Melatonin, cortisol and body temperature rhythms in Lennox-Gastaut patients with or without circadian rhythm sleep disorders

Cycles in epilepsy

Epilepsy is among the most dynamic disorders in neurology. A canonical view holds that seizures, the characteristic sign of epilepsy, occur at random, but, for centuries, humans have looked for patterns of temporal organization in seizure occurrence. Observations that seizures are cyclical date back to antiquity, but recent technological advances have, for the first time, enabled cycles of seizure occurrence to be quantitatively characterized with direct brain recordings. Chronic recordings of brain activity in humans and in animals have yielded converging evidence for the existence of cycles of epileptic brain activity that operate over diverse timescales: daily (circadian), multi-day (multidien) and yearly (circannual). Here, we review this evidence, synthesizing data from historical observational studies, modern implanted devices, electronic seizure diaries and laboratory-based animal neurophysiology. We discuss advances in our understanding of the mechanistic underpinnings of these cycles and highlight the knowledge gaps that remain. The potential clinical applications of a knowledge of cycles in epilepsy, including seizure forecasting and chronotherapy, are discussed in the context of the emerging concept of seizure risk. In essence, this Review addresses the broad question of why seizures occur when they occur.

Seizing the moment: Zebrafish epilepsy models

Zebrafish are now widely accepted as a valuable animal model for a number of different central nervous system (CNS) diseases. They are suitable both for elucidating the origin of these disorders and the sequence of events culminating in their onset, and for use as a high-throughput in vivo drug screening platform. The availability of powerful and effective techniques for genome manipulation allows the rapid modelling of different genetic epilepsies and of conditions with seizures as a core symptom. With this review, we seek to summarize the current knowledge about existing epilepsy/seizures models in zebrafish (both pharmacological and genetic) and compare them with equivalent rodent and human studies. New findings obtained from the zebrafish models are highlighted. We believe that this comprehensive review will highlight the value of zebrafish as a model for investigating different aspects of epilepsy and will help researchers to use these models to their full extent.

Cortisol levels and seizures in adults with epilepsy: A systematic review

Stress has been suggested as a trigger factor for seizures in epilepsy patients, but little is known about cortisol levels, as indicators of stress, in adults with epilepsy. This systematic review summarizes the evidence on this topic. Following PRISMA guidelines, 38 articles were selected: 14 analyzing basal cortisol levels, eight examining antiepileptic drugs (AEDs) effects, 13 focused on seizure effects, and three examining stress. Higher basal cortisol levels were found in patients than in healthy people in studies with the most homogeneous samples (45% of 38 total studies). Despite heterogeneous results associated with AEDs, seizures were related to increases in cortisol levels in 77% of 38 total studies. The only study with acute stress administration found higher cortisol reactivity in epilepsy than in healthy controls. In studies using self-reported stress, high seizure frequency was related to increased cortisol levels and lower functional brain connectivity. Findings suggest that epilepsy could be considered a chronic stress model. The potential sensitizing role of accumulative seizures and issues for future research are discussed.

Epilepsy, Behavioral Abnormalities, and Physiological Comorbidities in Syntaxin-Binding Protein 1 (STXBP1) Mutant Zebrafish

Mutations in the synaptic machinery gene syntaxin-binding protein 1, STXBP1 (also known as MUNC18-1), are linked to childhood epilepsies and other neurodevelopmental disorders. Zebrafish STXBP1 homologs (stxbp1a and stxbp1b) have highly conserved sequence and are prominently expressed in the larval zebrafish brain. To understand the functions of stxbp1a and stxbp1b, we generated loss-of-function mutations using CRISPR/Cas9 gene editing and studied brain electrical activity, behavior, development, heart physiology, metabolism, and survival in larval zebrafish. Homozygous stxbp1a mutants exhibited a profound lack of movement, low electrical brain activity, low heart rate, decreased glucose and mitochondrial metabolism, and early fatality compared to controls. On the other hand, homozygous stxbp1b mutants had spontaneous electrographic seizures, and reduced locomotor activity response to a movement-inducing “dark-flash” visual stimulus, despite showing normal metabolism, heart rate, survival, and baseline locomotor activity. Our findings in these newly generated mutant lines of zebrafish suggest that zebrafish recapitulate clinical phenotypes associated with human syntaxin-binding protein 1 mutations.

Melatonin secretion in children with epilepsy

This study examined melatonin (MLT) system in children with epilepsy. Diurnal patterns of salivary MLT, urinary metabolite 6-sulphatoxymelatonin, core body temperature, pulse and blood pressure were measured in 51 children with epilepsy (6.6-17.9 years) and 29 comparison children (5.5-17.3 years). The children with epilepsy preserved MLT and other circadian rhythms. In nine children with epilepsy (17.6%), peak salivary MLT concentrations were very high. There were no associations between MLT secretion/excretion parameters (diurnal profile, peak nocturnal concentrations, area under the time curve, duration of elevated concentrations, acrophase) and seizure characteristics (time, type of seizures, antiepileptic medications). The study observations are important for understanding of the MLT system in epilepsy and for exploring the potential for seizure treatment with melatonin.

Sleep in children with cerebral palsy: a review

Children with neurodevelopmental disabilities, such as cerebral palsy, are considered to be a population at risk for the occurrence of sleep problems. Moreover, recent studies on children with cerebral palsy seem to indicate that this population is at higher risk for sleep disorders. The importance of the recognition and treatment of sleep problems in children with cerebral palsy cannot be overemphasized. It is well known that the consequences of sleep disorders in children are broad and affect both the child and family. This review article explores the types and possible risk factors associated with the development of sleep problems in children with cerebral palsy and the impact of this disorder on the child and family. In addition, a brief summary of current diagnostic and treatment modalities is provided. Finally, the characteristics, diagnostic techniques, and management of sleep-related breathing disorders in children with cerebral palsy are discussed.

Chronobiology of epilepsy: diagnostic and therapeutic implications of chrono-epileptology

The combination of chronobiology and epilepsy offers novel diagnostic and therapeutic management options. Knowledge of the interactions between circadian periodicity, entrainment, sleep patterns, and epilepsy may provide additional diagnostic options beyond sleep deprivation and extended release medication formulations. It may also provide novel insights into the physiologic, biochemical, and genetic regulation processes of epilepsy and the circadian clock, rendering new treatment options. Temporal fluctuations of seizure susceptibility based on sleep homeostasis and circadian phase in selected epilepsies may provide predictability based on mathematical models. Chrono-epileptology offers opportunities for individualized patient-oriented treatment paradigms based on chrono-pharmacology, differential medication dosing, chrono-drug delivery systems, and utilization of "zeitgebers" such as chronobiotics or light-therapy and desynchronization strategies among others.

Ketogenic diet treatment abolishes seizure periodicity and improves diurnal rhythmicity in epileptic Kcna1-null mice

INTRODUCTION

Seizures are known to perturb circadian rhythms in humans as well as in animal models of epilepsy. However, it is unknown whether treatment of the underlying epilepsy restores normal biologic rhythms. We asked whether: (1) seizure activity is characterized by diurnal rhythmicity, (2) chronically epileptic mice exhibit impaired rest-activity rhythms, and (3) treatment with the anticonvulsant ketogenic diet (KD) improves such perturbations.

METHODS

Chronically epileptic Kcna1-null mice were fed either a standard diet (SD) or KD for 4 weeks and subjected to continuous video-EEG (electroencephalography) and actigraphy monitoring for 3-5 days to assess seizure activity and rest-activity cycles.

RESULTS

Seizure activity in Kcna1-null mice demonstrated diurnal rhythmicity, peaking at zeitgeber (ZT)2.30 +/- 1.52. Rest-activity rhythms of epileptic mice were significantly disrupted. Whereas locomotor activity for wild-type mice peaked at ZT15.45 +/- 0.28 (ZT14:26-ZT16:51), peak activity of epileptic mice was more unpredictable, occurring over a 12.4 h range (ZT06:33-ZT18:57). In six of nine epileptic mice, peak activity was delayed to ZT17.42 +/- 0.38, whereas peak activity was advanced to ZT10.00 +/- 1.26 in the remaining mice. Treatment with the KD abolished seizure periodicity and restored the rest-activity rhythm to values resembling those of wild-type mice (i.e., activity peaking at ZT16.73 +/- 0.67).

CONCLUSIONS

Kcna1-null mice experience seizures with 24-h periodicity and impaired circadian behavior. KD reduces the number and periodicity of seizures and restores normal behavioral rhythms, suggesting that this nonpharmacologic therapy may benefit biologic rhythm disturbances in epileptic patients.

The circadian rhythm and its interaction with human epilepsy: a review of literature

Knowledge on the interaction between circadian rhythm and human epilepsy is relatively poor, although if it exists, this interaction may be of value for better knowledge of pathophysiology and for timing of diagnostic procedures and therapy. It appears that human seizure occurrence may have 24-h rhythmicity, depending on the origin. These findings are endorsed by animal studies. Rats placed in constant darkness showed spontaneous limbic seizures occurring in an endogenously mediated circadian pattern. More studies are available on the influence of epilepsy on circadian rhythms. Significant differences in chronotypes between patients with different epilepsy syndromes have been found and numerous studies have described influences of epilepsy and seizures on sleep. In contrast, knowledge on (core) body temperature and clock genes in patients is minimal. Reduced heart rate variability and changed hormone levels, which are under the influence of the biological clock, have been observed in people with epilepsy. In short, large gaps in the knowledge about the interaction of circadian rhythm and human epilepsy still remain. Proposals for studies in this borderline area between the biological clock and epilepsy will be discussed.

A single generalized seizure alters the amplitude, but not phase, of the circadian activity rhythm of the hamster

People with epilepsy exhibit high rates of sleep disturbances. In many cases, these sleep disruptions appear to be related to the occurrence of the seizures themselves. Changes in sleep structure may reflect underlying changes in the circadian clock, as circadian rhythms of locomotor activity, body temperature, and hormone release are disrupted following a seizure. The present study was designed to determine if a single generalized seizure could alter the phase and waveform of the circadian rhythm of wheel-running behavior in the Syrian hamster. Animals were housed in constant darkness, and were administered either a sham treatment or a maximal electroconvulsive shock at one of three time-points: 6 h before activity onset, 1 h after activity onset, or 6 h after activity onset. Seizures at all of these phases did not significantly affect the phase of the circadian activity rhythm. The circadian locomotor activity levels were significantly attenuated following seizures at all three phases. This attenuation was prominent over the 24 h following the seizure, and was also evident over the three post-seizure days. These data suggest that while seizures do not affect phase, they may alter the amplitude of the circadian clock. Because the amplitude of the circadian clock affects sleep quality, these findings suggest one mechanism by which persistent seizures may decrease the quality of sleep in patients with epilepsy.

How to assess circadian rhythm in humans: a review of literature

It is well known that seizures of some types of epilepsy tend to occur in patterns. The circadian rhythm may play a significant role in this phenomenon. In animal studies it has been found that seizures in experimental partial epilepsy are probably under the influence of the biological clock. In this review an introduction to the influence of the human circadian rhythm in epilepsy is given. Furthermore, the methodology of measuring the circadian rhythm in humans is explored. An overview of widely used methods includes protocols used to desynchronize circadian rhythm, and sleep-wake and biological markers such as the dim light melatonin onset, core body temperature, and cortisol that are employed to determine the phase of the circadian rhythm. Finally, the use of sleep parameters, actigraphy, and questionnaires is discussed. These are also important in assessment of the circadian rhythm.

A randomized, placebo-controlled trial of controlled release melatonin treatment of delayed sleep phase syndrome and impaired sleep maintenance in children with neurodevelopmental disabilities

The purpose of this study was to determine the efficacy of controlled-release (CR) melatonin in the treatment of delayed sleep phase syndrome and impaired sleep maintenance of children with neurodevelopmental disabilities including autistic spectrum disorders. A randomized double-blind, placebo-controlled crossover trial of CR melatonin (5 mg) followed by a 3-month open-label study was conducted during which the dose was gradually increased until the therapy showed optimal beneficial effects. Sleep characteristics were measured by caregiver who completed somnologs and wrist actigraphs. Clinician rating of severity of the sleep disorder and improvement from baseline, along with caregiver ratings of global functioning and family stress were also obtained. Fifty-one children (age range 2-18 years) who did not respond to sleep hygiene intervention were enrolled. Fifty patients completed the crossover trial and 47 completed the open-label phase. Recordings of total night-time sleep and sleep latency showed significant improvement of approximately 30 min. Similarly, significant improvement was observed in clinician and parent ratings. There was additional improvement in the open-label somnolog measures of sleep efficiency and the longest sleep episode in the open-label phase. Overall, the therapy improved the sleep of 47 children and was effective in reducing family stress. Children with neurodevelopmental disabilities, who had treatment resistant chronic delayed sleep phase syndrome and impaired sleep maintenance, showed improvement in melatonin therapy.

Endogenous melatonin predicts efficacy of exogenous melatonin in consolidation of fragmented wrist-activity rhythm of adult patients with developmental brain disorders: A double-blind, placebo-controlled, crossover study

OBJECTIVE

: We studied whether the endogenous melatonin patterns in adult patients with developmental brain disorders have any role in response to exogenous melatonin given as a sleep-promoting medicine.

METHODS

: Participants included 15 adults (18-60 years, five females) with developmental brain disorders of varying etiologies, motor handicaps, and long-term history of sleep problems. According to the 24-h patterns of serum melatonin, patients were divided into two subgroups: lower and higher secretors. The pretreatment sleep disorder was characterized by a structured interview, 24-h ambulatory polysomnography and 7-day wrist actigraphy. Patients received 1, 3, or 6mg fast-release melatonin tablets, each for 4 weeks in increasing order, at a constant time of 30min before the desired sleep onset. Similarly, placebos with different codes were given during 3x4 weeks. The 7-day actigraphy was repeated at the end of each drug period. Outcome measures were six different parameters of non-parametric circadian rhythm analysis. Drug effects and 40 confounding/modulating factors were evaluated by applying two-level regression analyses with co-variables.

RESULTS

: Exogenous melatonin decreased the fragmentation of the rest-activity rhythm, increased the day/night ratio of activity and advanced the onset of rest period. The effects on fragmentation and day/night ratio were more pronounced in the lower than higher secretors of melatonin. Other contributing factors in the drug effects were blindness and some features of the original sleep disorder (disrupted cyclicity of the sleep architecture in polysomnography or reported daytime somnolence).

CONCLUSIONS

: Exogenous melatonin consolidated the fragmented rest-activity in about half of the patients. Low endogenous serum melatonin levels at night predicted improvement by the drug. Higher doses were not more effective than the lowest dose.

Daily rhythms of seizure activity and behavior in a model of atypical absence epilepsy

We studied daily rhythms of chronic seizure activity and behavior in adult rats and mice treated with the cholesterol biosynthesis inhibitor AY-9944 (AY) during early postnatal development. Chronic atypical absence seizures were verified in the AY-treated animals by the presence of spontaneous 5- to 6-Hz slow spike-wave discharges (SSWDs) in the neocortex. General behavioral activity, as measured by total movements (TM), movement time (MT), ambulatory movement time (AMT), time spent in center of arena (CT), jumps (JFP), and rotational behavior (TURNS), were continuously recorded under a 12-hour light:12-hour dark photocycle. The average SSWD duration in AY-treated rats varied daily, with two peaks occurring at approximately dark phase and light phase onset. Mice treated with AY exhibited significant increases in all behavioral measures during the light and dark phases, with the exception of light-phase CT, which did not differ from that of controls. Consequently, the daily rhythm of total behavioral activity (TM) exhibited a significantly higher mean oscillation (mesor) and amplitude without evidence of phase shift compared with the TM rhythm of controls. The occurrence of SSWD activity in the AY model appears to be subject to regulation by biological timing mechanisms and, furthermore, associated with motor hyperactivity that does not alter the timing of behavioral rhythmicity.

Sleep and epilepsy: what we know, don't know, and need to know

Long-term video-EEG and, more recently, video-polysomnography, have provided the means to confirm and expand on the interconnections between sleep and epilepsy. Some of these relationships have become firmly established. When one of the authors (N.F.S.) presented part of this paper at a symposium on the Future of Sleep in Neurology at an American Clinical Neurophysiology Society annual meeting in 2004, the purpose was to summarize what we know, don't know, and need to know about the effects of sleep on epilepsy and epilepsy on sleep. Here we seek to summarize some of the more firmly established relationships between sleep and epilepsy and identify intriguing associations that require further elucidation.

A comparison of the circadian rhythms and the levels of melatonin in patients with diurnal and nocturnal complex partial seizures

The aim of the present work was to assess serum melatonin levels and melatonin circadian rhythm in patients with diurnal and nocturnal complex partial epilepsy. Daily rhythms of melatonin were studied in patients with diurnal complex partial epilepsy (n=10), patients with nocturnal complex partial epilepsy (n=10), and a control group (n=10). All patients were under carbamazepine treatment. Serum melatonin samples were taken at 1000, 2200, 0100, and 0500 hours. We found that melatonin circadian rhythm was normal in all patients when compared with controls. Melatonin levels were low in both patients with nocturnal and patients with diurnal complex partial epilepsy compared with the control group at 1000, 2200, 0100, and 0500 hours; a statistically significant decrease in melatonin levels was observed in the patients with epilepsy at 1000 hours only. These findings suggest that melatonin levels and circadian rhythm of melatonin do not differ between patients with nocturnal and patients with diurnal complex partial epilepsy. Further detailed research is necessary to determine the factors that govern the nocturnal or diurnal occurrence of complex partial seizures.

Sleep-inducing effects of exogenous melatonin administration

In this report current data is reviewed indicating that melatonin, the main hormone secreted by the pineal gland at night, participates in sleep regulation in humans. Evidence supporting this role relies on findings that abnormal melatonin secretion, induced by a variety of commonly used drugs, and in clinical disorders of the nervous system, are associated with sleep disturbances, and that melatonin has beneficial sleep-inducing effects in elderly melatonin-deficient insomniacs, and in children with sleep disorders. The time of melatonin administration, rather than the pharmacological dose, is a crucial factor regarding its potency as a sleep-inducing agent. Possible operating mechanisms explaining melatonin hypnotic effects are discussed.

Temporal lobe seizures alter the amplitude and timing of rat behavioral rhythms

Daily rhythms of spontaneous locomotor activity (SLA) in rats were studied before and after an episode of pilocarpine-induced convulsive status epilepticus (SE). A pronounced increase in activity levels during both the light and dark phases was found 1 week after SE as compared with baseline SLA and controls administered saline. Rats with bilateral lesions of the nucleus accumbens (shell) did not exhibit any significant change in SLA 1 week after SE compared with controls. We suggest that during the first week after SE the increase in SLA was induced by abnormal neuronal activity in the hippocampus driving a descending limbic-motor pathway via the nucleus accumbens. EEG recordings revealed high-amplitude interictal spikes in hippocampal CA1. During subsequent weeks, SLA rhythms of nonlesioned chronic epileptic rats remained elevated but progressively normalized over a period of 12 weeks. Although both chronic epileptic and control groups displayed near-24-hour activity patterns under light-dark conditions, significant delays (>4 hour) in acrophase were observed after spontaneous seizures had developed. The phase delay was positively correlated with seizure history and likely the result of postictal hyperactivity associated with seizures during the normal rest period. Despite these changes, cell density in the suprachiasmatic nucleus (SCN) and intergeniculate leaflet (IGL) did not differ significantly between epileptic and control groups. In the absence of damage to brain areas directly involved with the regulation of behavioral rhythms, chronic seizure activity presumably alters the timing of activity patterns through a nonphotic mechanism, perhaps involving activation of the SCN or IGL during limbic seizures.

Sleep fragmentation in mentally retarded people decreases with increasing daylength in spring

We studied the sleep-wake behavior of mentally retarded people from late winter to early summer at 60 degrees N. During this time the daylength increased 8 h 51 min. The data were collected by observing the sleep-wake status of 293 subjects at 20-min intervals for five randomized 24h periods (= recording days). The intervals during which the individual recording days of the same order (1st, 2nd, etc.) were carried out, were called recording periods. Consequently, there were five recording periods, each containing 293 individual recording days. Even though there was overlap among the recording periods, the median daylength from one period to another increased approximately by 100 min. In the initial statistical analysis, the number of wake-sleep transitions was found to differ significantly among the five recording periods (Friedman test, p < 0.001). The mean ranks in the Friedman test suggested that the number of wake-sleep transitions was highest during the 1st and lowest during the 5th recording period. In further statistical analyses using a program for mixed effects regression analysis (MIXOR 2.0) it was found that the increase in daylength during the study period was associated with a simultaneous decrease of approximately 0.5 wake-sleep transitions in the whole study population (p < 0.001). The decrease in the number of wake-sleep transitions was significant only in the subgroups of subjects with a daylength change of more than 350 min between the 1st and 5th recording days (Wilcoxon tests, p < 0.005). This suggests that after a marked prolongation of the natural photoperiod, the reduction in sleep episodes was more probable than after smaller changes in daylength. It is concluded that the sleep of mentally retarded people living in a rehabilitation center at a northern latitude is more fragmented in winter than in early summer and that the change is related probably to the simultaneous increase in the length of the natural photoperiod. The sleep quality of persons living in institutional settings might be improved by increasing the intensity and/or duration of daily artificial light exposure during the darker seasons.

Seizures induce phase shifts of rat circadian rhythms

RATIONALE

Epileptic seizures may alter neuroendocrinological cycles. Light pulses induce phase shifts in circadian rhythms. Using hippocampal-kindled rats to ensure maximal clinical expression, we determined if seizures likewise induce phase shifts.

METHODS

We monitored the circadian rhythm of temperature (CRT) with intraperitoneal radiotelemetry in rats (n=21) isolated from time cues and light for 3-week trials. Seizures were triggered with hippocampal electrical stimulation at different circadian phases. Optimized, least-error phase shifts were calculated from preictal and postictal CRTs. Induced seizures were referenced to CRT (t(max)=00:00, 24-h circadian cycle).

RESULTS

Phase shifts (individual responses=57) differed across the circadian cycle. Rather than forming a clear phase-response curve, phase shifts were especially variable between 00:00 and 06:00 h.

CONCLUSIONS

This study demonstrates that electrically-induced seizures induce advances and delays in CRT in a phase-dependent fashion but in a pattern different from typical light-induced phase shifts. Disorders of circadian regulation may contribute to some of the altered endogenous cycles associated with epilepsy.

Circadian rhythms: interactions with seizures and epilepsy

Circadian rhythms are endogenously-mediated 24 h cycles of behavioral or physiological activity. The interactions among the mammalian circadian clock, acute seizures, and chronic epilepsy are not well-characterized. Evidence suggests that seizures are susceptible to circadian modulation, and that this modulation varies with epilepsy syndrome and location of seizure foci. The circadian timing system and secondary circadian cycles of hormone secretion, sleep and wakefulness, and recurrent environmental factors are discussed as potential systems that effect spontaneous seizure recurrence. Experimental designs should take into account time-of-day effects on seizure threshold and occurrence. Further work is required to determine what mechanisms account for daily variation in seizure susceptibility.

Hypothalamic neuronal loss and altered circadian rhythm of temperature in a rat model of mesial temporal lobe epilepsy

PURPOSE

Numerous dysfunctions in endogenous hypothalamic function have been associated with mesial temporal lobe epilepsy (MTLE). One endogenous activity is the circadian rhythm of temperature (CRT). In this study we examined whether hypothalamically mediated function is altered in the electrically induced, self-sustained, limbic status epilepticus model of MTLE. We then wished to determine whether there was a structural basis for regulatory alterations.

METHODS

We measured CRT with peritoneal temperature telemetry obtained in light-entrained (LD) and in free-running, constant-dark (DD) conditions. CRT from epileptic and controls of normal animals and kindled animals were quantized by fast Fourier transform-nonlinear least squares analysis to determine rhythmic complexity.

RESULTS

The circadian component of CRT was preserved in all animals. In DD, CRTs of epileptic animals were more complex than those of normal animals. CRT of kindled animals showed no increased complexity after electrically induced seizures. Neuronal density was decreased in regions of the anterior and posterior hypothalamus but not in the suprachiasmatic nuclei from the epileptic rats.

CONCLUSIONS

Alterations in CRT due to the epileptic state were independent of isolated seizures. Altered circadian thermoregulation in epileptic rats corresponded to regional hypothalamic neuronal loss. Structural changes of the hypothalamus may explain alterations in endogenous rhythms in MTLE.

Temporal distribution of partial seizures: comparison of an animal model with human partial epilepsy

Seizures do not often strike randomly but may occur in circadian patterns. We compared daily times of partial seizures determined by continuous electroencephalography among patients with mesial temporal lobe epilepsy (MTLE; n = 64), those with extratemporal lobe (XTLE; n = 26) or lesional temporal lobe epilepsy (LTLE; n = 8), and a rat model similar to MTLE in which rats become epileptic after electrically induced limbic status epilepticus (postlimbic status [PLS]; n = 20). Rats were maintained on a 12-hour light/dark cycle with lights on at 0700 hours. The distributions of seizures were fitted by cosinor analysis to determine time of peak seizure incidence +/- 95% confidence interval (95% CI). The mean fraction +/- SD of seizures recorded during light was 63 +/- 17% in PLS animals and 60 +/- 21% in humans. Peak incidence of seizures for PLS rats (547 seizures) was 1645 (95% CI = 1448,1830) and for MTLE subjects (774 seizures) was 1500 (95% CI = 1324,1636). Seizures from XTLE (465 seizures) and LTLE (48 seizures) did not fit a cosinor model and occurred no more frequently during light than dark. In conclusion, limbic seizures in humans and PLS rats occur more often during light than dark and have similar cosinor daily distributions. The chronological similarity between human MTLE and PLS rat epilepsy suggests that limbic seizure occurrence has a relation to the circadian regulatory system.

Melatonin: a clinical perspective

Over the last several decades the pineal gland has emerged as an active neuroendocrine transducer of important environmental information. However, the current understanding of the function of its major hormone, melatonin, in humans remains ill defined and based exclusively on correlative observations. In a similar manner, the multitude of phenomenological descriptions of the effects of exogenous melatonin is contrasted by the limited understanding of the underlying mechanisms and the lack of firmly established clinical applications for the hormone. Future randomized, double-blind, placebo-controlled clinical studies will be necessary to determine the precise indications, treatment regimens, and safety of melatonin in clinical practice. The recent rapid progress in the area of melatonin research should lead to a better understanding of its role in human health and disease.

Circadian rhythm studies in neuronal ceroid-lipofuscinosis (NCL)

Sleep disorders are common in NCL patients. The patients have problems such as frequent awakenings, difficulties with sleep onset, nightmares, and night terrors. The aim of the study was to examine whether the sleep disturbance in NCL can be explained on the basis of desynchronised circadian rhythms. Therefore we studied diurnal patterns of melatonin, cortisol, body temperature, and motor activity of 14 patients. The group consisted of 8 JNCL patients, 5 INCL children, and one boy with Jansky-Bielschowsky disease of the variant type. There were healthy age- and sex-matched control subjects. The blood samples for serum melatonin and cortisol were collected every 2 hours during 24-hour periods. Body temperature was recorded continuously for a 24-hour period by a polygraph. Diurnal motor activity was measured by wrist actigraphy for 5 days. In most of our patients sleep was fragmented and the sleep phase was irregular. Disturbances in the daily hormonal rhythms occurred only in the minority of the patients and only at an advanced stage of the disease. Although disturbances in the body temperature rhythm were found in about half of the patients, a general failure in the circadian regulatory system does not explain the frequent disturbances of the sleep-wake cycle of the NCL patients.

Twenty-four-hour rhythms in relation to the natural photoperiod: a field study in humans

The daily rhythms of salivary melatonin, salivary cortisol, and axillary body temperature were measured in nine healthy volunteers in midsummer, around the autumn equinox, and in midwinter, at a latitude of 60 degrees N. The aim was to find out whether these rhythms were dependent on variations of the natural daylength. The samples were collected every 2 hr during 24-hr periods in everyday conditions. The individual rhythms were characterized with the acrophase estimates of the best-fitting cosine curve models and with the half-rise and half-decline times calculated from the raw data. The melatonin and cortisol rhythms were delayed significantly (about 1 hr) in midwinter as compared with summer and autumn. The most advanced rhythms were found in autumn. The shifts of the melatonin and cortisol rhythms could be explained as a result of the changes of natural illumination. The overt temperature rhythms did not differ significantly among the sampling months. The lack of seasonal patterns in temperature rhythms probably primarily reflected the socially determined rest-activity cycles of the subjects.