Changes in protein content of developing brain synaptic membranes, mitochondria and myelin.

The development of myelin, synaptosomal plasma membranes (SPM) and mitochondria in neonatal rat cortex has been followed by examining the electrophoretic profiles of protein in brain subcellular fractions. The appearance of the myelin proteins parallels the time course of myelination and confirms previous reports of the order of appearance of the proteins. Few changes occur in mitochondria during the developmental period. Plasma membranes in the SPM fraction show a progressive change from an ante-synaptogenesis profile to that characteristic of adult SPM. Tubulin, which is the major synaptic junctional protein, reaches its adult level in the developing SPM earlier than other SPM proteins, indicating that it may be involved in establishing the basic framework of the junction.