Regressional changes of human cerebellar cortex and hypoglossal nucleus during development

In the development of nervous system, two processes are of a particular interest. It is well known that after a primary migration of cells, there appears a consecutive regression in cellular number, closely connected with the maturation of the nervous system. The dynamics of this reduction was investigated following the changes in number of cells in nucleus hypoglossus as well as that of Purkinje cells in two structures of cerebellar cortex--in vermis and in hemispheres. Cell nuclei were counted using the stereological technique, after a usual preparation. Data were collected from 20 human brains of different gestation age, i.e. at 12.5, 14, 17.5, 19.5, 24, 31, weeks of gestation and 6 day old newborn. After the graphical and numerical analysis of the data obtained, an adequate mathematical model was proposed. It is confirmed that a close agreement between biological data and decreasing two-exponential equation can be demonstrated, pointing out that the cellular reduction shows a proportional relation. The possible explanation could be that only the cells forming proper and useful connections and entering the informational system have a privilege to survive, and that all improper contacts lead to the rejection of cells or even of groups of cells.