[Effect of cortisol on the cellular proliferation and maturation in the cerebrum and the cerebellum of the rat: Importance of the age of the animals at the beginning of treatment].

Young rats were given either a single subcutaneous injection (1 mg at 0, 1, 4 or 8 days), or four consecutive daily injections (0.2 mg/day between 0 and 3 days; 0.4 mg/day between 4 and 7 days; 0.6 mg/day between 8 and 11 days) of cortisol acetate in order to test the influence of age on the action of corticosteroids on the biochemical maturation of the cerebrum and cerebellum in terms of their DNA, RNA, and protein contents. The results showed that: 1 The diminution of the DNA content at 35 days was greater in the cerebellum (- 16 to - 32%) than in the cerebrum (- 9 to 20%); the DNA content of the cerebrum was more affected by treatment at birth, whereas that of the cerebellum was more affected by the delayed treatments. Results were different when expressed in terms of reduction of the normal increase: the gain of DNA decreased more in the cerebrum (-70%) than in the cerebellum (-40%); but the most delayed treatment induced a greater effect in both organs. These abnormalities were not always accompanied by a significant decrease of the body weight. 2 Generally, the treatments led to an increase of the mean cell territory, expressed either in terms of decrease of the DNA concentration, or in terms of increase of the organ weight/DNA ratio. Moreover, the increase of the RNA/DNA and the protein/DNA ratios constituted an indication of an accelerated cellular maturation.