Rodent brain growth stages: an analytical review.

Study of data in the literature on rat and mouse brain growth from birth to weaning reveals a stagewise growth in average brain weight. Rapid growth occurs in the intervals between days 0-6, 8-12, and 17-23 after birth. Slow growth periods then lie in the intervals 6-8, 12-17, and after 23 days. The first slow growth period is signalled by events occurring at its end: substantial acceleration of synthesis of RNA, DNA, protein, and myelin. The second slow growth period is characterized by at least a 3-day interval during which there is very little increase in average brain weight compared with what occurs just before and just after that period; the correlation among 12 studies is highly significant. Implications are discussed for cross-species' extrapolation of findings about brain development.