Developmental processes are activated and shaped by stimulation. Sources of stimulation, or experience, can be found within the developing organism's habitat. We have identified and quantified biological stimuli that are normally present in the prenatal and natal habitats of the Norway rat (Rattus norvegicus). Maternal behavior and physiology provide abundant tactile, vestibular and thermal stimulation to fetal and newborn mammals. During gestation, the mother's locomotion and self-grooming stimulate fetuses in utero. During labor, uterine contractions compress and accelerate fetuses. During birth, pups are exposed to prolonged cooling, and to additional stimulation associated with the mother's licking and retrieving. Maternally-derived stimuli are detected by perinatal rats, as evidenced by behavioral and autonomic responses. Maternally-derived stimuli make important contributions to postpartum adaptation of the neonate, by facilitating breathing at birth and the onset of suckling. Arousal appears to play an important role in the developmental emergence of these milestone events. In the current application, we propose studies of behavioral and physiological arousal in newborn rats. Motor activity, heart rate, metabolic activity, respiratory frequency, and ultrasonic vocalizations, will be measured during the postpartum period. Circulating catecholamines (norepinephrine, epinephrine and dopamine) will also be measured. Tests of nipple attachment will be performed to relate behavioral and physiological variables to neonatal behavioral function. This series of investigations will lead to improved understanding of the relations between behavioral/physiological variables, neonatal arousal and prenatal learning. These studies will address important issues regarding the transition from prenatal to postnatal life. Studies of early development can provide a framework for interpreting and integrating new data, and can help direct future investigations in basic science and in applied science.