Cell Kinetic Studies of Chick Brain Cells In Culture: an Autoradiographic Study With [3H]- and [14C]-Thymidine

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Abstract
Labeling index, S-phase duration and cell-cycle time of proliferating brain cells from 6-day-old chick embryos in culture were investigated autoradiographically after labeling with [3H]- and/or [14C]-thymidine. The dissociated cells were cultured in the absence or in the presence of brain extract from 8-day-old chick embryos. Cultures contained essentially 2 cell types, which could be easily distinguished by the size of their nuclei: small nuclei identified as belonging to precursor cells of neurons and large nuclei corresponding to astroglial cells. The labeling index of astroglial cells (16.4%) was about 2 times higher than that of the neuronal cells (9.9%). Under the influence of brain extract the labelling index of neuroblasts was nearly doubled while that of the astroglial cells remained nearly unchanged. From double-labeling experiments with [3H]- and [14C]-thymidine, the same S-phase duration of about 7 h was found for both cell types cultured with or without brain extract. A cell-cycle duration of 39 h for neuronal and of 29 h for astroglial cells was found. The cycle times remained constant under the influence of brain extract. From the measured data mentioned above, a growth fraction of 50% (neuroblasts) and 68% (astroglial cells) was calculated in control cultures without brain extract. After addition of brain extract, the growth fraction increased for both cell types (neuroblasts: 92%; astroglial cells: 80%). More cells proliferate in the presence of brain extract, but the durations of the S-phase and the cell cycle remain unchanged.