York, A. K. | bioRxiv Science

bioRxiv2024

Regulation of REM Sleep Onset and Homeostasis by Preoptic Glutamatergic Neurons

The preoptic area of the hypothalamus is key for the control of sleep onset and sleep homeostasis. Although traditionally considered exclusively somnogenic, recent studies identified a group of preoptic glutamatergic neurons that promote wakefulness. Specifically, our previous investigations demonstrated that chemogenetic stimulation of glutamatergic neurons within the medial-lateral preoptic area (MLPO_VGLUT2) promotes wakefulness, fragments non-rapid eye movement sleep (NREMs), and suppresses REM sleep (REMs). This evidence is further supported by recent work showing that preoptic glutamatergic neurons are activated during microarousals that fragment sleep in response to stress, and optogenetic stimulation of these neurons promotes microarousals and wakefulness. Thus, while the wake-promoting function of MLPO_VGLUT2 is clear, their role in sleep homeostasis has not been assessed. We tested the hypothesis that MLPO_VGLUT2 are wake-active, and their activation will increase wakefulness and disrupt sleep homeostasis via projections to arousal-promoting systems. Using fiber photometry, we found that MLPO_VGLUT2 were highly active during REMs, wakefulness and brief arousals, and remained minimally active during NREMs. Chemogenetic stimulation of MLPO_VGLUT2 inhibited REMs onset and suppressed the REMs homeostatic response after total sleep deprivation. Chemogenetic inhibition of MLPO_VGLUT2 increased REMs time (during the light phase only) but did not influence REMs and NREMs homeostasis. Anterograde projection mapping revealed that MLPO_VGLUT2 innervate central regions that promote wakefulness and inhibit REMs. We conclude that MLPO_VGLUT2 powerfully suppress REMs and that exogenous --and possibly pathologic-- activation of these neurons disrupts REMs recovery, presumably by directly or indirectly activating REMs-inhibitory mechanisms. SIGNIFICANCE STATEMENTThe preoptic area of the hypothalamus has been extensively studied and its role in sleep regulation is well-established. Importantly, recent work identified a group of preoptic glutamatergic neurons (MLPO_VGLUT2) that are wake-active and promote wakefulness. However, whether these neurons influence sleep homeostasis remains unknown. We demonstrate that MLPO_VGLUT2 are maximally active during REM sleep (REMs), wakefulness and brief arousals from sleep, and innervate wake-promoting and REMs-inhibitory regions. MLPO_VGLUT2 stimulation inhibits REMs and REMs rebound after sleep deprivation, whereas their inactivation increases REMs but does not alter REMs homeostatic response. We thus identified a preoptic mechanism that powerfully suppresses REMs, which we propose may engage during normal sleep-to-wake transitions to block REMs intrusions into subsequent wakefulness.

neuroscience↗

bioRxiv2020

Causal role for sleep-dependent reactivation of learning-activated sensory ensembles for fear memory consolidation

Learning-activated engram neurons play a critical role in memory recall. An untested hypothesis is that these same neurons play an instructive role in offline memory consolidation. Here we show that a visually-cued fear memory is consolidated during post-conditioning sleep in mice. We then use TRAP (targeted recombination in active populations) to genetically label or optogenetically manipulate primary visual cortex (V1) neurons responsive to the visual cue. Following fear conditioning, mice respond to activation of this visual engram population in a manner similar to visual presentation of fear cues. Cue-responsive neurons are selectively reactivated in V1 during post-conditioning sleep. Mimicking visual engram reactivation optogenetically leads to increased representation of the visual cue in V1. Optogenetic inhibition of the engram population during post-conditioning sleep disrupts consolidation of fear memory. We conclude that selective sleep-associated reactivation of learning-activated sensory populations serves as a necessary instructive mechanism for memory consolidation.

neuroscience↗

bioRxiv2019

Correcting for sparsity and non-independence in glycomic data through a system biology framework

Glycans are fundamental cellular building blocks, involved in many organismal functions. Advances in glycomics are elucidating the roles of glycans, but it remains challenging to properly analyze large glycomics datasets, since the data are sparse (each sample often has only a few measured glycans) and detected glycans are non-independent (sharing many intermediate biosynthetic steps). We address these challenges with GlyCompare, a glycomic data analysis approach that leverages shared biosynthetic pathway intermediates to correct for sparsity and non-independence in glycomics. Specifically, quantities of measured glycans are propagated to intermediate glycan substructures, which enables direct comparison of different glycoprofiles and increases statistical power. Using GlyCompare, we studied diverse N-glycan profiles from glycoengineered erythropoietin. We obtained biologically meaningful clustering of mutant cell glycoprofiles and identified knockout-specific effects of fucosyltransferase mutants on tetra-antennary structures. We further analyzed human milk oligosaccharide profiles and identified novel impacts that the mothers secretor-status on fucosylation and sialylation. Our substructure-oriented approach will enable researchers to take full advantage of the growing power and size of glycomics data.

systems biology↗