Lidocaine induced heart block in patients with bundle branch block

The proliferation of glial cells outside the subependymal layer of the lateral ventricle as well as of endothelial cells was studied autoradiographically in the brain of the adult and untreated mouse. The double labeling method with ³H and ¹⁴C thymidine was applied in order to show experimentally the existence of a DNA synthesis phase (S phase) and to measure its duration. Adult mice received a first injection of ¹⁴C thymidine, 2 or 4 hr later a second injection of ³H thymidine and were sacrificed 1 hr after the last injection by perfusion fixation. Double layer autoradiographs were made from serial sections of the region from the corpus callosum/commissura anterior up to the corpus callosum/commissura fornicis ventralis in order to register purely ³H, doubly ³H and ¹⁴C, and purely ¹⁴C labeled nuclei. From the ratio of all ³H labeled cells with and without ¹⁴C to the purely ³H labeled cells a DNA synthesis phase of 9.4±0.5 hr for glial cells and one of 11.0±2.2 hr for endothelial cells was obtained. Based on the first appearance of labeled mitoses and labeled pairs of glial cells after injections of labeled thymidine the G₂ phase was estimated to be < 3 hr and G₂ + M about 5 hr. The duration of the measured S phase as well as the appearance of labeled mitoses about 3 hr after application of labeled thymidine are very similar to these cycle parameters in many other somatic cells in different kinds of animals. This has led to the conclusion that a well defined DNA synthesis phase with doubling of the DNA content and a successive mitosis also exists in glial and endothelial cells of the adult mouse brain.