Systemic bacterial invasion induced by sleep deprivation

Profound sleep disruption in humans is generally believed to cause health impairments. Through comparative research, specific physical effects and underlying mechanisms altered by sleep deprivation are being elucidated. Studies of sleep-deprived animals previously have shown a progressive, chronic negative energy balance and gradual deterioration of health, which culminate in fatal bloodstream infection without an infectious focus. The present study investigated the conditions antecedent to advanced morbidity in sleep-deprived rats by determining the time course and distribution of live microorganisms in body tissues that are normally sterile. The tissues cultured for microbial growth included the blood, four major organs, six regional lymph nodes, the intestine, and the skin. The principal finding was early infection of the mesenteric lymph nodes by bacteria presumably translocated from the intestine and bacterial migration to and transient infection of extraintestinal sites. Presence of pathogenic microorganisms and their toxins in tissues constitutes a septic burden and chronic antigenic challenge for the host. Bacterial translocation and pathogenic sequelae provide mechanisms by which sleep deprivation appears to adversely affect health.

Functional consequences of sustained sleep deprivation in the rat

Sleep deprivation disrupts vital biological processes that are necessary for cognitive ability and physical health, but the physiological changes that underlie these outward effects are largely unknown. The purpose of the present studies in the laboratory rat is to prolong sleep deprivation to delineate the pathophysiology and to determine its mediation. In the rat, the course of prolonged sleep deprivation has a syndromic nature and eventuates in a life-threatening state. An early and central symptom of sleep deprivation is a progressive increase in peripheral energy expenditure to nearly double normal levels. An attempt to alleviate this negative energy balance by feeding rats a balanced diet that is high in its efficiency of utilization prolongs survival and attenuates or delays development of malnutrition-like symptoms, indicating that several symptoms can be manipulated to some extent by energy and nutrient consumption. Most changes in neuroendocrine parameters appear to be responses to metabolic demands, such as increased plasma catecholamines indicating sympathetic activation. Plasma total thyroid hormones, however, decline to severely low levels; a metabolic complication that is associated with other sleep deprivation-induced symptoms, such as a decline in body temperature to hypothermic levels despite increased energy expenditure. Metabolic mapping of the brain revealed a dissociation between the energy metabolism of the brain and that of the body. Sleep deprivation's effects on cerebral structures are heterogeneous and unidirectional toward decreased functional activity. The hypometabolic brain structures are concentrated in the hypothalamus, thalamus and limbic systems, whereas few regions in the rest of the brain and none in the medulla, are affected. Correspondence can be found between some of the affected cerebral structures and several of the peripheral symptoms, such as hyperphagia and possible heat retention problems. The factor predisposing to mortality is a decreased resistance to infection. Lethal opportunistic organisms are permitted to infect the bloodstream, which presumably results in a cascade of toxic-like reactions. Host defense is thus the first system to fail. There is neither fever nor marked tissue inflammatory reactions typical of infectious disease states, suggesting that sleep deprivation is immunosuppressive. Each of the four abnormalities identified--(1) a deep negative energy balance and associated malnutrition; (2) heterogeneous decreases in cerebral function; (3) low thyroid hormone concentrations; and (4) decrease resistance to infection--can be viewed as having an early origin during the sleep deprivation process to signify the foremost pathogenic situation to which the other abnormalities might be secondarily related.(ABSTRACT TRUNCATED AT 400 WORDS)

Pituitary and peripheral thyroid hormone responses to thyrotropin-releasing hormone during sustained sleep deprivation in freely moving rats

Sleep deprivation is associated with poor cognitive ability and impaired physical health, but the ways in which the brain and body become compromised are not understood. In sleep-deprived rats, plasma total T4 and T3 concentrations decline progressively to 78% and 47% below baseline values, respectively, brown adipose tissue 5'-deiodinase type II activity increases 100-fold, and serum TSH values are unknown. The progressive decline in plasma thyroid hormones is associated with a deep negative energy balance despite normal or increased food intake and malnutrition-like symptoms that eventuate in hypothermia and lethal systemic infections. The purpose of the present experiment was to evaluate the probable causes of the low plasma total T4 during sleep deprivation by measuring the free hormone concentration to minimize binding irregularities and by challenging the pituitary-thyroid axis with iv TRH to determine both 1) the pituitary release of TSH and 2) the thyroidal response of free T4 (FT4) and free T3 (FT3) release to the TSH increment. Sleep-deprived rats were awake 91% of the total time compared with 63% of the total time in yoked control rats and 50% of the total time during the baseline period. Cage control comparison rats were permitted to sleep normally. Sustained sleep deprivation resulted in a decline from baseline in plasma FT4 of 73 +/- 6% and FT3 of 45 +/- 12%, which were similar to the declines in total hormone concentrations observed previously; nonstimulated TSH was unchanged. In the yoked and cage control groups, FT4 also declined, but much less than that of the sleep-deprived group. The relative changes in free compared with total hormone concentrations over the study were also less parallel than those in the sleep-deprived group. The plasma TSH response to TRH was similar in all groups across experimental days. The plasma FT4 and FT3 concentrations in sleep-deprived rats increased after TRH-stimulated TSH release to an extent comparable to control values. Taken together, low basal FT4 and FT3 hormone concentrations and unchanged TSH and thyroidal responses to TRH suggest a pituitary or hypothalamic contribution to the hypothyroxinemia during sleep deprivation.

Effects of prolonged sleep deprivation on local rates of cerebral energy metabolism in freely moving rats

Although sleep deprivation interferes with biological processes essential for performance, health, and longevity, previous studies have failed to reveal any structural or functional changes in brain. We have therefore measured local rates of cerebral glucose utilization (ICMRglc) with the quantitative autoradiographic 2-14C-deoxyglucose method in an effort to determine if and, if so, where sleep deprivation might affect function in sleep-deprived rats. Sleep deprivation was maintained for 11-12 d, long enough to increase whole body energy metabolism, thus confirming that pathophysiological processes that might involve brain functions were evolving. Deep brain temperature was also measured in similarly treated rats and found to be mildly elevated relative to core body temperature. Despite the increased deep brain temperature, systemic hypermetabolism, and sympathetic activation, ICMRglc was not elevated in any of the 60 brain structures examined. Average glucose utilization in the brain as a whole was unchanged in the sleep-deprived rats, but regional decreases were found. The most marked decreases in ICMRglc were in regions of the hypothalamus, thalamus, and limbic system. Mesencephalic and pontine regions were relatively unaffected except for the central gray area. The medulla was entirely normal. The effects of sleep deprivation on brain tended, therefore, to be unidirectional toward decreased energy metabolism, primarily in regions associated with mechanisms of thermoregulation, endocrine regulation, and sleep. Correspondence was found between the hypometabolic brain regions and some aspects of peripheral symptoms.

Sustained sleep deprivation impairs host defense

Prolonged sleep deprivation in rats causes an unexplained hypercatabolic state, secondary malnutrition symptoms, and mortality. The nature of the vital impairment has long been a mystery. Its determination would help to elucidate the type of organic dysfunction that sleep prevents. There are no gross detectable disturbances in intermediary metabolism, clinical chemistry, or hematological indexes that provide substantial clues to the mediation of sleep-deprivation effects. Furthermore, postmortem examinations reveal no systematic morphological or histopathological findings. Taken together, the cachexia and the absence of evidence of structural damage or organ dysfunction pointed to involvement of a regulatory system that was diffuse, possibly the immune system. Blood cultures revealed invasion by opportunistic microbes to which there was no febrile response. These results suggest that the life-threatening condition of prolonged sleep deprivation is a breakdown of host defense against indigenous and pathogenic microorganisms.

Nutritional and metabolic adaptations to prolonged sleep deprivation in the rat

To understand how and why sleep deprivation is physically harmful, we explored the possible causal relationship between its two main effects, 1) negative energy balance and 2) a composite of symptoms that resemble protein malnutrition, both of which occur despite increased food consumption. We provided balanced diets augmented with either protein or calories (by increased fat content) to freely moving rats. Interactions between sleep deprivation symptoms and energy and protein supplies were assessed from measurements of body weight regulation, consumption of macronutrients, clinical chemistry and hematology profiles, and physical appearance. The results indicate that sleep deprivation causes malnutrition, which is secondary to increased energy expenditure. Even though food consumption remained normal in sleep-deprived rats fed a diet of high protein-to-calorie ratio, body weight loss was more than 16% of baseline, development of skin lesions was hastened, and longevity was shortened by 40% compared with sleep-deprived rats fed the calorie-augmented diet. Food consumption of the calorie-fed rats was lower during baseline than that of the protein-fed group but during sleep deprivation increased to amounts 250% of normal without net body weight gain. Despite a fat-laden diet the calorie-fed hyperphagic group did not have abnormal levels of plasma cholesterol, triglycerides, or glucose, indicating accelerated turnover of nutrients. As would be consistent with calorie malnutrition, pronounced clinical chemistry or hematological abnormalities were not found in any group. Beneficial effects of the calorie-augmented diet are attributed to 1) caloric density of fat, 2) induction of hyperphagia, and 3) efficiency of utilization of fat. We conclude that diet composition interacts strongly with sleep deprivation, affecting the time course and development of pathologies, whereas it exerted negligible influence on body weight regulation under normal conditions.

Sleep deprivation in the rat: IX. Recovery

Eight rats were subjected to total sleep deprivation, paradoxical sleep deprivation, or high amplitude sleep deprivation until they showed major deprivation-induced changes. Then they were allowed to sleep ad lib. Three rats that had shown the largest temperature declines died within two to six recovery days. During the first 15 days of ad lib sleep, surviving rats showed complete or almost complete reversal of the following deprivation-induced changes: debilitated appearance, lesions on the paws and tail, high energy expenditure, large decreases in peritoneal temperature, high plasma epinephrine and norepinephrine levels, and low thyroxine levels. The most prominent features of recovery sleep in all rats were immediate and large rebounds of paradoxical sleep to far above baseline levels, followed by lesser temporally extended rebounds. Rebounds of high amplitude non-rapid eye movement (NREM) sleep occurred only in some rats and were smaller and less immediate.

Sleep deprivation in the rat: VI. Skin changes

All rats subjected to total or paradoxical sleep deprivation by the disk apparatus developed severe ulcerative and hyperkeratotic skin lesions localized to the plantar surfaces of their paws and to their tails. Yoked control rats only occasionally developed similar appearing lesions, which were always much less severe than in deprived rats. The deprived rat lesions could not be explained by pressure, disk rotation, water immersion, infection, necrotizing vasculitis, tyrosinemia, protein deficiency, or reduced rates of mitosis. Thus, although paw and tail lesions constitute a very reliable and severe symptom of total or selective sleep deprivation in the rat that potentially could yield insights into the pathogenic mechanisms induced by sleep loss, the mediation of the lesions remains unknown.

Sleep deprivation in the rat: VII. Immune function

Immune function studies were performed on splenic lymphocytes obtained from rats subjected to total or paradoxical sleep deprivation. Spleen cell counts, in vitro lymphocyte proliferation responses to mitogens, and in vitro and in vivo plaque-forming cell responses to antigens were obtained. Sleep-deprived rats were roughly equivalent to both their yoked controls and home-cage controls in all assays. The results do not support the hypothesis that sleep deprivation results in immune suppression as measured by the above-mentioned parameters.

Sleep deprivation in the rat: III. Total sleep deprivation

Ten rats were subjected to total sleep deprivation (TSD) by the disk apparatus. All TSD rats died or were sacrificed when death seemed imminent within 11-32 days. No anatomical cause of death was identified. All TSD rats showed a debilitated appearance, lesions on their tails and paws, and weight loss in spite of increased food intake. Their yoked control (TSC) rats remained healthy. Since dehydration was ruled out and several measures indicated accelerated use rather than failure to absorb nutrients, the food-weight changes in TSD rats were attributed to increased energy expenditure (EE). The measurement of EE, based upon caloric value of food, weight, and wastes, indicated that all TSD rats increased EE, with mean levels reaching more than twice baseline values.

Sleep deprivation in the rat: I. Conceptual issues

Sleep deprivation is a potentially powerful strategy for discovering the function(s) of sleep, but the approach has had limited success. Few studies have described serious physiological consequences of sleep deprivation, perhaps because the deprivation has not been maintained long enough. However, prolonging deprivation usually requires sustained, frequently intense stimulation, which makes it difficult to determine whether subsequent impairment resulted from the sleep loss or from the stimulation per se. Accordingly, several older studies that showed severe impairment have been neglected or discounted, because the impairment could have resulted from the stimulation. To evaluate the effects of sleep deprivation independent of the stimulation used to enforce deprivation, we have used an apparatus that can awaken experimental rats while delivering the same gentle stimulation to control rats according to a schedule that only moderately shortens their sleep.

Sleep deprivation in the rat: X. Integration and discussion of the findings

The results of a series of studies on total and selective sleep deprivation in the rat are integrated and discussed. These studies showed that total sleep deprivation, paradoxical sleep deprivation, and disruption and/or deprivation of non-rapid eye movement (NREM) sleep produced a reliable syndrome that included death, debilitated appearance, skin lesions, increased food intake, weight loss, increased energy expenditure, decreased body temperature during the late stages of deprivation, increased plasma norepinephrine, and decreased plasma thyroxine. The significance of this syndrome for the function of sleep is not entirely clear, but several changes suggested that sleep may be necessary for effective thermoregulation.

Sleep deprivation in the rat: V. Energy use and mediation

We investigated the use and possible mechanisms mediating the increased energy expenditure (EE) previously described for rats subjected to total or paradoxical sleep deprivation. Bomb calorimetry of wastes showed that during deprivation the efficiency of energy utilization was not reduced. Estimates of CO2 production by the doubly labelled water method of indirect calorimetry correlated with EE estimated from the caloric value of food, weight change, and wastes and confirmed an increase in EE during deprivation. Core temperatures decreased during the later stages of deprivation, suggesting the hypothesis that excessive heat loss may have required increased EE to protect body temperature. The increased EE could not be explained by the metabolic cost of increase wakefulness, water exposure, or motor activity; an increase in resting EE was indicated. The contribution of the hypothalamic-pituitary-adrenal axis, thyroid gland, and sympathoadrenal system to the mediation of the EE increases was evaluated by measuring the plasma levels of their hormones. Results appear to rule out the first as a mediator. Evidence for the other two was equivocal.

Sleep deprivation in the rat: II. Methodology

Methods common to several studies in this series are described. A key feature is a sleep deprivation apparatus in which an experimental and a yoked control rat are housed on opposite sides of a divided disk suspended over shallow water. When the experimental rat enters a "forbidden" sleep stage, the disk is automatically rotated, forcing the experimental rat to walk to avoid being carried into the water. The control rat receives the same physical stimulation but can sleep ad lib when the disk is stationary.