[Postnatal development of Rattus norvegicus B. cortical neurons and the influence of trauma]

The differentiation of the pyramid neurons during ontogenesis and the effects of a trauma on the process of neuron differentiation and synaptogenesis were investigated in the rat cerebral cortex after Golgi-impregnation. 1. There are temporal differences in the differentiation of the processes of cortical neurons. Axons differentiate earlier than dendrites, apical dendrites earlier than basal ones. 2. Varicosities in the processes of cortical neurons during the early postnatal period are regarded as a feature of growth processes. 3. The appearance of the dendritic spines is an important process in the ontogenetic and phylogenetic development of cortical neurons. 4. The different cortical layers show a different degree of differentiation during development. The deeper layers precede the upper layers in the process of differentiation. 5. Ingrowing afferents have an essential influence on the differentiation - especially on the differentiation of the dendritic postsynaptic structures. 6. The cortex of 6 month old rats shows no principle differences in comparison with 24 days old animals. It is concluded that the visible differentiation processes of cortical neurons are nearly finished 24 days post partum. 7. As an effect of the trauma a considerable loss of dendritic spines of layer III and V pyramid cells is found in addition to general degeneration features. 8. The following factors are thought to be responsible for the loss of spines: (i) transneuronal processes with spine degeneration and subsequent phagocytosis of the synaptosome. (ii) destruction of differentiation furthering afferents results in differentiation defects of the neuron with the failure of further postsynaptic differentiation (spines).