Effects induced by chronic treatment with selective D1 or D2 antagonists on open-field behavior and colonic...

We have studied the behavioral responses in open-field and the changes in body temperature induced after chronic treatment with a selective D1 antagonist, SCH 23390, a selective D2+ antagonist, sulpiride, or a non specific but preferential D2 antagonist, haloperidol. After chronic treatment with SCH 23390 or sulpiride, rats were challenged with SKF 38393, selective D1 agonist, or LY 171555, selective D2 agonist, in order to study the responses of D1 and D2 stimulation. After chronic SCH 23390, an increase of the locomotion and of the number of rears were observed whereas, no changes were induced by chronic sulpiride or haloperidol. Acute treatment with sulpiride blocked the hyperlocomotion induced by chronic SCH 23390. In naive rats acute administration of SKF 38393 or LY 171555 did not produce any change in locomotion or rearing. In rats treated chronically with SCH 23390 this acute administration of LY 171555 induced an increase of the number of squares and of the number of rears. In these animals, acute administration of SKF 38393 also augmented the number of squares crossed. In contrast, chronic sulpiride did not modify behavioral responses obtained after acute SKF 38393 or LY 171555. Colonic temperature was not changed after acute SKF 38393 while acute LY 171555 induced a hypothermia. Chronic sulpiride did not modify the responses of SKF 38393 or LY 171555, but an increase in body temperature was observed after acute SKF 38393 in animals chronically treated with SCH 23390. The present results support a different behavioral expression of D1 and D2 supersensitivity in rats. Furthermore, chronic treatment with a D1 antagonist induced facilitatory effects on D2 behavioral responses; however, these D1-D2 interactions were not observed in body temperature responses.