Thermal, olfactory, and tactile stimuli increase oral grasping of an artificial nipple by the newborn rat.

Caesarean-delivered rat pups tested before any suckling experience show oral grasp responses after stimulation with an artificial nipple. Manipulating the sensory stimuli present at the time of testing alters behavioral responses to the nipple. Specifically, when the nipple is warm, when pups are tested in the presence of amniotic fluid or milk odor, or when pups are tested in the presence of a conspecific, oral grasping of the artificial nipple is increased. Pups respond to the nipple with a shorter latency, show more oral grasp responses, and the individual grasp responses are longer in duration. The experiments suggest that the newborn rat pup exhibits a basic set of behaviors in response to the nipple early in development and that sensory stimuli normally present during the expression of suckling increase oral appetitive behaviors evoked by the nipple.