Molecular Cloning of Forebrain mRNAs which are Modulated by Sleep Deprivation

Neurogranin-like immunoreactivity in the zebrafish brain during development

Neurogranin (Nrgn) is a neural protein that is enriched in the cerebral cortex and is involved in synaptic plasticity via its interaction with calmodulin. Recently we reported its expression in the brain of the adult zebrafish (Alba-González et al. J Comp Neurol 530:1569–1587, 2022). In this study we analyze the development of Nrgn-like immunoreactivity (Nrgn-like-ir) in the brain and sensory structures of zebrafish embryos and larvae, using whole mounts and sections. First Nrgn-like positive neurons appeared by 2 day post-fertilization (dpf) in restricted areas of the brain, mostly in the pallium, epiphysis and hindbrain. Nrgn-like populations increased noticeably by 3 dpf, reaching an adult-like pattern in 6 dpf. Most Nrgn-like positive neurons were observed in the olfactory organ, retina (most ganglion cells, some amacrine and bipolar cells), pallium, lateral hypothalamus, thalamus, optic tectum, torus semicircularis, octavolateralis area, and viscerosensory column. Immunoreactivity was also observed in axonal tracts originating in Nrgn-like neuronal populations, namely, the projection of Nrgn-like immunopositive primary olfactory fibers to olfactory glomeruli, that of Nrgn-like positive pallial cells to the hypothalamus, the Nrgn-like-ir optic nerve to the pretectum and optic tectum, the Nrgn-like immunolabeled lateral hypothalamus to the contralateral region via the horizontal commissure, the octavolateralis area to the midbrain via the lateral lemniscus, and the viscerosensory column to the dorsal isthmus via the secondary gustatory tract. The late expression of Nrgn in zebrafish neurons is probably related to functional maturation of higher brain centers, as reported in the mammalian telencephalon. The analysis of Nrgn expression in the zebrafish brain suggests that it may be a useful marker for specific neuronal circuitries.

Increased expression of dendrin in the dorsal horn of the spinal cord during stress is regulated by sex hormones

Chronic stress has various effects on organisms and is sex-specific. The aim of the study was to describe the expression of synapse strengthening protein, dendrin, in the spinal cord (SC) and the dependence of its expression on chronic stress and sex hormones. Thirteen-month-old female and male rats were castrated (ovariectomy [F-OVX] or orchidectomy [M-ORX]) or sham-operated (F-SH or M-SH), respectively. At age 15 months, three 10-day-sessions of sham stress (control, C) or chronic stress (S) were conducted. Dendrin expression was present in the thoracic SC segments and the dorsal root ganglia (DRG). In the SC, dendrin expression was prominent in superficial laminae of the dorsal horn and lamina X (central canal). The M-ORX-S group had the highest dendrin expression in the dorsal horn, being significantly higher than the M-ORX-C or M-SH-S groups (P < 0.05). Dendrin expression was significantly higher in the F-SH-S group than the F-SH-C group (P < 0.05), as well as in the F-SH-S than the M-SH-S (P < 0.05). Co-localization with the α-d-galactosyl-specific isolectin B4 (IB4) in central projections of the DRG neurons in the dorsal horn of the SC was 7.43 ± 3.36%, while with the calcitonin gene-related peptide (CGRP) was 8.47 ± 4.45%. Localization of dendrin was observed in soma and nuclei of neurons in the dorsal horn. Dendrin expression in pain-processing areas of the SC, the DRG neurons and their peripheral projections suggest possible roles in pain perception and modulation. Stress-induced increase in dendrin expression and its dependence on sex hormones may partially explain sex-specific pain hypersensitivity induced by stress.

Quantitative Proteomics of Sleep-Deprived Mouse Brains Reveals Global Changes in Mitochondrial Proteins

Sleep is a ubiquitous, tightly regulated, and evolutionarily conserved behavior observed in almost all animals. Prolonged sleep deprivation can be fatal, indicating that sleep is a physiological necessity. However, little is known about its core function. To gain insight into this mystery, we used advanced quantitative proteomics technology to survey the global changes in brain protein abundance. Aiming to gain a comprehensive profile, our proteomics workflow included filter-aided sample preparation (FASP), which increased the coverage of membrane proteins; tandem mass tag (TMT) labeling, for relative quantitation; and high resolution, high mass accuracy, high throughput mass spectrometry (MS). In total, we obtained the relative abundance ratios of 9888 proteins encoded by 6070 genes. Interestingly, we observed significant enrichment for mitochondrial proteins among the differentially expressed proteins. This finding suggests that sleep deprivation strongly affects signaling pathways that govern either energy metabolism or responses to mitochondrial stress. Additionally, the differentially-expressed proteins are enriched in pathways implicated in age-dependent neurodegenerative diseases, including Parkinson’s, Huntington’s, and Alzheimer’s, hinting at possible connections between sleep loss, mitochondrial stress, and neurodegeneration.

Genetic dissection of sleep homeostasis

Sleep is a complex behavior both in its manifestation and regulation, that is common to almost all animal species studied thus far. Sleep is not a unitary behavior and has many different aspects, each of which is tightly regulated and influenced by both genetic and environmental factors. Despite its essential role for performance, health, and well-being, genetic mechanisms underlying this complex behavior remain poorly understood. One important aspect of sleep concerns its homeostatic regulation, which ensures that levels of sleep need are kept within a range still allowing optimal functioning during wakefulness. Uncovering the genetic pathways underlying the homeostatic aspect of sleep is of particular importance because it could lead to insights concerning sleep's still elusive function and is therefore a main focus of current sleep research. In this chapter, we first give a definition of sleep homeostasis and describe the molecular genetics techniques that are used to examine it. We then provide a conceptual discussion on the problem of assessing a sleep homeostatic phenotype in various animal models. We finally highlight some of the studies with a focus on clock genes and adenosine signaling molecules.

A high-fat diet induces lower expression of retinoid receptors and their target genes GAP-43/neuromodulin and RC3/neurogranin in the rat brain

Numerous studies have reported an association between cognitive impairment in old age and nutritional factors, including dietary fat. Retinoic acid (RA) plays a central role in the maintenance of cognitive processes via its nuclear receptors (NR), retinoic acid receptor (RAR) and retinoid X receptor (RXR), and the control of target genes, e.g. the synaptic plasticity markers GAP-43/neuromodulin and RC3/neurogranin. Given the relationship between RA and the fatty acid signalling pathways mediated by their respective NR (RAR/RXR and PPAR), we investigated the effect of a high-fat diet (HFD) on (1) PUFA status in the plasma and brain, and (2) the expression of RA and fatty acid NR (RARbeta, RXRbetagamma and PPARdelta), and synaptic plasticity genes (GAP-43 and RC3), in young male Wistar rats. In the striatum of rats given a HFD for 8 weeks, real-time PCR (RT-PCR) revealed a decrease in mRNA levels of RARbeta ( - 14 %) and PPARdelta ( - 13 %) along with an increase in RXRbetagamma (+52 %). Concomitantly, RT-PCR and Western blot analysis revealed (1) a clear reduction in striatal mRNA and protein levels of RC3 ( - 24 and - 26 %, respectively) and GAP-43 ( - 10 and - 42 %, respectively), which was confirmed by in situ hybridisation, and (2) decreased hippocampal RC3 and GAP-43 protein levels (approximately 25 %). Additionally, HFD rats exhibited a significant decrease in plasma ( - 59 %) and brain ( - 6 %) n-3 PUFA content, mainly due to the loss of DHA. These results suggest that dietary fat induces neurobiological alterations by modulating the brain RA signalling pathway and n-3 PUFA content, which have been previously correlated with cognitive impairment.

The genetic and molecular regulation of sleep: from fruit flies to humans

It has been known for a long time that genetic factors affect sleep quantity and quality. Genetic screens have identified several mutations that affect sleep across species, pointing to an evolutionary conserved regulation of sleep. Moreover, it has also been recognized that sleep affects gene expression. These findings have given valuable insights into the molecular underpinnings of sleep regulation and function that might lead the way to more efficient treatments for sleep disorders.

What are microarrays teaching us about sleep?

Many fundamental questions about sleep remain unanswered. The presence of sleep across phyla suggests that it must serve a basic cellular and/or molecular function. Microarray studies, performed in several model systems, have identified classes of genes that are sleep-state regulated. This has led to the following concepts: first, a function of sleep is to maintain synaptic homeostasis; second, sleep is a stage of macromolecule biosynthesis; third, extending wakefulness leads to downregulation of several important metabolic pathways; and, fourth, extending wakefulness leads to endoplasmic reticulum stress. In human studies, microarrays are being applied to the identification of biomarkers for sleepiness and for the common debilitating condition of obstructive sleep apnea.

Adenosine and sleep deprivation promote NF-kappaB nuclear translocation in cholinergic basal forebrain

In our investigations related to the homeostatic sleep factor adenosine (AD), we previously demonstrated that the DNA-binding activity of the transcription factor NF-kappaB in rat cholinergic basal forebrain increased following 3 h of sleep deprivation (SD). However, the neurotransmitter nature of the cells and the SD-induced stimuli responsible for NF-kappaB activation were not defined. In this report, we demonstrate, using double labeling immunohistochemistry, that nuclear translocation of NF-kappaB occurs almost exclusively in the cholinergic neurons of the basal forebrain following 3 h of SD. Furthermore, cholinergic basal forebrain microinjection of AD (25 nmol/L) or the A(1) receptor agonist N(6)-cyclo-hexyladenosine (100 nmol/L) induced nuclear translocation of NF-kappaB, thus suggesting that SD-induced increased extracellular concentrations of AD, acting via the A(1) AD receptor, may be responsible for the nuclear translocation of NF-kappaB in cholinergic neurons. Moreover, blocking the nuclear translocation of NF-kappaB by injection of inhibitor peptide, SN50, immediately prior to 6 h SD significantly reduced delta activity (1-4 Hz) during the first two hours of recovery sleep. Together, these data suggest a role in sleep homeostasis for the SD-induced activation of NF-kappaB in cholinergic basal forebrain, and that transcription factor NF-kappaB may code for factor(s) that play a role in sleep homeostasis.

Extensive and divergent effects of sleep and wakefulness on brain gene expression

Sleep is present in all species where it has been studied, but its functions remain unknown. To investigate what benefits sleep may bring at the cellular level, we profiled gene expression in awake and sleeping rats by using high-density microarrays. We find that approximately 10% of the transcripts in the cerebral cortex change their expression between day and night and demonstrate that half of them are modulated by sleep and wakefulness independent of time of day. We also show that molecular correlates of sleep are found in the cerebellum, a structure not known for generating sleep rhythms. Finally, we show that different functional categories of genes are selectively associated with sleep and wakefulness. The approximately 100 known genes whose expression increases during sleep provide molecular support for the proposed involvement of sleep in protein synthesis and neural plasticity and point to a novel role for sleep in membrane trafficking and maintenance.

Expression of neurogranin and neuromodulin is affected in the striatum of vitamin A-deprived rats

Our previous data showed that vitamin A deficiency (VAD) induces, in whole brain, a reduced amount of mRNA for brain retinoic acid (RA) and triiodothyronine (T3) nuclear receptors (i.e., RAR, RXR, and TR, respectively), which is accompanied by reduced amounts of mRNA and protein of neurogranin (RC3, a neuronal protein involved in synaptic plasticity) as well as selective behavioral impairment. Given the important role of retinoids for optimal brain functioning, the effects of vitamin A depletion and subsequent administration of RA or T3 on the mRNA levels of RA and T3 nuclear receptors and on two target genes' (RC3 and neuromodulin or GAP43) mRNA and protein levels were examined in the hippocampus, striatum, and cerebral cortex. A quantitative real-time polymerase chain reaction (PCR), in situ hybridization, and Western blot analysis demonstrated that the striatal region is the brain site where both RA and T3 signaling pathways are most affected by VAD. Indeed, rats fed a vitamin A-free diet for 10 weeks exhibited decreased expression of RAR, RXR, TR, RC3, and GAP43 in the striatum. The administration of T3 to these vitamin A-deprived rats reversed the reduction in mRNA levels of RA and T3 nuclear receptors and in mRNA and protein levels of target genes in this region. These data suggest that modifications that appear preferentially in the striatum, a region highly sensitive to vitamin A bioavailability, may contribute to neurobiological alterations and the spatial learning impairment that occurs in vitamin A-deprived animals.

Functional genomics of sleep

Functional genomics is a systematic and high-throughput effort to analyze the functions of genes and gene products. Functional genomics is divided into gene- and phenotype-driven approaches. Gene-driven approaches to the functional genomics of sleep have demonstrated that transcripts of many genes change as a function of behavioral state. A phenotype-driven approach includes identification and characterization of gene function through the analyses of natural polygenic traits, creation of transgenic animals or high-throughput mutagenesis. Identification of a gene for narcolepsy through QTL analyses and concomitantly using a transgenic approach is one example of the phenotype-driven approach to the functional genomics of sleep. Though the majority of functional genomics is currently performed in mice, the rat is emerging as an important model for genomic research. Since rest in Drosophila shares many features with mammalian sleep, this allows a comparative functional genomics approach to the study of rest and sleep. The concepts outlined here for the functional genomics of sleep are applicable to respiration research.

Chronic ethanol consumption restores the age-related decrease in neurogranin mRNA level in the hippocampus of mice

Neurogranin (Ng) is a Ca(2+)-sensitive calmodulin-binding neuron-specific protein that has been implicated in the regulation of numerous post-synaptic signalling pathways. Here, we investigate the effects of 5 months low level ethanol consumption (approximately 20% of total calories intake) on Ng mRNA expression in the brain of adult (approximately 7-8 months) and aged (approximately 21-22 months) mice using in situ hybridization histochemistry. Results showed that ageing was accompanied by a decrease in amounts of mRNA coding for Ng, especially in the hippocampus (approximately 25% of adults) known to play a critical role in higher cognitive functions. Chronic ethanol consumption restored this decline up to pre-senescent (adult) levels without altering Ng mRNA levels in adult mice. On the basis of recent data indicating a central role for Ng in the regulation of hippocampal synaptic plasticity and spatial learning, our results suggest that moderate ethanol consumption might have a beneficial influence on cognitive deterioration during senescence. Such a possibility is in fact congruent with recent follow-up studies conducted in elderly people.

Selective age-related changes in the PKC-sensitive, calmodulin-binding protein, neurogranin, in the mouse brain

Brain ageing is associated with a dysregulation of intracellular calcium (Ca(2+)) homeostasis which leads to deficits in Ca(2+)-dependent signalling pathways and altered neuronal functions. Given the crucial role of neurogranin/RC3 (Ng) in the post-synaptic regulation of Ca(2+) and calmodulin levels, age-dependent changes in the levels of Ng mRNA and protein expression were analysed in 3, 12, 24 and 31-month-old mouse brains. Ageing produced significant decreases in Ng mRNA expression in the dorsal hippocampal subfields, retrosplenial and primary motor cortices, whereas no reliable changes were seen in any other cortical regions examined. Western blot indicated that Ng protein expression was also down-regulated in the ageing mouse brain. Analysis of Ng immunoreactivity in both hippocampal CA1 and retrosplenial areas indicated that Ng protein in aged mice decreased predominantly in the dendritic segments of pyramidal neurones. These data suggest that age-related changes of post-synaptic Ng in selected brain areas, and particularly in hippocampus, may contribute to altered Ca(2+)/calmodulin-signalling pathways and to region-specific impairments of synaptic plasticity and cognitive decline.

Gene expression in the brain across the sleep-waking cycle

Sleep and waking differ significantly in terms of behavior, metabolism, and neuronal activity. Recent evidence indicates that sleep and waking also differ with respect to the expression of certain genes. To systematically investigate such changes, we used mRNA differential display and cDNA microarrays to screen approximately 10000 transcripts expressed in the cerebral cortex of rats after 8 h of sleep, spontaneous waking, or sleep deprivation. We found that 44 genes had higher mRNA levels after waking and/or sleep deprivation relative to sleep, while 10 were upregulated after sleep. Known genes that were upregulated in waking and sleep deprivation can be grouped into the following categories: immediate early genes/transcription factors (Arc, CHOP, IER5, NGFI-A, NGFI-B, N-Ras, Stat3), genes related to energy metabolism (glucose type I transporter Glut1, Vgf), growth factors/adhesion molecules (BDNF, TrkB, F3 adhesion molecule), chaperones/heat shock proteins (BiP, ERP72, GRP75, HSP60, HSP70), vesicle- and synapse-related genes (chromogranin C, synaptotagmin IV), neurotransmitter/hormone receptors (adrenergic receptor alpha(1A) and beta(2), GABA(A) receptor beta(3), glutamate NMDA receptor 2A, glutamate AMPA receptor GluR2 and GluR3, nicotinic acetylcholine receptor beta(2), thyroid hormone receptor TRbeta), neurotransmitter transporters (glutamate/aspartate transporter GLAST, Na(+)/Cl(-) transporter NTT4/Rxt1), enzymes (aryl sulfotransferase, c-jun N-terminal kinase 1, serum/glucocorticoid-induced serine/threonine kinase), and a miscellaneous group (calmodulin, cyclin D2, LMO-4, metallothionein 3). Several other genes that were upregulated in waking and all the genes upregulated in sleep, with the exception of the one coding for membrane protein E25, did not match any known sequence. Thus, significant changes in gene expression occur across behavioral states, which are likely to affect basic cellular functions such as RNA and protein synthesis, neural plasticity, neurotransmission, and metabolism.

Gene expression in the brain across the hibernation cycle

The purpose of this study was to characterize changes in gene expression in the brain of a seasonal hibernator, the golden-mantled ground squirrel, Spermophilus lateralis, during the hibernation season. Very little information is available on molecular changes that correlate with hibernation state, and what has been done focused mainly on seasonal changes in peripheral tissues. We produced over 4000 reverse transcription-PCR products from euthermic and hibernating brain and compared them using differential display. Twenty-nine of the most promising were examined by Northern analysis. Although some small differences were observed across hibernation states, none of the 29 had significant changes. However, a more direct approach, investigating expression of putative hibernation-responsive genes by Northern analysis, revealed an increase in expression of transcription factors c-fos, junB, and c-Jun, but not junD, commencing during late torpor and peaking during the arousal phase of individual hibernation bouts. In contrast, prostaglandin D2 synthase declined during late torpor and arousal but returned to a high level on return to euthermia. Other genes that have putative roles in mammalian sleep or specific brain functions, including somatostatin, enkephalin, growth-associated protein 43, glutamate acid decarboxylases 65/67, histidine decarboxylase, and a sleep-related transcript SD464 did not change significantly during individual hibernation bouts. We also observed no decline in total RNA or total mRNA during torpor; such a decline had been previously hypothesized. Therefore, it appears that the dramatic changes in body temperature and other physiological variables that accompany hibernation involve only modest reprogramming of gene expression or steady-state mRNA levels.

Differences in brain gene expression between sleep and waking as revealed by mRNA differential display and cDNA microarray technology

The consequences of sleep and sleep deprivation at the molecular level are largely unexplored. Knowledge of such molecular events is essential to understand the restorative processes occurring during sleep as well as the cellular mechanisms of sleep regulation. Here we review the available data about changes in neural gene expression across different behavioural states using candidate gene approaches such as in situ hybridization and immunocytochemistry. We then describe new techniques for systematic screening of gene expression in the brain, such as subtractive hybridization, mRNA differential display, and cDNA microarray technology, outlining advantages and disadvantages of these methods. Finally, we summarize our initial results of a systematic screening of gene expression in the rat brain across behavioural states using mRNA differential display and cDNA microarray technology. The expression pattern of approximately 7000 genes was analysed in the cerebral cortex of rats after 3 h of spontaneous sleep, 3 h of spontaneous waking, or 3 h of sleep deprivation. While the majority of transcripts were expressed at the same level among these three conditions, 14 mRNAs were modulated by sleep and waking. Six transcripts, four more expressed in waking and two more expressed in sleep, corresponded to novel genes. The eight known transcripts were all expressed at higher levels in waking than in sleep and included transcription factors and mitochondrial genes. A possible role for these known transcripts in mediating neural plasticity during waking is discussed.

Differences in gene expression during sleep and wakefulness

Compared with our understanding of the electrophysiological correlates of sleep and wakefulness, the search for correlates at the molecular level is still in its infancy. However, the evidence obtained so far supports the hypothesis that reliable molecular correlates do exist. As will be summarized in this review, levels of receptor binding, second messengers and protein phosphorylation differ between sleep and wakefulness. Moreover, compelling data obtained in different animal species suggest that the transition between sleep and wakefulness is accompanied by significant changes in gene expression. Many immediate early genes, transcription factors, plasticity-related genes and mitochondrial genes are expressed at higher levels in wakefulness than in sleep, while a few still unknown genes are up-regulated during sleep. The ongoing systematic screening of gene expression across behavioural states should prove crucial in elucidating the regulatory mechanisms of sleep homeostasis and the functions of sleep.

Transcriptional activity in the brain during sleep deprivation

Molecular biological techniques combined with experimental sleep deprivation have revealed alterations in gene transcriptional activity of several proteins which may mediate the effects of prolonged wakefulness in the brain. During sleep deprivation gene transcription is altered in neuronal systems known to participate in the regulation of vigilance and sleep, ie the norardenergic and cholinergic systems, and several neuropeptides and cytokines. The study of immediate early genes during sleep deprivation has revealed increased transcriptional activity in those brain areas that are active during wakefulness. Systemic search for alterated levels of messenger RNA in sleep-deprived brain has revealed signal transduction proteins and metabolic enzymes which may mediate changes in neuronal function during prolonged wakefulness. The purpose of this article is to give a short overview of those genes whose transcription is affected by sleep deprivation according to the current literature, and to characterize the possible role of these genes in sleep regulation.

Identification of two novel diurnal genes by screening of a rat brain cDNA library

While the hypothalamus is fundamental for sleep and circadian regulation, the molecular mechanisms involved are poorly understood. We have used a differential gene expression technique to identify hypothalamic genes which have altered expression in rat sleep periods. Complex cDNA probes from rat hypothalami removed at Zeitgeber times 4 and 15 were hybridised to rat brain cDNA library girds. From 30 differentially expressed clones, six were further analysed and two were confirmed to exhibit increased expression at Zeitgeber time 4. A Northern blot hybridization of brain, heart, kidney, lung, testis and skin mRNA showed that both clones were brain specific. Therefore, we have identified two novel brain specific diurnally expressed hypothalamic genes. Both genes may have roles in sleep or circadian regulation.

Differences in gene expression between sleep and waking as revealed by mRNA differential display

In order to systematically investigate differences in gene expression between sleep and waking, mRNA differential display was used to examine mRNAs from the cerebral cortex of rats who had been spontaneously asleep, spontaneously awake, or sleep deprived for a period of 3 h. It was found that, while the vast majority of transcripts were expressed at the same level among these three conditions, the expression of a subset of mRNAs was modulated by sleep and waking. Half of these transcripts had known sequences in databases. RNAs expressed at higher levels during waking included those for the transcription factors c-fos, NGFI-A, and rlf, as well as three transcripts encoded by the mitochondrial genome, those for subunit I of cytochrome c oxidase, subunit 2 of NADH dehydrogenase, and 12S rRNA. As shown by in situ hybridization, the level of RNAs encoded by the mitochondrial genome was uniformly higher during waking in many cortical regions and in several extracortical structures. By contrast, mRNA levels corresponding to two mitochondrial protein subunits encoded by the nuclear genome were unchanged. This finding suggests the hypothesis that an increase in the level of mitochondrial RNAs may represent a rapid regulatory response of neural tissue to adapt to the increased metabolic demand of waking with respect to sleep.

RC3/neurogranin, a postsynaptic calpacitin for setting the response threshold to calcium influxes

In this review, we attempt to cover the descriptive, biochemical and molecular biological work that has contributed to our current knowledge about RC3/neurogranin function and its role in dendritic spine development, long-term potentiation, long-term depression, learning, and memory. Based on the data reviewed here, we propose that RC3, GAP-43, and the small cerebellum-enriched peptide, PEP-19, belong to a protein family that we have named the calpacitins. Membership in this family is based on sequence homology and, we believe, a common biochemical function. We propose a model wherein RC3 and GAP-43 regulate calmodulin availability in dendritic spines and axons, respectively, and calmodulin regulates their ability to amplify the mobilization of Ca2+ in response to metabotropic glutamate receptor stimulation. PEP-19 may serve a similar function in the cerebellum, although biochemical characterization of this molecule has lagged behind that of RC3 and GAP-43. We suggest that these molecules release CaM rapidly in response to large influxes of Ca2+ and slowly in response to small increases. This nonlinear response is analogous to the behavior of a capacitor, hence the name calpacitin. Since CaM regulates the ability of RC3 to amplify the effects of metabotropic glutamate receptor agonists, this activity must, necessarily, exhibit nonlinear kinetics as well. The capacitance of the system is regulated by phosphorylation by protein kinase C, which abrogates interactions between calmodulin and RC3 or GAP-43. We further propose that the ratio of phosphorylated to unphosphorylated RC3 determines the sliding LTP/LTD threshold in concept with Ca2+/ calmodulin-dependent kinase II. Finally, we suggest that the close association between RC3 and a subset of mitochondria serves to couple energy production with the synthetic events that accompany dendritic spine development and remodeling.

NGFI-A expression in the rat brain after sleep deprivation

The effects of total sleep deprivation (SD) on the expression of the immediate-early gene NGFI-A were studied in the rat brain by in situ hybridization. Rats were manually sleep-deprived for 3, 6, 12 and 24 h starting at light onset (08:00 h) and for 12 h starting at dark onset (20:00 h). SD performed during the day induced a marked increase in NGFI-A mRNA levels with respect to sleep controls in many cerebrocortical areas and caudate-putamen, which was most evident after 6 h SD. A decrease was seen in hippocampus and thalamus, particularly after 12 h SD. Rats sleep-deprived for 12 h during the night showed an increase in NGFI-A expression in some cortical areas while rats sleep-deprived for 24 h showed few changes with respect to controls. The pattern of NGFI-A expression after forced wakefulness showed some differences from that observed after spontaneous wakefulness [M. Pompeiano, C. Cirelli and G. Tononi, Immediate early genes in spontaneous wakefulness and sleep: expression of c-fos and NGFI-A mRNA and protein, J. Sleep Res., 3 (1994) 80-96]. These observations are discussed with respect to the functional consequences of wakefulness in specific brain areas.

Sleep deprivation differentially alters the mRNA and protein levels of neurogranin in rat brain

The mRNA level of the 17-kDa protein neurogranin (NG), a postsynaptic substrate of the protein kinase C, has previously been found to be decreased in rat forebrain after 24-h sleep deprivation (SD). To investigate the functional significance of this finding in various forebrain regions, the effect of 24-h SD on the mRNA level and the protein level of NG was determined in the cerebral cortex, hippocampus, and the total of the remaining subcortical forebrain plus midbrain areas (SFMA) of rats. In these areas, high levels of both NG mRNA and NG protein were detected by in situ hybridization and immunohistochemistry, respectively. NG protein was recognized in brain tissue by newly developed polyclonal antibodies. As determined by RNase protection assays, the level of NG mRNA was decreased in SFMA by 34 +/- 7% (P < 0.05) after 24-h SD, and was not significantly affected in the cerebral cortex and hippocampus. In contrast, on Western blots, the protein concentration of NG was reduced in the cerebral cortex by 37 +/- 7% (P < 0.05) whereas no significant changes were present in other brain areas tested. The results indicate that the mRNA and protein levels of NG are differentially modulated in rat brain by the prolongation of the waking period.

The sequential hypothesis of the function of sleep

In addition to modulatory roles concerning bodily functions, sleep is assumed to play a main processing role with regard to newly acquired neural information. Elaboration of memory traces acquired during the waking period is assumed to require two sequential steps taking place during slow wave sleep (SWS) and eventually during paradoxical sleep (PS). This view is suggested by several considerations, not the least of which concerns the natural sequence of appearance of SWS and PS in the adult animal. While the involvement of PS in memory processing is well documented, the involvement of SWS is supported by the results of baseline and post-trial EEG analyses carried out in rats trained for a two-way active avoidance task or a spatial habituation task. Together with control analyses, these data indicate that the marked increase in the average duration of post-trial SWS episodes does not reflect the outcome of non-specific contingent factors, such as sleep loss or stress, but is related to memory processing events. Several considerations have furthermore led to the proposal that, during SWS, after a preliminary selection step, the first processing operation consists in the weakening of non-adaptative memory traces. The remaining memory traces would then be stored again under a better configuration during the ensuing PS episode. This view is in agreement with several relevant features of sleep, including the EEG waveforms prevailing during SWS and PS, as well as the ontogenetic sequence of appearance of SWS and PS. Some theoretical considerations on the role of sleep are also in agreement with the sequential hypothesis. More recent data indicate that the learning capacity of rats is correlated with several baseline EEG features of sleep and wakefulness. They include the average duration of PS episodes and of SWS episodes followed by wakefulness (longer in fast learning rats), and the waking EEG power spectrum of fast learning rats whose output is more balanced in the frequency range below 10 Hz than in slow learning and in non-learning rats. Additional EEG data suggest that fast learning rats may accomplish 'on line' processing of newly acquired information according to a sequence of events not dissimilar from the one proposed by the sequential hypothesis.

Sleep deprivation and c-fos expression in the rat brain

This study examined the effects of sleep deprivation on the expression of the immediate early gene c-fos in the brain with both in situ hybridization and immunocytochemistry. Rats were manually sleep-derived for 3 h, 6 h, 12 h, and 24 h starting at light onset (08.00 hours), and for 12 h starting at dark onset (20.00 hours). c-Fos expression was found to be higher in sleep-deprived rats with respect to control animals in several brain areas. The increase was evident both in terms of c-fos mRNA and Fos protein, although with a different time course. Among the areas that showed a consistent induction of c-fos were many cortical regions, the medial preoptic area and the posterior hypothalamic area, some thalamic nuclei, and several nuclei of the dorsal pontine tegmentum. The pattern of c-fos expression after sleep deprivation was very similar to that observed after comparable periods of spontaneous wakefulness (Pompeiano et al. 1994). In general, the increase in c-fos expression was not simply proportional to the amount of previous wakefulness. In many areas, the highest levels of c-fos were seen after 3 h of sleep deprivation. These observations are discussed with respect to the homeostatic regulation of sleep and to the functional consequences of wakefulness in specific brain areas.

Towards a molecular biology of the circadian clock and sleep of mammals

Behavioral states of rest and activity are temporally organized. Since the beginning of life on Earth, plants and animals have been forced to adapt to the daily rhythm of the planet's rotation about its axis. In complex vertebrates (birds and mammals), rest and activity have evolved into the electrophysiologically and behaviorally distinct states of sleep and wakefulness. The evolutionary emergence of bouts of rapid eye movement (REM) sleep may be even more recent; the echidna, one of the earliest mammals, lacks this sleep stage (Siegel et al., 1994), The cycling of these behavioral states is under neural control, and much is known about their cellular basis, but the underlying events at the molecular level are virtually unknown. Here each of us highlights some of the new approaches for investigating the molecular substrate for behavioral state control of circadian rhythmicity (WJS) and sleep (PJS) in mammals.

Glutamine synthetase modulation in the brain of rats subjected to deprivation of paradoxical sleep

Changes in the level of glutamine synthetase (GS), an enzyme mainly located in astrocytes, were investigated in rat brain after deprivation of paradoxical sleep (PSD) and during recovery. An immunotitration method was used to evaluate the relative level of GS in brain tissue. At the end of a 24 h PSD, a significant increase in GS protein was observed both in the frontoparietal cortex (CX) and in the locus coeruleus area (LC). Four hours later during recovery, the level of GS protein returned to normal level in the CX but fell below control levels in the LC. In contrast, in the CX, the level of glial fibrillary acidic protein, an astroglial marker, did not change after PSD or during recovery. GS mRNA was quantified in the entire cortex by northern blot hybridization using of an oligonucleotidic GS-cDNA probe. We observed an increase in the GS mRNA level in the cortex of PSD rats of the same magnitude as the increase in GS protein. Both GS mRNA and GS protein tended to return to control values 4 h later during recovery. These results are discussed with particular attention to stress effects and possible physiological mechanisms regarding the regulation of amino acid levels by neurotransmitters during prolonged waking or neuronal excitation.

c-fos mRNA is spontaneously induced in the rat brain during the activity period of the circadian cycle

The basal expression of the proto-oncogene c-fos was studied by Northern blot analysis in different regions of the rat brain during 24 h. A striking spontaneous oscillation of c-fos mRNA expression was detected in animals kept in basal conditions with a 12 h light/12 h dark cycle. In these animals c-fos mRNA was just detectable during the rest hours (morning through afternoon), and was high during the activity hours (night). The periodicity of this oscillation persisted and became free-running when the animals were exposed for 6 consecutive days to constant light or darkness. It was thus demonstrated that the fluctuation of c-fos expression is circadian and is not created by the light-dark cycle, but the latter exerts a synchronizing effect. The oscillation of c-fos mRNA was modified by manipulations of the rest-activity cycle. In particular, the fluctuation observed in basal conditions was inverted, keeping the animals awake during the rest hours (diurnal) and allowing them to sleep in the activity period (nocturnal). These data indicated a close relationship between the oscillation of c-fos expression and the rest-activity cycle. Finally, electroencephalographic (EEG) monitoring was performed under behavioural control for 3 h before the animals were killed. These experiments confirmed that, irrespective of the time of day, the EEG pattern typical of a state of sleep (including both slow waves and paradoxical sleep) was associated with low or undetectable c-fos levels, whereas the protracted EEG desynchronization corresponding to wakefulness was associated with high c-fos expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypnotics and sleep physiology: a consensus report. European Sleep Research Society, Committee on Hypnotics and Sleep Physiology

The effects of hypnotics on descriptive and functional aspects of electrophysiological sleep parameters are assessed in this report. Because of the arbitrary definition of some of the criteria underlying the conventional sleep stage scoring procedure, computer-aided methods of EEG analysis have become increasingly important for recording and interpreting pharmacological effects on sleep. Of particular interest are the changes of EEG slow-wave activity, since this parameter varies as a function of prior sleep and waking. Several types of interaction between hypnotics and sleep regulation are discussed, some recent pharmacological developments are highlighted, and some common problems in clinical trials are specified.