Age-dependent changes in the oxygen consumption of the cerebral cortex, hypothalamus, hippocampus, and amygdaloid in rats.

The oxygen consumption of the cerebral cortex, hypothalamus, hippocampus, and amygdala, of both sexes, ranging in age from 21-805 days for male rats and from 21-780 days for the estrus and diestrus female rats, was measured. The oxidative activity of the hypothalamus, hippocampus, and amygdala decreased rapidly from Day 21 until the 4th mo. and stabilized till the 27th mo. in the hippocampus and amygdala and gradually decreased from the 12th mo. to the 27th mo. in the hypothalamus. The cerebral cortex showed a different pattern which kept a constant level from day 21 to 12 mo. of age. There was no statistically significant change in any of the regions at the time of vaginal opening. Low oxidative activity of the hypothalamus and amygdala in old age was still observed in castrated/hypophysectomized male rats compared with young ones. Therefore, the decreased oxygen consumption in old age seems to be due primarily to changes in the brain tissue itself and not due secondarily to changes in the gonadotropin and sex hormone levels. Female rats had higher oxygen consumption values than males in the cerebral cortex, the hypothalamus, and the hippocampus. In the amygdala the males had a higher consumption. Estrus female rats showed significantly higher oxygen consumption than diestrus females only in the hypothalamus.