Biomedical subjects

Tom Deboer

Publications and source records attributed to Tom Deboer.

10 recordsLinked to original sources

PubMed2003

Sleep states alter activity of suprachiasmatic nucleus neurons.

The timing of sleep and wakefulness in mammals is governed by a sleep homeostatic process and by the circadian clock of the suprachiasmatic nucleus (SCN), which has a molecular basis for rhythm generation. By combining SCN electrical activity recordings with electroencephalogram (EEG) recordings in the same animal (the Wistar rat), we discovered that changes in vigilance states are paralleled by strong changes in SCN electrophysiological activity. During rapid eye movement (REM) sleep, neuronal activity in the SCN was elevated, and during non-REM (NREM) sleep, it was lowered. We also carried out selective sleep deprivation experiments to confirm that changes in SCN electrical activity are caused by changes in vigilance state. Our results indicate that the 24-hour pattern in electrical activity that is controlled by the molecular machinery of the SCN is substantially modified by afferent information from the central nervous system.

Action Potentials↗

PubMed2003

Dissociation between circadian Per1 and neuronal and behavioral rhythms following a shifted environmental cycle.

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus contains a major circadian pacemaker that imposes or entrains rhythmicity on other structures by generating a circadian pattern in electrical activity. The identification of "clock genes" within the SCN and the ability to dynamically measure their rhythmicity by using transgenic animals open up new opportunities to study the relationship between molecular rhythmicity and other well-documented rhythms within the SCN. We investigated SCN circadian rhythms in Per1-luc bioluminescence, electrical activity in vitro and in vivo, as well as the behavioral activity of rats exposed to a 6-hr advance in the light-dark cycle followed by constant darkness. The data indicate large and persisting phase advances in Per1-luc bioluminescence rhythmicity, transient phase advances in SCN electrical activity in vitro, and an absence of phase advances in SCN behavioral or electrical activity measured in vivo. Surprisingly, the in vitro phase-advanced electrical rhythm returns to the phase measured in vivo when the SCN remains in situ. Our study indicates that hierarchical levels of organization within the circadian timing system influence SCN output and suggests a strong and unforeseen role of extra-SCN areas in regulating pacemaker function.

Animals↗

PubMed2003

Sleep regulation in the Djungarian hamster: comparison of the dynamics leading to the slow-wave activity increase after sleep deprivation and daily torpor.

STUDY OBJECTIVES: Emerging from daily torpor, Djungarian hamsters (Phodopus sungorus) show an initial increase in electroencephalographic slow-wave activity (power density between 0.75 and 4.0 Hz) during sleep that gradually declines. This feature is typical for sleep following prolonged waking and supports the hypothesis that sleep pressure increases during daily torpor. After hamsters were subjected to sleep deprivation or partial non-rapid eye movement sleep deprivation immediately following torpor, slow-wave activity remained high and decreased only when sleep was allowed. An analysis of the dynamics of the process underlying the build-up of sleep pressure during episodes of waking and torpor may provide insights into the regulation of normal sleep and wakefulness. We have analyzed in more detail the timecourse of the process that is common for waking and daily torpor and that could account for the subsequent increase in slow-wave activity. DESIGN: Continuous 24-hour recordings of electroencephalography, electromyography, cortical temperature, and electroencephalographic spectral analysis were performed. Torpor data of 28 hamsters and sleep-deprivation data of diverse durations collected previously in 15 hamsters were analyzed. SETTING: N/A. PATIENTS OR PARTICIPANTS: N/A. INTERVENTIONS: Sleep deprivation. MEASUREMENTS AND RESULTS: Slow-wave activity invariably increased as a function of the duration of both prior waking and torpor. However, the time constant of the build-up of slow-wave activity was approximately 2.75 times slower during torpor compared to sleep deprivation. Brain temperature recorded during the torpor bouts was 10 degrees to 12 degrees C below euthermic brain temperature. Therefore, the temperature coefficient of the time constant for the slow-wave-activity increase is between 2.3 and 2.8, a range typical for biochemical processes. CONCLUSIONS: We conclude that the processes occurring during daily torpor in the Djungarian hamster are similar to those occurring during sleep deprivation, but the build-up of sleep pressure during torpor appears to be slowed down by the lower brain temperature.

Animals↗

PubMed2003

Seasonal aspects of sleep in the Djungarian hamster.

BACKGROUND: Changes in photoperiod and ambient temperature trigger seasonal adaptations in the physiology and behaviour of many species, including the Djungarian hamster. Exposure of the hamsters to a short photoperiod and low ambient temperature leads to a reduction of the polyphasic distribution of sleep and waking over the light and dark period. In contrast, a long photoperiod enhances the daily sleep-wake amplitude leading to a decline of slow-wave activity in NREM sleep within the light period. It is unknown whether these changes can be attributed specifically to photoperiod and/or ambient temperature, or whether endogenous components are contributing factors. The influence of endogenous factors was investigated by recording sleep in Djungarian hamsters invariably maintained at a low ambient temperature and fully adapted to a short photoperiod. The second recording was performed when they had returned to summer physiology, despite the maintenance of the 'winter' conditions. RESULTS: Clear winter-summer differences were seen in sleep distribution, while total sleep time was unchanged. A significantly higher light-dark cycle modulation in NREM sleep, REM sleep and waking was observed in hamsters in the summer physiological state compared to those in the winter state. Moreover, only in summer, REM sleep episodes were longer and waking bouts were shorter during the light period compared to the dark period. EEG power in the slow-wave range (0.75-4.0 Hz) in both NREM sleep and REM sleep was higher in animals in the summer physiological state than in those in the 'winter' state. In winter SWA in NREM sleep was evenly distributed over the 24 h, while in summer it decreased during the light period and increased during the dark period. CONCLUSION: Endogenous changes in the organism underlie the differences in sleep-wake redistribution we have observed previously in hamsters recorded in a short and long photoperiod.

Adaptation, Physiological↗

PubMed2003

Differential responses of circadian activity onset and offset following GABA-ergic and opioid receptor activation.

The circadian pacemaker in the mammalian suprachiasmatic nuclei is responsive to photic and nonphotic stimuli. In the present study, the authors have investigated the response of activity onset and offset to application of nonphotic stimuli: the benzodiazepine midazolam and the opioid receptor agonist fentanyl. In correspondence with previous studies, both stimuli induced phase advances of the activity onset when given in the mid- to late subjective day. In contrast, activity offset did not phase advance following these injections. Injections during the early subjective day induced small phase delays of the activity onset, while large phase delays occurred in activity offset. Phase shifts, induced at both circadian time zones, were paralleled by an increase in the length of daily activity (alpha). The increase in a remained present during several days after the injection. The different kinetics in phase shifting of the activity onset and offset indicate complexity in phase-shifting behavior of the circadian pacemaker in response to nonphotic stimuli. Moreover, the data show responsiveness of the circadian system to GABA-ergic and opioid receptor activation, not only during the mid- to late subjective day but also during the early subjective day. The data implicate that the early subjective day is an interesting phase for analysis of molecular and biochemical processes involved in nonphotic phase shifting.

Activity Cycles↗

PubMed2002

Sleep EEG in mice that are deficient in the potassium channel subunit K.v.3.2.

Voltage-gated potassium channels containing the K.v.3.2 subunit are expressed in specific neuronal populations such as thalamocortical neurons and fast spiking GABAergic interneurons of the neocortex and hippocampus. These K(+)-channels play a major role in the regulation of firing properties in these neurons. We investigated whether the K.v.3.2 subunit contributes to the generation of the sleep electroencephalogram (EEG). The EEG of a frontal and occipital derivation of K.v.3.2-deficient mice and littermate controls was recorded during a 24-h baseline, 6-h sleep deprivation (SD) and subsequent 18-h recovery to assess also the effects of the K.v.3.2 subunit deficiency under physiological sleep pressure. The K.v.3.2-deficient mice had lower EEG power density in the frequencies between 3.25 and 6 Hz in nonREM (NREM) sleep and 3.25-5 Hz in REM sleep. These differences were more prominent in the frontal derivation than in the occipital derivation. The waking EEG spectrum was not affected by the deletion. In both genotypes SD induced a prominent increase in slow-wave activity in NREM sleep (mean EEG power density between 0.75 and 4.0 Hz), and a concomitant decrease in sleep fragmentation. The effects of SD did not differ significantly between the genotypes. The results indicate that K.v.3.2 channels may be involved in the generation of EEG oscillations in the high delta and low theta range in sleep. They support the notion that GABA-mediated synchronization of cortical activity contributes to the electroencephalogram.

Animals↗

PubMed2002

Electroencephalogram theta frequency changes in parallel with euthermic brain temperature.

To test whether moderate changes in brain temperature can influence electroencephalogram (EEG) frequencies in a significant way the behaviour of peak theta frequency (approximately 6 Hz) in the rapid-eye movement (REM) sleep EEG was investigated in the Djungarian hamster under influence of the spontaneous euthermic changes in brain temperature. In contrast to in vitro data, collected from hippocampal tissue, theta peak frequency shifted significantly when temperature changed between 33 and 37 degrees C. The results support the hypothesis that moderate changes in brain temperature can influence EEG power density spectra.

Animals↗

PubMed2002

Sleep deprivation in prion protein deficient mice sleep deprivation in prion protein deficient mice and control mice: genotype dependent regional rebound.

We have previously reported a larger and more prolonged increase of slow wave activity (SWA) in NREM sleep after sleep deprivation (SD) in prion protein deficient mice (PrP) compared to wild-type mice. Regional differences in the SWA increase were investigated by comparing the effect of 6 h SD on a frontal and occipital derivation in PrP deficient mice and wild-type mice. The larger increase of SWA after SD in PrP deficient mice was restricted to the occipital derivation. The difference appeared after the waking-NREM sleep transitions, making it unlikely that PrP is involved in the mechanisms enabling the transition to sleep. Our findings may reflect differences between the genotypes in the need for recovery in this particular brain region.

Animals↗

PubMed2002

Selective sleep deprivation after daily torpor in the Djungarian hamster.

Sleep, daily torpor and hibernation are no longer considered homologous processes. Animals emerging from these states spend most of their time in sleep. After termination of the torpor-associated hypothermia, there is an initial high electroenecephalogram (EEG) slow-wave activity (SWA; 0.75-4.0 Hz) and a subsequent monotonic decline. Both of these features are similar to the effects elicited by prolonged waking. It was previously shown that when hamsters are not allowed to sleep immediately after emerging from torpor, an additional SWA increase above the level reached after sleep deprivation (SD) alone occurs during the delayed recovery. A similar manipulation in hibernating ground squirrels abolished the subsequent SWA increase, shedding doubt on the similarity of the regulatory aspects following torpor and hibernation. To further investigate the extent to which SWA is homeostatically regulated after torpor, Djungarian hamsters were subjected to 1.5 h partial non-rapid eye movement (NREM) sleep deprivation (NSD) that either immediately followed the emergence from torpor (T + NSD) or 4-h SD (SD + NSD). The NSD was attained by disturbing the animals when they exhibited NREM sleep with high amplitude slow-waves. To investigate whether regional aspects of sleep homeostasis are similar after torpor and SD, the EEG was recorded from a parietal and frontal derivation after 4-h SD. An increase in SWA in NREM sleep occurred after all conditions in both EEG derivations. There was no significant difference in SWA during the initial 1.5-h recovery when torpor, T + NSD and SD + NSD were compared. During recovery from torpor and SD, SWA was higher in the frontal than in the parietal derivation. Our results provide further evidence that torpor and SD have similar effects on sleep. The SWA increase did not disappear after the NSD; therefore, SWA is homeostatically regulated after daily torpor. The frontal predominance of slow waves encountered both after torpor and SD indicates that waking and torpor induce similar regional changes in EEG SWA.

Animals↗

PubMed2002

Tumor necrosis factor (TNF) ligand and TNF receptor deficiency affects sleep and the sleep EEG.

Tumor necrosis factor (TNF) and lymphotoxin-alpha (LT-alpha) are proinflammatory cytokines involved in host defense and pathogenesis of various diseases. In addition, there is evidence that TNF is involved in sleep. TNF and LT-alpha both bind to the tumor necrosis factor receptors (TNFR). Recently, it was shown that TNF receptor 1 (TNFR1) knockout mice (R1KO) sleep less during the light period than controls. We investigated the effect of a TNF and LT-alpha double deficiency on sleep in mice (Ligand KO) and compared their sleep with that of R1KO, TNFR2 knockout (R2KO) mice, and wild-type (WT) controls. All mice were adapted to a 12:12 h light:dark cycle and their electroencephalographs (EEG) and electromyographs (EMG) were continuously recorded during a baseline day, 6-h sleep deprivation (SD), and 18-h recovery. Ligand KO and R2KO had 15% less rapid eye movement (REM) sleep during the baseline light period due to a reduction in REM sleep episode frequency. After SD, all genotypes showed an initial increase in slow-wave activity (SWA) (EEG power density between 0.75 and 4.0 Hz) in non-REM sleep, which gradually declined in the following hours. In Ligand KO the increase was mainly caused by an increase in fast SWA (2.75-4.0 Hz), which was also increased in R2KO. In contrast, in R1KO mice the increase was limited to the slow portion of SWA (0.75-2.5 Hz). R2KO and WT mice showed increases in both frequency ranges. The sub-division into fast and slow SWA frequencies corresponds to previous electrophysiological data where the two types of slow-waves were induced by either excitatory or inhibitory stimuli. Our data suggest that in Ligand KO the SWA increase is caused by an increase in excitatory input to the cortex, whereas in R1KO this input seems to be almost absent.

Animals↗