Ontogeny of thymidine kinase and DNA in the hypothalamus and cerebral cortex of the rat: effects of neonatal estrogen.

Developmental patterns of activity for thymidine kinase and DNA content were determined for the hypothalamus and cerebral cortex of the female rat during the first 3 postnatal weeks. The DNA content and thymidine kinase activity for both brain structures were maximal at ages 1 and 3 days, respectively. Total DNA content for the hypothalamus significantly increased 21% between ages 1 and 21 days. Administration of 17 beta-estradiol benzoate (EB) during the sexually critical period of brain differentiation had no effect on thymidine kinase in either brain structure. However, a transient and highly significant decrease in DNA content occurred in the hypothalamus of the 2-day-old EB-treated rat. These data indicate that (a) DNA synthesis occurs in the postnatal hypothalamus, (b) DNA synthesis in the hypothalamus and cortex is not tightly coupled to the activity of thymidine kinase and, (c) the EB-induced decrease in hypothalamic DNA is not related to changes in thymidine kinase.