Dopamine D1 and D2 effects on fetal mouthing responses to milk

Rat fetuses exhibit prompt responses to an intraoral infusion of milk, including mouthing movements and an increase in motor activity. Two experiments examined the involvement of dopamine D1 and D2 receptors in mediating these fetal responses to milk. The D1 agonist SKF-38393 and the D2 antagonist sulpiride diminished fetal mouthing responses. Mouthing responses appeared normal in fetuses treated with the D2 agonist quinpirole or the D1 antagonist SCH-23390. These findings suggest that activity in the dopamine system may inhibit mouthing within 30 s of milk infusion.