Cold exposure impairs dark-pulse capacity to induce REM sleep in the albino rat

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73940/1/j.1365-2869.2008.00658.x.pd

c-Fos expression in preoptic nuclei as a marker of sleep rebound in the rat

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71961/1/j.1460-9568.2009.06848.x.pd

Short Meditation Trainings Enhance Non-REM Sleep Low-Frequency Oscillations.

STUDY OBJECTIVES:We have recently shown higher parietal-occipital EEG gamma activity during sleep in long-term meditators compared to meditation-naive individuals. This gamma increase was specific for NREM sleep, was present throughout the entire night and correlated with meditation expertise, thus suggesting underlying long-lasting neuroplastic changes induced through prolonged training. The aim of this study was to explore the neuroplastic changes acutely induced by 2 intensive days of different meditation practices in the same group of practitioners. We also repeated baseline recordings in a meditation-naive cohort to account for time effects on sleep EEG activity. DESIGN:High-density EEG recordings of human brain activity were acquired over the course of whole sleep nights following intervention. SETTING:Sound-attenuated sleep research room. PATIENTS OR PARTICIPANTS:Twenty-four long-term meditators and twenty-four meditation-naïve controls. INTERVENTIONS:Two 8-h sessions of either a mindfulness-based meditation or a form of meditation designed to cultivate compassion and loving kindness, hereafter referred to as compassion meditation. MEASUREMENTS AND RESULTS:We found an increase in EEG low-frequency oscillatory activities (1-12 Hz, centered around 7-8 Hz) over prefrontal and left parietal electrodes across whole night NREM cycles. This power increase peaked early in the night and extended during the third cycle to high-frequencies up to the gamma range (25-40 Hz). There was no difference in sleep EEG activity between meditation styles in long-term meditators nor in the meditation naïve group across different time points. Furthermore, the prefrontal-parietal changes were dependent on meditation life experience. CONCLUSIONS:This low-frequency prefrontal-parietal activation likely reflects acute, meditation-related plastic changes occurring during wakefulness, and may underlie a top-down regulation from frontal and anterior parietal areas to the posterior parietal and occipital regions showing chronic, long-lasting plastic changes in long-term meditators

Cold Exposure and Sleep in the Rat: REM Sleep Homeostasis and Body Size

Study Objectives: Exposure to low ambient temperature (Ta) depresses REM sleep (REMS) occurrence. In this study, both short and long-term homeostatic aspects of REMS regulation were analyzed during cold exposure and during subsequent recovery at Ta 24 degrees C. Design: EEG activity, hypothalamic temperature, and motor activity were studied during a 24-h exposure to Tas ranging from 10 degrees C to -10 degrees C and for 4 days during recovery. Setting: Laboratory of Physiological Regulation during the Wake-Sleep Cycle, Department of Human and General Physiology, Alma Mater Studiorum-University of Bologna. Subjects: 24 male albino rats. Interventions: Animals were implanted with electrodes for EEG recording and a thermistor to measure hypothalamic temperature. Measurements and Results: REMS occurrence decreased proportionally with cold exposure, but a fast compensatory REMS rebound occurred during the first day of recovery when the previous loss went beyond a "fast rebound" threshold corresponding to 22% of the daily REMS need. A slow REMS rebound apparently allowed the animals to fully restore the previous REMS loss during the following 3 days of recovery. Conclusion: Comparing the present data on rats with data from earlier studies on cats and humans, it appears that small mammals have less tolerance for REMS loss than large ones. In small mammals, this low tolerance may be responsible on a short-term basis for the shorter wake-sleep cycle, and on long-term basis, for the higher percentage of REMS that is quickly recovered following REMS deprivation

c-Fos expression in the limbic thalamus following thermoregulatory and wake-sleep changes in the rat

A cellular degeneration of two thalamic nuclei belonging to the "limbic thalamus", i.e., the anteroventral (AV) and mediodorsal (MD) nuclei, has been shown in patients suffering from Fatal Familial Insomnia (FFI), a lethal prion disease characterized by autonomic activation and severe insomnia. To better assess the physiological role of these nuclei in autonomic and sleep regulation, c-Fos expression was measured in rats during a prolonged exposure to low ambient temperature (Ta, - 10 °C) and in the first hours of the subsequent recovery period at normal laboratory Ta (25 °C). Under this protocol, the thermoregulatory and autonomic activation led to a tonic increase in waking and to a reciprocal depression in sleep occurrence, which was more evident for REM sleep. These effects were followed by a clear REM sleep rebound and by a rebound of Delta power during non-REM sleep in the following recovery period. In the anterior thalamic nuclei, c-Fos expression was (1) larger during the activity rather than the rest period in the baseline; (2) clamped at a level in-between the normal daily variation during cold exposure; (3) not significantly affected during the recovery period in comparison to the time-matched baseline. No significant changes were observed in either the MD or the paraventricular thalamic nucleus, which is also part of the limbic thalamus. The observed changes in the activity of the anterior thalamic nuclei appear, therefore, to be more specifically related to behavioral activation than to autonomic or sleep regulation

Meditation-naïve individuals recorded at the same time points as practitioners to control for aspecific effect of adaptation to the lab environment did not show changes in scalp EEG between sessions.

<p>Average NREM sleep scalp topographies across cycles in control participants at the time points corresponding to baseline (B) and meditation sessions (M, pooled) for practitioners. The naïve individuals did not undergo day of practice. The first 3 sleep cycles are indexed as 1, 2, and 3. For each cycle, topographical maps of t-values (T) are plotted in the same [-5 5] scale across frequency bins and cycles. SnPM statistics confirmed the absence of changes between time points.</p

Practitioners’ sleep structure parameters.

<p>Times (average across participants ± standard deviation) are expressed in minutes.</p