The prenatal development of the tectum mesencephali and substantia nigra in man

: The development of tectum of the midbrain was studied in situ in human 6-11 wks embryos. Using electron microscopy and immunocytochemistry processes that occur in the anlage of tectum of the midbrain at early stages of formation of dopaminergic populations of cells were followed up. Growth of pallium zone due to migration of cells from ventricular zone and their differentiation is proportional to growth of the terms of embryonal development. Proliferating cells were located not only in ventricular zone. Expression of tyrosine hydroxylase was found in 6.5 wks embryos in the fraction of cells that migrated from ventricular zone and was observed only during neuroblast migration. Cells migrate along the radial glia fibres in dorsoventral direction. Microgliocytes with short processes near to vessels located in the vicinity of ventricular zone were found in 7 wks embryos for the first time. Peculiarities of morphogenetic processes participating in anlage of tectum of the midbrain and possible role of microgliocytes in development of embryonal nerve tissue are discussed.