The role of reticular activating system in altering medial preoptic neuronal activity in anesthetized rats

Electrophysiological characterization of medial preoptic neurons in lactating rats and its modulation by hypocretin-1

The medial preoptic area (mPOA) undergoes through neuroanatomical changes across the postpartum period, during which its neurons play a critical role in the regulation of maternal behavior. In addition, this area is also crucial for sleep-wake regulation. We have previously shown that hypocretins (HCRT) within the mPOA facilitate active maternal behaviors in postpartum rats, while the blockade of endogenous HCRT in this area promotes nursing and sleep. To explore the mechanisms behind these HCRT actions, we aimed to evaluate the effects of juxta-cellular HCRT-1 administration on mPOA neurons in urethane-anesthetized postpartum and virgin female rats. We recorded mPOA single units and the electroencephalogram (EEG) and applied HCRT-1 juxta-cellular by pressure pulses. Our main results show that the electrophysiological characteristics of the mPOA neurons and their relationship with the EEG of postpartum rats did not differ from virgin rats. Additionally, neurons that respond to HCRT-1 had a slower firing rate than those that did not. In addition, administration of HCRT increased the activity in one group of neurons while decreasing it in another, both in postpartum and virgin rats. The mechanisms by which HCRT modulate functions controlled by the mPOA involve different cell populations.

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.

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.

Functional MRI shows activation of the medial preoptic area during sleep

Changes in the activity of the basal forebrain sleep regulating areas were studied noninvasively in conscious rats by employing functional magnetic resonance imaging (fMRI). Sleep-wakefulness (S-W) stages were identified with the help of electrophysiological recordings carried out simultaneously. An increase in the signal intensity was observed in the medial preoptic area (mPOA) during sleep indicating a heightened activity of neurons in this area. In some rats, there was a decrease in the activity of the fronto-parietal cortex. The sleep-induced increase in activity in the mPOA and decrease in the fronto-parietal cortex are in relation to their levels in the awake state. The findings helped to localize the critical area for the maintenance of slow wave sleep at the mPOA. These results further corroborate some of the previous suggestions based on neurotoxic lesion, chemical stimulation and electrophysiological recordings.

Excitation of the pedunculopontine tegmental NMDA receptors induces wakefulness and cortical activation in the rat

Microinjection of the excitatory amino acid, L-glutamate into the brainstem pedunculo pontine tegmentum (PPT) has been shown to induce wakefulness, however, it has been unclear that receptors mediate this effect. The aim of this study was to test the hypothesis that in the PPT, L-glutamate induces cortical activation and wakefulness via activation of NMDA receptors. To test this hypothesis, three sets of micro-injections into the PPT were carried out on two different groups of rats that were then allowed to move freely although chronic instrumentation recorded sleep/wake states. Three days after the initial control injections of saline, in a contra-lateral site, Group I was micro-injected with saline + glutamate (saline first, and glutamate 15 min later); after another 3 days, the same rats were micro-injected with the NMDA-receptor-specific antagonist, 2-amino-5-phosphonopentanoic acid, (AP5) + glutamate. Group II received the same initial control injections (saline only), then AP5 + glutamate and the saline + glutamate micro-injections last. In rats that were not pretreated with AP5, microinjection of a 90 ng dose of L-glutamate (0.48 nmol in a volume of 0.1 microl vehicle) kept animals awake for 2-3 hr by eliminating both slow-wave sleep (SWS) and rapid eye movement (REM) sleep. These behavioral state changes were accompanied by concomitant increase in the power of gamma (gamma) frequency (20-60 Hz) waves in the cortical EEG. Pretreatment of L-glutamate injection sites with 0.48 nmol of AP5 blocked L-glutamate-induced-wakefulness and preserved a normal amount of wakefulness and sleep. Pretreatment with AP5 decreased the power of gamma-wave activity below its control level. These results support the hypothesis that the glutamate-induced-wakefulness and cortical activation effects are mediated via the NMDA receptors.

Neuronal activity in the peribrachial area: relationship to behavioral state control

Extensive studies have ascribed a role to the brainstem cholinergic system in the generation of rapid eye movement (REM) sleep and ponto-geniculo-occipital (PGO) waves. Much of this work stems from systemic and central cholinergic drug administration studies. The brainstem cholinergic system is also implicated in cortical activation via basal forebrain, thalamic, and hypothalamic relay neurons. This cholinergic ascending reticular activating hypothesis has also been suggested by in vivo experiments under anesthetics and by in vitro studies using cholinergic agonists in thalamic and hypothalamic slices. During the last ten years, brainstem cholinergic neurons have been discovered to be in the peribrachial area (PBL). With the discovery of PBL cholinergic neurons, many studies were devoted to the examination of PBL neuronal activity and their connectivity. This article reviews PBL neuronal activity in behaving animals and the anatomical features of these neurons in relation to behavioral state control. The role of the PBL in the generation of REM sleep, PGO waves, and the ascending reticular activating system (ARAS) has been evaluated at the cellular and neurochemical level. Based on recent literature, tentative mechanisms of REM sleep generation, PGO waves generation, and the cortical activation process are also outlined.