Effects of neonatal estrogenization on thymidine kinase activity and DNA content in the cerebellum of the rat.

Abstract

Cerebellar thymidine kinase activity and DNA content were determined following the administration of 17 beta-estradiol benzoate (EB) to neonatal rats during the sexually critical period of brain development. Male and female littermates were injected s.c. 24 and 72 h after birth with either 500 microgram EB or vehicle. At 3, 4, 6, 7, 8, 10, 12 and 15 days of age cerebellar thymidine kinase activity and DNA content were measured. A sexual dimorphism in thymidine kinase activity occurred in control rats between 6 and 15 days of age, i.e., enzyme activity was significantly higher in the cerebellum of the female rats. Thymidine kinase activity in both male and female EB-treated rats was (1) significantly greater than that of their littermate controls at 3 and 4 days of age, (2) the same as that for their controls at 6 days of age, (3) significantly lower than control levels between 7 and 12 days of age and, (4) the same as their controls by day 15. Alterations in cerebellar DNA content were similar to those described for the enzyme. These data demonstrate the occurrence of age-dependent estrogen-induced relationship(s) between thymidine kinase activity and DNA synthesis in the cerebellum of the rat during early postnatal development.