Chapter 9 268 neurotransmitters. Treatment with estrogen and testosterone can change the serotonin receptor distribution in the raphe nuclei (Bethea et al., 2002; Sumner & Fink, 1995), which could change the duration of REM sleep, NREM sleep, and wakefulness (Monti & Jantos, 2006; Popa et al., 2005). Estradiol can also affect the locus coeruleus (Deurveilher et al., 2008), which can enhance norepinephrine activity and affecting wakefulness (Liang et al., 2021). Dopaminergic activity in the ventral tegmental area shows changes along the estrous cycle in rodents (Vandegrift et al., 2017), which can contribute to increased arousal in certain stages of the estrous cycle (EbanRothschild et al., 2016). Lastly, estradiol and testosterone can also affect the orexinergic neurons in the hypothalamus, which could affect wakefulness, although these effects seem to be sex-specific (Silveyra et al., 2009). An illustration of these mechanisms is provided in Figure 9.3. Figure 9.3. Illustration of sleep- and wake-regulating neural mechanisms that could be affected by sex hormones. For full review, see Dorsey et al., 2021. Created using Biorender.com. 2.4. Sex hormones, depression and sleep Studies on depression commonly find associations between depression and sleep. Poor sleep, insomnia, short SWS and late chronotype have all been found to be risk factors for (chronic) depression (Chan et al., 2014; Li et al.,
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