Changes in protein levels in perfusates of freely moving cats: relation to behavioral state

The interaction between diet and neurobehavior in very low birth weight infants

BACKGROUND

Modulation of behavior and physiology by dietary perturbations early in life can provide clues to the pathogenesis of adult diseases. We tested the hypothesis that a period of early protein supplementation modulates sympathetic nervous system activity demonstrated indirectly by an increase in active sleep state distribution in very low birth weight (VLBW) infants.

METHODS

VLBW infants (n = 71) were randomized to a total parenteral nutritional regimen providing 18% of the energy intake as amino acids (AA) or a conventional regimen providing 12.5% to achieve targeted AA intakes of 4 g/kg/day (0.004 kcal/kg/day) and 3 g/kg/day (0.003 kcal/kg/day), respectively. Both groups were weaned to enteral feeding and advanced to provide similar AA intake of 4 g/kg/day (0.004 kcal/kg/day). Six-hour daytime, behavioral sleep studies were performed when the infants reached full enteral intake (165 ml/kg/day).

RESULTS

Infants in the high protein group spent more time in active sleep (77.2 ± 10.5% vs. 70.7 ± 11.8%), p < 0.01 and less time in quiet sleep (12.9 ± 3.4% vs. 17.7 ± 7.0%, p < 0.01) as compared to the conventional group. No group differences were observed for indeterminate sleep, awake, or crying states.

CONCLUSIONS

These results suggest that dietary intake may indirectly influence sympathetic nervous system activity.

IMPACT

Infants randomized to an early, high protein nutritional regimen spent an increased percentage of time in active sleep, supporting the hypothesis that nutrition and behavior are interactive. Furthermore, sleep states are an indirect measure of sympathetic nervous system activity, suggesting that dietary intake may influence sympathetic nervous system activity. This study highlights the importance of considering the impact of nutrition during critical periods of development in order to further understand and improve the long-term outcomes of very low birth weight infants.

A Molecular Window on Sleep: Changes in Gene Expression between Sleep and Wakefulness

Sleep is thought to be “by the brain and for the brain,” but despite decades of behavioral and neurophysiologic research, we still do not know why the brain actually needs to sleep. Recently, gene expression studies have allowed researchers to investigate the molecular correlates of sleep and wakefulness and to gain new insights into the benefits that sleep may bring at the cellular level. In the latest series of studies, a genome-wide screening of brain gene expression was performed in rats that had been asleep, spontaneously awake, or sleep deprived for 8 hours. It was found that of ~15,000 transcripts expressed in the cerebral cortex, about 5% change their expression levels depending on behavioral state but independently of time of day. Half of the modulated genes increase in wakefulness and half in sleep. Moreover, wakefulness-related and sleep-related transcripts belong to different functional categories. Waking-related transcripts are involved in energy metabolism, excitatory neurotransmission, transcriptional activation, synaptic potentiation and memory acquisition, and the response to cellular stress. Sleep-related transcripts are involved in brain protein synthesis, synaptic consolidation/depression, and membrane trafficking and maintenance, including cholesterol metabolism, myelin formation, and synaptic vesicle turnover.

Differential impact of REM sleep deprivation on cytoskeletal proteins of brain regions involved in sleep regulation

Rapid eye movement (REM) sleep is involved in memory consolidation, which implies synaptic plasticity. This process requires protein synthesis and the reorganization of the neural cytoskeleton. REM sleep deprivation (REMSD) has an impact on some neuronal proteins involved in synaptic plasticity, such as glutamate receptors and postsynaptic density protein 95, but its effects on cytoskeletal proteins is unknown. In this study, the effects of REMSD on the content of the cytoskeletal proteins MAP2 and TAU were analyzed. Adult female rats were submitted to selective REMSD by using the multiple platform technique. After 24, 48 or 72 h of REMSD, rats were decapitated and the following brain areas were dissected: pons, preoptic area, hippocampus and frontal cortex. Protein extraction and Western blot were performed. Results showed an increase in TAU content in the pons, preoptic area and hippocampus after 24 h of REMSD, while in the frontal cortex a significant increase in TAU content was observed after 72 h of REMSD. A TAU content decrease was observed in the hippocampus after 48 h of REMSD. Interestingly, a marked increase in TAU content was observed after 72 h of REMSD. MAP2 content only increased in the preoptic area at 24 h, and in the frontal cortex after 24 and 72 h of REMSD, without significant changes in the pons and hippocampus. These results support the idea that REM sleep plays an important role in the organization of neural cytoskeleton, and that this effect is tissue-specific.

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.

Molecular correlates of sleep and wakefulness in the brain of the white-crowned sparrow

In the mammalian brain, sleep and wakefulness are associated with widespread changes in gene expression. The extent to which the molecular correlates of vigilance state are conserved across phylogeny, however, is only beginning to be explored. The goal of this study was to determine whether sleep and wakefulness affect gene expression in the avian brain. To achieve this end we performed an extensive microarray analysis of gene expression during sleep, wakefulness, and short-term sleep deprivation in the telencephalon of the white-crowned sparrow (Zonotrichia leucophrys gambelii). We found that, as in the rodent cerebral cortex, behavioral state, independent of time of day, has widespread effects on avian brain gene expression, affecting the transcript levels of 255 genes (1.4% of all tested transcripts). Wakefulness-related transcripts (n = 114) code for proteins involved in energy metabolism and oxidative phosphorylation, immediate early genes and transcription factors associated with activity-dependent neural plasticity, as well as heat-shock proteins and molecular chaperones associated with the unfolded protein response. Sleep-related transcripts (n = 141) code for proteins involved in membrane trafficking, lipid/cholesterol synthesis, translational regulation, cellular adhesion, and cytoskeletal organization. Remarkably, despite the considerable differences in morphology and cytology between the mammalian neocortex and the avian telencephalon, the functional categories of transcripts identified in this study exhibit a significant degree of overlap with those identified in the rodent cortex.

Potential participation of cystatin C in rapid eye movement sleep (REMS) modulation

It has been hypothesized that proteins modulate rapid eye movement sleep (REMS). Studies have shown an increase in the liberation of proteins in the mesencephalic reticular formation of cats during REMS. It has also been determined that protein-synthesis inhibitors diminish REMS and that protease-inhibitors increase this sleep phase. These and other studies support the importance of "di novo" protein molecules in sleep, and in particular, in REMS regulation. In this context, it is important to determine the role of endogenous proteases and their endogenous inhibitors in sleep regulation. In this study, we found that Cystatin C (CC), an endogenous protease inhibitor, diminishes wakefulness and increases REMS. We have also found an increase in CC expression after REMS deprivation and a tendency to decrease after a 2 h period of REMS rebound. We further showed that REMS deprivation increases the expression of Cathepsin H (CH), a protease inhibited by CC. These results suggest that naturally occurring protease-inhibitors enhance REMS, perhaps by facilitating the availability of proteins.

Filling the gut activates paradoxical sleep in suckling rats

Recent studies with rat pups suggest that suckling and sleeping are coordinated through milk-related events in the gut. Our experiments revealed that suckling rats respond to milk in the upper gastrointestinal tract by displaying more paradoxical sleep (PS) as the volume increases to 4% of the pup's body weight. Conversely, gastric loads larger than 4% reduced PS as a function of the volume. We also discovered that filling the stomach with warm non-nutritive paraffin is as effective as an equivalent volume of warm milk for enhancing PS. Although the temperature of the gut load did not appear to play a major role in the amount of PS displayed, increasing ambient temperature from 22 degrees C to 32 degrees C increased PS significantly. Moreover, a gut load of milk (4% body weight) was more effective than the same volume of water or no load for enhancing PS. Gut loads that stay in the stomach and warm ambient temperature appear to work in an additive manner to enhance PS. The electrophysiological data together with the stomach volume data and behavioral observations of nipple attachment revealed that milk-related stimuli along the gastrointestinal tract, especially gastric distension, alter sleep patterns in predictable ways that permit us to distinguish postingestive satiety from a deprivation state and nimiety in suckling rats.

Effects of intravenously administered vitamin B12 on sleep in the rat

Vitamin B12 (VB12) has been reported to normalize the entrainment of circadian rhythms in the non-24-h sleep wake cycle and delayed sleep phase insomnia in humans. The purpose of this work was to clarify whether the peripheral administration of VB12 has any sleep-promoting effect on the sleep-wake rhythm in freely moving rats. After a baseline day of saline infusion. VB12 (500 micrograms/kg/day) was administered continuously for 4 days via the jugular vein. Polysomnographic recordings were carried out concurrently. In both the light and the 24-h periods, the amount of non-rapid eye movement (NREM) sleep increased significantly on VB12-days 2 and 3, while the amount of REM sleep increased significantly on VB12-day 2. In the light period, the increase in NREM sleep was due to increased duration of the episode, while the tendency to an increase in REM sleep was due to an increased number of episodes. Changes in the diurnal sleep-wake rhythm tended to appear in the earlier light period. The serum VB12 concentrations in the VB12 group were 40 times higher than in controls. These findings suggest that peripherally infused VB12 has promoting effects on the rat's sleep, especially in the light period.

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.

Chloramphenicol prevents carbachol-induced REM sleep in cats

Twenty-four cats were implanted for chronic sleep recordings. One week after the surgery, cats were divided into four groups. Two groups were treated with three i.p. injections of 150 mg/kg chloramphenicol (CAP) separated by 12 h. Carbachol (8 micrograms/1 microliter) or saline (1 microliter) was injected into the pontine reticular formation (PRF) 1 h after the last injection of CAP. The other two groups received saline or carbachol into the PRF without CAP pre-treatment. Polygraphic recordings were started immediately after the microinjection and lasted 11 h. Carbachol increased REM sleep (P < 0.001) and reduced SWS2 (P < 0.05). In contrast, chloramphenicol reduced REM sleep (P < 0.001) and increased SWS2 (P < 0.01). The combination of these drugs increased wakefulness (P < 0.01) and reduced both SWS2 and REM sleep (P < 0.001). This data shows that chloramphenicol prevents carbachol induced REM sleep. Results are discussed in terms of an interaction between brain proteins and the cholinergic system to induce REM.

Secretion of newly synthesized proteins into the extracellular fluid of the rabbit hippocampus

Extracellular proteins were collected continuously from the hippocampus of the rabbit by slow perfusion of a protein-permeable thin tubing. After pulse labelling with radioactive amino acids via the tubing a rapid appearance of labelled proteins was seen in the extracellular fluid. The half-life of the proteins in the extracellular space varied between 15 min and 2 h. Protein fractions were separated with gel electrophoresis or HPLC. The extracellular fraction differed distinctly from intracellular proteins with respect to the labelling pattern.

Alimentary sleep satiety in suckling rats

Sleep/wake states were investigated in rat pups at 12-13 days of age following deprivation of milk and their dam for 9-12 hr. Early in the deprivation period each pup was equipped with bipolar stainless steel electrodes for electroencephalographic (EEG) and electromyographic (EMG) recordings. Four groups of pups were tested using anesthetized dams. The pups were either allowed to root in the dam's fur, but were not allowed to attach to a nipple; allowed to root after receiving a gut load of rat's milk; allowed to attach and suck a nipple without receiving milk; or allowed to attach and suck a nipple following a gut load of rat's milk. The results indicate that suckling elicits sleep, especially slow-wave sleep. Milk in the gut enhanced paradoxical sleep, primarily in the context of sucking. This experiment confirms that the types of sleep can be affected separately by specific internal and external events. The shift in the sleep/wake condition to slow-wave sleep in the suckling situation suggests one type of satiety. Furthermore, the selective enhancement of paradoxical sleep following the gut load of milk suggests postingestive satiety.

Extracellular fluid proteins of goldfish brain: evidence for the presence of proteases and esterases

Preparations of enriched fractions of extracellular fluid (ECF) proteins from goldfish brain were found to contain protease(s) and esterase(s). The N-substituted furanacryloyl (FA) peptides FA-Phe-Gly-Gly and FA-Phe-OMe were used as model substrates for determining protease and esterase activity, respectively, in a spectrophotometric assay. Studies of the profile of substrate specificity and identification of the types of compounds that were effective as inhibitors showed that these ECF enzymes have some distinctive properties. GSH, but not GSSG, and EDTA inhibited the protease(s) without influencing the esterase(s), whereas L-1-tosylamide-2-phenylethylchloromethyl ketone blocked both protease and esterase activities of ECF. Most of the protease and esterase properties of ECF could be bound to concanavalin A-Sepharose affinity chromatographic columns in association with ependymin--a brain extracellular protein. These observations indicate that ECF may contain a metalloprotease(s) and raise the possibility that the ependymins might be a substrate for these ECF enzymes.

Paradoxical sleep augmentation after imprinting in the domestic chick

The EEG and EMG of two groups of chicks (Gallus domesticus), (an experimental one who was imprinted, and a control one who was not), were recorded during 3 hours before and 3 hours after imprinting. The fertilized eggs were kept in an incubator under controlled temperature and humidity until ecclosion occurred. The recording session began 10 hours after ecclosion and after two hours of habituation to the recording conditions. During the imprinting session, E group met a natural stuffed white hen moved by a slow motor. The total amount of time spent in paradoxical sleep (PS), as well as the number of PS episodes increased significantly following imprinting in the E group. Opposite results were found in C group: total amount and number of PS episodes decreased significantly after the pseudo-imprinting session. Neither slow wave sleep, nor wakefulness were modified.

An electrochemical approach to sleep metabolism: a pO2 paradoxical sleep system

Oxygen cathodes chronically implanted in the cat brain recorded changes of local oxygen concentration during paradoxical sleep. Phasic high amplitude pO2 changes were consistently observed in some regions and were characterized by a dramatic increase in the amplitude of the oscillations. The regions displaying these responses included part of the reticular formation, hypothalamus, amygdala and cerebellum which we refer to as the "pO2 paradoxical sleep system." This pO2 pattern was not observed in white matter, in the neocortex or in specific thalamic nuclei. It is postulated that the phasic response is due to a local increase of neuronal activity requiring increased oxygen availability and augmented protein synthesis during paradoxical sleep and may form part of a system related to "plastic" phenomena.

Protein release from hippocampus in vitro

Physiologically viable slices of rat hippocampus in vitro continuously release protein into the superfusion medium at a rate of about 2 micrograms/mg tissue/h. Assays of a cytoplasmic marker enzyme (lactate dehydrogenase) indicate that this material is not the result of cell lysis. Pulse-chase experiments using [3H]valine indicate that a substantial fraction of the newly synthesized proteins eventually appear in the incubation medium (18.7% +/- 3% of the total TCA precipitable radioactivity during a 6-h superfusion) and that the releasable protein pool has an apparent half-life of about 4 h. Simultaneous labeling of newly synthetized proteins with [3H]fucose and [14C]valine showed a 3-fold higher ratio of [3H]fucose to [14C]valine in the released protein fraction compared to the soluble cytoplasmic protein and to the crude membrane protein fraction, suggesting that the soluble released proteins are more highly glycosylated than the proteins retained in the tissue. Electrophoretic migration patterns on SDS-polyacrylamide gels with both labeled and unlabeled proteins show differences between the released proteins and the soluble cytoplasmic proteins of the tissue. Several molecular weights between 14 kdalton and 86 kdalton appear to be characteristic of the released protein fraction. These results suggest that a distinct group of proteins and glycoproteins exists in hippocampal tissue which is destined to be selectively released into the extracellular space.

Effects of protein synthesis inhibitors on sleep and amygdala-kindled seizure thresholds in cats

This study examined the effects of protein synthesis inhibitors on sleep and seizure susceptibility in amygdala-kindled cats. Six cats with stable seizure thresholds were treated with 150 mg/kg of chloramphenicol or its cogener, thiamphenicol, at 12-h intervals over a 30-h period. State pattern variables were monitored continuously during the first 18 h. At 30 h, kindled seizure thresholds were measured in terms of minimum stimulus intensities (microA) required to elicit generalized tonic clonic convulsions. All cats were exposed to both drugs, with a 1-week intertrial interval and the order of drug treatment counterbalanced. Rapid eye movement (REM) sleep was significantly attenuated after chloramphenicol but was unaffected by thiamphenicol, as previously shown. Seizure thresholds were unaltered regardless of changes in sleep state physiology. The results extend previous work showing that protein synthesis inhibitors which suppress REM sleep increase seizure susceptibility only in animals that are either highly predisposed to seizures or that display REM sleep disruption as the sole sleep deficit associated with their seizure condition.

Effects of REM deprivation on the lordosis response induced by gonadal steroids in ovariectomized rats

Ovariectomized rats were submitted to REM sleep deprivation (REMd) using the water tank technique and their behavioral responsiveness (lordosis) to gonadal steroids was tested. In Experiment 1, animals received 2 micrograms of estradiol benzoate (EB) followed by 2 mg of progesterone (P) 44 hours later. Several REMd periods (12, 72, 96 and 120 hr) were applied, all ending four hr after P. REMd animals showed significantly lower lordosis quotients (LQ) than undisturbed sleep animals regardless of the duration of the deprivation period. In Experiment 2, animals received a single dose of EB (2 micrograms) and were REMd for 120 hours. Animals were tested daily to evaluate their LQ. EB, at this dose level, failed to elicit significant lordosis behavior in undisturbed sleep rats. REMd rats gradually increased their LQ values reaching maximal levels at 72 hours. Adrenalectomized control groups receiving the same hormonal treatment responded similarly to the experimental groups, thus discarding the participation of adrenal steroids in these effects. The present results show that REMd differentially affects the response to E and P in ovariectomized rats, enhancing the former and inhibiting the latter.

Proteins of the extracellular fluid of mouse brain: extraction and partial characterization

An extraction procedure for the isolation of proteins from the brain extracellular fluid (ECF) was developed and applied to studies of the ECF components of mouse brain. Perfused intact brains were incubated in an isotonic medium for periods of up to 2 h at 0 degrees C to allow the release of ECF into the medium without disruption of the integrity of the tissue. The validity of the extraction procedure was established by (a) the fact that the total yield of ECF proteins was constant per unit weight of brain tissue, (b) the absence of tyrosine hydroxylase, an enzyme marker of the cytoplasmic fraction, from the extracts, and (c) the distinctive features of the one- and two-dimensional gel electrophoretic patterns of ECF proteins as compared with those of the cytoplasmic and membrane fractions. The results indicate that the extracellular fluid of mouse brain contains a mixture of proteins with a wide distribution of molecular weights (10,000-100,000 daltons) at a concentration level of about 0.3%.

Sleep and medial reticular unit responses to protein synthesis inhibitors: effects of chloramphenicol and thiamphenicol

This study utilized a newly developed combination push-pull cannula/microdrive-microwire device to record single-unit activity within the diffusion field of substances introduced into the brainstem. Single unit activity within the midbrain and pontine medial reticular formation (RF) and sleep were recorded following either perfusion or oral administration of protein synthesis inhibitors, chloramphenicol and thiamphenicol. Chloramphenicol administration led to significant reductions in the frequency, but not the duration, of individual REM episodes without altering slow-wave sleep. During control experiments in slow-wave sleep, incipient REM was characterized by substantial increases in medial RF unit activity which occurred in association with the appearance of PGO spikes. On the other hand, discharge rates of medial RF neurons were markedly attenuated by chloramphenicol but were not consistently affected by thiamphenicol. These findings suggest that reduced unit activity contributes to the REM-suppressive effects of protein synthesis inhibitors.

Enhancement of tyrosine hydroxylase activity by Oxotremorine does not affect sleep in the rat

Marked enhancement of tyrosine hydroxylase (TH) activity was observed in the rostral pons of Wistar albino rats, 3 days after a single injection of Oxotremorine. TH activity in other brain areas, and regional levels of norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid were unaffected. Enhancement of TH activity did not affect length or number of REM episodes, or the amount of REM occurring in 24 hr. REM occurrence did not, thus, vary in accordance with activity of the rate-limiting enzyme for catecholamine synthesis. These data suggest that, although REM may reflect neuronal protein synthesis, REM is not part of a mechanism regulating the activity of enzymes in the pontine CA synthesis pathway.

Paradoxical sleep deprivation: effects on brain energy metabolism

A study was made of brain nucleotides and glycolytic intermediates in paradoxical sleep (PS)-deprived and recovery-sleeping rats. It was observed that PS deprivation of 24 h produced a fall in glucose, glucose 6-phosphate and pyruvate in cerebral frontal lobes. After three hours of recovery sleep all values returned toward their predeprivational levels. In cerebellar hemispheres ATP was increased, while glucose 6-phosphate and pyruvate were decreased. After three hours of recovery sleep, glucose 6-phosphate was increased and pyruvate decreased, indicating restoration of glycogen and creatine phosphate respectively.

Neurohumoral correlates of sleep: further biochemical and physiological characterization of sleep perfusates

Twenty cats were prepared surgically with electrodes for recording the EEG, Eye Movements and EMG and a push-pull cannula system in the midbrain reticular formation (MRF) allowing the extraction of perfusates during wakefulness or REM sleep. Proteins in the perfusates were analyzed by Isoelectric Focusing (IEF) polyacrylamide gels and Sodium Dodesyl Sulphate (SDS) slab gels. In addition analysis of glycoproteins was done by gas chromatography. In some cats the contribution of cerebrospinal fluid (CSF) proteins to perfusate proteins from brain tissue was studied by intraventricular injections of labelled leucine. The effect of sleep alterations on the protein cycle during sleep and wakefulness was also studied. The results of these experiments showed that most of the proteins in the perfusates are acidic, and that REM sleep perfusates contain 2 proteins M.W. 73.000 and 45.000 not present in awake perfusates, CSF or serum. It was also shown that CSF proteins do not appear to contribute to the proteins in perfusates, and that altering the sleep wake cycle, induces changes in the rhythm of protein release in perfusates. It is suggested that some relatively large polypeptides may participate in the regulation of REM sleep.