Estrous cycle and sex as regulating factors of baseline brain oxidative metabolism and behavior

The existence of sex differences in brain function is still today a controversial issue, and contradictory results are reported in the scientific literature. Part of this controversy would be solved by taken into consideration the rhythmic changes in the levels of circulating gonadal steroids during the menstrual or estrous cycle in females as compared to males. The aim of this study was to evaluate the changes in oxidative metabolism of limbic brain regions in male and female rats at two different stages of estral cycle (estrous and diestrous). Cytochrome oxidase activity was used as a reliable marker of neuronal oxidative metabolism. We found the highest levels of oxidative metabolism during the diestrous phase in several brain regions, when estrogen levels are high. Males displayed similar cytochrome oxidase activity as compared to females in estrous phase. Our results support behavioral and neurobiological studies reporting sex differences in rodents and humans.