Changes in monoamines and their metabolite concentrations in REM sleep-deprived rat forebrain nuclei

The Effects of Recovery Sleep on Experimental Pain

Recent research suggests that recovery sleep (RS) has the potential to restore pain sensitivity and modulation after hyperalgesia due to preceding sleep deprivation. However, it has not yet been systematically examined whether the restoration of these pain parameters is driven by sleep characteristics of RS. Thus, the present study assessed changes in experimental pain during RS after total sleep deprivation (TSD) to test whether RS parameters predicted the restoration of the pain system. Thirty healthy participants completed one night of habitual sleep, one night of TSD and a subsequent recovery night. At-home sleep during baseline and recovery was assessed using portable polysomnography and a questionnaire. Before and after each night pressure pain thresholds (PPTs), temporal pain summation (TSP) and conditioned pain modulation (CPM) were assessed. PPTs decreased after TSD and increased following RS, indicating a restoration of pain sensitivity after hyperalgesia. RS characteristics did not predict this restoration, suggesting other mechanisms (eg, changes in serotonergic activity) underlying the observed pain changes. TSP indicated a lack of effect of experimental sleep manipulations on excitatory processes whereas CPM lacked sufficient reliability to investigate inhibitory processes. Thus, results indicate moderate effects of sleep manipulations on pain sensitivity, but not on pain modulation. PERSPECTIVE: This article highlights the potential of recovery sleep to let pain thresholds return to normal following their decrease after a night of total sleep deprivation. In contrast, endogenous pain modulation (temporal pain summation, conditioned pain modulation) was not affected by sleep deprivation and recovery sleep.

Sleep-mediated regulation of reward circuits: implications in substance use disorders

Our modern society suffers from both pervasive sleep loss and substance abuse-what may be the indications for sleep on substance use disorders (SUDs), and could sleep contribute to the individual variations in SUDs? Decades of research in sleep as well as in motivated behaviors have laid the foundation for us to begin to answer these questions. This review is intended to critically summarize the circuit, cellular, and molecular mechanisms by which sleep influences reward function, and to reveal critical challenges for future studies. The review also suggests that improving sleep quality may serve as complementary therapeutics for treating SUDs, and that formulating sleep metrics may be useful for predicting individual susceptibility to SUDs and other reward-associated psychiatric diseases.

Interaction between cocaine use and sleep behavior: A comprehensive review of cocaine's disrupting influence on sleep behavior and sleep disruptions influence on reward seeking

Dopamine, orexin (hypocretin), and adenosine systems have dual roles in reward and sleep/arousal suggesting possible mechanisms whereby drugs of abuse may influence both reward and sleep/arousal. While considerable variability exists across studies, drugs of abuse such as cocaine induce an acute sleep loss followed by an immediate recovery pattern that is consistent with a normal response to loss of sleep. Under more chronic cocaine exposure conditions, an abnormal recovery pattern is expressed that includes a retention of sleep disturbance under withdrawal and into abstinence conditions. Conversely, experimentally induced sleep disturbance can increase cocaine seeking. Thus, complementary, sleep-related therapeutic approaches may deserve further consideration along with development of non-human models to better characterize sleep disturbance-reward seeking interactions across drug experience.

Addiction-like response in brain and behavior in a rat experimental model of night-eating syndrome

STUDY OBJECTIVES

Individuals ailing from night eating syndrome (NES) consume more than 25% of their daily food intake during the normal sleep time, delaying their sleep or waking up in the middle of the night to eat. This study explored two experimental conditions resembling NES in Wistar rats by offering palatable food during the sleep phase, alone or combined with sleep delay. Also we explored their impact on addiction-like changes in the brain and behavior.

METHODS

Experiment 1 explored the brain response after a first NES-like event; experiment 2 and 3 explored addiction-like behaviors c-Fos and FosB/ΔFosB in corticolimbic regions after 4 weeks exposition to NES-like conditions and after one week of withdrawal, respectively. For all 3 experiments 6 experimental groups were used: 1. Control; 2. Restricted access (1 h) to high-sugar diet (HSD) or to 3. high-fat diet (HFD); 4., Sleep delay for 4 h (SD) (from ZT0-ZT4, rats using slow rotating wheels); 5. SD + HSD; 6. SD + HFD.

RESULTS

A first event of eating a palatable diet with or without SD was sufficient to stimulate c-Fos and ΔFosB. Along 4 weeks of exposure to the palatable diets rats exhibited escalation and binge eating, which was highest for the HFD. At this stage, SD did not influence behavioral changes nor the neuronal response. After one-week in withdrawal, rats exhibited craving and effort to obtain their palatable diet. The brains of rats previously exposed to sleep delay maintained high levels of FosB/ΔFosB in the accumbens shell and high c-Fos activation in the insular cortex.

CONCLUSIONS

In our experimental models of NES-like a HFD in the sleep phase and SD are risk factors to develop binge eating and addiction-like behaviors.

The effects of recovery sleep on pain perception: A systematic review

Experimental studies highlight profound effects of sleep disruptions on pain, showing that sleep deprivation (SD) leads to hyperalgesic pain changes. On the other hand, given that sleep helps normalizing bodily functions, a crucial role of restorative sleep in the overnight restoration of the pain system seems likely. Thus, a systematic review of experimental studies on effects of recovery sleep (RS; subsequently to SD) on pain was performed with the aim to check whether RS resets hyperalgesic pain changes occurring due to SD. Empirical animal and human studies including SD-paradigms, RS and pain assessments were searched in three databases (PubMed, Web of Science, PsycINFO) using a predefined algorithm. 29 studies were included in this review. Most results indicated a reset of enhanced pain sensitivity and vulnerability following RS, especially when total SD was implemented and pressure pain or painful symptoms (human studies) were assessed. Further research should focus on whether and how recovery is altered in chronic pain patients, as this yields implications for pain treatment by enhancing or stabilizing RS.

Neurobehavioural complications of sleep deprivation: Shedding light on the emerging role of neuroactive steroids

Sleep deprivation (SD) is associated with a broad spectrum of cognitive and behavioural complications, including emotional lability and enhanced stress reactivity, as well as deficits in executive functions, decision making and impulse control. These impairments, which have profound negative consequences on the health and productivity of many individuals, reflect alterations of the prefrontal cortex (PFC) and its connectivity with subcortical regions. However, the molecular underpinnings of these alterations remain elusive. Our group and others have begun examining how the neurobehavioural outcomes of SD may be influenced by neuroactive steroids, a family of molecules deeply implicated in sleep regulation and the stress response. These studies have revealed that, similar to other stressors, acute SD leads to increased synthesis of the neurosteroid allopregnanolone in the PFC. Whereas this up-regulation is likely aimed at counterbalancing the detrimental impact of oxidative stress induced by SD, the increase in prefrontal allopregnanolone levels contributes to deficits in sensorimotor gating and impulse control, signalling a functional impairment of PFC. This scenario suggests that the synthesis of neuroactive steroids during acute SD may be enacted as a neuroprotective response in the PFC; however, such compensation may in turn set off neurobehavioural complications by interfering with the corticolimbic connections responsible for executive functions and emotional regulation.

Reduced frontal slow wave density during sleep in first-episode psychosis

BACKGROUND

Sleep disturbances are commonly reported in psychotic patients and often contribute to the manifestation and severity of their symptoms. Slow waves characterize the deepest stage of NREM sleep, and their occurrence is critical for restorative sleep. Slow wave abnormalities have been reported in patient with schizophrenia, especially when experiencing an exacerbation of psychosis. However, their presence and delineation, with an emphasis on topography, in first-episode psychosis patients (FEP) have not yet been characterized.

METHODS

We performed sleep high density (hd)-EEG recordings in twenty FEP patients and twenty healthy control subjects (HC). Slow wave activity (SWA) and several other slow wave parameters, e.g. density, amplitude, up- and down-slopes, were calculated at each electrode location and compared across groups. Additionally, the association between slow wave characteristics and clinical symptoms was assessed.

RESULTS

FEP patients showed a reduction selectively in slow-wave density relative to HC, and this reduction was significant in a large frontal area, including channels overlying the prefrontal cortex. Furthermore, slow wave density was inversely correlated with the severity of FEP positive symptoms.

CONCLUSIONS

Abnormalities in slow waves are present at the beginning of psychosis, occur in frontal-prefrontal regions that are highly dysfunctional in psychotic patients, and are associated with their positive symptom severity. Building on these findings, future work will help establish the direction of these associations (i.e., if clinical symptoms precede, coincide, or follow SW deficits), which will determine whether ameliorating slow wave sleep deficits is a viable treatment target in early psychosis.

The Function(s) of Sleep

Sleep is a highly conserved phenomenon in endotherms, and therefore it must serve at least one basic function across this wide range of species. What that function is remains one of the biggest mysteries in neurobiology. By using the word neurobiology, we do not mean to exclude possible non-neural functions of sleep, but it is difficult to imagine why the brain must be taken offline if the basic function of sleep did not involve the nervous system. In this chapter we discuss several current hypotheses about sleep function. We divide these hypotheses into two categories: ones that propose higher-order cognitive functions and ones that focus on housekeeping or restorative processes. We also pose four aspects of sleep that any successful functional hypothesis has to account for: why do the properties of sleep change across the life span? Why and how is sleep homeostatically regulated? Why must the brain be taken offline to accomplish the proposed function? And, why are there two radically different stages of sleep?The higher-order cognitive function hypotheses we discuss are essential mechanisms of learning and memory and synaptic plasticity. These are not mutually exclusive hypotheses. Each focuses on specific mechanistic aspects of sleep, and higher-order cognitive processes are likely to involve components of all of these mechanisms. The restorative hypotheses are maintenance of brain energy metabolism, macromolecular biosynthesis, and removal of metabolic waste. Although these three hypotheses seem more different than those related to higher cognitive function, they may each contribute important components to a basic sleep function. Any sleep function will involve specific gene expression and macromolecular biosynthesis, and as we explain there may be important connections between brain energy metabolism and the need to remove metabolic wastes.A deeper understanding of sleep functions in endotherms will enable us to answer whether or not rest behaviors in species other than endotherms are homologous with mammalian and avian sleep. Currently comparisons across the animal kingdom depend on superficial and phenomenological features of rest states and sleep, but investigations of sleep functions would provide more insight into the evolutionary relationships between EEG-defined sleep in endotherms and rest states in ectotherms.

The Effects of Total Sleep Deprivation on the Generation of Random Sequences of Key-Presses, Numbers and Nouns

According to a recent hypothesis, executive functions should be particularly vulnerable to the effects of total sleep deprivation. Random generation is a task that taps executive functions. In three experiments we examined the effects of total sleep deprivation on random generation of keypresses, numbers, and nouns, in particular on the suppression of prepotent responses and the selection of next responses by way of applying a local-representativeness heuristic. With random key-presses suppression of prepotent responses did not suffer from lack of sleep, but it became poorer at a sufficiently high pacing rate. In contrast, suppression of prepotent responses suffered when numbers and nouns were generated. According to these findings different types of random generation tasks involve different types of inhibitory process. With only four response alternatives, but not with larger response sets, application of the local-representativeness heuristic was impaired after a night without sleep. In terms of a simple formal model, serial-order representations of the preceding responses are used in selecting the next response only for the small response set, and not for larger response sets. Thus, serial-order representations are likely to suffer from loss of sleep. These findings strongly suggest that random generation involves multiple processes and that total sleep deprivation does not impair all sorts of executive functions, but only some.

Sleep Fragmentation Hypersensitizes Healthy Young Women to Deep and Superficial Experimental Pain

The effect of sleep deprivation on pain sensitivity has typically been studied using total and partial sleep deprivation protocols. These protocols do not mimic the fragmented pattern of sleep disruption usually observed in individuals with clinical pain conditions. Therefore, we conducted a controlled experiment to investigate the effect of sleep fragmentation on pain perception (deep pain: forearm muscle ischemia, and superficial pain: graded pin pricks applied to the skin) in 11 healthy young women after 2 consecutive nights of sleep fragmentation, compared with a normal night of sleep. Compared with normal sleep, sleep fragmentation resulted in significantly poorer sleep quality, morning vigilance, and global mood. Pin prick threshold decreased significantly (increased sensitivity), as did habituation to ischemic muscle pain (increased sensitivity), over the course of the 2 nights of sleep fragmentation compared with the night of normal sleep. Sleep fragmentation did not increase the maximum pain intensity reported during muscle ischemia (no increase in gain), and nor did it increase the number of spontaneous pains reported by participants. Our data show that sleep fragmentation in healthy, young, pain-free women increases pain sensitivity in superficial and deep tissues, indicating a role for sleep disruption, through sleep fragmentation, in modulating pain perception.

PERSPECTIVE

Our findings that pain-free, young women develop hyperalgesia to superficial and deep muscle pain after short-term sleep disruption highlight the need for effective sleep management strategies in patients with pain. Findings also suggest the possibility that short-term sleep disruption associated with recurrent acute pain could contribute to increased risk for future chronic pain conditions.

Neural Rhythmicity, Feature Binding, and Serotonin: A Hypothesis

Natural selection favors animals that make successful predictive theories about the world. The first step in the formation of these theories is the construction of complex, multifea ture percepts. This process requires resolution of the binding problem, possibly via rhyth mic cortical oscillations, as suggested by von der Malsburg, Singer, Koch & Crick, and others. If the binding process were made rewarding, animals might enjoy theory-making and spontaneously become "smarter." I argue that the serotonergic raphe may have been used by evolution to link cortical binding with limbic reward centers and so serve as a neural substrate for the enjoyment of successful theory-making. I present evidence, from the study of such disorders as obsessive-compulsive disorder and autism and such drugs as d-lysergic acid diethylamide (LSD) and 3,4-methylenedioxymethamphetamine (MDMA), suggesting that rhythmicity, reward, and pattern recognition are causally linked. I also propose that the genus Homo has tied powerful symbol manipulation hardware ("language") to the binding/theory-making circuits, allowing the construction, rehearsal, and communication of sophisticated models of the world. I suggest that many interesting phenomena, such as music-induced euphoria, déjà vu, and the so-called "temporal lobe personality" can be explained by the interactions between these systems. NEURO SCIENTIST 5:79-85, 1999

Animal Models for Elucidation of the Mechanisms of Neuropsychiatric Disorders Induced by Sleep and Dietary Habits

Numerous changes in human lifestyle in modern life increase the risk of disease. Especially, modern sleep and dietary habits are crucial factors affecting lifestyle disease. In terms of sleep, decreases in total sleep time and in rapid eye movement sleep time have been observed in attention-deficit/hyperactivity disorder (ADHD) patients. From a dietary perspective, mastication during eating has several good effects on systemic, mental, and physical functions of the body. However, few animal experiments have addressed the influence of this decline in sleep duration or of long-term powdered diet feeding on parameters reflecting systemic health. In our studies, we examined both the influence of intermittent sleep deprivation (SD) treatment and long-term powdered diet feeding on emotional behavior in mice, and focused on the mechanisms underlying these impaired behaviors. Our findings were as follows: SD treatment induced hypernoradrenergic and hypodopaminergic states within the frontal cortex. Furthermore, hyperactivity and an explosive number of jumps were observed. Both the hypernoradrenergic state and the jumps were improved by treatment with ADHD therapeutic drugs. On the other hand, long-term powdered diet feeding increased social interaction behaviors. The feeding affected the dopaminergic function of the frontal cortex. In addition, the long-term powdered diet fed mice presented systemic illness signs, such as elevations of blood glucose, and hypertension. This review, describing the SD mice and long-term powdered diet fed mice can be a useful model for elucidation of the mechanism of neuropsychiatric disorders or the discovery of new therapeutic targets in combatting effects of the modern lifestyle.

One night of total sleep deprivation promotes a state of generalized hyperalgesia: a surrogate pain model to study the relationship of insomnia and pain

Sleep disturbances are highly prevalent in chronic pain patients. Understanding their relationship has become an important research topic since poor sleep and pain are assumed to closely interact. To date, human experimental studies exploring the impact of sleep disruption/deprivation on pain perception have yielded conflicting results. This inconsistency may be due to the large heterogeneity of study populations and study protocols previously used. In addition, none of the previous studies investigated the entire spectrum of nociceptive modalities. To address these shortcomings, a standardized comprehensive quantitative sensory protocol was used in order to compare the somatosensory profile of 14 healthy subjects (6 female, 8 male, 23.5 ± 4.1 year; mean ± SD) after a night of total sleep deprivation (TSD) and a night of habitual sleep in a cross-over design. One night of TSD significantly increased the level of sleepiness (P<0.001) and resulted in higher scores of the State Anxiety Inventory (P<0.01). In addition to previously reported hyperalgesia to heat (P<0.05) and blunt pressure (P<0.05), study participants developed hyperalgesia to cold (P<0.01) and increased mechanical pain sensitivity to pinprick stimuli (P<0.05) but no changes in temporal summation. Paradoxical heat sensations or dynamic mechanical allodynia were absent. TSD selectively modulated nociception, since detection thresholds of non-nociceptive modalities remained unchanged. Our findings show that a single night of TSD is able to induce generalized hyperalgesia and to increase State Anxiety scores. In the future, TSD may serve as a translational pain model to elucidate the pathomechanisms underlying the hyperalgesic effect of sleep disturbances.

A novel model of chronic sleep restriction reveals an increase in the perceived incentive reward value of cocaine in high drug-taking rats

Substance abuse and sleep deprivation are major problems in our society. Clinical studies suggest that measures of poor sleep quality effectively predict relapse to substance abuse. Previously, our laboratory has shown that acute sleep deprivation increases the rate and efficiency (i.e., the goal-directed nature of responding) of cocaine self-administration using a progressive ratio (PR) schedule of reinforcement. However, the problem of sleep deprivation in our nation is largely one of chronicity. Therefore, the current study used a rodent model of chronic sleep restriction more akin to that experienced by humans (approximately 25% reduction in baseline sleep over the course of 8 days) to assess the impact of chronic sleep deprivation on cocaine-seeking and cocaine-taking behaviors in rats early during acquisition of self-administration. While low drug-taking rats were unaffected by chronic sleep restriction, high drug-takers in the chronic sleep restriction (CSR) group exhibited enhanced fixed ratio (FR) responding by the fourth day of FR training and significantly higher PR breakpoints than their non-sleep restriction (NSR) counterparts. This study is the first to directly assess the impact of chronic sleep deprivation on drug self-administration. These results show that chronic sleep deprivation early during acquisition of self-administration has a significant effect on the perceived incentive reward value of cocaine in high drug-takers, as indicated by both increased FR responding and an increased willingness to work for drug. Thus, it is important to be mindful of such factors in clinical settings designed for treatment of addiction and relapse prevention.

Influence of paradoxical sleep deprivation and sleep recovery on testosterone level in rats of different ages

This study was performed to assess serum testosterone alterations induced by paradoxical sleep deprivation (PSD) and to verify their attenuation during sleep recovery (SR) based on different durations and ages. Wistar male rats aged 12 weeks for the younger group and 20 weeks for the elder group were randomly distributed into one of the following groups: a control group (cage and platform), 3-day SD, 5-day SD, 7-day SD, 1-day SR, 3-day SR and 5-day SR groups. For PSD, the modified multiple platform method was used to specifically limit rapid eye movement (REM) sleep. Differences in the testosterone and luteinizing hormone levels between the younger group and the elder group according to duration of PSD and SR recovery were analysed. Testosterone continued to fall during the sleep deprivation period in a time-dependent manner in both the younger (P=0.001, correlation coefficient r=-0.651) and elder groups (P=0.001, correlation coefficient r=-0.840). The elder group showed a significantly lower level of testosterone compared with the younger group after PSD. Upon SR after 3 days of PSD, the testosterone level continued to rise for 5 days after sleep recovery in the younger group (P=0.013), whereas testosterone concentrations failed to recover until day 5 in the elder group. PSD caused a more detrimental effect on serum testosterone in the elder group compared to the younger group with respect to decreases in luteinizing hormone (LH) levels. The replenishment of serum testosterone level was prohibited in the elder group suggesting that the effects of SD/SR may be age-dependent. The mechanism by which SD affects serum testosterone and how age may modify the process are still unclear.

Place conditioning and neurochemical responses elicited by the aftereffect of acute stressor exposure involving an elevated stand

Acute exposure to an elevated stand has been used as an inescapable mild stressor for rats. The present study examined the effects of this stressor using a place conditioning behavioral test and neurochemical assays of dopamine and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in the medial prefrontal cortex and nucleus accumbens. The behavioral data showed that a conditioned place preference was formed as an aftereffect of the elevated stand stressor. In a separate experiment, neurochemical assay showed an immediate increase of dopamine in the nucleus accumbens after 30min exposure to the elevated stand stressor. In addition, the DOPAC content in the nucleus accumbens was significantly increased at 30min after this stressor. No significant change in dopamine or DOPAC levels in the medial prefrontal cortex was detected for up to 60min after stressor manipulation. These results suggest that an increase in dopamine activity in the nucleus accumbens is involved in the development of conditioned place preference elicited by the aftereffects of the elevated stand stressor.

REM sleep deprivation produces a motivational deficit for food reward that is reversed by intra-accumbens amphetamine in rats

Prolonged sleep deprivation in rats produces a characteristic syndrome of increase in food intake accompanied by, paradoxically, decrease in weight, suggesting a potential alteration in motivation for food reward. Using the multiple platform method to produce REM sleep deprivation (REMSD), we investigated the effect of REMSD on motivation for food reinforcement with a progressive ratio operant task, which yields a measure of the motor effort that a hungry animal is willing to expend to obtain food (the point at which the animal quits responding is termed the "break-point"). We found that REMSD rats decreased the break point for sucrose pellet reinforcement in comparison to controls, as revealed by a within-session decline in responding. This behavioral deficit is similar to that observed in rats with diminished dopamine transmission within the nucleus accumbens (Acb), and, considering that stimulants are frequently used in the clinical setting to reverse the effects of sleepiness, we examined the effect of systemic or intra-Acb amphetamine on break point in REMSD rats. Animals were given either systemic or intra-Acb amphetamine injections on days 3 and 5 of REMSD. Systemic amphetamine (0.1, 0.5, or 2.5mg/kg) did not increase break point in REMSD rats. In contrast, intra-Acb infusions of amphetamine (1, 10, or 30μg/0.5μl bilaterally) reversed the REMSD-induced suppression of progressive ratio responding. Specifically, the two higher doses of intra-Acb amphetamine were able to prolong responding within the session (resulting in an increased break point) on day 3 of REMSD while only the highest dose was sufficient following 5 days of REMSD. These data suggest that decreased motivation for food reward caused by REMSD may result from a suppression of dopamine function in the Acb.

Paradoxical sleep deprivation: neurochemical, hormonal and behavioral alterations. Evidence from 30 years of research

Sleep comprises approximately one-third of a person's lifetime, but its impact on health and medical conditions remains partially unrecognized. The prevalence of sleep disorders is increasing in modern societies, with significant repercussions on people's well-being. This article reviews past and current literature on the paradoxical sleep deprivation method as well as data on its consequences to animals, ranging from behavioral changes to alterations in the gene expression. More specifically, we highlight relevant experimental studies and our group's contribution over the last three decades.

Sleep disorders as core symptoms of depression

Links between sleep and depression are strong. About three quarters of depressed patients have insomnia symptoms, and hypersomnia is present in about 40% of young depressed adults and 10% of older patients, with a preponderance in females. The symptoms cause huge distress, have a major impact on quality of life, and are a strong risk factor for suicide. As well as the subjective experience of sleep symptoms, there are well-documented changes in objective sleep architecture in depression. Mechanisms of sleep regulation and how they might be disturbed in depression are discussed. The sleep symptoms are often unresolved by treatment, and confer a greater risk of relapse and recurrence. Epidemiological studies have pointed out that insomnia in nondepressed subjects is a risk factor for later development of depression. There is therefore a need for more successful management of sleep disturbance in depression, in order to improve quality of life in these patients and reduce an important factor in depressive relapse and recurrence.

Distinct behavioral and neurochemical alterations induced by intermittent hypoxia or paradoxical sleep deprivation in rats

The current study investigated the effects of paradoxical sleep deprivation and intermittent hypoxia by examining whether a combination of the two would induce anxiety-like alterations in behavior. The neurochemical effects of these manipulations were investigated by measuring cortical, striatal and hippocampal monoamine concentrations. Wistar Hannover rats were submitted to subchronic (3 days) intermittent hypoxia exposure (alternating cycles of 2 min room air-2 min 10% O2 from 0700-1900 h) and paradoxical sleep deprivation using the single platform method. Rats were randomly assigned to four different protocols: 1) control, 2) intermittent hypoxia during the light period (12 h/day), 3) paradoxical sleep deprivation (24 h/day), and 4) intermittent hypoxia combined with paradoxical sleep deprivation. Rats subjected to intermittent hypoxia showed no modification in the behavioral or neurochemical parameters assessed. Although paradoxical sleep deprivation did not produce alterations in anxiety-like behavior, the rats did increase exploratory activity in the elevated plus-maze. Moreover, a significant increase in striatal epinephrine and hippocampal homovanilic acid (HVA) concentrations was found in the paradoxical sleep deprivation groups, but not in the intermittent hypoxia/paradoxical sleep deprivation group. Of note, both paradoxical sleep deprivation and intermittent hypoxia/paradoxical sleep deprivation groups showed an increase in plasma corticosterone concentration. These results suggest that paradoxical sleep deprivation induces behavioral alterations, and these abnormalities may reflect altered neurotransmission in the brain. When paradoxical sleep deprivation was combined with intermittent oxygen depletion, the behavioral and biochemical parameters were comparable to those of control rats.

Relations among functional systems in behavior analysis

This paper proposes that an organism's integrated repertoire of operant behavior has the status of a biological system, similar to other biological systems, like the nervous, cardiovascular, or immune systems. Evidence from a number of sources indicates that the distinctions between biological and behavioral events is often misleading, engendering counterproductive explanatory controversy. A good deal of what is viewed as biological (often thought to be inaccessible or hypothetical) can become publicly measurable variables using currently available and developing technologies. Moreover, such endogenous variables can serve as establishing operations, discriminative stimuli, conjoint mediating events, and maintaining consequences within a functional analysis of behavior and need not lead to reductionistic explanation. I suggest that explanatory misunderstandings often arise from conflating different levels of analysis and that behavior analysis can extend its reach by identifying variables operating within a functional analysis that also serve functions in other biological systems.

Cocaine-induced genital reflexes in paradoxical sleep deprived rats: Indications of mediation by serotonin receptors

As paradoxical sleep deprivation (PSD) modifies cocaine-induced genital reflexes (penile erection [PE] and ejaculation [EJ]) and since cocaine is a serotonin (5-HT) reuptake inhibitor, we hypothesized that 5-HT also plays a role in these genital reflexes in PSD male rats. After a 4-day period of PSD each group was administered with serotonergic drugs prior to cocaine and placed in observation cages. The selective 5-HT(1) agonist (8-OH-DPAT) completely abolished PE events whereas the antagonist (pindolol) did not produce significant effects in the number of animals displaying PE. It was found that both drugs reduce the frequency of PE. There were no significant effects on the number of animals that ejaculated or in its frequency after pindolol although both parameters were reduced by the agonist at the highest doses (2 and 4 mg/kg, SC). Pretreatment with the 5-HT(2) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.12; 0.5 and 1 mg/kg, SC) significantly reduced the number of rats displaying PE and all doses reduced both PE and EJ frequencies. The number of animals displaying PE after 5-HT(2) antagonist (ketanserin) pretreatment at 1 and 2.5 mg/kg doses was significantly decreased in relation to vehicle rats and all doses reduced PE frequency. 5-HT(2) compounds at any dose did not affect the number of animals ejaculating, but the frequency was significantly reduced by all doses of DOI and by 1 to 5 mg/kg doses of ketanserin. Taken together, the results suggest that serotonergic receptors play an important role in genital reflexes induced by cocaine in sleep deprived males.

Effect of rapid-eye-movement sleep deprivation on rat hypothalamic prostaglandins

In this study, we investigated thyroid hormones, thyroid stimulating hormone (TSH), prostaglandin D(2) (PGD(2)) and prostaglandin E(2) (PGE(2)) levels in rapid-eye-movement (REM) sleep-deprived rats compared with controls. The aim of the present study was to detect the effect of REM sleep deprivation (RSD) especially on hypothalamic prostaglandin levels. Twenty-seven male rats were randomly assigned in three groups as dry cage control, yoked control, and RSD. RSD rats were sleep deprived for 10 consecutive days. At the end of 10th day all rats were sacrificed for measurement. Our results indicated that total triiodothyronine (T(3)) and thyroxine (T(4)) decreased in the RSD group while there was no change in TSH. We also measured hypothalamic PGD(2) and PGE(2) levels, but we could not find any significant change between groups.

The effect of REM sleep deprivation on motivation for food reward

Prolonged sleep deprivation in rats produces a characteristic syndrome consisting of an increase in food intake yet a decrease in weight. Moreover, the increase in food intake generally precedes the weight loss, suggesting that sleep deprivation may affect appetitive behaviors. Using the multiple platform method to produce rapid eye movement (REM) sleep deprivation, we investigated the effect of REM sleep deprivation (REMSD) on motivation for food reward utilizing food-reinforced operant tasks. In acquisition or maintenance of an operant task, REM sleep-deprived rats, with or without simultaneous food restriction, decreased responding for sucrose pellet reward in comparison to controls, despite the fact that all REM sleep-deprived rats lost weight. Furthermore, the overall response deficit of the REM sleep-deprived rats was due to a within-session decline in responding. REM sleep-deprived rats showed evidence of understanding the contingency of the task comparable to controls throughout deprivation period, suggesting that the decrements in responding were not primarily related to deficits in learning or memory. Rather, REM sleep deprivation appears to alter systems involved in motivational processes, reward, and/or attention.

Insomnia in somatoform pain disorder: sleep laboratory studies on differences to controls and acute effects of trazodone, evaluated by the Somnolyzer 24 x 7 and the Siesta database

Patients with chronic pain often suffer from sleep disturbances, specifically decreased deep sleep, and thus may get into a vicious circle which maintains their pain condition. Utilizing polysomnography and psychometry, objective and subjective sleep and awakening quality was investigated in 11 patients with nonorganic insomnia (F51.0) related to somatoform pain disorder (SPD; F45.4) as compared with age- and sex-matched healthy controls of the Siesta normative database. Patients demonstrated a markedly deteriorated Pittsburgh Sleep Quality Index, a decreased Quality of Life Index, slightly increased self-reported anxiety (Zung SAS) and depression scores (Zung SDS), as well as an increased Epworth Sleepiness Scale and International Restless Legs Syndrome Scale score. Subjective sleep and awakening quality was markedly reduced, while somatic complaints were increased. Polysomnographic evaluation by a recently developed automatic sleep classifier (Somnolyzer 24 x 7) based on the rules of Rechtschaffen and Kales demonstrated reduced slow-wave sleep (SWS), the target variable in the present study, a decreased stage shift index, increased SWS latency and stage 4 sleep (S4) latency and an increased frequency of shifts from S2 to wakefulness (W) in patients as compared with controls. Minimal oxygen saturation was found decreased, periodic leg movements (PLMs) were increased. In the morning, patients showed deteriorated well-being, drive, mood and wakefulness. There were no significant noopsychic or psychophysiological differences between patients and controls (except for a reduced numerical memory and a slightly increased morning diastolic blood pressure in patients). Subsequent evaluation of the acute effects of 100 mg of a controlled-release formulation of trazodone (Trittico retard) in the patients demonstrated an increase in the target variable SWS, accompanied by a reduction in the number of awakenings and stage shifts. It normalized the frequency of shifts from S2 to W and reduced the frequency of shifts from W to S1, from S1 to S2, as well as from any stage to S1 and S2. Trazodone, however, also significantly reduced the total sleep period and S2 and increased the latency to S1. Moreover, the drug increased the reduced minimal O(2 )saturation, reduced the arousal index and the PLMs-in-wake index and normalized the increased morning diastolic blood pressure. In conclusion, our study demonstrated that SPD induced significant changes in subjective and objective sleep and awakening quality, which were partially mitigated by trazodone therapy. The data on the target variable SWS support our hypothesis of a key-lock principle in the diagnosis and drug treatment of sleep disorders. Our study provided the first evidence on the usefulness of the Somnolyzer 24 x 7 and the Siesta database in clinical practice.

Endocrinological and catecholaminergic alterations during sleep deprivation and recovery in male rats

Since previous data of our group showed increased concentrations in HPA axis hormones in sleep deprived rats, we hypothesized that this augmentation could produce effects in other hormonal systems, particularly in the sexual system. Considering that little is known about how the hormonal system changes during the recovery period after sleep deprivation (SD), our objective was to examine from what point SD alters sexual and stress-related hormones along with plasma catecholamine concentrations during 4 days. We also sought to verify the time course of their recovery after an equivalent period of recovery sleep. Rats were deprived of sleep by the platform technique for 1-4 days and were allowed to recover for the same period. Plasma catecholamines [dopamine (DA) and noradrenaline (NOR)], testosterone, estrone, progesterone, prolactin, corticosterone and adrenocorticotropic hormone (ACTH) concentrations were measured. Comparisons between groups showed that the SD procedure used in the present study produced marked alterations in almost all studied hormones from 24 h of SD, except for estrone and prolactin (which required 96 h of SD to become altered). Testosterone and estrone decreased, whereas progesterone, prolactin, corticosterone, ACTH, DA and NOR increased. During recovery period, progesterone, prolactin and corticosterone concentrations returned to control levels, whereas testosterone, estrone, NOR and DA did not. In addition, after 48 h of recovery ACTH and NOR decreased below control concentrations, remaining low until 96 h of sleep recovery. Thus, SD showed long lasting, differential effects upon these neurochemicals suggesting that each has its own pattern of responses to SD as well as variable periods of recovery.

Sleep deprivation affects thermal pain thresholds but not somatosensory thresholds in healthy volunteers

OBJECTIVE

Sleep disturbances have been thought to augment pain. Sleep deprivation has been proven to produce hyperalgesic effects. It is still unclear whether these changes are truly specific to pain and not related to general changes in somatosensory functions. The aim of the present study was to evaluate the effect of total sleep deprivation on thermal pain thresholds (heat, cold) and pain complaints. Thermal detection thresholds (warmth, cold) were included as covariates to determine the contribution of somatosensory functions to changes in pain processing.

METHODS

Twenty healthy volunteers were randomly assigned either to two nights of total sleep deprivation or to two nights of undisturbed night sleep. Sleep deprivation nights were separated by two days with normal night sleep. Heat and cold pain thresholds as well as warmth and cold detection thresholds were measured by use of a peltier thermode in the evening before and the morning after each deprivation or control night. Pain complaints were examined by use of a questionnaire in parallel.

RESULTS

During treatment nights, sleep deprivation produced a significant overnight decrease in heat pain thresholds. Cold pain thresholds tended to decrease also during sleep deprivation, whereas the warmth and cold detection thresholds remained unaffected. Accordingly, no substantial contributions of the changes in thermal detection thresholds to the changes in thermal pain thresholds were determined by regression analyses. Pain complaints were not induced by sleep deprivation.

CONCLUSIONS

The present findings suggest that sleep deprivation produces hyperalgesic changes that cannot be explained by nonspecific alterations in somatosensory functions.

Effects of morphine or naloxone on cocaine-induced genital reflexes in paradoxical sleep-deprived rats

The involvement of opioidergic neurotransmission in the modulation of genital reflexes induced by paradoxical sleep deprivation (PSD) and cocaine in rats was the aim of the present study. Morphine (0, 1, 5 and 10 mg/kg) and naloxone (0, 0.3, 3 and 30 mg/kg) were administered prior to saline or cocaine to rats that had been deprived of sleep and the incidence of penile erections (PE) and ejaculations (EJ) was measured. PSD alone induced PE in 50% and EJ in 20% of the rats, but these behaviors were not influenced by morphine or naloxone. Cocaine potentiated the incidence of genital reflexes in PSD rats to 90% (PE) and 70% (EJ). Morphine and not naloxone significantly reduced the percentage of rats displaying this response at the highest doses. Morphine also significantly reduced PE and EJ frequencies at 10 mg/kg. Furthermore, this inhibitory effect of morphine on genital reflexes was prevented by the prior injection of naloxone. Although a number of factors are involved in such a complex phenomenon as PE and EJ, our data show that activation of the opioidergic systems by the agonist morphine reduces genital reflexes-induced by cocaine in PSD males while the antagonist, naloxone, did not have any significant effect. The findings suggest that the stimulating effects of cocaine in potentiating genital reflexes in PSD rats can be unidirectionally modified by opioidergic systems.

Effects of paradoxical sleep deprivation on blood parameters associated with cardiovascular risk in aged rats

The effects of 96 h of paradoxical sleep deprivation (PSD) on blood parameters associated with cardiovascular risk were studied in young (3-month old) and aged (22-month old) rats. In general, aging was associated with an overall increase in most measures, irrespective of sleep deprivation condition. The latter manipulation also had significant effects on blood variables, but not in a consistent pattern. Thus, PSD significantly reduced triglyceride levels in both young and aged rats; it reduced blood viscosity in aged but not in young rats, and had no effect on the increased cholesterol levels observed in aged controls. Examinations of cholesterol fractions revealed significant increases in low density lipoprotein and high density lipoprotein in aged PSD rats compared to respective controls, whereas very low density lipoprotein was significant decreased after PSD in both young and aged animals. PSD increased vitamin B(12) levels in aged rats, and significantly decreased homocysteine levels in young but not in aged rats which in turn were already reduced. Folate levels were the only variable that was unaffected by aging and/or PSD. These results indicate that PSD has significant but heterogeneous physiological effects in aged rats and may intensify certain aging-related effects which contribute to cardiovascular disease risk while attenuating others.

Cholinergic mechanisms in cocaine-induced genital reflexes in paradoxical sleep-deprived male rats

In view of the fact that paradoxical sleep deprivation (PSD) modifies cocaine-induced genital reflexes (penile erection [PE] and ejaculation [EJ]), the aim of this study was to address the interaction of cholinergic agents with the action of cocaine on the genital reflexes of PSD male rats. After a 4-day period of PSD, each group was administered with cholinergic drugs 1 h prior to cocaine and was placed in observation cages. The administration of nicotine (0.12, 0.25, 0.5 and 1 mg/kg sc) reduced the frequency and number of animals displaying PE and increased PE latency. Pretreatment with mecamylamine (1.25, 5, 10 and 20 mg/kg sc) also significantly reduced PE frequency for all doses used. The percentage of rats showing EJ was significantly reduced in the group pretreated with 1 mg/kg of nicotine compared with the saline group. The administration of pilocarpine (1.25, 2.5, 5 and 10 mg/kg sc) and atropine (1.25, 5, 10 and 20 mg/kg sc) led to a reduction in the frequency of PE displayed by the rats. These data show that agonist and antagonist cholinergic drugs inhibit genital reflexes in PSD male rats injected with cocaine. The data also suggest that the stimulating action of cocaine in potentiating the sexual effects in PSD rats does not override the effects of the cholinergic mechanisms of sexual behavior.

Total sleep deprivation increases extracellular serotonin in the rat hippocampus

Sleep deprivation exerts antidepressant effects after only one night of deprivation, demonstrating that a rapid antidepressant response is possible. In this report we tested the hypothesis that total sleep deprivation induces an increase in extracellular serotonin (5-HT) levels in the hippocampus, a structure that has been proposed repeatedly to play a role in the pathophysiology of depression. Sleep deprivation was performed using the disk-over-water method. Extracellular levels of 5-HT were determined in 3 h periods with microdialysis and measured by high performance liquid chromatography coupled with electrochemical detection. Sleep deprivation induced an increase in 5-HT levels during the sleep deprivation day. During an additional sleep recovery day, 5-HT remained elevated even though rats displayed normal amounts of sleep. Stimulus control rats, which had been allowed to sleep, did not experience a significant increased in 5-HT levels, though they were exposed to a stressful situation similar to slee-deprived rats. These results are consistent with a role of 5-HT in the antidepressant effects of sleep deprivation.

Facilitation of ejaculation after methamphetamine administration in paradoxical sleep deprived rats

This study investigated the effects of methamphetamine (MA) on genital reflexes in paradoxical sleep deprived (PSD) rats. Different doses of MA (0, 4, 16 and 64 mg/kg) were acutely given after PSD or the equivalent time to control animals. We observed enhancement of spontaneous ejaculation in PSD rats with larger doses of MA, the highest of which induced ejaculation in 100% of the PSD rats. This was significantly higher than the 30% in the control. Although testosterone exerts motivational effects on male sexual behavior, our data shows that testosterone levels were lower after the PSD period in saline and in the 64 mg/kg MA groups, which present ejaculation at different rates (20% and 100%, respectively). Progesterone levels were significantly higher in PSD-saline in relation to control group and in the 16 and 64 mg/kg of MA groups compared to the other doses. Since PSD induces dopaminergic alterations and dopamine (DA) has a key role in male sexual behavior, plasma DA was also measured. The DA concentration was enhanced in all PSD groups compared with their control group. The mechanism that activates steroid hormones may represent an important physiological effect through which neurotransmitters can affect behavioral events. These data show that MA facilitates ejaculation in PSD rats, however, further studies need to be carried out in order to clarify the hormonal-neurochemical mechanisms involved.

Differential effects of intraspecific interactions on the striatal dopamine system in social and non-social voles

We used in vivo microdialysis to examine the responses to intraspecific social interactions in the striatal dopamine systems of females of two vole species displaying vastly different social structures. Both highly social prairie voles and asocial meadow voles had similar increases in extracellular dopamine associated with mating. There was a species-specific effect of social condition on extracellular dihydroxyphenylacetic acid (DOPAC). Exposure to a conspecific male significantly decreased extracellular DOPAC in female prairie voles isolated for approximately 18 h during surgical recovery. Such decrease in DOPAC was not seen if females experienced continued isolation or if they were housed with a sibling during surgical recovery. No changes in extracellular DOPAC were seen in meadow voles after manipulations of social environment. Together, our data indicate that mating-associated dopamine release is independent from mating systems. However, species-specific patterns of extracellular DOPAC suggest that social isolation may be a more stressful stimulus for the social prairie vole than for the asocial meadow vole.

One night of total sleep deprivation impairs implicit learning in the serial reaction task, but not the behavioral expression of knowledge

Implicit sequence learning in the serial reaction task suffers from total sleep deprivation. The authors compared implicit-learning scores in a sleep-deprivation (SD) group (n = 12) and a control group (n = 6). Both groups were tested immediately after learning a 1st sequence; a delayed test was conducted on the next day (after a night without sleep in the SD group). Immediately after the delayed test a 2nd sequence was learned, followed by an immediate test and a delayed test toward the end of the experiment. In the SD group implicit-learning scores were reduced in both tests of the 2nd sequence, but in neither test of the 1st sequence. Thus, 1 night of total sleep deprivation impairs the acquisition of implicit sequence knowledge, but not its behavioral expression.

Increases in avoidance responding produced by REM sleep deprivation or serotonin depletion are reversed by administration of 5-hydroxytryptophan

Our objective was to directly compare the effects of rapid eye movement (REM) sleep deprivation (REMSD) and serotonin 5-hydroxytryptamine (5-HT) depletion on free-operant avoidance behavior in rats. These experiments were designed to determine if declining 5-HT levels observed during REMSD might mediate the increases in avoidance responding observed in REM sleep deprived rats. Rats were trained on a free-operant avoidance task. Following training, the animals were assigned to one of three sleep conditions (REMSD, tank control, or cage control). Animals in each sleep condition were exposed to four 5-HT manipulations: (a) saline plus saline; (b) p-chlorophenylalanine (PCPA) plus saline; (c) saline plus 5-hydroxytryptophan (5-HTP) and (d) PCPA plus 5-HTP. Both REMSD and 5-HT depletion via PCPA resulted in an increase in avoidance responding that was reversed by administration of 5-HTP. REMSD and 5-HT depletion via PCPA resulted in increased avoidance efficiency and were reversed by 5-HTP administration, but only changes following PCPA injection were statistically significant. Decreases in 5-HT levels that occur during REMSD likely mediate increases in avoidance responding.

How REM sleep deprivation and amantadine affects male rat sexual behavior

There are conflicting findings about the sexual effects of REM sleep deprivation (REMd). Otherwise, several studies show a dopaminergic hypersensitivity after REMd. The effect of REMd and amantadine (AMA) was studied for standard measures and temporal patterning in the first experiment, in four groups: normal with vehicle, normal with AMA (5.0 and 10 mg/kg), REMd with vehicle and REMd with AMA (5.0 and 10.0 mg/kg). REMd reduced mount latency (ML), intromission latency (IL) and mount number (MN) and increased copulatory efficiency (CE) and hit rate factor. REMd also reduced the mount bout number (MBN) and increased the sexual interaction (mount bout time, MBT) among male and female during copula. AMA stimulates initiation and hit rate factors and accelerates the temporal patterning of sexual behavior, evoking fewer and quicker mount bouts. In the experiments with combination of REMd and AMA administration, AMA did not increase behavior effects evoked by REM deprivation, probably due to a top or a bottom effect, depending on the measures considered. A second experiment studied the effects of AMA (1.25 to 5.0 mg/kg) and REMd on the sexual reflexes of nonimmobilized male rats. REMd enhanced the AMA effects upon the seminal emission reflex, but inhibited the penile erection reflex elicited by 1.25 mg/kg of AMA. Curiously, our results showed that REMd, like AMA, a dopaminergic agonist, causes similar effects of sexual behavior in the male rat, particularly those related to arousal mechanism and hit rate factor. The results are discussed and the effects of REMd probably involve dopaminergic hypersensitivity and increased sexual motivational response.

Vocalization thresholds related to noxious paw pressure are decreased by paradoxical sleep deprivation and increased after sleep recovery in rat

The aim of this study was to assess the effect of paradoxical sleep deprivation (PSD) and sleep recovery on the vocalization threshold in rats submitted to a mechanical noxious stimulus. Sixteen male Wistar rats were randomly assigned in two groups: controls (n=8), paradoxical sleep deprived rats (n=8). PSD was performed using the 'inverted flower pot' technique. Paw pressure test was used to assess the sensitivity to mechanical noxious stimulus (vocalization threshold). The experiment was divided into three periods: baseline (day 1, day 2), PSD (day 3, day 4, day 5) and recovery (day 6, day 7, day 8, day 9). After 48 and 72 h of PSD, the vocalization thresholds decreased significantly in comparison to the control rats (day 4: 245+/-21 vs. 303+/-20 g, P=0.05; day 5: 256+/-17 vs. 324+/-22 g, P=0.02). In PSD group, relative to controls, vocalization thresholds increased significantly after 48, 72, and 96 h of recovery sleep periods (day 7: 378+/-24 vs. 307+/-8 g P=0.01; day 8: 384+/-27 vs. 316+/-23 g, P=0.02; day 9: 395+/-24 vs. 328+/-15 g, P=0.02). Vocalization thresholds on day 6 were not significantly different in both groups (375+/-20 vs. 324+/-24 g, P=0.08). In conclusion, experimental PSD in rats induces a significant decrease in vocalization threshold to mechanical noxious stimulus, which is totally reversed during the sleep recovery period.

Effect of sleep deprivation on neuroendocrine response to a serotonergic probe in healthy male subjects

Neuroendocrine responses to stimulation with a selective serotonin reuptake inhibitor (citalopram) were measured to investigate the effects of all-night sleep deprivation on serotonergic function in healthy male subjects (n = 7). We studied citalopram-stimulated prolactin and cortisol plasma concentrations in a placebo-controlled cross-over protocol following sleep and sleep deprivation. Citalopram infusion (20 mg i.v. at 14:20-14:50 h) after a night of undisturbed sleep prompted robust increases in both plasma prolactin and cortisol concentrations. Following a night of sleep deprivation, by contrast, the citalopram-induced prolactin response was blunted, but the cortisol response was not significantly altered. This differential response pattern relates to the distinct pathways through which serotonin may activate the corticotrophic and the lactotrophic systems. While an unchanged cortisol response does not indicate (but also does not refute the possibility of) an altered serotonergic responsivity following sleep deprivation, the suppressed prolactin response could reflect a downregulation of 5-HT1A or 2 receptors. An alternative, not mutually exclusive, explanation points to the possibility that sleep deprivation activates the tubuloinfundibular dopaminergic system, the final inhibitory pathway of prolactin regulation.