ASYMMETRICAL DEVELOPMENT OF THE DOPAMINE SYSTEM IN THE FETAL-RAT AS INDICATED BY LATERALIZED ADMINISTRATION OF SKF-38393 AND SCH-23390

The dopamine D-1 agonist SKF-38393 and the D-1 antagonist SCH-23390 we re administered into the left or right cerebral hemisphere of the rat fetus on E21 of gestation. Intrahemispheric (IH) injection of the agon ist promoted a large-magnitude increase in fetal motor behavior, which involved movements of the head, limbs, and body trunk. Although no la teral asymmetries were evident in left or right injections of the agon ist, IH injection of the antagonist into the fetus's left hemisphere p roduced more pronounced effects on oral behavior, including mouth, lic k, and facial wipe movements. Administration of SCH-23390 into the sam e hemisphere as SKF-38393 was effective in reversing the behavioral ef fects of the agonist, with left IH injections showing more immediate a nd complete blockade of agonist-induced behavioral activation. These d ata provide evidence for functional asymmetries in D-1 receptors of th e dopamine system in the term rat fetus.