Asymmetrical development of the dopamine system in the fetal rat as indicated by lateralized administration of SKF-38393 and SCH-23390.

The dopamine D1 agonist SKF-38393 and the D1 antagonist SCH-23390 were administered into the left or right cerebral hemisphere of the rat fetus on E21 of gestation. Intrahemispheric (IH) injection of the agonist promoted a large-magnitude increase in fetal motor behavior, which involved movements of the head, limbs, and body trunk. Although no lateral asymmetries were evident in left or right injections of the agonist, IH injection of the antagonist into the fetus's left hemisphere produced more pronounced effects on oral behavior, including mouth, lick, and facial wipe movements. Administration of SCH-23390 into the same hemisphere as SKF-38393 was effective in reversing the behavioral effects of the agonist, with left IH injections showing more immediate and complete blockade of agonist-induced behavioral activation. These data provide evidence for functional asymmetries in D1 receptors of the dopamine system in the term rat fetus.