Summary
The ultrastructure of layers I and II of the motor cerebral cortex of rat brain has been studied at birth, 4, 7 and 14 days postnatal and in the adult.
Compared with the adult, neonatal rat motor cortex exhibited a large extracellular space which decreases with increasing age. At all stages studied the neurons were seen to contain the organelles usually found in adult neurons. Growth cones were present in decreasing numbers up to 14 days old.
Synapses were detectable at birth and there was an obvious increase in their number throughout the postnatal development. At the earliest stages studied there was a lack of specialization characteristic of the adult. Many synapses were either avesicular or relatively so and lacked the high degree of modification of adult pre- and postsynaptic membranes. By 7 days after birth many synapses existed which in all morphological respects resembled those of the adult, and by 14 days, the majority were of the adult type.
These findings, particularly with reference to the postnatal development of synapses, have been discussed in relation to the known electrophysiological findings.
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The authors wish to express their thanks to Mr. R. Birchenough and Mr. J. Manston for their technical assistance.
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Johnson, R., Armstrong-James, M. Morphology of superficial postnatal cerebral cortex with special reference to synapses. Z. Zellforsch. 110, 540–558 (1970). https://doi.org/10.1007/BF00330103
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DOI: https://doi.org/10.1007/BF00330103