Pituitary-adrenal activity and appetitive reinforcement

Corticosterone levels during extinction of runway response in rats

This investigation examined whether the hypothalamic-pituitary-adrenocortical axis would activate during extinction of a straight runway response. Four groups of rats were trained to run in a straight runway for 3 (for 3S and 3L groups) or 10 (for 10S and 10L groups) food pellets as a reward for either 15 (for 3S and 10S groups) or 25 (for 3L and 10L groups) acquisition days followed by 3 extinction days. Blood samples for determination of serum corticosterone concentration were taken from all animals under 5 different situations: 10 min after entering the experimental room, after the 24th acquisition day, after the first and third extinction days and under the deprivation control. Running speed of 10S and 10L groups in extinction days were reduced more quickly than that of 3S and 3L groups. After the third extinction day, serum corticosterone concentrations were significantly elevated in 10S and 10L, but not in 3S and 3L groups. These results indicate that the amount of reward in the acquisition phase influences not only the running speed, but also the corticosterone concentration in the extinction phase.

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.