Effect of chlordiazepoxide on the partial reinforcement extinction effect

Facilitation of extinction of operant behaviour in C57Bl/6 mice by chlordiazepoxide and D-cycloserine

RATIONALE AND OBJECTIVE

Effects on the extinction of GABAergic drug, chlordiazepoxide (CDP), and glutamatergic drug, D: -cycloserine (DCS), in C57BL/6 mice were compared.

MATERIALS AND METHODS

Following a palatability test (Experiment 1), Experiments 2-6 involved food-reinforced lever press training followed by extinction sessions at 1- or 4-day intervals. The effects of drugs were examined. Experiment 7 involved a two-lever task.

RESULTS

CDP did not affect food palatability (Experiment 1), but facilitated extinction when administered prior to extinction sessions via intracerebral (Experiment 2) or peripheral administration at 1-day (Experiments 3-7) or 4-day intervals (Experiment 6). Reducing the amount of training prior to extinction reduced the delay in the effect of CDP typically seen, and CDP had a larger effect in early sessions on mice that had received less training (Experiment 3). There was some evidence that CDP could be blocked by flumazenil (Experiment 4), and CDP withdrawal reversed extinction facilitation (Experiments 5 and 7). With 4-day intervals, DCS administered immediately following extinction sessions, or pre-session CDP, facilitated extinction with 48-trial sessions (experiment 6B). With six-trial sessions, the co-administration of post-session DCS enhanced facilitation produced by pre-session CDP (experiment 6A). Finally, CDP facilitated extinction in a dose-related fashion following training on a two-lever food-reinforced task (Experiment 7).

CONCLUSIONS

The findings are consistent with the hypotheses that two neurotransmitter systems have different roles in operant extinction and that glutamatergic systems are involved in extinction learning and GABAergic systems involved in the expression of that learning. This parallels findings with extinction following Pavlovian conditioning, which has been more extensively investigated.

Effect of anxiolytics and antidepressants on extinction and negative contrast

Anxiolytics, particularly the benzodiazepines and barbiturates tend to retard, but not prevent, extinction, promote recovery from negative contrast, and elevate S- responding in discrimination training. Anxiolytics, administered during acquisition, tend to eliminate the partial reinforcement extinction effect, but this result is substantially influenced by parametric considerations. Behaviors that are energized in extinction may have a different pharmacological profile than behaviors that decline. Conclusions regarding the effects of antidepressants must be more tentative but, in general, acutely administered antidepressants are relatively ineffective in all of these paradigms. However, antidepressants may enhance the efficiency of responding on DRL schedules whereas anxiolytics tend to disrupt such behavior.

The neurochemistry and pharmacology of extinction behavior

The role of various neurotransmitter systems in the brain in extinction behavior is examined. An attempt is made to suggest psychological mechanisms (such as attention, secondary reinforcement or internal inhibition) by which the neurotransmitter systems or drugs act to produce the observed alteration in extinction behavior. The putative neurotransmitters acetylcholine, noradrenaline, dopamine, serotonin, endorphins and the peptides are reviewed, as are pharmacological agents such as the benzodiazepines, the barbiturates, the psychodelics, the neuroleptics, the psychomotor stimulants and cannabinoids. Other treatments and factors are considered such as peripheral hormones and the adrenal-pituitary axis. It is suggested that the noradrenergic system may be involved in the expression of extinction behavior by a role in selective attention, the dopamine system via an involvement with secondary reinforcement, the cholinergic system by a mechanism of response inhibition and the barbiturates and benzodiazepines by a block of nonreward.

Chlordiazepoxide and resistance to punishment

Rats were given intermittent electric foot-shock during food-rewarded alley training. In the test phase, food and shock were given on every trial. These animals persisted in running down the alley in the test phase compared to those without prior shock experience. The effects of chlordiazepoxide (CDP) on this learned resistance to punishment were examined using a long and short interval between trials. It was found that CDP abolished the effect at a long inter-trial interval, but left it unaltered if the interval was short. The results match those found previously with an analogous effect using non-reward. It is suggested that the effects of punishment and non-reward may be mediated by a common process, and that the benzodiazepines may act on this process.

The partial reinforcement extinction effect after treatment with chlordiazepoxide

Two experiments are reported, in which rats were run in a straight alley for food reward with or without injections of the anti-anxiety drug, chlordiazepoxide (CDP). The experiments were directed to two questions. (1) Can one predict the effects of CDP from knowledge of the effects of a second anti-anxiety drug, sodium amylobarbitone (SA) (2) can the effects of CDP be predicted from the hypothesis that anti-anxiety drugs attenuate responses to conditioned frustrative stimuli? The experiments examined the effects of CDP on the partial reinforcement extinction effect (PREE) at one trial a day. CDP injected throughout acquisition and extinction reduced the PREE. This effect was probably due to the presence of the drug during acquisition. Injected during extinction only, CDP increased resistance to extinction in both continuous and partial reinforcement groups. These effects of CDP were closely similar to those previously reported for SA, thus answering question (1) in the affirmative. The effects of CDP on the PREE were also consistent with the conditioned-frustration hypothesis (question 2).