Facial wiping in the rat fetus: variation of chemosensory stimulus parameters

Fetal rats reliably express a facial wiping response to novel chemosensory stimuli. Previous research has examined facial wiping as an early form of motor coordination and as a behavioral indicator of sensory responsiveness. The present study examined how variation in stimulus parameters of lemon odor infusion (concentration, volume, and infusion time) affected the wiping response of E20 rat fetuses. Infusions of higher concentration or greater volume generally elicited wiping responses of greater duration and more strokes. Most facial wipes involved strokes by single forelimbs; however, bilaterally synchronous wiping was expressed only in bouts of at least seven wipes, and was facilitated by stimuli of moderate intensity. These findings suggest that the total number of wiping strokes or bout duration are well suited as measures of overall sensory responsiveness in the fetus and that chemosensory stimulus parameters exert a permissive influence on interlimb coordination during a bout of facial wiping.