Biology subjects

Hauglund, N. L.

Publications and source records attributed to Hauglund, N. L..

4 recordsLinked to original sources

bioRxiv2026

Is torpor a quiescent state? Periodic motility and transient brain activation during daily torpor in Djungarian hamsters

Torpor is a hypometabolic state employed by many mammalian and non-mammalian species to cope with harsh environments. When exposed to a short photoperiod, Djungarian hamsters (Phodopus sungorus) enter daily torpor with body temperatures dropping to as low as 15{degrees}C. Despite the widely-held notion that torpor is a form of deep sleep, torpid animals are not completely inactive but exhibit occasional movements reflected in an increase in EMG tone. Little is known about these EMG events during torpor and whether they have a functional role during the torpid state. We here analysed EEG, EMG, and brain temperature data from Djungarian hamsters, and used an automatic detection algorithm to identify periods of EMG activation during spontaneous daily torpor. The hamsters exhibited regular periods of motility that were invariably initiated during a decline in brain temperature and were followed by a brain temperature increase. The frequency of EMG events exhibited a negative correlation with brain temperature, such that lower brain temperature was associated with a higher frequency of EMG events. In addition, EMG events were associated with a pronounced increase in EEG power, especially between 9.5-15.5 Hz, which often started with an EEG pattern similar to an evoked potential preceding the increase in the EMG activity. On the contrary, micro-arousals during normothermic NREM sleep were associated with a decrease in EEG power, a decrease in brain temperature and were of shorter duration than torpor EMG events, indicating that the two phenomena may serve different purposes. We speculate that periodic motility associated with increased brain activity during torpor may play a role in thermoregulation, and help retain vigilance to potentially mitigate predation risk during this hypometabolic state.

neuroscience↗

bioRxiv2025

Increased slow wave activity in response to sleep deprivation is highest immediately after micro-arousals

Non-rapid eye movement (NREM) sleep is not uniform but characterized by brief intrusions of wake-like brain activity, known as micro-arousals or brief awakenings. Although micro-arousals are an inherent feature of both human and animal sleep, knowledge about the neural correlates of micro-arousals across the cortical column is sparse. We here developed an algorithm for automatic detection of micro-arousals based on EMG activity and used it to explore how micro-arousals modulate laminar neural activity in the motor cortex, and how this relationship is affected by sleep pressure in mice. Our analysis showed that micro-arousals were associated with a general suppression of local field potential (LFP) power across the cortical column. Slow wave activity (SWA, 1-4 Hz) immediately after micro-arousals was tightly correlated with sleep pressure and even surpassed average SWA levels during NREM sleep in sleep deprived animals. In addition, analysis of single-channel firing showed that some channels exhibited increased activity immediately prior to micro-arousals, while others exhibited decreased activity. This study provides new insights into the neural mechanisms underlying micro-arousals and identifies a new link between micro-arousals and sleep homeostasis.

neuroscience↗

bioRxiv2022

Loss of aquaporin-4 results in glymphatic system dysfunction via brain-wide interstitial fluid stagnation

The glymphatic system is a fluid transport network of cerebrospinal fluid (CSF) entering the brain along arterial perivascular spaces, exchanging with interstitial fluid (ISF), ultimately establishing directional clearance of interstitial solutes. CSF transport is facilitated by the expression of aquaporin-4 (AQP4) water channels on the perivascular endfeet of astrocytes. Mice with genetic deletion of AQP4 (AQP4 KO) exhibit abnormalities in the brain structure and molecular water transport. Yet, no studies have systematically examined how these abnormalities in structure and water transport correlate with glymphatic function. Here we used high-resolution 3D magnetic resonance (MR) non-contrast cisternography, diffusion-weighted MR imaging (MR-DWI) along with intravoxel-incoherent motion (IVIM) DWI, while evaluating glymphatic function using a standard dynamic contrast-enhanced MR imaging to better understand how water transport and glymphatic function is disrupted after genetic deletion of AQP4. AQP4 KO mice had larger interstitial spaces and total brain volumes resulting in higher water content and reduced CSF space volumes, despite similar CSF production rates and vascular density compared to wildtype mice. The larger interstitial fluid volume likely resulted in increased slow but not fast MR diffusion scores and coincided with reduced glymphatic influx. This markedly altered brain fluid transport in AQP4 KO mice may result from a reduction in glymphatic clearance, leading to stagnation of ISF movement and enlargement of the interstitial space. Overall, diffusion MR is a useful tool to evaluate glymphatic function and may serve as valuable translational biomarker to study glymphatics in human disease.

neuroscience↗

bioRxiv2020

Dynamic fluctuations of the locus coeruleus-norepinephrine system underlie sleep state transitions

We normally regard sleep and wake as two distinct opposing brain states, where sleep requires silence of wake-promoting structures such as the locus coeruleus (LC)-norepinephrine (NE) system. We set out to investigate how cortical NE dynamics and NE-related astrocytic activity relates to LC population activity during sleep states. We show that LC displays regular phasic activity bouts during NREM sleep leading to a slow oscillatory pattern of prefrontal NE levels of which the majority of NE increases does not lead to awakening. NE troughs link to sleep spindles and continued NE decline transitions into REM sleep. Last, we show that prefrontal astrocytes have reduced sensitivity towards NE during sleep. Our results suggest that dynamic changes in the activity of wake-promoting systems during sleep create alternation between crucial sleep processes and broadening of sensitivity towards incoming sensory input. HighlightsO_LIExtracellular levels of norepinephrine display dynamic changes during NREM and REM sleep C_LIO_LIPhasic activity of locus coeruleus neurons during NREM underlies slow norepinephrine oscillations C_LIO_LISpindles occur at norepinephrine troughs and are abolished by norepinephrine increases C_LIO_LIIncreased spindles prior to REM reflect the beginning of a long-lasting norepinephrine decline C_LIO_LIREM episodes are characterized by a sub-threshold continuous norepinephrine decline C_LIO_LIThe responsiveness of astrocytic Ca2+ to norepinephrine is reduced during sleep C_LI

neuroscience↗