RESPONSES TO ECOLOGICALLY RELEVANT STIMULI IN THE RAT FETUS - INTERACTIVE EFFECTS OF MILK AND AN ARTIFICIAL NIPPLE

Stimuli normally encountered during suckling after birth-the nipple an d milk-elicit behavioral responses from fat fetuses on E20. A series o f experiments demonstrated that milk, unlike other chemosensory stimul i, consistently evoked mouthing activity during the 15 s after present ation. Unlike other perioral tactile stimuli, an artificial nipple evo ked mouthing activity and an active oral grasping response during pres entation. Prior exposure to milk altered fetal responsiveness to some forms of perioral tactile stimulation, but did not affect grasping of the nipple. In contrast, prior exposure to an artificial nipple increa sed mouthing activity in response to milk. The nipple and milk exhibit a temporally asymmetric relationship in fetal rats, which lack experi ence with suckling stimuli. These findings suggest that responsiveness to ecologically relevant stimuli and their temporal presentation deve lops before birth, and may facilitate functional behavioral responses of the newborn during the first suckling episode. (C) 1993 John Wiley & Sons, Inc.