Deficiency of corticotropin-releasing hormone type-2 receptor alters sleep responses to bacterial lipopolysaccharide in mice

Restoring Serotonergic Homeostasis in the Lateral Hypothalamus Rescues Sleep Disturbances Induced by Early-Life Obesity

Early-life obesity predisposes to obesity in adulthood, a condition with broad medical implications including sleep disorders, which can exacerbate metabolic disturbances and disrupt cognitive and affective behaviors. In this study, we examined the long-term impact of transient peripubertal diet-induced obesity (ppDIO, induced between 4 and 10 weeks of age) on sleep-wake behavior in male mice. EEG and EMG recordings revealed that ppDIO increases sleep during the active phase but reduces resting-phase sleep quality. This impaired sleep phenotype persisted for up to 1 year, although animals were returned to a non-obesiogenic diet from postnatal week 11 onwards. To better understand the mechanisms responsible for the ppDIO-induced alterations in sleep, we focused on the lateral hypothalamus (LH). Mice exposed to ppDIO did not show altered mRNA expression levels of orexin and melanin-concentrating hormone, two peptides that are important for sleep-wake behavior and food intake. Conversely, the LH of ppDIO-exposed mice had reduced contents of serotonin (5-hydroxytryptamine, 5-HT), a neurotransmitter involved in both sleep-wake and satiety regulation. Interestingly, an acute peripheral injection of the satiety-signaling peptide YY 3-36 increased 5-HT turnover in the LH and ameliorated the ppDIO-induced sleep disturbances, suggesting the therapeutic potential of this peptide. These findings provide new insights into how sleep-wake behavior is programmed during early life and how peripheral and central signals are integrated to coordinate sleep.SIGNIFICANCE STATEMENT Adult physiology and behavior are strongly influenced by dynamic reorganization of the brain during puberty. The present work shows that obesity during puberty leads to persistently dysregulated patterns of sleep and wakefulness by blunting serotonergic signaling in the lateral hypothalamus. It also shows that pharmacological mimicry of satiety with peptide YY_3-36 can reverse this neurochemical imbalance and acutely restore sleep composition. These findings add insight into how innate behaviors such as feeding and sleep are integrated and suggest a novel mechanism through which diet-induced obesity during puberty imposes its long-lasting effects on sleep-wake behavior.

Circadian Disruption Alters the Effects of Lipopolysaccharide Treatment on Circadian and Ultradian Locomotor Activity and Body Temperature Rhythms of Female Siberian Hamsters

The effect of circadian rhythm (CR) disruption on immune function depends on the method by which CRs are disrupted. Behavioral and thermoregulatory responses induced by lipopolysaccharide (LPS) treatment were assessed in female Siberian hamsters in which circadian locomotor activity (LMA) rhythms were eliminated by exposure to a disruptive phase-shifting protocol (DPS) that sustains arrhythmicity even when hamsters are housed in a light-dark cycle. This noninvasive treatment avoids genome manipulations and neurological damage associated with other models of CR disruption. Circadian rhythmic (RHYTH) and arrhythmic (ARR) hamsters housed in a 16L:8D photocycle were injected with bacterial LPS near the onset of the light (zeitgeber time 1; ZT1) or dark (ZT16) phase. LPS injections at ZT16 and ZT1 elicited febrile responses in both RHYTH and ARR hamsters, but the effect was attenuated in the arrhythmic females. In ZT16, LPS inhibited LMA in the dark phase immediately after injection but not on subsequent nights in both chronotypes; in contrast, LPS at ZT1 elicited more enduring (~4 day) locomotor hypoactivity in ARR than in RHYTH hamsters. Power and period of dark-phase ultradian rhythms (URs) in LMA and Tb were markedly altered by LPS treatment, as was the power in the circadian waveform. Disrupted circadian rhythms in this model system attenuated responses to LPS in a trait- and ZT-specific manner; changes in UR period and power are novel components of the acute-phase response to infection that may affect energy conservation.

The roles of prostaglandin E2 and D2 in lipopolysaccharide-mediated changes in sleep

When living organisms become sick as a result of a bacterial infection, a suite of brain-mediated responses occur, including fever, anorexia and sleepiness. Systemic administration of lipopolysaccharide (LPS), a common constituent of bacterial cell walls, increases body temperature and non-rapid eye movement (NREM) sleep in animals and induces the production of pro-inflammatory prostaglandins (PGs). PGE2 is the principal mediator of fever, and both PGE2 and PGD2 regulate sleep-wake behavior. The extent to which PGE2 and PGD2 are involved in the effect of LPS on NREM sleep remains to be clarified. Therefore, we examined LPS-induced changes in body temperature and NREM sleep in mice with nervous system-specific knockouts (KO) for the PGE2 receptors type EP3 or EP4, in mice with total body KO of microsomal PGE synthase-1 or the PGD2 receptor type DP, and in mice treated with the cyclooxygenase (COX) inhibitor meloxicam. We observed that LPS-induced NREM sleep was slightly attenuated in mice lacking EP4 receptors in the nervous system, but was not affected in any of the other KO mice or in mice pretreated with the COX inhibitor. These results suggest that the effect of LPS on NREM sleep is partially dependent on PGs and is likely mediated mainly by other pro-inflammatory substances. In addition, our data show that the main effect of LPS on body temperature is hypothermia in the absence of nervous system EP3 receptors or in the presence of a COX inhibitor.

Vagotomy attenuates brain cytokines and sleep induced by peripherally administered tumor necrosis factor-α and lipopolysaccharide in mice

STUDY OBJECTIVE

Systemic tumor necrosis factor-α (TNF-α) is linked to sleep and sleep altering pathologies in humans. Evidence from animals indicates that systemic and brain TNF-α have a role in regulating sleep. In animals, TNF-α or lipopolysaccharide (LPS) enhance brain pro-inflammatory cytokine expression and sleep after central or peripheral administration. Vagotomy blocks enhanced sleep induced by systemic TNF-α and LPS in rats, suggesting that vagal afferent stimulation by TNF-α enhances pro-inflammatory cytokines in sleep-related brain areas. However, the effects of systemic TNF-α on brain cytokine expression and mouse sleep remain unknown.

DESIGN

We investigated the role of vagal afferents on brain cytokines and sleep after systemically applied TNF-α or LPS in mice.

MEASUREMENTS AND RESULTS

Spontaneous sleep was similar in vagotomized and sham-operated controls. Vagotomy attenuated TNF-α- and LPS-enhanced non-rapid eye movement sleep (NREMS); these effects were more evident after lower doses of these substances. Vagotomy did not affect rapid eye movement sleep responses to these substances. NREMS electroencephalogram delta power (0.5-4 Hz range) was suppressed after peripheral TNF-α or LPS injections, although vagotomy did not affect these responses. Compared to sham-operated controls, vagotomy did not affect liver cytokines. However, vagotomy attenuated interleukin-1 beta (IL-1β) and TNF-α mRNA brain levels after TNF-α, but not after LPS, compared to the sham-operated controls.

CONCLUSIONS

We conclude that vagal afferents mediate peripheral TNF-α-induced brain TNF-α and IL-1β mRNA expressions to affect sleep. We also conclude that vagal afferents alter sleep induced by peripheral pro-inflammatory stimuli in mice similar to those occurring in other species.

Prognostic and symptomatic aspects of rapid eye movement sleep in a mouse model of posttraumatic stress disorder

Not every individual develops Posttraumatic Stress Disorder (PTSD) after the exposure to a potentially traumatic event. Therefore, the identification of pre-existing risk factors and early diagnostic biomarkers is of high medical relevance. However, no objective biomarker has yet progressed into clinical practice. Sleep disturbances represent commonly reported complaints in PTSD patients. In particular, changes in rapid eye movement sleep (REMS) properties are frequently observed in PTSD patients. Here, we examined in a mouse model of PTSD whether (1) mice developed REMS alterations after trauma and (2) whether REMS architecture before and/or shortly after trauma predicted the development of PTSD-like symptoms. We monitored sleep-wake behavior via combined electroencephalogram/electromyogram recordings immediately before (24 h pre), immediately after (0-48 h post) and 2 months after exposure to an electric foot shock in male C57BL/6N mice (n = 15). PTSD-like symptoms, including hyperarousal, contextual, and generalized fear, were assessed 1 month post-trauma. Shocked mice showed early onset and sustained elevation of REMS compared to non-shocked controls. In addition, REMS architecture before trauma was correlated with the intensity of acoustic startle responses, but not contextual fear, 1 month after trauma. Our data suggest REMS as prognostic (pre-trauma) and symptomatic (post-trauma) marker of PTSD-like symptoms in mice. Translated to the situation in humans, REMS may constitute a viable, objective, and non-invasive biomarker in PTSD and other trauma-related psychiatric disorders, which could guide pharmacological interventions in humans at high risk.

Sleep phenotyping in a mouse model of extreme trait anxiety

Background

There is accumulating evidence that anxiety impairs sleep. However, due to high sleep variability in anxiety disorders, it has been difficult to state particular changes in sleep parameters caused by anxiety. Sleep profiling in an animal model with extremely high vs. low levels of trait anxiety might serve to further define sleep patterns associated with this psychopathology.

Methodology/Principal Findings

Sleep-wake behavior in mouse lines with high (HAB), low (LAB) and normal (NAB) anxiety-related behaviors was monitored for 24 h during baseline and recovery after 6 h sleep deprivation (SD). The amounts of each vigilance state, sleep architecture, and EEG spectral variations were compared between the mouse lines. In comparison to NAB mice, HAB mice slept more and exhibited consistently increased delta power during non-rapid eye movement (NREM) sleep. Their sleep patterns were characterized by heavy fragmentation, reduced maintenance of wakefulness, and frequent intrusions of rapid eye movement (REM) sleep. In contrast, LAB mice showed a robust sleep-wake rhythm with remarkably prolonged sleep latency and a long, persistent period of wakefulness. In addition, the accumulation of delta power after SD was impaired in the LAB line, as compared to HAB mice.

Conclusions/Significance

Sleep-wake patterns were significantly different between HAB and LAB mice, indicating that the genetic predisposition to extremes in trait anxiety leaves a biological scar on sleep quality. The enhanced sleep demand observed in HAB mice, with a strong drive toward REM sleep, may resemble a unique phenotype reflecting not only elevated anxiety but also a depression-like attribute.