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

Impulsivity as a confounding factor in certain animal tests of cognitive function

Performance in cognitive tasks which require the subject to wait and/or to process a large amount of information can be disrupted by an increase in impulsive-like behaviour. Accordingly, a decrease in impulsive-like behaviour can improve performance in such tasks. Conversely, impulsive-like behaviour may improve performance in cognitive tasks where simple and fast responses and/or only little information processing is required. Thus, impulsivity constitutes a confounding factor in studies of cognitive function. Impulsive-like behaviour may be modified by serotonergic (5-HT) activity, with underactivity in 5-HT neurotransmission increasing impulsivity and vice versa. Drug- or lesion-induced alteration in 5-HT neurotransmission may, therefore, constitute suitable tools to investigate the role of impulsivity in animal tests of cognitive function. Benzodiazepines also increase impulsive-like behaviour, possibly by decreasing 5-HT neurotransmission. Hence, the effects of modulation of 5-HT systems and of the benzodiazepine-binding site on performance in animals tests of cognitive function will be discussed. It is predicted that the effects of manipulations of serotonergic activity or of benzodiazepine administration depend upon the nature of the response required, and that these effects may be mediated through changes in impulse control.

Effects of bifemelane on discrimination learning of serotonergic-dysfunction rats

To investigate the effect of bifemelane hydrochloride on learning achievements of serotonin-deficient rats, animals were fed with tryptophan-deficient diets and operant type discrimination learning tests were performed. In general, serotonin-deficient rats show hyperactivity. In this study, total number of responses in reverse learning experiments was lower in rats that received 50 mg/kg bifemelane compared to the other serotonin-deficient groups. The ratio of correct responses to the total number of responses revealed low learning achievements in the control and low-dose groups, whereas the ratio in the high-dose group was nearly the same as in normal rats in the final few sessions of both the primary and reverse learning experiments. Throughout this study, the high-dose group showed a better improvement in learning achievement than the low-dose group. Therefore, bifemelane has certain effects on learning achievement from a) the functional activation of the serotonergic nervous system and b) changes in neurotransmitter levels in the brain (e.g., acetylcholine, noradrenaline) and overall energy metabolism.

Diazepam-induced impairment of a go-no go successive discrimination

Diazepam (2.0 and 4.0 mg/kg, but not 1.0 mg/kg) administered in eight acquisition sessions significantly impaired the light-cued successive discrimination of male Sprague-Dawley rats. In two postdrug (vehicle) sessions, groups previously treated with the drug demonstrated good recovery in discrimination. An analysis of response components indicated that the impairment was due to the failure of drugged subjects to inhibit or withhold responses during the no go periods of the task. These findings are consistent with a "disinhibitory hypothesis" of drug impairment. The similarity of the present findings to those previously reported with chlordiazepoxide suggests that such effects are a generalized characteristic of the benzodiazepine class of drugs.

A role for the mesolimbic dopamine system in the reinforcing properties of diazepam

The conditioned place preference paradigm was used to investigate the neurochemical and neuroanatomical substrates which mediate the rewarding properties of diazepam. The results confirmed that diazepam (1 and 2.5 mg/kg, IP) produced place preference for a distinctive environment that had previously been paired with injections of the drug. Pretreatment with haloperidol (0.1 mg/kg) antagonised the place preference induced by diazepam (1 mg/kg). Pretreatment with domperidone (2 mg/kg) failed to influence this effect of diazepam. Haloperidol (0.1 mg/kg) and domperidone (2 mg/kg) alone did not produce place aversion. In separate experiments the diazepam-induced place preference was examined in rats having 6-hydroxydopamine (6-OHDA) lesions of the nucleus accumbens. These animals did not show preference for the compartment associated with diazepam. Depletion of central noradrenaline produced by systemic injections of DSP4 did not affect diazepam-induced place preference conditioning. These findings suggest that dopamine-containing neurons of the mesolimbic system are a component of the neural circuitry that mediates the reinforcing properties of diazepam.

Dose-dependent reversal of chlordiazepoxide-induced discrimination impairment by Ro 15-1788

Chlordiazepoxide (10 mg/kg), administered on eight successive acquisition sessions, impaired a light-cued, successive discrimination in male Sprague-Dawley rats by increasing the number of incorrect responses. The benzodiazepine receptor antagonist Ro 15-1788 (5 and 10 mg/kg) reversed the discrimination impairment and reduced the number of incorrect responses in a generally dose-dependent manner when co-administered with chlordiazepoxide. These findings suggest that the impairment of successive discrimination by chlordiazepoxide is mediated by central benzodiazepine receptor sites. When administered alone, however, the 10 mg/kg dose of Ro 15-1788 (but not the 5 mg/kg dose) produced a mild benzodiazepine-like impairment in discrimination, which was accompanied by a small but significant increase in incorrect responses. These findings suggest that Ro 15-1788 may also have some intrinsic action of its own, which needs to be assessed independently of its use as a mediational research tool.

Are the effects of benzodiazepines on discrimination and punishment dissociable?

Studies have shown that benzodiazepines (BZs) both disrupt discrimination and increase resistance to punishment. Using a delayed response task, we provide evidence that effects of BZs on discrimination cannot be fully explained by deficits in either short or long term memory, or by intolerance for delay of reward. A schedule with rewarded, nonrewarded (Time out: TO) and conflict components was used to investigate effects in rats of compounds active at the BZ receptor on successive discrimination and punished responding in parallel. The GABA transaminase inhibitor ethanolamine-O-sulphate exerted additive effects with chlordiazepoxide (CDP) on punished but not TO responding. Both GABA and CDP injected into the amygdala selectively increased conflict rates, but with peripheral treatment CDP also increased TO rates. Two inverse BZ agonists, CGS 8216 and FG 7142 antagonzied the anti-conflict effects of GABA and CDP, given within the amygdala or peripherally, but the increase in TO rates induced by systemic CDP was counteracted only by peripheral treatments. These compounds also reduced rates of conflict responding below baseline, consistent with anxiogenic activity. Effects of the BZ antagonist Ro 15-1788 were broadly similar to those of the inverse agonists, except that it did not antagonise the anti-conflict action of intra-amygdaloid GABA, nor significantly reduce punished responding at the single dose used. We conclude from these results that the anti-conflict effects of BZs are mediated by a GABAergic amygdaloid mechanism, but that the same mechanism is not involved in BZ effects on discrimination.

Kindling and withdrawal changes at the benzodiazepine receptor

Drugs acting at benzodiazepine receptors can have two types of pharmacological profile: benzodiazepine agonists are anxiolytic, anticonvulsant and sedative, whilst benzo diazepine inverse agonists cause anxiety and convulsions. In 1982 we showed that a benzo diazepine antagonist, Ro 15-1788, prevented the effects of both types of compound at doses without intrinsic activity in the tests used. We put forward the hypothesis that the benzo diazepine receptor complex could undergo two possible conformational changes, resulting in increases (benzodiazepine agonists) or decreases (benzodiazepine inverse agonists) in the effects of the inhibitory transmitter γ-aminobutyric acid (GABA). This concept has been widely accepted. We have now studied the effects of inverse agonists after chronic treatment with inverse agonists themselves and with benzodiazepine agonists, in order to see if tolerance develops (as seen with the agonists) or whether an opposite change occurs.

Effects of chlordiazepoxide and sodium valproate in two tests of spatial behaviour

The effects of chlordiazepoxide (CDP) and sodium valproate (VPA) were studied in rats trained to asymptotic performance on two tests of spatial behaviour, the 8-arm radial maze and the 8-choice arena. The task in the 8-arm maze was to locate a single food pellet at the end of each arm. Both CDP and VPA caused an increase in errors, an increase in performance time, and the utilization of a non-spatial response strategy. The task in the 8-choice arena was to locate a single water bottle from an octagonal array of eight otherwise empty bottles. For one group the goal bottle remained in the same place from trial to trial; for a second group the position of the goal bottle was cued by a black card over the nozzle; for the third group the goal bottle was uncued and moved randomly from trial to trial. VPA had no effect on performance, but CDP impaired performance in all three groups. These patterns of effects suggest that VPA may specifically disrupt working memory, but that the impairment of spatial performance by CDP probably results from a non-specific perceptual or attentional deficit.

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.

Behavioural and pharmacological dissociation of chlordiazepoxide effects on discrimination and punished responding

Effects of chlordiazepoxide (CDP) and ethanolamine-O-sulphate (EOS) alone and in combination were tested on the acquisition and performance of continuous reinforcement - time out (CR-TO) and variable interval reinforcement - time out (VI-TO) operant discriminations in rats. CDP disrupted acquisition of CR-TO discrimination; effects were short lived, and neither CR-TO performance nor its reversal were impaired. Acquisition of VI-TO discrimination was increasingly impaired, and performance disrupted in pre-trained animals. EOS alone was inactive, and with CDP exerted only slight interactive effects. When a conflict component was added to the VI-TO schedule, however, EOS showed substantial additive effects with CDP on punished responding. The results suggest that CDP-induced increases in non-rewarded (TO) responding were related to task difficulty, pointing to a discrimination impairment rather than an anxiolytic effect. In addition, the specificity of EOS potentiation may reflect a pharmacological dissociation between CDP effects on discrimination and on punished responding, and suggest that GABA is selectively involved in resistance to punishment.

Dose-dependent impairment in the performance of a go-no go successive discrimination by chlordiazepoxide

After learning a light-cued, go-no go successive discrimination to criterion, male Sprague-Dawley rats received 0, 5, or 10 mg/kg chlordiazepoxide on six performance sessions, followed by two drug-recovery (saline) sessions. Chlordiazepoxide impaired discrimination performance in a dose-dependent manner, with animals in the 5 mg/kg dose condition demonstrating tolerance to the drug after two performance sessions. The degree of discrimination impairment in both drug dose conditions paralleled an increase in responding during no-go phases of the performance task. These findings are consistent with a "disinhibitory hypothesis" of performance impairment and suggest that CDP-drugged animals have difficulty in withholding incorrect responses.

Chlordiazepoxide and successive discrimination: different effects on acquisition and performance

Benzodiazepines have been reported to increase low rates of responding during a stimulus correlated with non-reinforcement while leaving prestimulus rates unaffected (successive discrimination). However, the results have been obtained by superimposition of the drug upon a discrimination which was learned in the absence of drug. The observed effects may therefore have been due to the sudden change in drug state (state-dependency) rather than to a specific action of the drug. The present experiments found that chronic administration of chlordiazepoxide (5 mg/kg, IP) impaired acquisition but not performance of successive discrimination. Intermittent administration of chlordiazepoxide impaired discrimination by increasing low rates of responding during the stimulus signalling non-reinforcement. This effect was obtained with saline-drug but not drug-saline state changes (asymmetric state-dependency). A final experiment showed that chronic administration of the drug did reduce well-learned inhibition resulting from signalled shock. It was concluded that chlordiazepoxide has not only pure anxiolytic but also state-dependent effects and that if successive discrimination depends on conditioned frustration it does so only while the discrimination is being learned.

Animal models for the study of anti-anxiety agents: a review

Animal models for the study of anxiolytic agents are reviewed and evaluated according to pharmacological and behavioral criteria. Although there are important exceptions, in general, most early animal models have not provided a reliable basis for identifying compounds with potential anxiolytic action, or for delineating the mechanisms of anxiolytic drug action. The possibility that phylogenetically 'prepared' forms of defensive learning might serve as a basis for the study of anxiolytic agents is introduced.