Functional MRI shows activation of the medial preoptic area during sleep

Where do we stand on fMRI in awake mice?

Imaging awake animals is quickly gaining traction in neuroscience as it offers a means to eliminate the confounding effects of anesthesia, difficulties of inter-species translation (when humans are typically imaged while awake), and the inability to investigate the full range of brain and behavioral states in unconscious animals. In this systematic review, we focus on the development of awake mouse blood oxygen level dependent functional magnetic resonance imaging (fMRI). Mice are widely used in research due to their fast-breeding cycle, genetic malleability, and low cost. Functional MRI yields whole-brain coverage and can be performed on both humans and animal models making it an ideal modality for comparing study findings across species. We provide an analysis of 30 articles (years 2011-2022) identified through a systematic literature search. Our conclusions include that head-posts are favorable, acclimation training for 10-14 d is likely ample under certain conditions, stress has been poorly characterized, and more standardization is needed to accelerate progress. For context, an overview of awake rat fMRI studies is also included. We make recommendations that will benefit a wide range of neuroscience applications.

In Vitro and In Vivo Evaluation of Pellotine: A Hypnotic Lophophora Alkaloid

Quality of life is often reduced in patients with sleep-wake disorders. Insomnia is commonly treated with benzodiazepines, despite their well-known side effects. Pellotine (1), a Lophophora alkaloid, has been reported to have short-acting sleep-inducing properties in humans. In this study, we set out to evaluate various in vitro and in vivo properties of 1. We demonstrate that 1 undergoes slow metabolism; e.g. in mouse liver microsomes 65% remained, and in human liver microsomes virtually no metabolism was observed after 4 h. In mouse liver microsomes, two phase I metabolites were identified: 7-desmethylpellotine and pellotine-N-oxide. In mice, the two diastereomers of pellotine-O-glucuronide were additionally identified as phase II metabolites. Furthermore, we demonstrated by DESI-MSI that 1 readily enters the central nervous system of rodents. Furthermore, radioligand-displacement assays showed that 1 is selective for the serotonergic system and in particular the serotonin (5-HT)1D, 5-HT6, and 5-HT7 receptors, where it binds with affinities in the nanomolar range (117, 170, and 394 nM, respectively). Additionally, 1 was functionally characterized at 5-HT6 and 5-HT7, where it was found to be an agonist at the former (EC50 = 94 nM, Emax = 32%) and an inverse agonist at the latter (EC50 = 291 nM, Emax = -98.6). Finally, we demonstrated that 1 dose-dependently decreases locomotion in mice, inhibits REM sleep, and promotes sleep fragmentation. Thus, we suggest that pellotine itself, and not an active metabolite, is responsible for the hypnotic effects and that these effects are possibly mediated through modulation of serotonergic receptors.

Local administration of bicuculline into the ventrolateral and medial preoptic nuclei modifies sleep and maternal behavior in lactating rats

The preoptic area (POA) is a brain structure classically involved in a wide variety of animal behavior including sleep and maternal care. In the current study, we evaluate the specific effect of disinhibition of two specific regions of the POA, the medial POA nucleus (mPOA) and the ventrolateral POA area (VLPO) on sleep and maternal behavior in lactating rats. For this purpose, mother rats on postpartum day 1 (PPD1) were implanted for polysomnographic recordings and with bilateral cannulae either in the mPOA or in the VLPO. The rats were tested for sleep and maternal behavior on PPD4-8 after the infusion of the GABA-A antagonist, bicuculline (0, 10 or 30 ng/0.2 µl/side). Infusion of bicuculline into the mPOA augmented retrieving and nest building behaviors and reduced both nursing and milk ejections but had almost no effect on sleep. When bicuculine was microinjected into the VLPO, the rats significantly increase the number of retrievings and mouthings and reduced the nursing time without changes in milk ejections, which was associated with an increase in wakefulness and a reduction in light sleep. Our results show that disinhibition of the mPOA, a key area in the control of maternal behavior, increased active maternal behaviors and reduced nursing without affecting wakefulness or sleep time. In contrast, the enhancement of some active maternal behaviors when the drug was infused into the VLPO, a sleep-promoting area, with a concomitant increase in wakefulness suggests that mother rats devote this additional waking time in the active maternal care of the pups. We hypothesize that maternal behavior changes after bicuculine microinjection into the VLPO are caused by a reduction in the sleep drive, rather than a direct effect on maternal behavior.

Basal forebrain thermoregulatory mechanism modulates auto-regulated sleep

Regulation of body temperature and sleep are two physiological mechanisms that are vital for our survival. Interestingly neural structures implicated in both these functions are common. These areas include the medial preoptic area (POA), the lateral POA, the ventrolateral POA, the median preoptic nucleus, and the medial septum, which form part of the basal forebrain (BF). When given a choice, rats prefer to stay at an ambient temperature of 27°C, though the maximum sleep was observed when they were placed at 30°C. Ambient temperature around 27°C should be considered as the thermoneutral temperature for rats in all sleep studies. At this temperature the diurnal oscillations of sleep and body temperature are properly expressed. The warm sensitive neurons of the POA mediate the increase in sleep at 30°C. Promotion of sleep during the rise in ambient temperature from 27 to 30°C, serve a thermoregulatory function. Autonomous thermoregulatory changes in core body temperature and skin temperature could act as an input signal to modulate neuronal activity in sleep-promoting brain areas. The studies presented here show that the neurons of the BF play a key role in regulating sleep. BF thermoregulatory system is a part of the global homeostatic sleep regulatory mechanism, which is auto-regulated.

Cellular and chemical neuroscience of mammalian sleep

Extraordinary strides have been made toward understanding the complexities and regulatory mechanisms of sleep over the past two decades thanks to the help of rapidly evolving technologies. At its most basic level, mammalian sleep is a restorative process of the brain and body. Beyond its primary restorative purpose, sleep is essential for a number of vital functions. Our primary research interest is to understand the cellular and molecular mechanisms underlying the regulation of sleep and its cognitive functions. Here I will reflect on our own research contributions to 50 years of extraordinary advances in the neurobiology of slow-wave sleep (SWS) and rapid eye movement (REM) sleep regulation. I conclude this review by suggesting some potential future directions to further our understanding of the neurobiology of sleep.

EEG monitoring during functional MRI in animal models

Despite its excellent temporal resolution, electroencephalogram (EEG) has poor spatial resolution to study the participation of different brain areas in epileptic discharges, and the propagation of seizures to subcortical areas is not revealed. Furthermore, EEG provides no information about metabolic changes that occur in the brain before and during the epileptic discharges. Thus, monitoring variations in blood flow and oxygenation in response to epileptic discharges can provide additional complementary information. Functional magnetic resonance imaging (fMRI) technology can be used to study the hemodynamic changes associated with interictal epileptiform discharges or epileptic seizures (i.e., before, during or after them) in experimental animal models and may noninvasively monitor these changes over time. Blood oxygenation level-dependent fMRI has superior spatial resolution compared with other functional imaging modalities and utilizes changes in local magnetic field properties to measure the amount of deoxyhemoglobin in each brain areas as an indicator of brain activity. Simultaneous recording of EEG and fMRI is required to achieve this objective. This article describes methods of acquiring and monitoring EEG during fMRI studies in experimental animals. Particular attention will be paid to methods used to eliminate artifacts induced in the acquired magnetic resonance images by EEG equipment and MR-related artifacts in EEG recordings.

Neurobiological mechanisms for the regulation of mammalian sleep-wake behavior: reinterpretation of historical evidence and inclusion of contemporary cellular and molecular evidence

At its most basic level, the function of mammalian sleep can be described as a restorative process of the brain and body; recently, however, progressive research has revealed a host of vital functions to which sleep is essential. Although many excellent reviews on sleep behavior have been published, none have incorporated contemporary studies examining the molecular mechanisms that govern the various stages of sleep. Utilizing a holistic approach, this review is focused on the basic mechanisms involved in the transition from wakefulness, initiation of sleep and the subsequent generation of slow-wave sleep and rapid eye movement (REM) sleep. Additionally, using recent molecular studies and experimental evidence that provides a direct link to sleep as a behavior, we have developed a new model, the cellular-molecular-network model, explaining the mechanisms responsible for regulating REM sleep. By analyzing the fundamental neurobiological mechanisms responsible for the generation and maintenance of sleep-wake behavior in mammals, we intend to provide a broader understanding of our present knowledge in the field of sleep research.

Alpha-1 adrenergic receptors in the medial preoptic area are involved in the induction of sleep

This paper reviews the recent studies that led to the conclusion that the noradrenergic neurons projecting to the medial preoptic area (mPOA) are hypnogenic and that they mediate this action through alpha(1) adrenergic receptors. Microinjection of noradrenaline (NA) into the mPOA induced arousal. Studies using alpha(2) adrenergic drugs showed that the arousal induced by intrapreoptic injection of NA was due to its action on presynaptic alpha(2) adrenergic receptors. A combination of lesion and chemical stimulation techniques demonstrated that when NA acted on the postsynaptic alpha(1 )receptors in the mPOA, it induced sleep. Intrapreoptic injection of alpha(1) agonist, methoxamine could induce sleep, when the hypothermia, which was simultaneously produced, was behaviorally compensated for by the animal. Increased arousal produced by the destruction of noradrenergic fibers in the mPOA further confirmed the hypnogenic role of these fibers.

Neuroimaging of sleep and sleep disorders

Herein are presented the results of research in the area of sleep neuroimaging over the past year. Significant work has been performed to clarify the basic mechanisms of sleep in humans. New studies also extend prior observations regarding altered brain activation in response to sleep deprivation by adding information regarding vulnerability to sleep deprivation and regarding the influence of task difficulty on aberrant responses. Studies in sleep disorder medicine have yielded significant findings in insomnia, depression, and restless legs syndrome. Extensive advances have been made in the area of sleep apnea where physiologic challenges have been used to probe brain activity in the pathophysiology of sleep apnea syndrome.

Simultaneous EEG and fMRI in the macaque monkey at 4.7 Tesla

Simultaneous electroencephalography (EEG)/functional magnetic resonance imaging (fMRI) acquisition can identify the brain networks involved in generating specific EEG patterns. Yet, the combination of these methodologies is hampered by strong artifacts that arise due to electromagnetic interference during magnetic resonance (MR) image acquisition. Here, we report corrections of the gradient-induced artifact in phantom measurements and in experiments with an awake behaving macaque monkey during fMRI acquisition at a magnetic field strength of 4.7 T. Ninety-one percent of the amplitude of a 10 microV, 10 Hz phantom signal could successfully be recovered without phase distortions. Using this method, we were able to extract the monkey EEG from scalp recordings obtained during MR image acquisition. Visual evoked potentials could also be reliably identified. In conclusion, simultaneous EEG/fMRI acquisition is feasible in the macaque monkey preparation at 4.7 T and holds promise for investigating the neural processes that give rise to particular EEG patterns.

Differences in the effects of medial and lateral preoptic lesions on thermoregulation and sleep in rats

The effects of the destruction of the medial preoptic area and the lateral preoptic area with N-methyl-d-aspartic acid on sleep-wakefulness, brain temperature and thermoregulation were studied in two groups of male Wistar rats. Electroencephalogram, electrooculogram and electromyogram, along with brain temperature, were recorded for 3 days, prior to the destruction of the medial preoptic area and the lateral preoptic area, and on the 7th and 21st days after the destruction of these areas. The thermoregulatory capacity of the rats was assessed by recording their brain temperature when they were exposed to severe cold (5+/-1 degrees C) and heat (37+/-1 degrees C) before and after the lesion. Though sleep was decreased after the destruction of both the medial preoptic area and the lateral preoptic area, paradoxical sleep was reduced only by the destruction of the medial preoptic area. Decrease in sleep after the medial preoptic area lesion was brought about by a decrease in the duration of the slow wave sleep episodes and the frequency of paradoxical sleep episodes. Decrease in sleep after the lateral preoptic area lesion was brought about by a decrease in the frequency of slow wave sleep episodes. There was a significant increase in brain temperature after the medial preoptic area lesion but not after the lateral preoptic area lesion. The rats with lesion in the medial preoptic area showed deficits in thermoregulation on exposure to cold, while those with the lateral preoptic area lesion showed deficits in heat defense ability. The present findings suggest that the medial preoptic area and the lateral preoptic area regulate sleep by different modalities and that there is an anatomical segregation of heat and cold defense functions within the basal forebrain.

Mechanisms and functions of coupling between sleep and temperature rhythms

Energy metabolism is strongly linked to the circadian rhythms in sleep and body temperature. Both heat production and heat loss show a circadian modulation. Sleep preferably occurs during the circadian phase of decreased heat production and increased heat loss, the latter due to a profound increase in skin blood flow and, consequently, skin warming. The coupling of these rhythms may differ depending on whether they are assessed in experimental laboratory studies or in habitual sleeping conditions. In habitual sleeping conditions, skin blood flow is for a prolonged time increased to a level hardly ever seen during wakefulness. Possible mechanisms linking the rhythms in sleep and core body and skin temperature are discussed, with a focus on causal effects of changes in core and skin temperature on sleep regulation. It is shown that changes in skin temperature rather than in core temperature causally affect sleep propensity. Contrary to earlier suggestions of a functional role of sleep in heat loss, it is argued that sleep facilitates a condition of increased skin blood flow during a prolonged circadian phase, yet limits heat loss and the risk of hypothermia. Sleep-related behavior including the creation of an isolated microclimate of high temperature by means of warm clothing and bedding in humans and the curling up, huddling and cuddling in animals all help limit heat loss The increase in skin blood flow that characterizes the sleeping period may thus not primarily reflect a thermoregulatory drive. There is indirect support for an alternative role of the prolonged period of increased skin blood flow: it may support maintenance of the skin as a primary barrier in host defense.