CAP and arousals are involved in the homeostatic and ultradian sleep processes. (49/175)

There is growing evidence that cyclic alternating pattern (CAP) and arousals are woven into the basic mechanisms of sleep regulation. In the present study, the overnight sleep cycles (SC) of 20 normal subjects were analyzed according to their stage composition, CAP rate, phase A subtypes and arousals. Individual SC were then divided into 10 normalized temporal epochs. CAP parameters and arousals were measured in each epoch and averaged in relation to the SC order. Subtypes A2 and A3 of CAP in non-rapid eye movement (NREM) sleep, and arousals, both in REM and NREM sleep when not coincident with a A2 or A3 phases, were lumped together as fast electroencephalographic (EEG) activities (FA). Subtypes A1 of CAP, characterized by slow EEG activities (SA), were analyzed separately. The time distribution of SA and FA was compared to the mathematical model of normal sleep structure including functions representing the homeostatic process S, the circadian process C, the ultradian process generating NREM/REM cycles and the slow wave activity (SWA) resulting from the interaction between homeostatic and ultradian processes. The relationship between SA and FA and the sleep-model components was evaluated by multiple regression analysis in which SA and FA were considered as dependent variables while the covariates were the process S, process C, SWA, REM-on and REM-off activities and their squared values. Regression was highly significant (P < 0.0001) for both SA and FA. SA were prevalent in the first three SC, and exhibited single or multiple peaks immediately before and in the final part of deep sleep (stages 3 + 4). The peaks of FA were delayed and prevailed during the pre-REM periods of light sleep (stages 1 + 2) and during REM sleep. SA showed an exponential decline across the successive SC, according to the homeostatic process. In contrast, the distribution of FA was not influenced by the order of SC, with periodic peaks of FA occurring before the onset of REM sleep, in accordance with the REM-on switch. The dynamics of CAP and arousals during sleep can be viewed as an intermediate level between cellular activities and macroscale EEG phenomena as they reflect the decay of the homeostatic process and the interaction between REM-off and REM-on mechanisms while are slightly influenced by circadian rhythm.  (+info)

The actions of dihydroxyphenylalanine and dihydroxyphenylserine on the sleep-wakefulness cycle of the rat after peripheral decarboxylase inhibition. (50/175)

1. The actions of dihydroxyphenylalanine (DOPA) and dihydroxyphenylserine (DOPS) were assessed on the sleep-wakefulness cycle of male Wistar rats. 2. In comparative studies the extracerebral decarboxylase was inhibited with serinetrihydroxybenzylhydrazide (RO 4-4602) before injection of DOPA or DOPS. 3. DOPA (80-160 mg/kg, i.p.) with or without previous inhibition of the peripheral decarboxylase gave rise to an initial significant increase of slow wave activity, which may be related to a release of 5-hydroxytryptamine. 4. During the subsequent 8 h sessions, DOPA significantly decreased slow wave sleep and rapid eye movement sleep (REM) and increased wakefulness. 5. DOPS (80-160 mg/kg, i.p.) did not significantly modify the sleep-wakefulness cycle apart from a decrease of the latency for the first REM episode after 160 mg/kg in the RO 4-4602 pretreated animals.  (+info)

Ultradian ghrelin pulsatility is disrupted in morbidly obese subjects after weight loss induced by malabsorptive bariatric surgery. (51/175)

BACKGROUND: Suppression of ghrelin production after Roux-en-Y gastric bypass that suggested its contribution to appetite reduction has been reported. OBJECTIVE: Because biliopancreatic diversion (BPD) does not affect appetite, we compared ghrelin production and 24-h pulsatility between healthy control subjects and obese subjects before and after BPD. DESIGN: A computerized algorithm identified peak heights, clearance rate, and peak frequency of ghrelin over 24 h. Twenty-four-hour energy expenditure was measured in the calorimetric chamber, and energy intakes were computed. Insulin sensitivity was measured with a euglycemic-hyperinsulinemic clamp. RESULTS: Mean (+/-SD) 24-h plasma ghrelin concentrations were significantly (P < 0.0001) higher in control than in obese subjects (338.17 +/- 22.09 and 164.47 +/- 29.19 microg/L, respectively), but they increased to 204.64 +/- 28.51 microg/L in the obese subjects after BPD (P < 0.01). The pulsatility index was 0.098 +/- 0.016 and 0.041 +/- 0.014 microg . L(-1) . min(-1) in control and obese subjects, respectively (P < 0.01), and decreased to 0.025 +/- 0.007 microg . l(-1) . min(-1) after BPD (P < 0.05). Energy intakes before and after BFP did not differ significantly. Although metabolizable energy after BPD was 40% of the energy intake, that (per kg fat-free mass) after BPD did not different significantly from that before BPD. CONCLUSIONS: Weight loss induced by malabsorptive bariatric surgery is associated with greater ghrelin concentrations, which, however, remain consistently lower than those in control subjects, whereas ghrelin pulsatility is subverted. Higher ghrelin concentrations may contribute to the high calorie intakes observed in post-BPD subjects. The lack of normal pulsatility may explain the new impulse of these subjects to eat very frequently.  (+info)

Ultradian oscillations in somatostatin and growth hormone-releasing hormone mRNAs in the brains of adult male rats. (52/175)

In the adult male rat, growth hormone (GH) secretion is characterized by an ultradian rhythm generated by the rhythmic interplay of the stimulatory effects of GH-releasing hormone (GHRH) and the inhibitory effects of somatostatin (Ss). Although considerable evidence indicates that GHRH and Ss are secreted in reciprocal 3- to 4-hr rhythms, the mechanism underlying the rhythmic secretion of these two neuropeptides is unknown. We tested the hypothesis that the rhythmic and reciprocal oscillations in secretion of Ss and GHRH are associated with parallel changes in synthesis and that this would be reflected by coincident oscillations in levels of the respective mRNAs. In the first experiment, Ss mRNA was significantly greater in the periventricular nucleus of animals sacrificed at the time of a presumed peak in the GH rhythm than in animals sacrificed at the time of a presumed trough; this variation was limited to the anterior third of this nucleus. Conversely, GHRH mRNA content throughout the arcuate nucleus was significantly greater at the time of a GH trough. In the second experiment, groups of animals were sacrificed during two consecutive cycles. In this set of animals, Ss mRNA content was 40% greater (P less than 0.005) during peak GH concentrations, whereas GHRH mRNA content was 42% greater (P less than 0.005) during the GH trough. This difference persisted when the two cycles were analyzed separately. The findings that the cellular mRNA content for Ss and GHRH varies in a reciprocal manner with the presumed secretion of these neuropeptides suggest that, like secretion, the synthesis of Ss and GHRH also varies rhythmically. The occurrence of this rhythm suggests a model for a transcriptional oscillator that may subserve the generation of this and possibly other neuroendocrine rhythms.  (+info)

Pre-Botzinger complex: a brainstem region that may generate respiratory rhythm in mammals. (53/175)

The location of neurons generating the rhythm of breathing in mammals is unknown. By microsection of the neonatal rat brainstem in vitro, a limited region of the ventral medulla (the pre-Botzinger Complex) that contains neurons essential for rhythmogenesis was identified. Rhythm generation was eliminated by removal of only this region. Medullary slices containing the pre-Botzinger Complex generated respiratory-related oscillations similar to those generated by the whole brainstem in vitro, and neurons with voltage-dependent pacemaker-like properties were identified in this region. Thus, the respiratory rhythm in the mammalian neonatal nervous system may result from a population of conditional bursting pacemaker neurons in the pre-Botzinger Complex.  (+info)

Neural ensemble coding of satiety states. (54/175)

The motivation to start or terminate a meal involves the continual updating of information on current body status by central gustatory and reward systems. Previous electrophysiological and neuroimaging investigations revealed region-specific decreases in activity as the subject's state transitions from hunger to satiety. By implanting bundles of microelectrodes in the lateral hypothalamus, orbitofrontal cortex, insular cortex, and amygdala of hungry rats that voluntarily eat to satiety, we have measured the behavior of neuronal populations through the different phases of a complete feeding cycle (hunger-satiety-hunger). Our data show that while most satiety-sensitive units preferentially responded to a unique hunger phase within a cycle, neuronal populations integrated single-unit information in order to reflect the animal's motivational state across the entire cycle, with higher activity levels during the hunger phases. This distributed population code might constitute a neural mechanism underlying meal initiation under different metabolic states.  (+info)

Extreme diving of beaked whales. (55/175)

Sound-and-orientation recording tags (DTAGs) were used to study 10 beaked whales of two poorly known species, Ziphius cavirostris (Zc) and Mesoplodon densirostris (Md). Acoustic behaviour in the deep foraging dives performed by both species (Zc: 28 dives by seven individuals; Md: 16 dives by three individuals) shows that they hunt by echolocation in deep water between 222 and 1885 m, attempting to capture about 30 prey/dive. This food source is so deep that the average foraging dives were deeper (Zc: 1070 m; Md: 835 m) and longer (Zc: 58 min; Md: 47 min) than reported for any other air-breathing species. A series of shallower dives, containing no indications of foraging, followed most deep foraging dives. The average interval between deep foraging dives was 63 min for Zc and 92 min for Md. This long an interval may be required for beaked whales to recover from an oxygen debt accrued in the deep foraging dives, which last about twice the estimated aerobic dive limit. Recent reports of gas emboli in beaked whales stranded during naval sonar exercises have led to the hypothesis that their deep-diving may make them especially vulnerable to decompression. Using current models of breath-hold diving, we infer that their natural diving behaviour is inconsistent with known problems of acute nitrogen supersaturation and embolism. If the assumptions of these models are correct for beaked whales, then possible decompression problems are more likely to result from an abnormal behavioural response to sonar.  (+info)

Relationships between sleep, physical activity and human health. (56/175)

Although sleep and exercise may seem to be mediated by completely different physiological mechanisms, there is growing evidence for clinically important relationships between these two behaviors. It is known that passive body heating facilitates the nocturnal sleep of healthy elderly people with insomnia. This finding supports the hypothesis that changes in body temperature trigger somnogenic brain areas to initiate sleep. Nevertheless, little is known about how the core and distal thermoregulatory responses to exercise fit into this hypothesis. Such knowledge could also help in reducing sleep problems associated with nocturnal shiftwork. It is difficult to incorporate physical activity into a shiftworker's lifestyle, since it is already disrupted in terms of family commitments and eating habits. A multi-research strategy is needed to identify what the optimal amounts and timing of physical activity are for reducing shiftwork-related sleep problems. The relationships between sleep, exercise and diet are also important, given the recently reported associations between short sleep length and obesity. The cardiovascular safety of exercise timing should also be considered, since recent data suggest that the reactivity of blood pressure to a change in general physical activity is highest during the morning. This time is associated with an increased risk in general of a sudden cardiac event, but more research work is needed to separate the influences of light, posture and exercise per se on the haemodynamic responses to sleep and physical activity following sleep taken at night and during the day as a nap.  (+info)