Effects of dopamine D-1 and D-2 antagonists on decision making by rats: no reversal of neuroleptic-induced attenuation by scopolamine.

The effects of the dopamine (DA) D-1 antagonist SCH 23390 and the D-2 antagonists haloperidol and sulpiride on decision making in thirsty rats were investigated. The problem given to the rats was to choose between two behaviours, locomoting or lever-pressing, in order to obtain rewards (water). SCH23390 and haloperidol dose-dependently reduced the number of rewards obtained. However, only minor effects were seen on the decision making parameters. DA is thus important for initiation and/or performance of learned behavioural acts, not for information sampling and processing leading to the decision of which behaviour to perform. There were no differences between D-1 and D-2 antagonism in this respect. After sulpiride, no significant effects were observed. A specific behavioural prolife obtained by extinction was not mimicked by any of the doses of neuroleptics tested. It has previously been shown that performance per se of the two behavioural options used in the task can be reinstated by scopolamine after haloperidol attenuation. However, when these options had to be organized into functional sequences to reach a goal, haloperidol-induced attenuation could not be counteracted by scopolamine.