Developmental changes in the mongrel canine brain during postnatal life

Normal values for changes in brain growth, chemical composition and morphologic features of the mongrel dog between birth and maturity were established in studies of 43 puppies between birth and 6 months of age and 3 adult dogs. Brain weight in puppies increased as the sodium, potassium and chloride contents of brain decreased between birth and 60 days; values similar to the adult were observed in puppies at 3 to 6 months of age. The concentrations of sodium and chloride decreased while the concentration of potassium increased in brain water between birth and 60 days, but the sum of sodium, potassium and chloride concentrations in brain water, an index of brain osmolality, did not change during postnatal development. Total protein (mg/g dry brain) did not change, but DNA (mg/g dry brain) decreased with age; ratios of total protein:DNA increased from birth and were maximal at 90 days. Morphologic changes in the canine brain were characterized by an extensive, densely cellular subependymal germinal zone at birth which, although diminished and focally discontinuous, was present at 30 days and had disappeared by 60 days of age. The gross appearance and histologic changes observed in the mongrel canine brain observed between 1 and 60 days of age are similar to changes described for the human brain between 28 and 40 weeks gestation. We conclude that the mongrel canine brain is a suitable model for studying mechanisms of injury to the neonatal human brain.