KNDy innervation of MCH neurons modulates sleep in an estradiol-dependent manner
Authors: Beekly Bethany , Furman Katherine , Burgess Christian , Elias Carol 
Published: May 2023

Levels of circulating gonadal hormones, including estrogens, affect both subjective and objective measures of sleep quality. However, the mechanisms linking sex variables to sleep architecture are incompletely understood. One brain region known to be potently regulated by circulating levels of estradiol is the arcuate nucleus of the hypothalamus (ARH). In particular, ARH neurons containing the trio of neuropeptides kisspeptin, neurokinin B (NKB), and dynorphin (“KNDy neurons”) express ERα and are well-known to respond to estradiol. We sought to determine whether ARH KNDy neurons are implicated in estrogenic effects on sleep.Melanin-concentrating hormone (MCH) neurons of the lateral hypothalamus are established regulators of sleep. A subset of MCH neurons also express the NKB receptor, NK3R, and are innervated by NKB immunoreactive fibers. Thus, we hypothesized that ARH KNDy neurons modulate sleep architecture in an estradiol-dependent manner via NKB signaling to NK3R-expressing MCH neurons. To test this hypothesis, we employed optogenetic stimulation in the LHA of female Kiss1-Cre;ChR2-eYFP transgenic mice, which express channelrhodopsin in kisspeptin-expressing neurons, to activate KNDy neuron terminals apposing MCH-expressing cells.We recorded sleep via electroencephalogram (EEG) with and without optogenetic stimulation in a randomized-crossover design. Adult ovariectomized female mice with and without estradiol replacement were used (“OVX and OVX+E2 mice”). Each mouse was recorded under both conditions to minimize the effects of individual variation, with the first condition (i.e., with vs without estradiol implant) randomly assigned. EEG data were first evaluated using a semiautomated scoring algorithm and then manually checked. These steps were performed by at least two different researchers to ensure accurate, reproducible scoring.During the light phase, when sleep pressure is highest for mice, stimulation of KNDy terminals in the LHA caused OVX females to spend more time awake, primarily at the expense of rapid-eye movement (REM) sleep. Conversely, OVX+E2 females exhibited reduced wakefulness when KNDy neuron terminals were stimulated. This corresponded to increases to both REM and non-REM sleep. During the dark phase, the reverse phenotype was observed. Optogenetic stimulation caused OVX females to spend less time awake and more time in both REM and non-REM sleep during the dark phase, while it resulted in OVX+E2 females spending more time awake at the expense of both REM and non-REM sleep. Taken together, these data suggest that the activation of KNDy neuron terminals in the LHA affects sleep in manner determined by both circulating estrogens and circadian rhythms. (NIH) Grants R01HD069702, R01HD096324; T32HD079342, F31HD102160; 1R01DK129366-01, the Michigan Diabetes Research Center Pilot and Feasibility Award, and the Whitehall Foundation New Investigator Grant #2018-08-50 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.