[Differentiation of neurons of the cingulate region in explant culture]

The structural changes in explant-cultures of the cingulate region from the brains of 18 day old rat embryos were investigated during several cultivation periods by neurohistological light microscopical methods. The differentiation and the growth of neurons were observed in cultures stained by the method of Klüver-Barrera, and cut perpendicular to the coverslips during the period from the 1st up to the 20th day in vitro. As parameters for the growth of the cells the density of neurons and glial cells per culture area were estimated and the diameters of nuclei and pericarya were measured at different stages of culture. The following results could be obtained. 1. The immature cells differentiated up to the 20th day in vitro to neurons that could be devided into three groups due to histological characteristics: pyramidal cells, multiform neurons and a group of small cells with few cytoplasm. 2. From the 1st to the 20th day in vitro the density of neurons and glial cells markedly decreased. The number of neurons per unit area decreased to 59.7% during this period. However, the most rapid decrease in the number of neurons occurred from the 10th to the 20th day in vitro. 3. The measurements of the diameters showed an increase in both the diameters of nucleus and pericarya from the 1st to the 20th day in vitro. The enlargement of the diameters is especially striking from the 1st up to the 10th day in vitro. The results are discussed in comparison results of ontogenetic investigations in vivo.