Complete sleep and local field potential analysis regarding estrus cycle, pregnancy, postpartum and post-weaning periods and homeostatic sleep regulation in female rats

Sleep and local field potential effect of the D2 receptor agonist bromocriptine during the estrus cycle and postpartum period in female rats

BACKGROUND

Pituitary lactotrophs are under tonic dopaminergic inhibitory control and bromocriptine treatment blocks prolactin secretion.

METHODS

Sleep and local field potential were addressed for 72 h after bromocriptine treatments applied during the different stages of the estrus cycle and for 24 h in the early- and middle postpartum period characterized by spontaneously different dynamics of prolactin release in female rats.

RESULTS

Sleep changes showed strong dependency on the estrus cycle phase of the drug application. Strongest increase of wakefulness and reduction of slow wave sleep- and rapid eye movements sleep appeared during diestrus-proestrus and middle postpartum treatments. Stronger sleep-wake effects appeared in the dark phase in case of the estrus cycle treatments, but in the light phase in postpartum treatments. Slow wave sleep and REM sleep loss in case of estrus cycle treatments was not compensated at all and sleep loss seen in the first day post-injection was gained further later. In opposition, slow wave sleep loss in the light phase after bromocriptine injections showed compensation in the postpartum period treatments. Bromocriptine treatments resulted in a depression of local field potential delta power during slow wave sleep while an enhancement in beta and gamma power during wakefulness regardless of the treatment timing.

CONCLUSIONS

These results can be explained by the interplay of dopamine D2 receptor agonism, lack of prolactin release and the spontaneous homeostatic sleep drive being altered in the different stages of the estrus cycle and the postpartum period.

Acute and chronic sleep restriction differentially modify maternal behavior and milk macronutrient composition in the postpartum rat

BACKGROUNDS

Sleep restriction is considered a stressful condition itself, causing a wide variety of physiological alterations, from cognitive and hormonal to immunological status. In addition, it is established that stress in mother rats can modify milk ejection, milk composition, and maternal care of the pups. Also, sleep disturbances during the early stages of motherhood are a common feature of all studied species. In this context, while the impacts of sleep disruption in non-lactating animals were extensively investigated, its repercussions during the initial phases of motherhood have been poorly explored. Therefore, we wonder if maternal behavior, milk ejection and its macronutrient composition would be disrupted when mother rats are subjected to an additional acute or chronic sleep restriction to the already existing sleep disturbances.

METHODS

Lactating rats were implanted with unilateral electrodes for polysomnographic recordings and for deep brain electrical stimulation into mesopontine waking-promoting area (for sleep deprivation). During the early postpartum period (postpartum day 5-9), mother rats were randomly assigned into one of three groups: chronic sleep restriction group (CSR; 6 h of sleep deprivation/day for five consecutive days), acute sleep restriction group (ASR; 6 h of sleep deprivation only for one day), or undisturbed group (control group). Active maternal behaviors (retrievals of the pups into the nest, mouthing, lickings [corporal and anogenital] and sniffing the pups) and passive maternal behaviors (kyphotic and supine nursing postures) were evaluated during a 30 min period without sleep restriction immediately after the sleep restriction or control period. The litter weight gain was assessed every day, and on the last experimental session mothers were milked for posterior macronutrients analysis (protein, carbohydrates and fat).

RESULTS

When compared to control group, CSR decreased the amount of milk ejected in the middle days of the sleep restriction period, while ASR did not affect this parameter. Moreover, ASR reduced milk protein content compared to control and CSR groups. Finally, compared to the control group, CSR reduced active maternal behaviors towards the end of the treatment days.

CONCLUSIONS

We demonstrated that not only acute but also chronic sleep restriction impacts on the postpartum period, each one affecting different aspects of maternal behavior and lactation. Our results suggest the existence of a homeostatic recovery mechanism in breastfeeding during CSR, possibly ensuring the survival of the litter, while the decline in active maternal behaviors appears to be cumulative.

Sleep- and sleep deprivation-related changes of vertex auditory evoked potentials during the estrus cycle in female rats

The estrus cycle in female rodents has been shown to affect a variety of physiological functions. However, little is known about its presumably thorough effect on auditory processing during the sleep-wake cycle and sleep deprivation. Vertex auditory evoked potentials (vAEPs) were evoked by single click tone stimulation and recorded during different stages of the estrus cycle and sleep deprivation performed in metestrus and proestrus in female rats. vAEPs showed a strong sleep-dependency, with the largest amplitudes present during slow wave sleep while the smallest ones during wakefulness. Higher amplitudes and longer latencies were seen in the light phase during all vigilance stages. The largest amplitudes were found during proestrus (light phase) while the shortest latencies were seen during estrus (dark phase) compared to the 2nd day diestrus baseline. High-amplitude responses without latency changes were also seen during metestrus with increased homeostatic sleep drive. More intense and faster processing of auditory information during proestrus and estrus suggesting a more effective perception of relevant environmental cues presumably in preparation for sexual receptivity. A 4-h sleep deprivation resulted in more pronounced sleep recovery in metestrus compared to proestrus without difference in delta power replacement suggesting a better tolerance of sleep deprivation in proestrus. Sleep deprivation decreased neuronal excitability and responsiveness in a similar manner both during metestrus and proestrus, suggesting that the negative consequences of sleep deprivation on auditory processing may have a limited correlation with the estrus cycle stage.

The Integration of the Maternal Care with Sleep During the Postpartum Period

Our entire life occurs in a constant alternation between wakefulness and sleep. The impossibility of living without sleep implies that any behavior must adapt to the need for sleep, and maternal behavior does not escape from this determination. Additionally, maternal behavior in mammals is a highly motivated behavior, essential for the survival of the offspring. Thus, the mother has to adapt her physiology of sleep to the constant demands of the pups, where each species will have different strategies to merge these two physiological needs. However, all studied female mammals will experience sleep disturbances at some point of the postpartum period.

Evaluation of cellular activity in response to sleep deprivation by a comprehensive analysis of the whole mouse brain

Sleep deprivation (SD) causes several adverse functional outcomes, and understanding the associated processes can improve quality of life. Although the effects of SD on neuronal activity in several brain regions have been identified, a comprehensive evaluation of the whole brain is still lacking. Hence, we performed SD using two different methods, gentle handling and a dedicated chamber, in targeted recombination in active populations 2 (TRAP2) mice crossed with Rosa-ZsGreen reporter mice and visualized cellular activity in the whole brain. Using the semi-automated post-imaging analysis tool Slice Histology Alignment, Registration, and Cell Quantification (SHARCQ), the number of activated cells was quantified. From the analysis of 14 brain regions, cellular activity was significantly increased in the olfactory areas and decreased in the medulla by the two SD methods. From the analysis of the further subdivided 348 regions, cellular activity was significantly increased in the vascular organ of the lamina terminalis, lateral hypothalamic area, parabigeminal nucleus, ventral tegmental area, and magnocellular reticular nucleus, and decreased in the anterior part of the basolateral amygdalar nucleus, nucleus accumbens, septohippocampal nucleus, reticular nucleus of the thalamus, preoptic part of the periventricular hypothalamic nucleus, ventromedial preoptic nucleus, rostral linear nucleus raphe, facial motor nucleus, vestibular nuclei, and some fiber tracts (oculomotor nerve, genu of corpus callosum, and rubrospinal tract) by the two SD methods. Two subdivided regions of the striatum (caudoputamen and other striatum), epithalamus, vascular organ of the lamina terminalis, anteroventral preoptic nucleus, superior colliculus optic layer, medial terminal nucleus of the accessory optic tract, pontine gray, and fiber tracts (medial lemniscus, columns of the fornix, brachium of the inferior colliculus, and mammillary peduncle) were differentially affected by the two SD methods. Most brain regions detected from these analyses have been reported to be involved in regulating sleep/wake regulatory circuits. Moreover, the results from the connectivity analysis indicated that the connectivity of cellular activity among brain regions was altered by SD. Together, such a comprehensive analysis of the whole brain is useful for understanding the mechanisms by which SD and/or sleep disruption affects brain function.

Modulation and neural correlates of postmating sleep plasticity in Drosophila females

Sleep is essential, but animals may forgo sleep to engage in other critical behaviors, such as feeding and reproduction. Previous studies have shown that female flies exhibit decreased sleep after mating, but our understanding of the process is limited. Here, we report that postmating nighttime sleep loss is modulated by diet and sleep deprivation, demonstrating a complex interaction among sleep, reproduction, and diet. We also find that female-specific pC1 neurons and sleep-promoting dorsal fan-shaped body (dFB) neurons are required for postmating sleep plasticity. Activating pC1 neurons leads to sleep suppression on standard fly culture media but has little sleep effect on sucrose-only food. Published connectome data suggest indirect, inhibitory connections among pC1 subtypes. Using calcium imaging, we show that activating the pC1e subtype inhibits dFB neurons. We propose that pC1 and dFB neurons integrate the mating status, food context, and sleep drive to modulate postmating sleep plasticity.

Oestrous cycle affects emergence from anaesthesia with dexmedetomidine, but not propofol, isoflurane, or sevoflurane, in female rats

BACKGROUND

Although sex differences in anaesthetic sensitivity have been reported, what underlies these differences is unknown. In rodents, one source of variability in females is the oestrous cycle. Here we test the hypothesis that the oestrous cycle impacts emergence from general anaesthesia.

METHODS

Time to emergence was measured after isoflurane (2 vol% for 1 h), sevoflurane (3 vol% for 20 min), dexmedetomidine (50 μg kg-1 i.v., infused over 10 min), or propofol (10 mg kg-1 i.v. bolus) during proestrus, oestrus, early dioestrus, and late dioestrus in female Sprague-Dawley rats (n=24). EEG recordings were taken during each test for power spectral analysis. Serum was analysed for 17β-oestradiol and progesterone concentrations. The effect of oestrous cycle stage on return of righting latency was assessed using a mixed model. The association between righting latency and serum hormone concentration was tested by linear regression. Mean arterial blood pressure and arterial blood gases were assessed in a subset of rats after dexmedetomidine and compared in a mixed model.

RESULTS

Oestrous cycle did not affect righting latency after isoflurane, sevoflurane, or propofol. When in the early dioestrus stage, rats emerged more rapidly from dexmedetomidine than in the proestrus (P=0.0042) or late dioestrus (P=0.0230) stage and showed reduced overall power in frontal EEG spectra 30 min after dexmedetomidine (P=0.0049). 17β-Oestradiol and progesterone serum concentrations did not correlate with righting latency. Oestrous cycle did not affect mean arterial blood pressure or blood gases during dexmedetomidine.

CONCLUSIONS

In female rats, the oestrous cycle significantly impacts emergence from dexmedetomidine-induced unconsciousness. However, 17β-oestradiol and progesterone serum concentrations do not correlate with the observed changes.

Hypocretins, sleep, and maternal behavior

The postpartum period is a demanding time during which mothers experience numerous physiological adaptations that enable them to care for their offspring while maintaining their wellbeing. Hypocretins, also known as orexins, are neuropeptides synthesized by hypothalamic neurons that play a fundamental role in several functions, including the promotion of wakefulness and motivated behaviors, such as maternal care. In this regard, several findings suggest that the activity of the hypocretinergic system increases in the early postpartum period and begins to decline as weaning approaches. In particular, hypocretins within the medial preoptic area, a crucial region during this period, modulate both maternal behavior and sleep. Although further studies are necessary to obtain a comprehensive understanding of the role of hypocretins in lactating females, current research suggests that this system participates in promoting active components of maternal behavior and regulating wakefulness and sleep adjustments during the postpartum period, potentially leading to increased wakefulness during this stage. These adaptive adjustments enable the mother to cope with the continuously changing demands of the pups.

Ketamine affects homeostatic sleep regulation in the absence of the circadian sleep-regulating component in freely moving rats

Pharmacological effects of ketamine may affect homeostatic sleep regulation via slow wave related mechanisms. In the present study effects of ketamine applied at anesthetic dose (80 mg/kg) were tested on neocortical electric activity for 24 h in freely moving rats. Ketamine effects were compared to changes during control (saline) injections and after 6 h gentle handling sleep deprivation (SD). As circadian factors may mask drug effects, an illumination protocol consisting of short light-dark cycles was applied. Ketamine application induced a short hypnotic stage with characteristic slow cortical rhythm followed by a long-lasting hyperactive waking resulting pharmacological SD. Coherence analysis indicated an increased level of local synchronization in broad local field potential frequency ranges during hyperactive waking but not during natural- or SD-evoked waking. Both slow wave sleep and rapid eye movement sleep were replaced after the termination of the ketamine effect. Our results show that both ketamine-induced hypnotic state and hyperactive waking can induce homeostatic sleep pressure with comparable intensity as 6 h SD, but ketamine-induced waking was different compared to the SD-evoked one. Both types of waking stages were different compared to spontaneous waking but all three types of wakefulness can engage the homeostatic sleep regulating machinery to generate sleep pressure dissipated by subsequent sleep. Current-source density analysis of the slow waves showed that cortical transmembrane currents were stronger during ketamine-induced hypnotic stage compared to both sleep replacement after SD and ketamine application, but intracortical activation patterns showed only quantitative differences. These findings may hold some translational value for human medical ketamine applications aiming the treatment of depression-associated sleep problems, which can be alleviated by the homeostatic sleep effect of the drug without the need for an intact circadian regulation.

Many faces of sleep regulation: beyond the time of day and prior wake time

The two-process model of sleep regulation posits two main processes regulating sleep: the circadian process controlled by the circadian clock and the homeostatic process that depends on the history of sleep and wakefulness. The model has provided a dominant conceptual framework for sleep research since its publication ~ 40 years ago. The time of day and prior wake time are the primary factors affecting the circadian and homeostatic processes, respectively. However, it is critical to consider other factors influencing sleep. Since sleep is incompatible with other behaviors, it is affected by the need for essential behaviors such as eating, foraging, mating, caring for offspring, and avoiding predators. Sleep is also affected by sensory inputs, sickness, increased need for memory consolidation after learning, and other factors. Here, we review multiple factors influencing sleep and discuss recent insights into the mechanisms balancing competing needs.

Role of Hypocretin in the Medial Preoptic Area in the Regulation of Sleep, Maternal Behavior and Body Temperature of Lactating Rats

Hypocretins (HCRT), also known as orexins, includes two neuroexcitatory peptides, HCRT-1 and HCRT-2 (orexin A y B, respectively), synthesized by neurons located in the postero-lateral hypothalamus, whose projections and receptors are widely distributed throughout the brain, including the medial preoptic area (mPOA). HCRT have been associated with a wide range of physiological functions including sleep-wake cycle, maternal behavior and body temperature, all regulated by the mPOA. Previously, we showed that HCRT in the mPOA facilitates certain active maternal behaviors, while the blockade of HCRT-R1 increases the time spent in nursing. As mother rats mainly sleep while they nurse, we hypothesize that HCRT in the mPOA of lactating rats reduce sleep and nursing, while intra-mPOA administration of a dual orexin receptor antagonist (DORA) would cause the opposite effect. Therefore, the aim of this study was to determine the role of HCRT within the mPOA, in the regulation and integration of the sleep-wake cycle, maternal behavior and body temperature of lactating rats. For that purpose, we assessed the sleep-wake states, maternal behavior and body temperature of lactating rats following microinjections of HCRT-1 (100 and 200 µM) and DORA (5 mM) into the mPOA. As expected, our data show that HCRT-1 in mPOA promote wakefulness and a slightly increase in body temperature, whereas DORA increases both NREM and REM sleep together with an increment of nursing and milk ejection. Taken together, our results strongly suggest that the endogenous reduction of HCRT within the mPOA contribute to the promotion of sleep, milk ejection and nursing behavior in lactating rats.

Neural basis for estrous cycle-dependent control of female behaviors

Females display changes in distinct behaviors along the estrous cycle. Levels of circulating ovarian sex steroid hormones peak around ovulation, which occur around estrus phase of the cycle. This increase of sex hormones is thought to be important for changes in behaviors, however, neural circuit mechanisms of periodic behavioral changes in females are not understood well. Different lines of research indicate sex hormonal effects on several forms of neuronal plasticity. This review provides an overview of behavioral and plastic changes that occur in an estrous cycle-dependent manner and explores the current research linking these changes to understand neural circuit mechanisms that control female behaviors.