Effects Of Constant Light Research Articles

Effects of constant light and dark conditions on the locomotor activity, body mass, and body temperature rhythms of Eurasian Tree Sparrows (Passer montanus)

Light is an essential environmental cue influencing the endogenous circadian clocks that regulate behavioral and physiological processes in animals. Despite extensive research on the circadian rhythms of avian behavior and physiology, the mechanisms by which they adapt and adjust to abnormal photoperiod conditions, such as artificial light, have yet to be fully elucidated. Here, the circadian rhythms of the body mass, activity, and core and peripheral body temperatures of the Eurasian Tree Sparrow (Passer montanus, ETS)—a diurnal passerine—were examined under three different lighting conditions: constant light (LL), constant darkness (DD), and normal light–dark cycles (LD). Our results showed that the activity, body mass, core, tarsometatarsus, and eye temperatures of the ETSs varied significantly with treatment, time, and the interaction between treatment and time; however, there was no significant change in body mass in response to the interaction between time and treatment. Under LD conditions, the ETSs exhibited significant circadian rhythms in activity and core, tarsometatarsus, and eye temperatures. Under LL conditions, only the core temperature exhibited significant rhythmicity. Under DD conditions, there were no significant circadian rhythms in activity, body mass, and eye temperature; however, the core and tarsometatarsus temperatures remained rhythmic. Our results indicate that the core body temperature rhythm of ETS is endogenous and can be maintained under abnormal photoperiods. In contrast, the activity and body surface temperature, uncoupled from the core body temperature under abnormal photoperiod conditions, strongly depend on light. These results differ from those of other diurnal avian species, suggesting a unique coping mechanism of ETS in response to an abnormal photoperiod.

The effect of constant light and melatonin on urethane-induced lung carcinogenesis in mice and expression of clock genes and proteins

Introduction. Circadian rhythms are an adaptational mechanism to day-night cycle. At the cellular level rhythms are supported by oscillations of transcription of Bmal1, 2, Clock and Npas2, Per1-3, Cry1, 2 clock genes; in the organism rhythms are synchronized with melatonin, the "hormone of darkness". Reliable data have been obtained that disruption of biological "clocks" at the cellular and/or organism level are associated with carcinogenesis, but the experimental results in this direction remain incomplete.
 Aim. Assessment of the continuous lighting and melatonin administration effects on chemically induced carcinogenesis in mice and expression of clock genes and proteins in normal and tumor lung tissue.
 Materials and methods. Lung tumors were induced by urethane in 120 male SHR mice. Animals were kept at constant (LL) or standard (LD) light; half of the animals received melatonin (MT) daily at 20 mg/l at night with water for 45 weeks of experiment. At the end of the experiment, the frequency and multiplicity of lung tumours of different size were assessed. Expression of clock genes Clock, Bmal1, Cry1 was assessed in tumor samples and normal lung tissue by real-time PCR; protein content of BMAL1, CLOCK, CRY1 and PER2 was determined by immunohistochemistry. Statistical data were processed using the programs MS Excel 2007, GraphPad Prism 6.0 with commonly used statistical criteria.
 Results. The number of animals with lung tumors was between 89 and 100% in different groups. Large tumors (>2 mm) were more frequently observed in LL group (62 tumors out of 294, 21,1%) than in LD group (59 tumors out of 405, 14,6%, p=0,0245). Administration of exogenous melatonin at constant lighting statistically significantly reduced the frequency of large tumors (28 tumors out of 320, 8.8%, p=0,0001 in comparison with LL). In normal lung tissue of animals kept at constant lighting (LL) the increase in relative expression of clock genes in comparison with LD group was revealed: Bmal1 by 3,1 times (p=0,02) and Cry1 by 3,6 times (p=0,0002). No such differences were found for Clock gene. The relative content of BMAL1 and CLOCK proteins in all experimental conditions was higher in adenomas and adenocarcinomas compared to normal tissue.
 Conclusion. Constant lighting promotes the development of chemically induced lung tumors, and melatonin administration inhibits carcinogenesis under constant lighting.
 The content of BMAL1 and CLOCK transcription activator proteins in lung tumors was found to increase in comparison with normal tissue, whereas no increase in the expression level of corresponding genes in tumors was observed.

Differential response of diurnal and nocturnal mammals to prolonged altered light-dark cycle: a possible role of mood associated endocrine, inflammatory and antioxidant system

ABSTRACT The circadian system maintains internal 24 h oscillation of behavior and physiology, and its misalignment with external light-dark (LD) cycle results in negative health outcomes. In order to elucidate the effect of prolonged constant condition and the differences in the response between nocturnal and diurnal species, we studied the effects of constant light (LL) and constant darkness (DD) on a diurnal (squirrel) and a nocturnal (mouse) rodent species, focusing on the endocrine, inflammatory and antioxidant systems associated with depression-like behavior. Squirrels and mice (n = 10/group) were placed in chronocubicle under 12:12 h LD cycle, LL and DD. After 4 weeks, animals were subjected to sucrose preference test and blood and brain tissues were collected for measuring melatonin, corticosterone, proinflammatory cytokine, tumor necrosis factor-α (TNF-α) and the activity of primary antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD). The results show that in diurnal squirrels, prolonged constant darkness reduced sucrose preference, CAT, and SOD, increased corticosterone and TNF-α levels, but caused no significant change in the melatonin compared to LD condition. In contrast, in nocturnal mice constant darkness caused no significant changes in sucrose preference and corticosterone levels, increased melatonin, CAT and SOD levels but decreased TNF-α levels. Chronic LL caused a similar response in both squirrels and mice: it decreased sucrose preference, melatonin, CAT and SOD levels but increased corticosterone and TNF-α levels. Together, the study demonstrates differential effects of altered light-dark cycle in a diurnal and a nocturnal rodent on interrelated endocrine, inflammatory and antioxidant systems associated with depression-like behavior, with constant light having adverse effects on both species but constant darkness having a negative effect mainly in the diurnal squirrels.

Effect of constant light on the morphology of the retina in domestic chick (Gallus g. domesticus): A scanning electron microscope study

Light induces variable levels of damage to the retina and often, death of the photoreceptor cells. It is reported that chick retina, havingabundant melanin in the retinal pigment epithelium, undergoes no or minimal damage from exposure to light. However, the morphology of cone and rod photoreceptor cells after continuous exposure of light has not been studied in detail. The present study investigated the detailed changes of photoreceptor cells, by scanning electron microscopy (SEM).Domestic chicks (Gallus g. domesticus) from post-hatch day (PH) 1 to 7 were initially reared at 700 lux at 12 h light (L): 12 h dark (D). From PH 7 to 18, they were exposed to 12L: 12D (control) and 24L: 0D (constant light) cycles at 700 lux. At PH18, chicks were sacrificed, their eyes enucleated and preserved in Karnovsky’s fixative. Theretina was then separated from the adherent choroid, mounted on photoreceptor side up and processed for SEM. There was significant damage to rod and cone outer segmentsfrom both dorsal and ventral part of the retina and decrease in the abundance of cells of inner nuclear layer in constant light, compared to that found in 12L: 12D cycles. It is likely that constant light affects the retinal cells in the vertical pathway, which could alter the photo transduction process.

Melatonin attenuates light-at-night effects on systolic blood pressure and body temperature but does not affect diastolic blood pressure and heart rate circadian rhythms

ABSTRACT Aim of the present study is to assess whether 1.5mg of exogenous melatonin provided under modified CR in constant light (~400 lx) is capable to mimic effects of dark phase. Forty-six young adults (YA), 17–24 years old of both genders were studied under amodified CR protocol for 26 h. Initially, participants were investigated under constant light (CR-LL) and 2 weeks later under the same conditions though 1.5mg melatonin (Melaxen) was given orally at 22:30. Systolic blood pressure (SBP) and diastolic blood pressure (DBP), heart rate (HR) and body temperature (BT) were measured every 2 h. To verify the effect of constant light, formerly published results obtained under light-dark conditions (CR-LD) were reanalyzed. Administration of 1.5 mg of exogenous melatonin modified the 24 h patterns of BT and SBP within short 3.5 h time window but did not influence DBP and HR. A short-term reduction of SBP and BT for 1.5–3.5 hours was observed. The values in the CR-LL+M group were significantly lower than in CR-LL at 2:00 h. Hence, exogenous melatonin did mimic the scotophase. Though this effect was gender-specific and found only in female YA. Results of this study prompt further research to qualify and quantify dosage-, duration- and time-dependent differences of melatonin effects, to discern between short-term (acute) and long-term (chronic) melatonin administration, and to clarify its underlying mechanisms.

Effect of constant light and immobilization stress on rat submandibular saliva secretory response induced by cholinergic and peptidergic agonists

The aim of this work was to analyse the parasympathetic control of submandibular saliva secretory response to cholinergic and peptidergic agonists in rats chronically exposed to constant light or repeated immobilization. Thirty two adult male Wistar rats were used: LL (8 rats exposed to constant light for 20 days), IMO (8 rats submitted to 14:10 h light: dark cycle and immobilized 2 hours daily for 7 days), and control (16 rats not exposed to stress and submitted to 14:10 hours light:dark cycle). Saliva was collected under anesthesia from the salivary ducts of submandibular glands under increasing doses of methacholine and substance P. Secretory responses (μg/saliva/mg dry weight gland) to methacholine were significantly higher in LL and IMO groups compared to control for the following doses (μg/kg body weight): 3 (153±9 versus 46±3, p<0.001 and 76±3 versus 40±3, p<0.001), 10 (379±23 versus 277±8, p<0.001 and 275±19 versus 250±10, p<0.01) and 30 (729±25 versus 695±19, p<0.05 and 1008±39 versus 640±20, p<0.001). Also, responses to substance P were significantly increased in LL and IMO groups compared to control for the following doses: 0.2 (80±3 versus 30±3, p<0.01 and 94±16 versus 31±3, p<0.001), 0.5 (328±20 versus 231±16, p<0.01 and 531±31 versus 219±25,p<0.001), 1 (681±35 versus 547±30, p<0.01 and 1031±63 versus 563±53, p<0.001), and 5 (2222±88 versus 1868±59, p<0.01 and 3230±145 versus 1921±218, p<0.001). In conclusion, supersensitivity of secretory response to both agonists suggests that chronic exposure of rats to stressors capable of activating the sympathetic adrenal system promotes inhibition of the parasympathetic control of salivary secretion.

Effect of desynchronosis on oxidative stress biomarkers and the state of glial intermediate filaments in the brains of rats subject to aging

Desynchronosis may be the cause of many diseases. Oxidative stress plays an important role in the pathogenesis of various diseases. The present study investigates the effect of constant light on biomarkers of oxidative stress and content of glial intermediate filaments protein in the brains of old rats. We found that desynchronosis led to development of oxidative stress in the hippocampus, cerebral cortex and cerebellum of old rats. Prolonged continuous lighting led to an increase in the content of TBA-reactive products in all studied regions of the brains of old rats. This indicates an activation of lipid peroxidation and oxidative stress. Significant changes in the content of TBA-reactive products were found in the departments responsible for the functions of the higher nervous activity, particularly in the hippocampus and cerebral cortex. The level of restored glutathione in all three regions of the brain decreased in the group of rats kept under constant illumination in comparison with the control group. The results of the indicators of locomotor and orienting-investigative activity of the animals in the "open field" test revealled changes in the indices for desynchronosis. This showed a reduction in locomotor activity, inhibition of exploratory activity and development of emotional stress. In the brains of old rats kept under constant illumination a significant increase in the content of glial fibrillary protein (GFAP) was shown. There was a significant increase in the intensity of the polypeptide zone 49 kDa in the filamentous and soluble fraction of the cerebellum and hippocampus. This fact indicates that desynchronosis activates fibrillogenesis in glial cells. At the same time, there is degradation of polypeptides GFAP with Mr in the field of 46 kDa. Melatonin is a universal adaptogen that regulates the function of many body systems. The amount of melatonin which is synthesized depends on the illumination mode. Violation of the global mode reduces the amount of melatonin and leads to the development of desynchronosis, which may be the cause of many diseases. The administration of melatonin helped reverse the changes – raising the level of restored glutathione and preventing the growth of the content of peroxidation products and indices of "open field" test, and also decreasing the degradation of GFAP and the amount of protein. The results indicate the protective effect of melatonin, showing reductions in glial reactivity and in the level of oxidative stress in the brains of old rats subject to desynchronosis.

Effects of long-term light, darkness and oral administration of melatonin on serum levels of melatonin

BackgroundContinuous light or darkness has various effects on different systems. In the present research work, the effects of constant light and darkness exposure of male rats and oral administration of exogenous melatonin on the serum levels of melatonin have been studied. MethodsThirty adult male Wistar rats were divided into six groups of: (1) Control, (2) melatonin, (3) light, (4) light and melatonin, (5) darkness, and (6) darkness and melatonin. All groups were placed according to light conditions for 10 days. Melatonin was administered orally after a period of 10 days to Groups 2, 4, and 6 (10 mg/kg of body weight). Serum levels of melatonin were measured using ELISA. ResultsThe results showed the significant difference on serum melatonin in darkness, no light, and control groups. Although serum levels of melatonin were different in melatonin groups, the difference is not significant. ConclusionsWe concluded that being exposed to continuous darkness leads to an increase in serum melatonin.

Increased anxiety-like behavior but no cognitive impairments in adult rats exposed to constant light conditions during perinatal development

Background. Shift-work is suggested to affect fetal development negatively. In particular, maternal hormonal disturbance arising from sleep deprivation or circadian rhythm changes may disturb fetal growth or lead to complications during pregnancy. Exposure to constant light is an environmental stressor that can affect the circadian system and has been shown to induce neurochemical and behavioral changes when used during the prenatal and/or postnatal period in experimental animals. However, studies investigating long-term effects of constant light in the offspring are sparse.Methods. An accidental power outage resulted in pregnant females being housed under constant light (LL) conditions for seven days of the offspring perinatal development (embryonic day 20 to postnatal day 4). The long-term effects of constant light on the behavior in the adult offspring were assessed by means of open field, object recognition, and water maze tests.Results. In adulthood, LL-animals displayed an intact recognition memory and no deficits in spatial learning or memory. In the open field test, LL-animals exhibited higher anxiety-like behavior, observed as significantly more thigmotaxis and less ambulation. These results were confirmed in the other behavioral tests as the LL-animals spent less time exploring the objects in the object recognition test, and showed thigmotactic behavior also in the water maze test.Conclusion. The results confirm that early life experience can cause changes in brain development that shape brain function and add to the sparse literature on long-term effects of constant light conditions during perinatal development on specific behaviors in adulthood.

Effects of constant light during perinatal periods on the behavioral and neuronal development of mice with or without dietary lutein

Constant light conditions (LL) carry a risk of disrupting the biological clock of developing animals. Our purpose in this study was to investigate what disorders occur in animals receiving an LL stress during the late embryonic and suckling periods as compared with animals housed in dark-light (14 h-10 h) conditions (DL). In addition, we examined ameliorating effects against the disorder by the oral administration of lutein as an antioxidant. LL caused hypertrophy of the spleen and induced a higher expression of serotonin transporter (5HTT) in the corpus striatum and hippocampus in 15-day-old pups. In 9-week-old offspring, LL caused abnormal behavior in the elevated plus-maze test. The expression levels of 5HTT in the brain of the LL group changed to lower than those in DL group. The oral administration of lutein lessened the abnormality in behavior and 5HTT expression in the hippocampus to a certain degree although the expression levels of 5HTT in the corpus striatum were not altered by lutein diet. LL also induced disorders in the maternal brain with lower expression levels of 5HTT and neuregulin 1. These results indicate that LL during the perinatal periods may induce some neuronal abnormalities in both offspring and mothers that may be partially ameliorated by dietary lutein as an antioxidant.

Induction of abnormal oocyte division under the constant light in the young adult rat

Abstract In order to study the effect of constant light on the ovary, 12 young adult female rats were exposed to constant light for 37 days and their estrous cycles were recorded by daily examination and the ovaries were examined histologically. The results showed that constant light induced in an abnormal and uncontrolled division of oocytes. In these divided-oocyte follicles (DOFs), two or more divided-oocytes shared one zona pellucida and usually floated freely in the follicular antrum. This fantastic phenomenon was discovered for the first time, and it was different from multioocyte follicles (MOFs) and polyovular follicles (POFs) founded in rats, humans, rabbits, mice and dogs.

The Circadian Clock Machinery During Early Development of Senegalese sole (Solea senegalensis): Effects of Constant Light and Dark Conditions

Circadian rhythms are established very early during vertebrate development. In fish, environmental cues can influence the initiation and synchronization of different rhythmic processes. Previous studies in zebrafish and rainbow trout have shown that circadian oscillation of clock genes represents one of the earliest detectable rhythms in the developing embryo, suggesting their significance in regulating the coordination of developmental processes. In this study, we analyzed the daily expression of the core clock components Per1, Per2, Per3, and Clock during the first several days of Senegalese sole development (0–4 d post fertilization or dpf) under different lighting regimes, with the aim of addressing when the molecular clock first emerges in this species and how it is affected by different photoperiods. Rhythmic expression of the above genes was detected from 0 to 1 dpf, being markedly affected in the next few days by both constant light (LL) and dark (DD) conditions. A gradual entrainment of the clock machinery was observed only under light-dark (LD) cycles, and robust rhythms with increased amplitudes were established by 4 dpf for all clock genes currently studied. Our results show the existence of an embryonic molecular clock from the 1st d of development in Senegalese sole and emphasize the significance of cycling LD conditions when raising embryos and early larvae. (Author correspondence: munoz.cueto@uca.es; carlos.pendon@uca.es)

The effects of lighting conditions and food restriction paradigms on locomotor activity of common spiny mice, Acomys cahirinus.

BackgroundAn endogenous circadian clock controls locomotor activity in common spiny mice (Acomys cahirinus). However, little is known about the effects of constant light (LL) on this activity or about the existence of an additional food entrainable clock. A series of experiments were performed to investigate the effects of LL and DD on tau and activity levels.MethodsSpiny mice were housed individually and their running wheel activity monitored. One group of mice was exposed to LD, DD and several intensities of LL. Another group was exposed to a restricted feeding (RF) paradigm in light: dark (LD) during one hour before the L to D transition. Significance of rhythmicity was assessed using Lomb-Scargle periodograms.ResultsIn LD all animals exhibited nocturnal activity rhythms that persisted in DD. When animals were exposed to RF (during L), all of these animals (n = 11) demonstrated significant food anticipatory activity as well as an increase in diurnal activity. This increase in diurnal activity persisted in 4/11 animals during subsequent ad libitum conditions. Under LL conditions, the locomotor rhythms of 2/11 animals appeared to entrain to RF. When animals were exposed to sequentially increasing LL intensities, rhythmicity persisted and, while activity decreased significantly, the free-running period was relatively unaffected. In addition, the period in LL was significantly longer than the period in DD. Exposure to LL also induced long-term changes (after-effects) on period and activity when animals were again exposed to DD.ConclusionsOverall these studies demonstrate clear and robust circadian rhythms of wheel-running in A. cahirinus. In addition, LL clearly inhibited activity in this species and induced after-effects. The results also confirm the presence of a food entrainable oscillator in this species.

Comparison of the effect of constant light on the circadian rhythm of white-eye mutant and wild-type blow fly Protophormia terraenovae

Compound eyes of white-eye mutant flies are considered to be more sensitive than those of the wild type because the former lack the screening pigment. The effects of constant light conditions on the circadian rhythm were examined in wild-type and white-eye mutant Protophormia terraenovae to identify plausible photoreceptors mediating constant light to clocks, which affect the free-running period and rhythmicity. Both the wild type and white-eye mutant showed clear rhythmicity under constant light conditions at 0.5 lx and 500 lx. Although the incidence of arrhythmia increased as light intensity increased, more than half of the flies were rhythmic at 500 lx. P. terraenovae seems to have a high threshold for light causing arrhythmia. Incidence of rhythmic flies and the free-running period under constant light conditions were not significantly different between the wild type and white-eye mutant. This suggests that photoreceptors operating under constant light conditions are extraretinal.

Light-Mediated TIM Degradation within Drosophila Pacemaker Neurons (s-LNvs) Is Neither Necessary nor Sufficient for Delay Zone Phase Shifts

Circadian systems are entrained and phase shifted by light. In Drosophila, the model of light-mediated phase shifting begins with photon capture by CRYPTOCHROME (CRY) followed by rapid TIMELESS (TIM) degradation. In this study, we focused on phase delays and assayed TIM degradation within individual brain clock neurons in response to light pulses in the early night. Surprisingly, there was no detectable change in TIM staining intensity within the eight pacemaker s-LNvs. This indicates that TIM degradation within s-LNvs is not necessary for phase delays, and similar assays in other genotypes indicate that it is also not sufficient. In contrast, more dorsal circadian neurons appear light-sensitive in the early night. Because CRY is still necessary within the s-LNvs for phase shifting, the results challenge the canonical cell-autonomous molecular model and raise the question of how the pacemaker neuron transcription-translation clock is reset by light in the early night.

Effect of continous light and darkness exposures on the petuitary-gonadal axis and thyroid activity in male rats

The effects of constant light and dark exposure of pubertal male rats on the pituitary-gonadal axis and thyroid activity were studied. The indices of thyroid activity were weight of the thyroid gland, estimation of serum levels of thyroxine (T4) by radioimmunoassay (RIA) technique and histological studies of the thyroid gland. The indices of gonadal activity chosen were weight and histological study of the testes and determination of serum levels of Luteinizing hormone (LH) and Follicle Stimulating Hormon (FSH) by RIA technique. In the rats exposed to continuous light, the weight of the thyroid gland increased significantly (P

Effects of different photoperiods on growth, stress and haematological parameters in juvenile great sturgeonHuso huso

The effects of constant light (24L:00D), no light (00L:24D) and two light–dark periods (18L:06D;12L:12D) on the growth, stress and haematological variables were assessed in juvenile great sturgeon, Huso huso. During the 8-week experimental period, juveniles (22.5 ± 0.6 g) were kept under a 150 lx light intensity in fibreglass tanks (0.8 m2, 500 L). Differences in growth were insignificant during the experiment, but lactate levels were higher in the 00L:24D and 24L:00D photoperiods compared with 12L:12D and 18L:06D photoperiods. Cortisol levels did not show differences among the various photoperiods. At the end of the experimental period, fish reared under a 12L:12D photoperiod had higher haemoglobin values and erythrocyte numbers than in the other photoperiods, while no differences were found between groups with regard to haematocrit values or leucocyte numbers. The highest survival rate (89%) was observed in the 12L:12D period in which the levels of lactate and cortisol as stress indicators were minimal. The results indicate that various photoperiods cause different stress levels in juvenile great sturgeon and have no significant effects on growth, at least in short time periods.

Circadian Time-Place Learning in Mice Depends on Cry Genes

Endogenous biological clocks allow organisms to anticipate daily environmental cycles. The ability to achieve time-place associations is key to the survival and reproductive success of animals. The ability to link the location of a stimulus (usually food) with time of day has been coined time-place learning, but its circadian nature was only shown in honeybees and birds. So far, an unambiguous circadian time-place-learning paradigm for mammals is lacking. We studied whether expression of the clock gene Cryptochrome (Cry), crucial for circadian timing, is a prerequisite for time-place learning. Time-place learning in mice was achieved by developing a novel paradigm in which food reward at specific times of day was counterbalanced by the penalty of receiving a mild footshock. Mice lacking the core clock genes Cry1 and Cry2 (Cry double knockout mice; Cry1(-/-)Cry2(-/-)) learned to avoid unpleasant sensory experiences (mild footshock) and could locate a food reward in a spatial learning task (place preference). These mice failed, however, to learn time-place associations. This specific learning and memory deficit shows that a Cry-gene dependent circadian timing system underlies the utilization of time of day information. These results reveal a new functional role of the mammalian circadian timing system.

Effect of Constant Light on Prolactin and Corticosterone Rhythms Evaluated Using a Noninvasive Urine Sampling Protocol in the Rat

Circadian prolactin and corticosterone rhythms are usually investigated in the rat by analysis of plasma hormone profiles. In order to develop a nonstressful methodology for long-term studies, we validated prolactin and corticosterone radioimmunoassays in rat urine samples. Among the criteria of validation, prolactin was identified in urine by Western blot whereas both prolactin and corticosterone levels were undetectable in the urine of hypophysectomized rats. The determination of prolactin and corticosterone levels on serial urine samples showed daily variations in male rats entrained by the light-dark cycle. The acrophases of the 24-hour prolactin and corticosterone profiles were located at 03:26 h and 23:32 h respectively, a delay of 3-4 hours compared with the values of the 24-hour plasma profiles reported in the literature. Corticosterone and prolactin rhythms were abolished or dramatically delayed after 3 weeks of constant illumination. As expected, constant light suppressed the rhythm of 6-sulfatoxymelatonin, the major hepatic metabolite of melatonin. The noninvasive and nonstressful methodology we developed could be of interest for studying the regulation of hormone rhythms and their mutual endocrine interactions in physiological conditions, especially their evolution in the aging process.

Effects of constant light on circadian rhythmicity in mice lacking functional cry genes: dissimilar from per mutants

Mutations in each of the genes mPer1, mPer2, mCry1 and mCry2 separately cause deviations from the wild type circadian system. Differences between these mutant strains have inspired the hypothesis that the duality of circadian genes (two mPer and two mCry genes involved) is related to the existence of two components in the circadian oscillator (Daan et al., J Biol Rhythms 16:105-116, 2001). We tested the predictions from this theory that the circadian period (tau) lengthens under constant illumination (LL) in mCry1 and mPer1 mutant mice, while it shortens in mCry2 and mPer2 mutants. mCry1 ( -/- ) and mCry2 ( -/- ) knockout mice both consistently increased tau with increasing light intensity, as did wild type mice. With increasing illumination, rhythmicity is reduced in mCry1, mCry2 and mPer1, but not in mPer2 deficient mice. Results for mPer mutant mice are in agreement with data reported on these strains earlier by Steinlechner et al. (J Biol Rhythms 17:202-209, 2002), and also with the predictions from the model. The increase in cycle length of the circadian system by light in the mCry2 deficient mice violates the predictions. The model is thereby rejected: the mCry genes do not play a differential role, although the opposite responses of mPer mutants to light remain consistent with a functional Evening-Morning differentiation.