012 - Sex differences in hippocampal neurosteroids following neonatal HI

Publication Number: 12.6984

Nur Aycan, University of Wisconsin, Madison, WI, United States; Teresita de Jesus Valdes Arciniega, University of Wisconsin Madison, Madison, WI, United States; Ela Bicki, State University of New York Downstate Medical Center College of Medicine, Brooklyn, NY, United States; Feyza Cetin, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States; Sefer Yapici, University of Wisconsin-Madison, Madison, WI, United States; Peter Ferrazzano, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States; Pelin Cengiz, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States

Background: Neonatal hypoxia-ischemia (HI) adversely affects ~20,000 US newborns annually, leading to death and lifelong disabilities. Clinical and experimental studies described that male infants experience more severe cognitive, language, and learning/memory deficits post-HI than girls. However, the female-specific neuroprotective mechanisms underlying these sex differences remain poorly understood. The brain synthesizes and metabolizes steroids that contribute to sexual differentiation and regulation of neural processes. Locally produced sex steroids play a critical role in brain function after injury. Neural aromatase activity and estradiol (E2) production are linked to neurogenesis, synaptic plasticity, neurotransmission, and memory. Brain-derived E2 mediates neuroprotection, while neonatal testosterone (T) may worsen HI-induced brain injury.

Objective: We hypothesized that the sex differences in HI outcomes are due to altered hippocampal neurosteroids.

Design/Methods: Here, we investigated male and female neonatal hippocampal neurosteroid contents 2 times after inducing HI at postnatal (P) day 9 in C57BL/6J mice (adrenals and gonads intact) using Vannucci’s HI model. Ipsilateral hippocampi (n=1 pooled from 2 mice hippocampi) and blood samples were harvested on days 1 (P10) and 3 (P12) post-HI. LCMS/MS determined E2, T, progesterone (P4), and corticosterone (CORT) hippocampal contents. Hippocampal hormone data (except T) were winsorized. E2 and P4 contents were log-transformed. Data were analyzed by multifactorial ANOVA (condition×day×sex; n=6-9).

Results: Hippocampal neurosteroid contents were not dependent on circulating sex hormones in sham and HI mice. Plasma steroid levels at P12 did not significantly differ between experimental groups but were lower than hippocampal levels. P10 serum analysis is pending. Male hippocampal T content was higher (P=0.01) at P12 (sham, 1852±570; HI, 2455± 425 pg/g) compared to P10 (sham, 409±115; HI, 186±61 pg/g). HI-females exhibited lower T levels at P12 than HI-males (P=0.01). Male hippocampal P4 content was higher (P=0.007) at P12 [3 ±0.13 log(pg/g)] vs. P10 [2 ±0.17 log(pg/g)] post-HI. Male hippocampal CORT content at P12 was higher (P=0.004) in HI vs. sham mice. Interestingly, CORT content at d3 post-HI was lower (P=0.05) in females than males, showing sex-specific differences after HI.

Conclusion(s): Hippocampal neurosteroid levels were not dependent on circulating sex hormones. Sex-specific differences in hippocampal T and CORT levels may result in sexually differential long-term outcomes post-HI. Further studies are needed to determine the role of neurosteroids post-HI.