The growth of non-pyramidal neurons in the primary motor cortex of man: a Golgi study

In Golgi-Cox-impregnated motor cortex (regio precentralis) of six children (36 weeks of gestation to 13 month after birth) four types of interneurons of laminae II-VI have been investigated qualitatively and quantitatively and finally, compared with interneurons of a child (3 month of age) with Down's Syndrome. All cell measurements have been made by using a computerized digital morphometric system. In order to study the developmental stage of interneurons in our cases we statistically compared analogue neuron types in the brains. As parameters for characterizing non-pyramidal neurons served the pattern of dendritic branching, dendritic length for all dendritic orders within single dendritic fields, and of the whole neuron. The quantitative morphological study of dendritic arborizations revealed that bitufted and large multipolar interneurons had significantly more branching material in the postnatal brains than their prenatal counterparts. These differences were due to the increase of both length and number of branches during perinatal period. Such constant increment in dendritic span and branching provides larger receptive areas and that should improve the development of connections in functional intracortical columns. The quantitative parameter area of dendritic fields and number of branching points of the brain with Down's syndrome revealed in comparison with normal brain of the same age differences such as lower dendritic areas and a higher amount of branching points.