Sleep deprivation increases brain serotonin turnover in the Djungarian hamster

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.

Intricate role of sleep deprivation in modulating depression: focusing on BDNF, VEGF, serotonin, cortisol, and TNF-α

In this review article, we aimed to discuss intricate roles of SD in modulating depression in preclinical and clinical studies. Decades of research have shown the inconsistent effects of SD on depression, focusing on SD duration. However, inconsistent role of SD seems to be more complicated, and SD duration cannot be the only one factor. Regarding this issue, we chose some important factors involved in the effects of SD on cognitive functions and mood including brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), serotonin, cortisol, and tumor necrosis factor-alpha (TNF-α). It was concluded that SD has a wide-range of inconsistent effects on BDNF, VEGF, serotonin, and cortisol levels. It was noted that BDNF diurnal rhythm is significantly involved in the modulatory role of SD in depression. Furthermore, the important role of VEGF in blood-brain barrier permeability which is involved in modulating depression was discussed. It was also noted that there is a negative correlation between cortisol and BDNF that modulates depression. Eventually, it was concluded that TNF-α regulates sleep/wake cycle and is involved in the vulnerability to cognitive and behavioral impairments following SD. TNF-α also increases the permeability of the blood-brain barrier which is accompanied by depressive behavior. In sum, it was suggested that future studies should focus on these mechanisms/factors to better investigate the reasons behind intricate roles of SD in modulating depression.

Modulating role of serotonergic signaling in sleep and memory

Serotonin is an important neurotransmitter with various receptors and wide-range effects on physiological processes and cognitive functions including sleep, learning, and memory. In this review study, we aimed to discuss the role of serotonergic receptors in modulating sleep-wake cycle, and learning and memory function. Furthermore, we mentioned to sleep deprivation, its effects on memory function, and the potential interaction with serotonin. Although there are thousands of research articles focusing on the relationship between sleep and serotonin; however, the pattern of serotonergic function in sleep deprivation is inconsistent and it seems that serotonin has not a certain role in the effects of sleep deprivation on memory function. Also, we found that the injection type of serotonergic agents (systemic or local), the doses of these drugs (dose-dependent effects), and up- or down-regulation of serotonergic receptors during training with various memory tasks are important issues that can be involved in the effects of serotonergic signaling on sleep-wake cycle, memory function, and sleep deprivation-induced memory impairments. This comprehensive review was conducted in the PubMed, Scopus, and ScienceDirect databases in June and July 2021, by searching keywords sleep, sleep deprivation, memory, and serotonin.

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.

Autoreceptor control of serotonin dynamics

BACKGROUND

Serotonin is a neurotransmitter that has been linked to a wide variety of behaviors including feeding and body-weight regulation, social hierarchies, aggression and suicidality, obsessive compulsive disorder, alcoholism, anxiety, and affective disorders. Full understanding involves genomics, neurochemistry, electrophysiology, and behavior. The scientific issues are daunting but important for human health because of the use of selective serotonin reuptake inhibitors and other pharmacological agents to treat disorders. This paper presents a new deterministic model of serotonin metabolism and a new systems population model that takes into account the large variation in enzyme and transporter expression levels, tryptophan input, and autoreceptor function.

RESULTS

We discuss the steady state of the model and the steady state distribution of extracellular serotonin under different hypotheses on the autoreceptors and we show the effect of tryptophan input on the steady state and the effect of meals. We use the deterministic model to interpret experimental data on the responses in the hippocampus of male and female mice, and to illustrate the short-time dynamics of the autoreceptors. We show there are likely two reuptake mechanisms for serotonin and that the autoreceptors have long-lasting influence and compare our results to measurements of serotonin dynamics in the substantia nigra pars reticulata. We also show how histamine affects serotonin dynamics. We examine experimental data that show very variable response curves in populations of mice and ask how much variation in parameters in the model is necessary to produce the observed variation in the data. Finally, we show how the systems population model can potentially be used to investigate specific biological and clinical questions.

CONCLUSIONS

We have shown that our new models can be used to investigate the effects of tryptophan input and meals and the behavior of experimental response curves in different brain nuclei. The systems population model incorporates individual variation and can be used to investigate clinical questions and the variation in drug efficacy. The codes for both the deterministic model and the systems population model are available from the authors and can be used by other researchers to investigate the serotonergic system.

REM sleep loss-induced elevated noradrenaline could predispose an individual to psychosomatic disorders: a review focused on proposal for prediction, prevention, and personalized treatment

Historically and traditionally, it is known that sleep helps in maintaining healthy living. Its duration varies not only among individuals but also in the same individual depending on circumstances, suggesting it is a dynamic and personalized physiological process. It has been divided into rapid eye movement sleep (REMS) and non-REMS (NREMS). The former is unique that adult humans spend the least time in this stage, when although one is physically asleep, the brain behaves as if awake, the dream state. As NREMS is a pre-requisite for appearance of REMS, the latter can be considered a predictive readout of sleep quality and health. It plays a protective role against oxidative, stressful, and psychopathological insults. Several modern lifestyle activities compromise quality and quantity of sleep (including REMS) affecting fundamental physiological and psychopathosomatic processes in a personalized manner. REMS loss-induced elevated brain noradrenaline (NA) causes many associated symptoms, which are ameliorated by preventing NA action. Therefore, we propose that awareness about personalized sleep hygiene (including REMS) and maintaining optimum brain NA level should be of paramount significance for leading physical and mental well-being as well as healthy living. As sleep is a dynamic, multifactorial, homeostatically regulated process, for healthy living, we recommend addressing and treating sleep dysfunctions in a personalized manner by the health professionals, caregivers, family, and other supporting members in the society. We also recommend that maintaining sleep profile, optimum level of NA, and/or prevention of elevation of NA or its action in the brain must be seriously considered for ameliorating lifestyle and REMS disturbance-associated dysfunctions.

Mouse Gambling Task reveals differential effects of acute sleep debt on decision-making and associated neurochemical changes

Sleep loss is associated with sleepiness, sustained attention, and memory deficits. However, vulnerability of higher cognitive processes (i.e. decision making) to sleep debt is less understood. Therefore, a major challenge is to understand why and how higher cognitive processes are affected by sleep debt. We had established in mice correlations between individual decision-making strategies, prefrontal activity, and regional monoaminergic levels. Now, we show that acute sleep debt (ASD) disturbs decision-making processes and provokes brain regional modifications of serotonin and dopamine that could explain why ASD promotes inflexible and more risk-prone behaviors. Finally, we highlight, for the first time, that in a large group of healthy inbred mice some of them are more sensitive to ASD by showing inflexible behavior and decision-making deficits. We were also able to predict mice that would be the most vulnerable to ASD depending of their behavior before ASD exposure.

Perspectives in affective disorders: Clocks and sleep

Mood disorders are often characterised by alterations in circadian rhythms, sleep disturbances and seasonal exacerbation. Conversely, chronobiological treatments utilise zeitgebers for circadian rhythms such as light to improve mood and stabilise sleep, and manipulations of sleep timing and duration as rapid antidepressant modalities. Although sleep deprivation ("wake therapy") can act within hours, and its mood-elevating effects be maintained by regular morning light administration/medication/earlier sleep, it has not entered the regular guidelines for treating affective disorders as a first-line treatment. The hindrances to using chronotherapeutics may lie in their lack of patentability, few sponsors to carry out large multi-centre trials, non-reimbursement by medical insurance and their perceived difficulty or exotic "alternative" nature. Future use can be promoted by new technology (single-sample phase measurements, phone apps, movement and sleep trackers) that provides ambulatory documentation over long periods and feedback to therapist and patient. Light combinations with cognitive behavioural therapy and sleep hygiene practice may speed up and also maintain response. The urgent need for new antidepressants should hopefully lead to reconsideration and implementation of these non-pharmacological methods, as well as further clinical trials. We review the putative neurochemical mechanisms underlying the antidepressant effect of sleep deprivation and light therapy, and current knowledge linking clocks and sleep with affective disorders: neurotransmitter switching, stress and cortico-limbic reactivity, clock genes, cortical neuroplasticity, connectomics and neuroinflammation. Despite the complexity of multi-system mechanisms, more insight will lead to fine tuning and better application of circadian and sleep-related treatments of depression.

Sleep homeostasis and the circadian clock: Do the circadian pacemaker and the sleep homeostat influence each other's functioning?

Sleep is regulated by a homeostatic and a circadian process. Together these two processes determine most aspects of sleep and related variables like sleepiness and alertness. The two processes are known to be able to work independently, but also to both influence sleep and sleep related variables in an additive or more complex manner. The question remains whether the two processes are directly influencing each other. The present review summarizes evidence from behavioural and electroencephalographic determined sleep, electrophysiology, gene knock out mouse models, and mathematical modelling to explore whether sleep homeostasis can influence circadian clock functioning and vice versa. There is a multitude of data available showing parallel action or influence of sleep homeostatic mechanisms and the circadian clock on several objective and subjective variables related to sleep and alertness. However, the evidence of a direct influence of the circadian clock on sleep homeostatic mechanisms is sparse and more research is needed, particularly applying longer sleep deprivations that include a second night. The strongest evidence of an influence of sleep homeostatic mechanisms on clock functioning comes from sleep deprivation experiments, demonstrating an attenuation of phase shifts of the circadian rhythm to light pulses when sleep homeostatic pressure is increased. The data suggest that the circadian clock is less susceptible to light when sleep pressure is high. The available data indicate that a strong central clock will induce periods of deep sleep, which in turn will strengthen clock function. Both are therefore important for health and wellbeing. Weakening of one will also hamper functioning of the other. Shift work and jet lag are situations where one tries to adapt to zeitgebers in a condition where sleep is compromised. Adaptation to zeitgebers may be improved by introducing nap schedules to reduce sleep pressure, and through that increasing clock susceptibility to light.

Recovery of neurological function despite immediate sleep disruption following diffuse brain injury in the mouse: clinical relevance to medically untreated concussion

STUDY OBJECTIVE

We investigated the relationship between immediate disruption of posttraumatic sleep and functional outcome in the diffuse brain-injured mouse.

DESIGN

Adult male C57BL/6 mice were subjected to moderate midline fluid percussion injury (n = 65; 1.4 atm; 6-10 min righting reflex time) or sham injury (n = 44). Cohorts received either intentional sleep disruption (minimally stressful gentle handling) or no sleep disruption for 6 h following injury. Following disruption, serum corticosterone levels (enzyme-linked immunosorbent assay) and posttraumatic sleep (noninvasive piezoelectric sleep cages) were measured. For 1-7 days postinjury, sensorimotor outcome was assessed by Rotarod and a modified Neurological Severity Score (NSS). Cognitive function was measured using Novel Object Recognition (NOR) and Morris water maze (MWM) in the first week postinjury.

SETTING

Neurotrauma research laboratory.

MEASUREMENTS AND RESULTS

Disrupting posttraumatic sleep for 6 h did not affect serum corticosterone levels or functional outcome. In the hour following the first dark onset, sleep-disrupted mice exhibited a significant increase in sleep; however, this increase was not sustained and there was no rebound of lost sleep. Regardless of sleep disruption, mice showed a time-dependent improvement in Rotarod performance, with brain-injured mice having significantly shorter latencies on day 7 compared to sham. Further, brain-injured mice, regardless of sleep disruption, had significantly higher NSS scores postinjury compared with sham. Cognitive behavioral testing showed no group differences among any treatment group measured by MWM and NOR.

CONCLUSION

Short-duration disruption of posttraumatic sleep did not affect functional outcome, measured by motor and cognitive performance. These data raise uncertainty about posttraumatic sleep as a mechanism of recovery from diffuse brain injury.

Antidepressant chronotherapeutics for bipolar depression

Chronotherapeutics refers to treatments based on the principles of circadian rhythm organization and sleep physiology, which control the exposure to environmental stimuli that act on biological rhythms, in order to achieve therapeutic effects in the treatment of psychiatric conditions. It includes manipulations of the sleep-wake cycle such as sleep deprivation and sleep phase advance, and controlled exposure to light and dark. The antidepressant effects of chronotherapeutics are evident in difficult-to-treat conditions such as bipolar depression, which has been associated with extremely low success rates of antidepressant drugs in naturalistic settings and with stable antidepressant response to chronotherapeutics in more than half of the patients. Recent advances in the study of the effects of chronotherapeutics on neurotransmitter systems, and on the biological clock machinery, allow us to pinpoint its mechanism of action and to transform it from a neglected or “orphan” treatment to a powerful clinical instrument in everyday psychiatric practice.

Changes in the serotonergic system and in brain-derived neurotrophic factor distribution in the main olfactory bulb of pcd mice before and after mitral cell loss

The serotonergic centrifugal system innervating the main olfactory bulb (MOB) plays a key role in the modulation of olfactory processing. We have previously demonstrated that this system suffers adaptive changes under conditions of a lack of olfactory input. The present work examines the response of this centrifugal system after mitral cell loss in the Purkinje cell degeneration (pcd) mutant mice. The distribution and density of serotonergic centrifugal axons were studied in the MOB of control and pcd mice, both before and after the loss of mitral cells, using serotonin (5-HT) and 5-HT transporter immunohistochemistry. Studies of the amount of 5-HT and its metabolite, 5-hydroxyindole acetic acid (5-HIAA), were performed by means of high-performance liquid chromatography (HPLC), and the relative amounts of brain-derived neurotrophin factor, BDNF, and its major receptor, tropomyosin-related kinase B (TrkB), were measured by Western blot. Our study revealed that the serotonergic system develops adaptive changes after, but not before, mitral cell loss. The lack of the main bulbar projection cells causes a decrease in the serotonergic input received by the MOB, whereas the number of serotonergic cells in the raphe nuclei remains constant. In addition, one of the molecules directly involved in serotonergic sprouting, the neurotrophin BDNF and its main receptor TrkB, underwent alterations in the MOBs of the pcd animals even before the loss of mitral cells. These data indicate that serotonergic function in the MOB is closely related to olfactory activity and that mitral cell loss induces serotonergic plastic responses.

Serotonin synthesis, release and reuptake in terminals: a mathematical model

BACKGROUND

Serotonin is a neurotransmitter that has been linked to a wide variety of behaviors including feeding and body-weight regulation, social hierarchies, aggression and suicidality, obsessive compulsive disorder, alcoholism, anxiety, and affective disorders. Full understanding of serotonergic systems in the central nervous system involves genomics, neurochemistry, electrophysiology, and behavior. Though associations have been found between functions at these different levels, in most cases the causal mechanisms are unknown. The scientific issues are daunting but important for human health because of the use of selective serotonin reuptake inhibitors and other pharmacological agents to treat disorders in the serotonergic signaling system.

METHODS

We construct a mathematical model of serotonin synthesis, release, and reuptake in a single serotonergic neuron terminal. The model includes the effects of autoreceptors, the transport of tryptophan into the terminal, and the metabolism of serotonin, as well as the dependence of release on the firing rate. The model is based on real physiology determined experimentally and is compared to experimental data.

RESULTS

We compare the variations in serotonin and dopamine synthesis due to meals and find that dopamine synthesis is insensitive to the availability of tyrosine but serotonin synthesis is sensitive to the availability of tryptophan. We conduct in silico experiments on the clearance of extracellular serotonin, normally and in the presence of fluoxetine, and compare to experimental data. We study the effects of various polymorphisms in the genes for the serotonin transporter and for tryptophan hydroxylase on synthesis, release, and reuptake. We find that, because of the homeostatic feedback mechanisms of the autoreceptors, the polymorphisms have smaller effects than one expects. We compute the expected steady concentrations of serotonin transporter knockout mice and compare to experimental data. Finally, we study how the properties of the the serotonin transporter and the autoreceptors give rise to the time courses of extracellular serotonin in various projection regions after a dose of fluoxetine.

CONCLUSIONS

Serotonergic systems must respond robustly to important biological signals, while at the same time maintaining homeostasis in the face of normal biological fluctuations in inputs, expression levels, and firing rates. This is accomplished through the cooperative effect of many different homeostatic mechanisms including special properties of the serotonin transporters and the serotonin autoreceptors. Many difficult questions remain in order to fully understand how serotonin biochemistry affects serotonin electrophysiology and vice versa, and how both are changed in the presence of selective serotonin reuptake inhibitors. Mathematical models are useful tools for investigating some of these questions.

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.

Chronotherapeutics in a psychiatric ward

Psychiatric chronotherapeutics is the controlled exposure to environmental stimuli that act on biological rhythms in order to achieve therapeutic effects in the treatment of psychiatric conditions. In recent years some techniques (mainly light therapy and sleep deprivation) have passed the experimental developmental phase and reached the status of powerful and affordable clinical interventions for everyday clinical treatment of depressed patients. These techniques target the same brain neurotransmitter systems and the same brain areas as do antidepressant drugs, and should be administered under careful medical supervision. Their effects are rapid and transient, but can be stabilised by combining techniques among themselves or together with common drug treatments. Antidepressant chronotherapeutics target the broadly defined depressive syndrome, with response and relapse rates similar to those obtained with antidepressant drugs, and good results are obtained even in difficult-to-treat conditions such as bipolar depression. Chronotherapeutics offer a benign alternative to more radical treatments of depression for the treatment of severe depression in psychiatric wards, but with the advantage of rapidity of onset.

Circadian genes, rhythms and the biology of mood disorders

For many years, researchers have suggested that abnormalities in circadian rhythms may underlie the development of mood disorders such as bipolar disorder (BPD), major depression and seasonal affective disorder (SAD). Furthermore, some of the treatments that are currently employed to treat mood disorders are thought to act by shifting or "resetting" the circadian clock, including total sleep deprivation (TSD) and bright light therapy. There is also reason to suspect that many of the mood stabilizers and antidepressants used to treat these disorders may derive at least some of their therapeutic efficacy by affecting the circadian clock. Recent genetic, molecular and behavioral studies implicate individual genes that make up the clock in mood regulation. As well, important functions of these genes in brain regions and neurotransmitter systems associated with mood regulation are becoming apparent. In this review, the evidence linking circadian rhythms and mood disorders, and what is known about the underlying biology of this association, is presented.

Changes in the serotonergic system in the main olfactory bulb of rats unilaterally deprived from birth to adulthood

The serotonergic system plays a key role in the modulation of olfactory processing. The present study examined the plastic response of this centrifugal system after unilateral naris occlusion, analysing both serotonergic afferents and receptors in the main olfactory bulb. After 60 days of sensory deprivation, the serotonergic system exhibited adaptive changes. Olfactory deprivation caused a general increase in the number of fibres immunopositive for serotonin but not of those immunopositive for the serotonin transporter. HPLC data revealed an increase in serotonin levels but not in those of its major metabolite, 5-hydroxyindole acetic acid, resulting in a decrease in the 5-hydroxyindole acetic acid/serotonin ratio. These changes were observed not only in the deprived but also in the contralateral olfactory bulb. Double serotonin-tyrosine hydroxylase immunolabelling revealed that the glomerular regions of the deprived olfactory bulb with a high serotonergic fibre density showed a strong reduction in tyrosine hydroxylase. Finally, the serotonin(2A) receptor distribution density and the number of juxtaglomerular cells immunopositive for serotonin(2A) receptor remained unaltered after olfactory deprivation. Environmental stimulation modulated the serotonergic afferents to the olfactory bulb. Our results indicate the presence of a bilateral accumulation of serotonin in the serotonergic axon network, with no changes in serotonin(2A) receptor density after unilateral olfactory deprivation.

Perspectives for the development of animal models of bipolar disorder

Bipolar disorder (BD) has been a particularly challenging illness for the development of adequate animal models for neurobiological studies. These difficulties are largely related to the peculiar clinical characteristics of this illness, with an intriguing alternation of mania, depression, euthymia, and mixed states. The etiology and brain mechanisms involved in this several mental illness remain unknown. Preclinical studies with animal models of mania or depression have been developed to evaluate the potential efficacy of new psychotropic drugs and generate information concerning the biochemical effects of these drugs on specific targets. These models try to mimic the behavioral components of mania and depression in human subjects and examine the pharmacological responses and mechanisms of action of potentially new therapeutic agents. The main limitation is that there is currently no model that would mimic mood cyclicity, which is a hallmark feature of BD. Thus, these models do not represent valid paradigms for the study of this illness, because they do not address key questions regarding cyclicity. In this review, we propose that new genetics approaches involving potential animal models of BD are a promising new area for further development.

Antidepressant effects of light therapy combined with sleep deprivation are influenced by a functional polymorphism within the promoter of the serotonin transporter gene

BACKGROUND

A functional polymorphism within the promoter of the serotonin transporter has been shown to influence the antidepressant response to serotonergic drug treatments and to total sleep deprivation (TSD). The short-term relapse that follows acute response to TSD has been successfully prevented by combining TSD with light therapy. The mechanism of action of this combined treatment is unknown.

METHODS

We tested the hypothesis that allelic variation of the serotonin transporter (5-HTT) linked polymorphic region (5-HTTLPR) could influence the response to the combination of light therapy and TSD. Twenty-two bipolar depressed inpatients were administered a night of TSD combined with 30 min light therapy given during the TSD night and in the morning after recovery sleep. 5-HTTLPR was genotyped using polymerase chain reaction techniques. Changes in perceived mood were rated on a visual analog scale.

RESULTS

Light therapy sustained the effect of TSD. The effect was more marked in homozygotes for the long variant of 5-HTTLPR than in heterozygotes and homozygotes for the short variant.

CONCLUSIONS

The influence of 5-HTTLPR on response to the combination of TSD and light therapy is similar to that observed on response to TSD and serotonergic drug treatments.

Acceleration and augmentation strategies for treating bipolar depression

Despite the prevalence and morbidity of bipolar depression, few randomized treatment trials have been conducted to assess clinical efficacy. Even fewer studies have assessed approaches that optimize treatment response for bipolar depression. This review will define three types of common combination strategies--adjunctive, acceleration and augmentation--and discuss the limited literature of controlled studies reported on acceleration and augmentation approaches.

Pharmacological properties and SAR of new 1,4-disubstituted piperazine derivatives with hypnotic-sedative activity

Preparation, pharmacological properties and structure-activity relationships of new pyrimidyl-piperazine derivatives, exhibiting sedative and hypnotic activity in mice, are reported. The hypnotic activity of the compounds was comparable with that of zopiclone (the known hypnotic-sedative agent), their interaction with ethanol, however, being much lower. The obtained results suggested that zopiclone and pyrimidylpiperazines 2, 4 and 5 exerted their pharmacological activity through a different mechanism - zopiclone through the interaction with benzodiazepine receptors and compounds 2, 4 and 5 through an unidentified molecular target. The pharmacological properties of compound 3 could be the result of a mixed mechanism of action, combining the properties of zopiclone and those of compounds 2, 4 and 5. A common feature of zopiclone and compounds 2 and 3 was that, after their systemic administration, independently of mechanism of action, together with the hypnotic effect a reduction of the 5-HT turnover in the mouse brain was observed. Minimum structural requirements for the hypnotic activity were formulated. Structural considerations have shown that removing the alpha-carbonyl group did not influence the drug's ability to inhibit the locomotor activity. However, it did influence its ability to disturb motor coordination or abolish the righting reflex within non-lethal doses.

Dorsal raphe nuclear stimulation of SCN serotonin release and circadian phase-resetting

Serotonin (5-HT) is strongly implicated in the regulation of mammalian circadian rhythms. However, little is known of the functional relationship between the circadian clock located in the suprachiasmatic nucleus (SCN) and its source of serotonergic innervation, the midbrain raphe nuclei. In previous studies, we reported that electrical stimulation of the dorsal or median raphe nuclei (DRN and MRN, respectively) induced 5-HT release in the SCN. Notably, DRN- but not MRN-stimulated 5-HT release was blocked by the 5-HT(1,2,7) antagonist, metergoline, suggesting that the DRN signals to the SCN indirectly via the activation of a 5-HT-responsive multisynaptic pathway. In the present study, pretreatment with the 5-HT(2,7) antagonist, ritanserin, also significantly inhibited DRN-electrically stimulated SCN 5-HT release. However, pretreatment with the 5-HT(1A) antagonist, NAN-190, or the 5-HT(2) antagonists ketanserin and cinanserin had little suppressive effect on this DRN-stimulated 5-HT release. In complementary behavioral trials, electrical stimulation of the DRN during subjective midday caused a 1.3-h advance in the free-running circadian activity rhythm under constant darkness, which was inhibited by metergoline. Collectively, these results are evidence that: (1) DRN-stimulated 5-HT release in the SCN requires the activation of an intermediate target with receptors having 5-HT(7) pharmacological characteristics; (2) electrical stimulation of the DRN induces phase-resetting of the circadian activity rhythm; and (3) activation of 5-HT receptors is necessary for this DRN-stimulated circadian phase-resetting. In view of the dynamic changes in DRN neuronal activity incumbent with the daily sleep-activity cycle, and its functional linkages to the SCN and intergeniculate leaflet, the DRN could serve to provide behavioral/arousal state information to various sites comprising the brain circadian system.

Ongoing lithium treatment prevents relapse after total sleep deprivation

Forty bipolar depressed inpatients underwent three consecutive cycles of total sleep deprivation (TSD). At the beginning of the study, 20 patients were free of psychotropic drugs and 20 had been receiving lithium medication for at least 6 months. Mood was rated on the Hamilton Rating Scale for Depression before and after TSD; perceived mood changes during treatment were evaluated with self-administered visual analog scales. Patients undergoing long-term lithium treatment showed a significantly better response to TSD as rated on both scales: 13 of 20 patients (vs. 2 of 20 patients without lithium) showed a sustained response during a follow-up period of 3 months. This preliminary evidence of a positive interaction of TSD and long-term lithium treatment could be explained by a synergistic effect of both treatments on brain serotonergic function, possibly via a desensitization of 5-hydroxytryptamine-1A inhibitory autoreceptors.

The unipolar-bipolar dichotomy and the response to sleep deprivation

Fifty-one inpatients affected by a major depressive episode were divided into four groups according to mood disorder diagnosis and previous clinical history (bipolar disorder type I; bipolar disorder type II; major depressive disorder with at least three previous depressive episodes; and single depressive episode patients) and administered three consecutive total sleep deprivation (TSD) cycles. Mood changes were rated with a reduced version of the Hamilton Depression Rating Scale and with self-administered visual analogue scales. TSD caused better clinical effects in bipolar and single-episode patients; in particular, unipolar patients lacked effects in perceived mood after the first TSD and showed worse Hamilton ratings in respect to the other groups after the three TSD treatments. Discriminant function analysis could correctly classify 80% of bipolar patients, post hoc, based on TSD response. Further researches on the clinical efficacy of TSD must take into account the heterogeneity of depression and of its biological substrate.

Platelet serotonin and interleukin-1 beta after sleep deprivation and recovery sleep in humans

Sleep deprivation (SD) represents a well-established therapy for major depression. Recent findings suggest that the antidepressive effects of sleep deprivation are mediated at least in part by pro-serotoninergic mechanisms. Furthermore, SD has been demonstrated to modify different host defense activities. We therefore investigated the serotonin (5-HT) content in platelets, platelet density distribution and 5-HT-induced IL-1 beta release from platelets in 10 healthy men before and after total SD (TSD) as well as after recovery sleep. Blood samples were drawn on 3 consecutive days at 7.00 h, 13.00 h, and 19.00 h, respectively. In addition, the psychophysiological parameters tiredness and wakefulness were assessed. After TSD the normal daily variation of IL-1 beta release with high morning levels and low evening levels was found to be significantly inverted. The release of IL-1 beta corresponded positively to the subjectively experienced tiredness of the probands. Analysis of platelet density distribution indicated a significant daily variation of low density platelets with low levels in the morning and high levels in the evening, which was absent after TSD. Our findings favour an increased pro-serotoninergic effect after TSD, which comprises respective variations of the host defense system, but is abolished by consecutive recovery sleep.

Sleep deprivation can attenuate light-induced phase shifts of circadian rhythms in hamsters

To determine whether sleep deprivation (SD) affects the response of circadian rhythms to light, hamsters were forced to walk on a slowly rotating treadmill for 6 or 24 h, ending early in the night, with or without a light pulse during the last 30 min. SD alone did not produce a significant phase shift. Light pulses (300 and 50 lx) alone induced significant delay shifts (55 and 35 min, respectively). Twenty-four hours SD significantly attenuated the delay to brighter light and 6 h SD significantly attenuated the delay to moderate light. Sleep loss or attendant low-intensity continuous activity appear to modulate the response of the hamster circadian system to light.

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.

Alterations of blood platelet MAO-B activity and LSD-binding in humans after sleep deprivation and recovery sleep

Sleep deprivation (SD) is an effective, however short-lived, method of treatment of depression. Preliminary findings suggest that the antidepressive effect of sleep deprivation is mediated by serotoninergic (5-HT) mechanisms. We therefore assessed serotoninergic activity before and after total SD (TSD) as well as after the following night sleep by investigating platelet LSD-binding, MAO B-activity, and 5-HT-content as well as plasma norepinephnne (NE) in 10 healthy men (age: 27.4 +/- 2.8 years). Blood samples were drawn on three consecutive days at 0700, 1300 and 1900 h, respectively. After TSD, a significant increase of LSD-binding KD and Bmax as well as of MAO-B KM and plasma NE could be observed, which, however, vanished after consecutive night sleep. Our findings favour an increased serotoninergic transmission after TSD and thus support the hypothesis, that sleep deprivation exerts its antidepressant effects by pro-serotoninergic mechanisms.

Effect of sleep deprivation on the growth hormone response to the alpha-3 adrenergic receptor agonist, clonidine, in normal subjects

One night's sleep deprivation (SD) increased the growth hormone (GH) response to clonidine (20 ug/kg i.v.) in 11 normal men ( p < 0.005). This finding may indicate that SD enhances alpha-2 adrenergic receptor function or that the GH response to GH releasing factor in increased by SD.

Sleep deprivation hastens the antidepressant action of fluoxetine

Among ten bipolar depressed patients admitted to our psychiatric ward, five patients were treated with fluoxetine alone and five subjects were treated with fluoxetine in association with total sleep deprivation (TSD) in order to evaluate the effect of the interaction between the administration of the serotonergic antidepressant compound fluoxetine and repeated cycles of TSD. Patients treated with fluoxetine plus repeated TSD showed a faster amelioration of depressive symptomatology compared with the other group. We discuss our findings hypothesizing an enhancement in dopaminergic and possibly in serotonergic transmission due to repeated TSD adding to the increase in serotonergic transmission due to fluoxetine medication.

Sleep deprivation reduces the citalopram-induced inhibition of serotoninergic neuronal firing in the nucleus raphe dorsalis of the rat

Sleep deprivation (SD) for one night induces mood improvement in depressed patients. However, relapse often occurs on the day after deprivation subsequently to a sleep episode. In light of the possible involvement of central serotonin (5-hydroxytryptamine, 5-HT) neurotransmission in both depression and sleep mechanisms, we presently investigated, in the rat, the effects of SD and recovery sleep on the electrophysiological response of 5-HT neurons in the nucleus raphe dorsalis (NRD) to an acute challenge with the 5-HT reuptake blocker citalopram. In all rats, citalopram induced a dose-dependent inhibition of the firing of NRD neurons recorded under chloral hydrate anaesthesia. After SD, achieved by placing rats in a slowly rotating cylinder for 24 h, the inhibitory action of citalopram was significantly reduced (with a concomitant 53% increase in its ED50 value). After a recovery period of 4 h, a normal susceptibility of the firing to citalopram was restored. The decreased sensitivity of 5-HT neuronal firing to the inhibitory effect of citalopram after SD probably results in an enhancement of 5-HT neurotransmission. Such an adaptive phenomenon (similar to that reported after chronic antidepressant treatment), and its normalization after recovery sleep, parallel the mood improvement effect of SD and the subsequent relapse observed in depressed patients. These data suggest that the associated changes in 5-HT autocontrol of the firing of NRD serotoninergic neurons are relevant to the antidepressant action of SD.