Behavioral effects of milk in the rat fetus.

Intraoral infusion of milk to the rat fetus promoted changes in behavior (mouth and rearlimb movements), reduced responsiveness to perioral cutaneous stimulation, and resulted in expression of a fetal stretch response. Milk also altered the temporal organization of fetal movements over periods up to 30 min. The orosensory characteristics of milk, in the absence of ingestion, was sufficient to evoke these behavioral effects. Reduced responsiveness to a perioral stimulus had a rapid onset (< 30 s) and brief duration (< 5 min). The ability to disrupt changes in motor organization and the stretch response with an intervening stimulus also exhibited a time course after milk infusion. The findings that tactile stimulation and biomechanical manipulations of fetal movement promote rearlimb activity and facilitate expression of the stretch are consistent with a dynamic perspective of early motor development in the fetus.