Jessica A. Mong, PhD

It is widely accepted that ovarian steroids play a significant role in maintaining normal sleep-wake patterns in both women and female rodents. What is not clearly understood are: (1) the mechanisms mediating ovarian steroid control of sleep; (2) whether sex differences exist in the sleep circuitry; and (3) the functional significance of ovarian steroid regulation of sleep.  To address these knowledge gaps, we use a multidisciplinary approach in a rat model that combines telemetric sleep electrophysiology, functional neuroanatomy, slice electrophysiology, in vivo optical imaging and transgenic mutants.  Below I summarize our significant advances in understanding estrogenic modulation of sleep-wake cycles, and current/future directions.

Mechanisms mediating ovarian steroid control of sleep

Sleep patterns in the female rat are exquisitely sensitive to natural fluctuations in ovarian steroids. My laboratory has consistently demonstrated that estradiol alone is sufficient to influence the pattern of sleep-wake cycles in female rats.  Together, with the fact that the rat brain is highly amenable to local manipulation of sleep-active nuclei, the female rat serves as an excellent model system to more directly test how estradiol modulates the sleep circuits to elicit changes in sleep behavior.

Our previous work suggested a role for the ventrolateral preoptic area (VLPO), a sleep-promoting nucleus, in mediating estradiol regulation of sleep. In females, estradiol (i) decreases the activation of sleep-active VLPO neurons and (ii) reduces protein levels of lipocalin-type prostaglandin D synthase (L-PGDS), the enzyme responsible for production of prostaglandin D2, a potent somnogen. In contrast, we found that fluctuations in testosterone in males do not influence the activation states of sleep-active neurons or L-PGDS protein levels in the VLPO.  These finding led us to hypothesize that estrogenic modulation of sleep behavior in females is due to the activational effects of estradiol on developmentally organized sleep circuits. As heuristic comparisons of biological processes between the sexeshave the potential to reveal novel mechanisms, we used a sex-based comparison to further elucidate mechanisms of estrogenic regulation of sleep.  In work supported by grants from the National Heart Lung and Blood Institute (R01) and the National Institute on Aging (awarded to my graduate student, Danielle Cusmano), we found that sex differences in sleep are in part due to different sensitivities to sex steroids.  In contrast to females, sleep patterns in males are insensitive to changes in both estradiol and testosterone.  Moreover, this sex difference in the sensitivity of sleep behavior to sex steroids is established by developmental programming effects of sex steroids. Female rats exposed to a masculinizing dose of testosterone during the sensitive window for brain sexual differentiation exhibit male-like lack of sensitivity of sleep behavior to estradiol and testosterone in adulthood. Additionally, activity of sleep-active neurons in the VLPO exhibited male-like patterns in masculinized females illustrating for the first time that a key nucleus involved in the initiation and maintenance of sleep is sensitive to the organizing effects of sex steroids.

Building on our findings that estradiol influences activation of sleep active neurons in the VLPO, we investigated whether the VLPO is necessary for estrogenic regulation of sleep. Through a series of pharmacological and neuroanatomical studies, we discovered that the median preoptic nucleus (MnPN), another well-established sleep-promoting nucleus, and not the VLPO is a direct mediator of estradiol actions on sleep (manuscript in submission).  Our discovery that the MnPN plays a central role in the estrogenic modulation of sleep is the first demonstration of how estradiol influences sleep circuitry.  We recently obtained a grant supported by National Heart Lung and Blood Institute (R01) to examine the cellular mechanisms through which estradiol regulates activity of the MnPN sleep active neurons and their downstream targets.  This work is employing an integrative approach that includes novel lesion techniques, optogenetics, and slice electrophysiology to investigate the MnPN as a nexus for the neuroendocrine control of sleep in females. Our findings thus far represent significant advances in our understanding of how estrogens modulate the sleep circuitry and have been presented as invited talks at several recent annual meetings including, SLEEP (2015), Organization for the Study of Sex Differences (2015), and Society for Behavioral Neuroendocrinology (2016).

Sex differences in the estrogenic regulation of the sleep circuitry

Recently, we were awarded an administrative supplement from the NIH Office of Research on Women’s Health (ORWH) to study whether sex differences exist in the neuronal excitability of preoptic area sleep-active neurons.  More specifically, we will address the questions of whether locally-synthesized estradiol in the preoptic area of males is required for baseline patterns of sleep behavior.  In collaboration with Dr. Brian Mathur, an assistant professor in the Department of Pharmacology at the University of Maryland, we will use the highly sensitive optical technique of TCSPC (Time-Correlated Single-Photon Counting)-based fiber photometry; TCSPC will allow direct, precisely quantifiable in vivo assessment of sleep-active neuronal firing in males and females in real-time. This technique represents a novel approach to studying the sleep circuits. The rich pool of data that will be derived from these experiments will lay the foundation for our future work that will further elucidate the cellular and molecular mechanisms mediating estrogenic actions on sleep/wake behavior.

Functional significance of estrogenic regulation of sleep

Another focus of my research program is understanding whether there is a functional significance to estrogenic regulation of sleep.  In women, fluctuations in sex steroids have been implicated as risk factors for sleep disruptions and insomnia. However, the precipitous loss of estrogens as a result of menopause is also highly associated with a significant rise in sleep disruptions and insomnia.   Answers to this seemingly paradoxical effect of ovarian steroids are hindered by our lack of understanding of the relationship between ovarian steroids and normal sleep. Using our rodent model, we have made some progress toward a better understanding.  We have found that the effects of estrogens on sleep appear to be chronotype dependent, such that estradiol consolidates sleep/wake behaviors to the appropriate circadian phase. Estradiol increases the duration and quality of sleep in the light phase. In further support of estradiol enhancing sleep quality, findings from sleep deprivations studies suggest that estradiol facilitates light phase sleep recovery. In a species more closely related to humans, the marmoset, we have recently published that estradiol improves sleep quality.  These data have formed the basis of a multi-investigator R21 grant, in collaboration with researchers at the University of Massachusetts-Amherst, to establish the marmoset as a non-human primate model of menopause. The grant was recently scored in the 15^th percentile.   My role will be investigating the mechanisms governing estrogenic regulation of sleep in the marmoset. This marmoset model has the potential to provide a bridge between our findings in rodents and development of new treatments for sleep disruptions in menopausal women.  

Mechanism underlying female sexual motivation

Also related to women’s health is my research project, funded by an R01 from the National Institute on Drug Addiction, that seeks to understand how methamphetamine works on the neural circuitry to increase female sexual motivation. Methamphetamine is a psychomotor stimulant strongly associated with increases in sexual drive and impulse in both men and women. These changes in sexual motivation have a greater impact on women due to their likelihood of facing the greater burden of unplanned pregnancies, as well as increased risk for psychiatric co-morbidities with drug use, such as depression. The overarching goals of this project are to investigate the nexus between ovarian steroids, sexual motivation/arousal and reward pathways. We established a rodent model of methamphetamine-facilitated increases in sexual motivation. Our work has led to several novel findings that have advanced our understanding of mechanisms driving female sexual motivation as well as novel mechanisms underlying methamphetamine’s actions on these neural circuits. Most notably, we identified the posterodorsal medial amygdala (MePD) as a key nexus for the drug-steroid interaction.  Within MePD, methamphetamine exposure activates signaling via the dopamine receptor 1 subtype that is necessary and sufficient for augmenting female sexual motivation (as indicated by proceptive/solicitation behaviors).  This augmentation also requires activation of progesterone receptors in MePD. Our more recent findings suggest that methamphetamine increases expression of progesterone receptors in MePD, suggesting a novel feed-forward mechanism that enhances progesterone signaling.  Although this work on amphetamines and sexual motivation is extremely exciting, our studies of sex differences in sleep have now expanded substantially, particularly with the development of the primate model.  To ensure I have adequate time to devote to the sleep projects, I am suspending the methamphetamine-sexual behavior studies for the present. 

Standing member and Co-Chair, SWHR, Interdisciplinary research network for the Studies in Sex-Differences in Sleep Health

“Mechanisms Governing the Estrogenic Modulation of Sleep”  NIH/NHLBI,  R01 HL129138  

T32 NS4074 Training Program in Integrative Neuroscience