Induction Of Slow-wave Sleep Research Articles

A Critical Time-Window for the Selective Induction of Hippocampal Memory Consolidation by a Brief Episode of Slow-Wave Sleep

Although extensively studied, the exact role of sleep in learning and memory is still not very clear. Sleep deprivation has been most frequently used to explore the effects of sleep on learning and memory, but the results from such studies are inevitably complicated by concurrent stress and distress. Furthermore, it is not clear whether there is a strict time-window between sleep and memory consolidation. In the present study we were able to induce time-locked slow-wave sleep (SWS) in mice by optogenetically stimulating GABAergic neurons in the parafacial zone (PZ), providing a direct approach to analyze the influences of SWS on learning and memory with precise time-windows. We found that SWS induced by light for 30 min immediately or 15 min after the training phase of the object-in-place task significantly prolonged the memory from 30 min to 6 h. However, induction of SWS 30 min after the training phase did not improve memory, suggesting a critical time-window between the induction of a brief episode of SWS and learning for memory consolidation. Application of a gentle touch to the mice during light stimulation to prevent SWS induction also failed to improve memory, indicating the specific role of SWS, but not the activation of PZ GABAergic neurons itself, in memory consolidation. Similar influences of light-induced SWS on memory consolidation also occurred for Y-maze spatial memory and contextual fear memory, but not for cued fear memory. SWS induction immediately before the test phase had no effect on memory performance, indicating that SWS does not affect memory retrieval. Thus, by induction of a brief-episode SWS we have revealed a critical time window for the consolidation of hippocampus-dependent memory.

Expression and Purification of Delta Sleep-Inducing Peptide Fused with Protein Transduction Domain and Human Serum Albumin in Pichia pastoris.

Sleep is a natural part of every individual's life. Delta sleep-inducing peptide (DSIP) is a nonapeptide that could promote sleep through the induction of slow wave sleep. However, little is known about the pharmacological effect of DSIP on insomnia. The main objective of this study was to analyze the pharmacological effect of DSIP on insomnia. We designed a fusion protein containing N-terminal TAT-based transduction domain followed by human serum albumin and DSIP and designated this protein as PHD fusion protein. The PHD fusion protein were expressed in Pichia pastoris and purified. Mice were administered single subcutaneous injections three concentrations of PHD fusion protein (0.5, 1, 2 mg/kg), and the pharmacological activity of PHD fusion protein was studied using classic pentobarbitalinduced sleep test. We expressed the PHD fusion protein in P. pastoris; furthermore, the PHD fused protein was purified to near homogeneity by DEAE Sepharose FF, Phenyl Sepharose HP and Blue Sepharose 6 FF. Our result showed that the increase of pentobarbital-induced hypnotic effect characterized by reducing sleep latency and prolonged sleep duration was observed for increasing concentrations of PHD fusion protein (P<0.05); moreover, different dose of PHD fusion protein could induce the mice to re-sleep in a dose-dependent manner, whereas higher doses of PHD fusion protein (1.0, 2.0 mg/kg) significantly increased the rate of sleep re-onset compared with the vehicle group of mice (P<0.05). PHD fusion protein increased the hypnotic effects of pentobarbital by reducing sleep latency and prolonged sleep duration. The present study suggested PHD fusion protein could be a new drug candidate for insomnia.

Acute Optogenetic Silencing of Orexin/Hypocretin Neurons Induces Slow-Wave Sleep in Mice

Orexin/hypocretin neurons have a crucial role in the regulation of sleep and wakefulness. To help determine how these neurons promote wakefulness, we generated transgenic mice in which orexin neurons expressed halorhodopsin (orexin/Halo mice), an orange light-activated neuronal silencer. Slice patch-clamp recordings of orexin neurons that expressed halorhodopsin demonstrated that orange light photic illumination immediately hyperpolarized membrane potential and inhibited orexin neuron discharge in proportion to illumination intensity. Acute silencing of orexin neurons in vivo during the day (the inactive period) induced synchronization of the electroencephalogram and a reduction in amplitude of the electromyogram that is characteristic of slow-wave sleep (SWS). In contrast, orexin neuron photoinhibition was ineffective during the night (active period). Acute photoinhibition of orexin neurons during the day in orexin/Halo mice also reduced discharge of neurons in an orexin terminal field, the dorsal raphe (DR) nucleus. However, serotonergic DR neurons exhibited normal discharge rates in mice lacking orexin neurons. Thus, although usually highly dependent on orexin neuronal activity, serotonergic DR neuronal activity can be regulated appropriately in the chronic absence of orexin input. Together, these results demonstrate that acute inhibition of orexin neurons results in time-of-day-dependent induction of SWS and in reduced firing rate of neurons in an efferent projection site thought to be involved in arousal state regulation. The results presented here advance our understanding of the role of orexin neurons in the regulation of sleep/wakefulness and may be relevant to the mechanisms that underlie symptom progression in narcolepsy.

Neurodegeneration, sleep, and cerebral energy metabolism: a testable hypothesis.

Varying degrees of metabolic arrest are used by many living species to survive in a harsh environment. For example, in hibernating mammals, neuronal activity and cerebral metabolism are profoundly depressed in most regions of the brain and limited energy resources are deployed to maintain vital cell functions. Gathering evidence suggests that energy resources are also limited in both Alzheimer's and Parkinson's diseases, and that this promotes metabolic stress and the degenerative process. Key steps in this process are energy requiring, and this further compromises cell energy reserves. It may be possible to slow the progress of these diseases by inducing slow-wave sleep (SWS) at night with gammahydroxybutyrate. Patients with these diseases sleep poorly and generate little SWS. SWS and hibernation are thought to be on a continuum of energy conservation. Thus, the induction of SWS may retard the degenerative process by depressing cell metabolism and by directing energy utilization to vital cell functions. In this way, GHB-induced SWS may duplicate the effects of hibernation and extend biologic time.

Cytokines in neuronal cell types

Cytokines are signals in the immune system, and may have effects on cells distant from the cells of origin. These proteins have been suggested as messengers in the communication between the immune system and the nervous system, in which signals travel only short distances. Neuroimmune interactions have been discussed in view of findings that nervous signals are important for the immune response. The occurrence of neurotransmitter receptors on lymphocytes and cytokine receptors on nerve cells or glia has initiated further studies e.g. on the localization of different cytokines in the nervous system and on long and short term actions of cytokines in the nervous system. Interleukin-1 has been studied extensively along these lines, and found to occur in the nervous and endocrine system, for example in the adrenal chromaffin cells, and to have effects such as induction of slow-wave sleep and stimulation of adrenocortical and gonadotropic hormones. Other cytokines implicated as signals in neuroimmune interactions are IL-2, IL-6, IFN-γ and TNF-α. The functional studies suggest the occurrence of cytokine receptors in the brain, and experiments using 125iodine-labelled IL-1α demonstrate differential distribution of binding sites in the mouse brain. Recently, evidence emerged of an endogenous receptor antagonist for IL-1, which may prove useful for the understanding of the mechanisms of IL-1's actions in the nervous system. A role for cytokines in regulation of the immune response but also in adjusting the organism to the host reaction is implicated. Furthermore, several findings indicate their role as growth promoting factors, and for example the induction of NGF production by IL-1 suggests involvement of this cytokine in regeneration and development in the nervous system. The significance of neuronally produced cytokines may be based upon the anatomically distinct releasing sites that the specific synaptic organization of the nervous system offer and future studies should determine whether cytokines act as neurotransmitters.

Bordetella pertussis tracheal cytotoxin and other muramyl peptides: distinct structure-activity relationships for respiratory epithelial cytopathology.

Tracheal cytotoxin (TCT) is a disaccharide-tetrapeptide released by Bordetella pertussis, the causative agent of pertussis (whooping cough). We have previously determined the structure of TCT to be GlcNAc-1,6-anhydro-MurNAc-L-Ala-gamma-D-Glu-meso-A2pm-D-Ala, where MurNAc = N-acetylmuramic acid and A2pm = diaminopimelic acid. Purified TCT reproduces the respiratory cytopathology observed during pertussis, including ciliostasis and extrusion of ciliated cells. We have tested structural analogs of TCT for their ability to reproduce native TCT toxicity in explanted hamster tracheal tissue and hamster trachea epithelial (HTE) cell cultures. Other investigators have evaluated many of these analogs, which are muramyl or desmuramyl peptides, for muramyl peptide activities such as immunopotentiation, induction of slow-wave sleep, and pyrogenicity. Four desmuramyl peptides were produced in our laboratory from B. pertussis peptidoglycan or by chemical synthesis, including unusual peptides containing alpha-aminopimelic acid in place of A2pm. Based on the relative ability of compounds to inhibit DNA synthesis in HTE cells, truncated analogs lacking A2pm entirely or lacking only the side-chain amine or carboxyl group of A2pm were less active than TCT by a factor of at least 1000. All active analogs included a native or near-native peptide moiety, independent of the presence, absence, or substitution of the sugar moiety. We conclude that the structural requirements for TCT toxicity differ considerably from those for most other muramyl peptide activities, in that the disaccharide moiety is irrelevant for toxicity and both the free amino and carboxyl groups of the A2pm side chain are required for activity.

Increase of multiple unit activity during slow wave sleep in the cat preoptic area

Multiple unit activities (MUA) in 307 brainstem sites were recorded by chronically implanted electrodes in cats, using a polygraph with 4 channel MUA recording units. During transition from waking to slow wave sleep, at 15 sites including the medial preoptic area (11), the diagonal band of Broca (2) and medial anterior hypothalamic area (2), consistently earlier increase of MUA in discharge rate was observed, while MUA in other areas decreased. Also, at 13 sites in these areas, a decrease in discharge rate was demonstrated during paradoxical sleep. These findings suggest a close relationship between the preoptic area and sleep mechanisms, supporting a notion that an active site for induction of slow wave sleep may reside in the preoptic area.

A GABAergic habenulo-raphe pathway mediates both serotoninergic and hypnogenic effects of vasotocin in cats

Extremely small amounts (10 −4 pg) of the pineal nonapeptide arginine vasotocin (AVT), injected into the pineal recess of freely moving cats, decreased the levels of 5-hydroxyindole acetic acid (5-HIAA) in the raphe dorsalis nucleus and induced slow wave sleep. In cats with lesions in the lateral habenula, 10 −4 pg AVT injected into the pineal recess, failed to decrease raphe dorsalis 5-HIAA levels and to induce slow wave sleep. The GABA antagonist picrotoxin (1 ng) injected into the pineal recess 15 min before the administration of AVT (10 −4 pg), completely prevented AVT from decreasing raphe dorsalis 5-HIAA levels and from inducing slow wave sleep. A highly significant correlation could be established between the decrease of raphe dorsalis 5-HIAA levels and the induction of slow wave sleep. No changes in raphe dorsalis 5-HIAA levels could be detected in cats injected with 10 −4 pg AVT into the lateral or into the fourth ventricle. Neither arginine vasopressin nor oxytocin (10 −4 pg) injected into the pineal recess, could alter raphe dorsalis 5-HIAA levels. It is concluded that AVT induces slow-wave sleep in cats by activating an inhibitory GABAergic lateral habenula-raphe dorsalis pathway.