Seasonal differences in the diurnal pattern of cortisol secretion in healthy participants and those with self-assessed seasonal affective disorder

This study compared the daily pattern of free salivary cortisol secretion in winter and in summer between two groups; participants with self-assessed seasonal affective disorder (SAD) and age- and sex-matched healthy controls. Fifty-two participants completed the study with an equal number in each group. The diurnal pattern of cortisol secretion was assessed across two consecutive weekdays in summer, and two in winter, with conditions being counterbalanced. On each study day participants collected multiple saliva samples in the domestic setting to capture the cortisol awakening response (CAR) and declining levels across the day. In addition, perceived stress, anxiety, depression, state stress and state arousal were assessed using validated questionnaires. There was no evidence for any seasonal changes in psychological data or cortisol pattern for the healthy control population. In summer, self-assessed SAD and control participants had similar psychological and cortisol profiles. In winter however, SAD participants reported greater depression, stress and anxiety, and lower levels of arousal. Furthermore, the CAR was significantly attenuated in SAD participants during winter months. There was no difference in cortisol levels during the rest of the day between controls and SAD participants in winter. In line with the above findings and previous research, there was an inverse relationship between the increase in cortisol following awakening and a measure of seasonality in winter. Furthermore in winter, a general dysphoria construct correlated inversely with the CAR, indicating that participants reporting greater depression, stress and anxiety and lower arousal, exhibited lower CARs. In conclusion, during the shortened photoperiod in winter, the cortisol response to awakening is attenuated in participants with self-assessed SAD in comparison to controls. These findings contribute to the understanding of the physiology of SAD.

Paradoxical function of orexin/hypocretin circuits in a mouse model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder involving progressive motor disturbances, cognitive decline, and desynchronized sleep-wake rhythms. Recent studies revealed that restoring normal sleep-wake cycles can improve cognitive function in HD mice, suggesting that some sleep/wake systems remain operational and thus represent potential therapeutic targets for HD. Hypothalamic neurons expressing orexins/hypocretins (orexin neurons) are fundamental orchestrators of arousal in mammals, but it is unclear whether orexin circuits operate normally in HD. Here we analyzed the electrophysiology, histology, and gene expression of orexin circuits in brain slices from R6/2 mice, a transgenic model of HD with a progressive neurological phenotype. We report that in R6/2 mice, the size of an electrically distinct subpopulation of orexin neurons is reduced, as is the number of orexin-immunopositive cells in some hypothalamic regions. R6/2 orexin cells display altered glutamatergic inputs, and have an abnormal circadian profile of activity, despite normal circadian rhythmicity of the suprachiasmatic nucleus (SCN), the "master clock" of the brain. Nevertheless, even at advanced stages of HD, intrinsic firing properties of orexin cells remain normal and suppressible by serotonin, noradrenaline, and glucose. Furthermore, histaminergic neurons (key cells required for the propagation of orexin-induced arousal) also display normal responses to orexin. Together, these data suggest that the orexin system remains functional and modifiable in HD mice, although its circadian activity profile is disrupted and no longer follows that of the SCN.

Agomelatine as chronopsychopharmaceutics restoring circadian rhythms and enhancing resilience to stress: a wishfull thinking or an innovative strategy for superior management of depression?

BACKGROUND

While the research and treatment focus of biological aspects of depression has traditionally centered on neutrotransmitters disturbances, there has been relatively little attention paid to the chronobiological aspects of depression that offer rapid acting chronotherapeutis and from recently also an innovative circadian rhythms resynchronizing antidepressant.

OBJECTIVE

This article discusses chronobiological aspects of psychiatric treatment, particularly related to depression. It is concerned with chronotherapeutics and pharmacological interventions to resychronize circadian rhythms, particularly focused on agomelatine, an innovative antidepressant targeting melatonergic M1/M2 and serotonergic 5-HT2c receptors.

DISCUSSION

Depression can be explained as dysfunction at the nexus of the body, brain and mind, three mutually very dependent components, associated through circadian pace makers at the molecular, cellular, physiological and behavioral levels. Mental disorders, particularly depression, are common in people with circadian rest-activity cycle disturbances and sleep-wake problems. The circadian rest-activity and sleep-wake cycle disturbances are risk factors for developing and recurrence of mental disorders as well as, what is very important, they are associated with worse outcome. The interrelationships between circadian rhythm disturbances and depression is very complex, and the fundamental question is whether they trigger depression or whether these disturbances arise as a consequence of the disease. However, both depression and circadian rhythm disturbances may have a common aetiology: a decreased cellurar resilience associated with lower resistance to stressful events. Treating depression pharmacologicaly through the restoration of circadian rhythms may open a new era of superior management of depression and other mental disorders.

CONCLUSION

Chronotherapeutic strategies that reset the internal clock may have specific advantage for the treatment of depression and other mental disorders. There is still a lot of research to be done on utilising chronotherapeutic principles in clinical practice, particularly regarding the specific indications. Agomelatine seems to be an promising resynchronizing agent expanding the field of chronopharmacology and inducing new treatment strategy.

Vasopressin and the output of the hypothalamic biological clock

The physiological effects of vasopressin as a peripheral hormone were first reported more than 100 years ago. However, it was not until the first immunocytochemical studies were carried out in the early 1970s, using vasopressin antibodies, and the discovery of an extensive distribution of vasopressin-containing fibres outside the hypothalamus, that a neurotransmitter role for vasopressin could be hypothesised. These studies revealed four additional vasopressin systems next to the classical magnocellular vasopressin system in the paraventricular and supraoptic nuclei: a sexually dimorphic system originating from the bed nucleus of the stria terminalis and the medial amygdala, an autonomic and endocrine system originating from the medial part of the paraventricular nucleus, and the circadian system originating from the hypothalamic suprachiasmatic nuclei (SCN). At about the same time as the discovery of the neurotransmitter function of vasopressin, it also became clear that the SCN contain the main component of the mammalian biological clock system (i.e. the endogenous pacemaker). This review will concentrate on the significance of the vasopressin neurones in the SCN for the functional output of the biological clock that is contained within it. The vasopressin-containing subpopulation is a characteristic feature of the SCN in many species, including humans. The activity of the vasopressin neurones in the SCN shows a pronounced daily variation in its activity that has also been demonstrated in human post-mortem brains. Animal experiments show an important role for SCN-derived vasopressin in the control of neuroendocrine day/night rhythms such as that of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes. The remarkable correlation between a diminished presence of vasopressin in the SCN and a deterioration of sleep-wake rhythms during ageing and depression make it likely that, also in humans, the vasopressin neurones contribute considerably to the rhythmic output of the SCN.

[Depression as chronobiological illness]

Chronobiological problems are always present as aetiological or pathoplastic conditions almost in all psychiatric disorders and considered as the greatest contributors to the mood and sleep disorders associated problems. The present review summarise the recent advances in the chronobiology research from the point of the clinician with particular emphasis on the psychobiology and pharmacotherapy of the depression. Human behaviour builds up from different length of circadian, ultradian and seasonal rhytms, strictly controlled by a hierarchical organisation of sub-cellullar, cellular, neuro-humoral and neuro-immunological clock systems. These internal clock systems are orchestrated at molecular level by certain clock genes and on the other hand--at neuro-humoral level--by the effect of the sleep hormone, melatonine, produced by the neurons of the suprachiasmatic nucleus (SCN). Beside the biological factors, social interactions are also considered as important regulators of the biological clock systems. The pacemaker centers of the SCN receive efferents from the serotoninergic raphe nuclei in order to regulate stress responses and neuroimmunological functions. The direction and the level of the chronobiological desynchronisation could be totally divergent in the case of the different affective disorders. Different chronobiological interventions are required therefore in the case of the advanced and delayed sleep disorders. Sleeping disorders are considered as the most recognised signs of the chronobiological desynchronisation in depression, but these symptoms are only the tip of the iceberg, since other chronobiological symptoms could be present due to the hidden physiological abnormalities. The serum melatonine profile is considered to be characteristic to age, gender and certain neuropsychiatric disorders. The natural and synthetic agonist of the melatonine receptors could be used as chronobiotics. The recently marketed agomelatine with a highly selective receptor binding profile (MT1 and MT2 agonism and 5HT2C antagonism) targets the desynchronised circadian rhytm in affective disorders and it has mainly antidepressive effect. Among the non-pharmacological chronobiological interventions, the different forms of the sleep deprivation, light and social rhytm therapies could offer alternative treatment options for the clinician.

[Biology and genetics of circadian rhythm]

In recent decades our knowledge of the molecular mechanisms of biological clocks has grown expontentially. This has helped to guide the choice of genes studied to explain inter-individual variations seen in circadian rhythms. In recent years analysis of circadian rhythms has advanced considerably into the study of pathological circadian rhythms in human beings. These findings, combined with those obtained from studying mice whose circadian genes have been rendered incapable, have revealed the role of genetic factors in circadian rhythms. This literature review presents an overview of these findings. Beyond our understanding of the functioning of these biological clocks, this knowledge will be extremely useful to analyse genetic factors involved in morbid conditions involving circadian rhythm abnormalities.

Changes in vasoactive intestinal peptide and arginine vasopressin expression in the suprachiasmatic nucleus of the rat brain following footshock stress

The neuropeptides, arginine vasopressin (AVP) and vasoactive intestinal polypeptide (VIP) are synthesized by neurons of the suprachiasmatic nucleus (SCN) of the hypothalamus and are important regulators of SCN function. Previous studies have demonstrated that acute exposure to stressors can disrupt circadian activity rhythms, suggesting the possibility of stress-related alterations in the expression of these neuropeptides within SCN neurons. In this study, we examined the effect of intermittent footshock stress on AVP mRNA and heterogeneous nuclear RNA (hnRNA) and VIP mRNA expression in neurons of the SCN. Young adult male Sprague/Dawley rats were subjected to 15 s of scrambled intermittent footshock (0.50 mA pulses, 1 pulse/s, 300 ms duration) every 5 min for 30 min. Animals were sacrificed 75 or 135 min after the onset of stress and brains examined for AVP mRNA and hnRNA, and VIP mRNA using in situ hybridization. Footshock stress increased AVP hnRNA levels at the 75 min time point whereas AVP mRNA was elevated at both the 75 and 135 min time points. In contrast, footshock stress decreased the number of cells expressing VIP mRNA in the SCN without changing hybridization level per cell. These data indicate that the disruptive effect of stress on activity rhythms correlate with alterations in the expression of regulatory peptides within the SCN.

Long term effects of sleep deprivation on the mammalian circadian pacemaker

STUDY OBJECTIVES

In mammals, sleep is controlled by a homeostatic process, which regulates depth of sleep, and by the circadian clock of the suprachiasmatic nucleus (SCN), which regulates 24-h rhythms in timing of sleep. Sleep deprivation is known to cause molecular and physiological changes and results in an alteration in the timing of sleep. It is generally assumed that following sleep deprivation, homeostatic mechanisms overrule the circadian clock, allowing animals to sleep during their active phase. However, recent evidence indicates that sleep states have direct access to the circadian pacemaker of the SCN. We questioned therefore whether sleep deprivation may have long-term effects on the circadian pacemaker, which may explain altered sleep patterns following sleep deprivation.

DESIGN

To test this hypothesis, we combined SCN recordings of electrical impulse frequency through stationary implanted electrodes in freely moving rats with electroencephalogram recordings in the same animal before, during, and after a mild 6-h sleep deprivation.

MEASUREMENTS AND RESULTS

Following sleep deprivation, SCN neuronal activity was significantly reduced to about 60% of baseline levels. The decrements in SCN activity were most obvious during NREM sleep and REM sleep and lasted for 6-7 hours.

CONCLUSIONS

The data show that sleep deprivation influences not only sleep homeostatic mechanisms, but also SCN electrical activity, resulting in a strong reduction in circadian amplitude in the major output signal from the SCN.

Central oxytocin enhances antinociception in the rat

The study aimed to investigate the effect of oxytocin on antinociception in the rat. The pain threshold was elevated by oxytocin following intraventricular (icv) or intrathecal injection (ith), and reduced by anti-oxytocin serum (icv or ith). But the pain threshold was not altered by intravenous injection (iv) of oxytocin or anti-oxytocin serum. Pain stimulation induced oxytocin concentration decrease in the hypothalamic supraoptic nucleus, and increase in the locus coeruleus, raphe magnus nucleus, caudate nucleus and spinal cord, but no change in the hypothalamic paraventricular nucleus and plasma. The results indicated that central, not peripheral oxytocin could enhance antinociception.

Disturbance and strategies for reactivation of the circadian rhythm system in aging and Alzheimer's disease

Circadian rhythm disturbances, such as sleep disorders, are frequently seen in aging and are even more pronounced in Alzheimer's disease (AD). Alterations in the biological clock, the suprachiasmatic nucleus (SCN), and the pineal gland during aging and AD are considered to be the biological basis for these circadian rhythm disturbances. Recently, our group found that pineal melatonin secretion and pineal clock gene oscillation were disrupted in AD patients, and surprisingly even in non-demented controls with the earliest signs of AD neuropathology (neuropathological Braak stages I-II), in contrast to non-demented controls without AD neuropathology. Furthermore, a functional disruption of the SCN was observed from the earliest AD stages onwards, as shown by decreased vasopressin mRNA, a clock-controlled major output of the SCN. The observed functional disconnection between the SCN and the pineal from the earliest AD stage onwards seems to account for the pineal clock gene and melatonin changes and underlies circadian rhythm disturbances in AD. This paper further discusses potential therapeutic strategies for reactivation of the circadian timing system, including melatonin and bright light therapy. As the presence of melatonin MT1 receptor in the SCN is extremely decreased in late AD patients, supplementary melatonin in the late AD stages may not lead to clear effects on circadian rhythm disorders.

Altered circadian and homeostatic sleep regulation in prokineticin 2-deficient mice

STUDY OBJECTIVES

Sleep is regulated by circadian and homeostatic processes. Recent studies with mutant mice have indicated that circadian-related genes regulate sleep amount, as well as the timing of sleep. Thus a direct link between circadian and homeostatic regulation of sleep may exist, at least at the molecular level. Prokineticin 2 (PK2), which oscillates daily with high amplitude in the suprachiasmatic nuclei (SCN), has been postulated to be an SCN output molecule. In particular, mice lacking the PK2 gene (PK2-/-) have been shown to display significantly reduced rhythmicity for a variety of circadian physiological and behavioral parameters. We investigated the role of PK2 in sleep regulation.

DESIGN

EEG/EMG sleep-wake patterns were recorded in PK2-/- mice and their wild-type littermate controls under baseline and challenged conditions.

MEASUREMENTS AND RESULTS

PK2-/- mice exhibited reduced total sleep time under entrained light-dark and constant darkness conditions. The reduced sleep time in PK2-/- mice occurred predominantly during the light period and was entirely due to a decrease in non-rapid eye movement (NREM) sleep time. However, PK2-/- mice showed increased rapid eye movement (REM) sleep time in both light and dark periods. After sleep deprivation, compensatory rebound in NREM sleep, REM sleep, and EEG delta power was attenuated in PK2-/- mice. In addition, PK2-/- mice had an impaired response to sleep disturbance caused by cage change in the light phase.

CONCLUSIONS

These results indicate that PK2 plays roles in both circadian and homeostatic regulation of sleep. PK2 may also be involved in maintaining the awake state in the presence of behavioral challenges.

Suppressors, receptors and effects of cytokines on the aging mouse biological clock

During aging, levels of inflammatory cytokines increase and circadian rhythms are frequently altered. We here investigated neurobiological correlates of neuroinflammation and its age-related variation in the hypothalamic suprachiasmatic nucleus (SCN), the master circadian pacemaker. Day/night variations of transcripts encoding cytokine receptors and suppressors of cytokine signaling (SOCS) were correlated in groups of mice of different ages with Fos induction elicited by intracerebroventricular injections of tumor necrosis factor-alpha and interferon-gamma. Cytokine-elicited Fos induction was high at early night, when SOCS1 and SOCS3 levels were low. Such Fos induction was significantly reduced in the older SCN at early night, and paralleled by reduced expression of interferon-gamma receptor transcripts as compared to the younger SCN. In addition, Fos induction at early night exhibited marked sub-regional differences in the SCN between the age groups. The study shows that SOCS1 and SOCS3 are expressed in the biological clock with a day/night variation that may regulate SCN responsiveness to cytokine exposure, and indicates that effects of pro-inflammatory cytokines on the SCN are markedly altered during senescence.

Circadian rhythm sleep disorders

Humans exhibit endogenous circadian rhythms that are regulated by the master circadian clock of the body, the suprachiasmatic nucleus. These endogenous circadian rhythms are aligned to the outside world by social and environmental cues. Circadian rhythm sleep disorders (CRSD) occur when there is an alteration of the internal timing mechanism or a misalignment between sleep and the 24-h social and physical environment. CRSD are often underrecognized yet should be considered in the differential of patients presenting with symptoms of insomnia and/or hypersomnia. Because behavioral and environmental factors often are involved in the development and maintenance of these conditions, a multimodal treatment approach of behavioral and/or pharmacologic approaches is usually required to synchronize a patient's circadian rhythm to the 24-h environment, consolidate sleep, and improve alertness. Rapid advances in our understanding of the physiologic, cellular, and molecular basis of circadian rhythm and sleep regulation will likely lead to improved diagnostic tools and treatments for CRSD.

Role for the Clock gene in bipolar disorder

Nearly all patients with bipolar disorder have severely disrupted circadian rhythms. Treatment with mood stabilizers can restore these daily rhythms, and this is correlated with patient recovery. However, it is still uncertain whether clock abnormalities are the cause of bipolar disorder or if these rhythm disruptions are secondary to alterations in other circuits. Furthermore, the mechanism by which the circadian clock might influence mood is still unclear. With cloning and characterization of the circadian genes and recent advances in molecular biology, we are starting to understand this strong association between circadian rhythms and bipolar disorder. Recent human genetic and mouse behavioral studies indicate that the Clock gene is particularly relevant in the mood disruptions associated with this disorder. Furthermore, it appears that Clock expression outside of the central pacemaker of the suprachiasmatic nucleus (SCN) is involved in mood regulation. In this chapter, the evidence linking circadian rhythms, the Clock gene, and bipolar disorder is discussed, along with the possible biology that underlies this connection.

Cross-talks between circadian timing system and cell division cycle determine cancer biology and therapeutics

The circadian clock orchestrates cellular functions over 24 hours, including cell divisions, a process that results from the cell cycle. The circadian clock and cell cycle interact at the level of genes, proteins, and biochemical signals. The disruption or the reinforcement of the host circadian timing system, respectively, accelerates or slows down cancer growth through modifications of host and tumor circadian clocks. Thus, cancer cells not only display mutations of cell cycle genes but also exhibit severe defects in clock gene expression levels or 24-hour patterns, which can in turn favor abnormal proliferation. Most of the experimental research actively ongoing in this field has been driven by the original demonstration that cancer patients with poor circadian rhythms had poor quality of life and poor survival outcome independently of known prognostic factors. Further basic research on the gender dependencies in circadian properties is now warranted, because a large clinical trial has revealed that gender can largely affect the survival outcome of cancer patients on chronotherapeutic delivery. Mathematical models further show that the therapeutic index of chemotherapeutic drugs can be optimized through distinct delivery profiles, depending on the initial host/tumor status and variability in circadian entrainment and/or cell cycle length. Clinical trials and systems-biology approaches in cancer chronotherapeutics raise novel issues to be addressed experimentally in the field of biological clocks. The challenge ahead is to therapeutically harness the circadian timing system to concurrently improve quality of life and down-regulate malignant growth.

Biological clocks and shift work: circadian dysregulation and potential long-term effects

Long-term epidemiologic studies on large numbers of night and rotating shift workers have suggested an increase in the incidence of breast and colon cancer in these populations. These studies suffer from poor definition and quantification of the work schedules of the exposed subjects. Against this background, the pathophysiology of phase shift and phase adaptation is reviewed. A phase shift as experienced in night and rotating shift work involves desynchronization at the molecular level in the circadian oscillators in the central nervous tissue and in most peripheral tissues of the body. There is a change in the coordination between oscillators with transient loss of control by the master-oscillator (the Suprachiasmatic Nucleus, SCN) in the hypothalamus. The implications of the pathophysiology of phase shift are discussed for long-term health effects and for the design of ergonomic work schedules minimizing the adverse health effects upon the worker.

Enhanced endocrine response to novel environment stress and lack of corticosterone circadian rhythm in staggerer (Rora sg/sg) mutant mice

The staggerer (Rora sg/sg) mutation is a deletion in the retinoid-related orphan receptor (RORalpha) gene that prevents translation of the ligand-binding domain (LBD), leading to the loss of RORalpha activity. RORalpha is a transcription factor that belongs to the nuclear receptor superfamily. In the brain, RORalpha is expressed in specific areas, including the cerebellum and suprachiasmatic nucleus (SCN). The homozygous Rora sg/sg mutant mouse, of which the most obvious phenotype is ataxia associated with cerebellar degeneration, also overproduces inflammatory cytokines. Here we compared the response to novelty stress of staggerer and wild-type mice as well as their diurnal cycles of adrenocorticotropic hormone and corticosterone secretion. We show that the staggerer mouse displays an enhanced endocrine response to novelty stress, which is not due to the enhanced production of interleukin-1 (IL-1), insofar as it is not blocked by pretreatment with IL-1ra and lacks the diurnal shift in corticosterone nonstressed levels; this last feature might be related to the expression of RORalpha in the SCN, a structure that maintains the circadian clock and plays a role in timing rhythmic physiology and behavior.

Diurnal rhythm in endogenous glucose production is a major contributor to fasting hyperglycaemia in type 2 diabetes. Suprachiasmatic deficit or limit cycle behaviour?

AIMS/HYPOTHESIS

An increase in endogenous glucose production (EGP) is a major contributor to fasting morning hyperglycaemia in type 2 diabetes. This increase is dissipated with fasting, later in the day. To understand its origin, EGP, gluconeogenesis and hormones that regulate metabolism were measured over 24 h. We hypothesised that EGP, and therefore glycaemia, would demonstrate a centrally mediated circadian rhythm in type 2 diabetes.

SUBJECTS AND METHODS

Seven subjects with type 2 diabetes and six age- and BMI-matched control subjects, fasting after breakfast (08.00 h), underwent a further 24-h fast, with the infusion of [U-(13)C]glucose and [3-(14)C]lactate, starting at 14.00 h. The MCR and production of total and gluconeogenic glucose were determined from the tracer concentrations using compartmental analysis.

RESULTS

MCR was near constant: 1.73+/-0.10 in control and 1.40+/-0.14 ml kg(-1) min(-1) in diabetic subjects (p=0.04). EGP in diabetes rose gradually overnight from 8.2+/-0.7 to 11.3+/-0.5 micromol kg(-1) min(-1) at 06.00 h (p<0.05). Glucose utilisation lagged EGP, rising from 8.5+/-0.6 to 10.5+/-0.4 micromol kg(-1) min(-1) (p<0.05), inducing a fall in glycaemia from a peak of 8.0+/-0.5 mmol/l to 6.3+/-0.4 mmol/l (p<0.05). Cortisol and melatonin showed diurnal variations, whereas insulin, glucagon and leptin did not. Melatonin was most closely related to EGP, but its secretion was attenuated in diabetes (p<0.05).

CONCLUSIONS/INTERPRETATION

In type 2 diabetes, EGP and gluconeogenesis display diurnal rhythms that drive the fasting hyperglycaemia and are absent in healthy control subjects. The rise in EGP may be related to a deficit in suprachiasmatic nucleus activity in diabetes, or result from non-linear behaviour plus a transition from a normal steady state to a limit cycle pattern in diabetes, or both.

Keeping time without a clock

The accepted dogma in circadian biology is that the transcription factor CLOCK lies at the heart of the molecular clock that drives behavioral and molecular rhythms. In this issue of Neuron, the generation of CLOCK-deficient mice with only subtle clock defects by DeBruyne et al. shakes up this view of the mammalian clock.

[A chronobiological approach in treatment of sleep disturbances in Alzheimer's dementia patients]

Alzheimer's dementia (AD) is a neurodegenerative disease that is often accompanied by severe sleep disturbances. The manifestation of the sleep disturbances is twofold: nighttime hyperarousal sometimes accompanied by irritability and agitation, and daytime excessive sleepiness. Thus, although treatment with sedatives or hypnotics may offer some relief to the nighttime hyperarousal, the daytime excessive sleepiness remains mostly unresolved. Recently, however, more promising results in relief of excessive daytime sleepiness, as well as nighttime hyperarousal, are offered by the chronobiological approach. This approach attributes the sleep problems of AD patients to a dysfunction in a broader neuronal mechanism, namely the biological clock, that paces various physiological functions, among which is the sleep-wake cycle. The biological clock, situated in the suprachiasmatic nuclei (SCN) of the hypothalamus, receives environmental light input via neuronal signals from the retina. The SCN, in turn, innervates the pineal gland, that is responsible for the production and release of melatonin. Light stimulus causes the attenuation of melatonin secretion from the pineal gland; whereas the cessation of light increases melatonin secretion. In diurnal mammals, the dim light melatonin onset (DLMO) is in accordance with sleep onset. The chronobiological approach offers two main treatments to the sleep problems in AD patients: morning exposure to bright light and evening administration of melatonin, both of which show at least moderate success in restoring the sleep-wake cycle in AD patients, that is more marked in the early stages of the disease.

Disruption of Circadian Coordination and Malignant Growth

Altered circadian rhythms predicted for poor survival in patients with metastatic colorectal or breast cancer. An increased incidence of cancers has been reported in flying attendants and in women working predominantly at night. To explore the contribution of circadian structure to tumor growth we ablated the 24-h rest-activity cycle and markedly altered the rhythms in body temperature, serum corticosterone and lymphocyte count in mice by complete stereotaxic destruction of the suprachiasmatic nuclei (SCN) or by subjecting the mice to experimental chronic jet-lag. Such disruption of circadian coordination significantly accelerated malignant growth in two transplantable tumor models, Glasgow osteosarcoma and Pancreatic adenocarcinoma. The mRNA expression of clock genes per2 and reverb-alpha in controls displayed significant circadian rhythms in the liver (Cosinor, p=0.006 and p=0.003, respectively) and in the tumor (p=0.04 and p<0.001, respectively). Both rhythms were suppressed in the liver and in the tumor of jet lagged mice. This functional disturbance of molecular clock resulted in down regulation of p53 and overexpression of c-Myc, two effects which may favor cancer growth.

CONCLUSIONS

These results indicate that circadian system could play an important role in malignant growth control. This should be taken into consideration in cancer prevention and therapy.