reflect the clinical antipsychotic action of this drug.

Drugs and taste aversion

The literature on the effects of drugs on the acquisition and the magnitude of taste aversion is reviewed and discussed. Then, the results of a series of experiments on the effects of phenobarbital and related drugs on taste aversion are reported. A standard taste aversion model was used in all experiments; test drugs were injected prior to drinking in a one bottle situation on the first test day following the taste aversion treatment. Phenobarbital in doses ranging from 20 to 80 mg/kg significantly attenuated taste aversion induced by lithium chloride (LiCl) and x-radiation, the maximal effect occurred with the 60 mg/kg dose. The attenuating effect was found to be dependent upon the magnitude of the aversion to the sapid solution. Phenobarbital completely abolished aversion produced by 0.375 mEq LiCl while the attenuation effect decreased linearly with higher doses of LiCl. Results also indicate that phenobarbital's attenuating effect cannot be solely attributed to its dipsogenic characteristic or to its state dependent learning effect. Attenuation of LiCl aversion to a saccharin solution was also observed following single doses of amobarbital, 30 mg/kg, pentobarbital, 15 mg/kg, and chloropromazine, 0.75 mg/kg. Taste aversion was not affected by other doses of those drugs or by hexobarbital, barbital, and chlordiazepoxide. Phenobarbital's attenuating effect on taste aversion is discussed in relation to other known behavioral and neurophysiological effects of the drug.

Differential attenuation of some effects of haloperidol in rats given scopolamine

In a series of pharmacological tests the ability of 0.6 mg/kg of the anticholinergic scopolamine to decrease the effectiveness of the neuroleptic heloperidol varied widely. Most severely attenuated was production of catalepsy followed in order of decreasing interference by inhibition of amphetamine-induced rotation, inhibition of amphetamine- or apomorphine-induced stereotyped behavior, inhibition of conditioned avoidance responding and lastly attenuation of the haloperidol-induced increase in striatal HVA. By use of such a relatively low dose of scopolamine the behavioral effects of heloperidol were dissociated from effects on dopamine turnover in the striatum. If behavioral tests in animals can be related to the clinical effects of neuroleptic drugs, those effects of haloperidol severely reduced by scopolamine may be related to extrapyramidal effects.

Effects of morphine and heroin on discrimination learning and consolidation in mice

Morphine and heroin were administered to mice learning to swim toward a light source (L procedure) or toward the dark (D procedure), in a Y water maze, under pre and post-trial drug treatment conditions. In the pre-trial experiments a clear disrupting effect on performance with the two procedures followed administration of both drugs, but for the L performance never fell below the 50% level of correct choices. Analysis of the performance within each session demonstrated a disruption in the long term memory consolidation mechanism. The administration of naloxone, or alternatively, discontinuation of the treatment, was followed by a gradual improvement, in performance by the treated animals. In both procedures, a performance disruption also followed the administration of the drugs immediately after each experimental session.

Effects of low doses of chlorpromazine on a conditioned emotional response in the rat

This experiment investigated the anxiety-reducing effect of chlorpromazine with 20 rats, divided into two groups. The drugged group received daily throughout the experiment an i.p. injection of chlorpromazine. Controls were given during the same period isotonic saline injections. The heart rate was taken as the index of anxiety. In the first phase of the experiment, both groups were habituated to the testing box; then, all Ss were given 10 spaced shocks in the testing chamber (conditioned emotional response training). The extinction of the conditioned emotional response was next measured. The results showed that in all phases the anxiety level, as measured by heart rate, was significantly lower for the chlorpromazine group. In the third phase, heart-rate recordings were correlated with a specific motor activity. Although heart rate was higher for both groups during activity, the distinction between drugged and normal Ss was maintained.