0046 A Mechanism by Which Estradiol (E2) Regulates Adenosinergic Signaling in the Median Preoptic Nucleus (MnPO)

Abstract Introduction Women report more sleep difficulties than men, particularly during times of hormonal fluctuations. This indicates that sex hormones likely play a role in a woman’s sleep-wake cycle, but the mechanism by which they do so is largely unknown. We have previously shown that estradiol (E2) increases wake and decreases NREM sleep in female rats, and that E2 action in the median preoptic nucleus (MnPO), a major sleep center in the brain, is necessary and sufficient to induce wakefulness. Additionally, in the MnPO, E2 increases extracellular adenosine, which is known to induce NREM sleep via activation of the A2A adenosine receptor (A2AR). Our previous work demonstrated that an A2AR agonist infused in the MnPO is not able to mediate its pro-sleep effects in the presence of E2, and the current work investigates a mechanism for this finding. Our preliminary data shows that E2 upregulates the mRNA of an orphan receptor, GPR37, in the MnPO; GPR37 has been shown to form heteromers with A2AR and reduce the expression and function of A2AR in the striatum. We hypothesize that E2-induced upregulation of GPR37 leads to inhibition of A2AR in the MnPO, thus preventing its pro-sleep effects. Methods To examine mRNA and protein expression, ovariectomized female rats were treated with subcutaneous injections of E2 or oil for two days and sacrificed on the third day, where their brains were collected. To examine if GPR37 knockdown in the MnPO affects E2’s ability to induce wakefulness, a GPR37 shRNA virus or scramble virus control was injected into the MnPO of female rats; they were also ovariectomized and had telemeters implanted to measure sleep-wake states in the presence of oil and E2. Results We found that E2 increases GPR37 mRNA and protein expression while decreasing A2AR mRNA expression in the MnPO. Furthermore, we found that knockdown of GPR37 in the MnPO significantly attenuates the effects of E2 on wakefulness, NREM sleep, and REM sleep in the dark phase but not the light phase. Conclusion E2 appears to have an effect on the sleep/wake phenotype through adenosinergic signaling and expression in the MnPO through E2-induced upregulation of GPR37. Support (if any)