Symmetrical effects of amphetamine and alpha-flupenthixol on conditioned punishment and conditioned reinforcement: contrasts with midazolam

Killcross, A.S., Everitt, B.J., & Robbins, T.W. (1997). Symmetrical effects of amphetamine and alpha-flupenthixol on conditioned punishment and conditioned reinforcement: contrasts with midazolam. Psychopharmacology, 129, 141-152.

There is evidence to suggest that forebrain dopaminergic systems are likely to be involved in both appetitive and aversive motivation. These authors studied the effects of dopamine (DA) agents on conditioned punishment (aversive learning) and conditioned reinforcement (appetitive learning) paradigms using DA agonists and antagonists injected systemically. In conditioned punishment, a Pavlovian CS predicting punishment is added to an instrumental bar-pressing paradigm, but only on one of the bars. Normal animals will adjust their bar-pressing away from this lever. (Note: These authors, however, implemented a punishment procedure by presenting a CS and shock upon bar-press, rather than a conditioned punishment procedure which would only present the CS upon bar-press). In conditioned reinforcement, a CS predicting reward is added to the instrumental bar-pressing paradigm on one of the bars. Animals will naturally come to favor this bar paired with the appetitive CS.

DA agonists increased the effect of a punishing CS, causing the animals to further decrease their bar pressing. DA agonists also enhanced the effect of an appetitive CS, increasing bar pressing. DA antagonists, on the other hand, decreased the effect of a punishing CS. They also reduced the effect of an appetitive CS. Thus, it appears dopaminergic agents modulate the behavioral impact of both appetitively and aversively motivated conditioned stimuli on instrumental performance. Systemic benzodiazepene administration was also explored with results showing a selective impact on aversively-motivated stimuli (i.e. no effect on the appetitive CS).