Regional differences in the critical period neurodevelopment in the mouse: implications for neonatal seizures

The voltage-sensitive calcium channel probe 125I-omega-GVIA conotoxin has been shown to be a developmental marker in whole brain preparations of Swiss Webster mice. The present study looks more carefully at regional dissections of the mouse brain (cerebrum, cerebellum, and brain stem) at postnatal day 8 and postnatal day 16. 125I-omega-GVIA conotoxin binding, thought to be presynaptic, showed a dramatic increase between postnatal days 8 and 16 in the cerebral cortex, a decrease in the cerebellum, and no change in the brain stem. The dramatic cerebral cortex increases indicated by these binding data correspond to a critical period between postnatal day 11 and postnatal day 14 in Swiss Webster mice; during this critical period, dendrites exhibit rapid outgrowth, sensory modalities come on line, electroencephalographic patterns mature, and the cortex reaches adult proportions. This period parallels a similar initiation of electrical maturation in the 28- to 32-week neonatal human brain. We conclude from these data that the unusual clinical presentation of neonatal seizures is not just the result of immature myelin formation. It includes incomplete synapse formation linking the cortex to the brain stem.