Sex differences in spatiotemporal expression of AR, ERα, and ERβ mRNA in the perinatal mouse brain

•Testosterone levels in the brain transiently increased around birth in male mice.•There were sex differences of steroid receptor mRNA levels in perinatal mouse brain.•Androgen receptor mRNA levels in the hypo and PFC were higher in males around birth.•ERα mRNA levels in the hypo and hippocampus were higher in males before birth.•ERβ mRNA levels in the PFC were higher in females immediately after birth. It has been shown that every masculinized function might be organized by a particular contribution of androgens vs. estrogens in a critical time window. Here, we aimed to investigate the sex differences in brain testosterone levels and in the spatiotemporal dynamics of steroid receptor mRNA expression in perinatal mice, by using enzyme immunoassay and real-time PCR, respectively. We found that testosterone levels in the forebrain transiently increased around birth in male mice. During the perinatal period, levels of androgen receptor mRNA in the hypothalamus (hypo) and prefrontal cortex (PFC) were higher in male mice than in female mice. Estrogen receptor α (ERα) mRNA levels in the hypo and hippocampus were higher in male mice than in female mice before birth. In contrast, ERβ mRNA expression in the PFC was higher in female mice immediately after birth. These spatiotemporal sex differences in steroid receptor expression might contribute to organizing sex differences of not only reproductive function, but also anxiety, stress responses, and cognition in mice.