A critical maturation period in neonatal-rat-lens development

The transition of the immature lens to the mature lens was investigated in the Sprague-Dawley rat during the neonatal period which extends for 21 days after birth. The lens of the newborn rat consists of uniformly hydrated cortical and primary fiber cells while the mature lens is characterized by the presence of a nucleus which has a lower water content relative to the surrounding cortex. Our studies reveal that a critical maturation period occurs between days 12-16. In this investigation, the period is defined by the following physiological and anatomical alterations: A significant decline in the rate of lens wet weight growth occurs between days 12-16. However, the growth in dry weight is linear throughout the neonatal period. There is a significant decline in lens percentage water during this 12-16-day period. The loss in lens water is primarily from the intracellular compartment since the lens extracellular space is constant throughout the neonatal period. Lens anterior-posterior and equatorial dimensions exhibit a zero growth rate between days 14-16 and 12-14, respectively. The permeability of lens extracellular space declines significantly during the critical maturation period as determined by Procion Yellow, an extracellular marker. The significant decline in lens percentage water and the decline in the depth of penetration of Procion Yellow to the lens interior during the critical maturation period is related to the transition of an immature to a mature lens.