On the DNA content of cerebellar Purkinje cells in vivo and in vitro

Abstract

Newborn rats were administered 3H-thymidine, 3H-thymine, 3H-adenine, or 3H-cytidine every 6–8 hr. from neonatal day four to day ten. Utilizing autoradiography, cerebellar Purkinje cells showed little or no nuclear label with 3H-thymidine or 3H-cytidine, although other cells known to divice postnatally (e.g., granule and glial cells) did incorporate these precursors into DNA. The few nuclear grains seen over Purkinje cells with 3H-cytidine were not seen if the fixed tissue was first digested with RNAase. 3H-thymine and 3H-adenine were not incorporated into any cerebellar cells including Purkinje cells in vivo despite the administration of equivalent or higher doses of these isotopes. Purkinje cells had undergone their major morphological maturation during the period of isotope exposure. Organotypic explants of newborn rat cerebellum also failed to display uptake of 3H-thymidine in Purkinje cells during continuous exposures for the first 18 days in vitro. 3H-thymine showed no clearcut labelling of Purkinje cells when cultures were labelled for the first 13 days in vitro; this in vitro method excluded the possibility that 3H-thymine had not been taken up in vivo because of permeability factors or excessive metabolism by other organs. The above results do not support the notion of development of early Purkinje cell “tetraploidy” obtained by Feulgen microdensitometry.