Growth, neurobehavioral and circadian rhythm development in newborn baboons

We measured body temperature continuously using telemetry to determine the development of circadian rhythmicity in neonatal baboons after birth. Twelve fetal baboons (nine males and three females) of known gestational age ranging from 167 to 193 d were studied. We eliminated the influence of maternal factors by hand rearing these infants from the moment of birth until 45 d of life. All infants showed steady growth in body weight, head circumference, and crown-rump length. Neurobehavioral responses including visual and auditory orientation, motor maturity, irritability, and consolability increased as a function of age. Circadian rhythms of body temperature were present in the second week of life, and the amplitude of this rhythm increased throughout the developmental period studied. The increase in the amplitude of circadian body temperature rhythm independent of environmental time cues may indicate the maturation of the brain. These neonatal nonhuman primates offer an excellent model for studying neurobehavioral development and maturation of circadian rhythms while controlling external factors in a manner that is not possible with human neonates.