Constant Bright Light Research Articles

Constant Bright Light (LL) during Lactation in Rats Prevents Arhythmicity Due to LL

Light has a strong effect on the circadian system. Light–dark (LD) cycles are the main zeitgebers for practically all organisms, and the exposure of animals to constant bright light (LL) alters the manifestation of circadian rhythms. In rats, exposure to LL in adulthood produces an arhythmic pattern in their motor activity, with a large number of ultradian components. In previous experiments, we found that rats born and kept under LL during lactation develop, after weaning, a circadian rhythm which is maintained for at least a couple of months. Here, we examined motor activity rhythms under LL of two groups of rats which differed in the lighting conditions under which they were kept during lactation: 1) rats kept under LL during lactation (LL-rats), which manifested a circadian rhythm after weaning, and 2) rats kept under constant darkness (DD-rats), which were arhythmic after weaning. We investigated whether the presence of rhythmicity under LL in LL-rats is a transitory effect or whether it persists throughout most of the life of the rat. Moreover, we examined motor activity rhythms of both groups of rats under different lighting conditions to find out other possible differences in the manifestation of their circadian rhythms. Results showed that there are no differences in the capacity of entrainment of both groups of rats to LD cycles or in the rhythm that rats show under DD. Most of the LL-rats maintained their circadian rhythms for the duration of the experiment (1 year), although we found differences in the rhythms manifested between males and females. We found that most of the LL-males became arhythmic; consequently, at the end of the experiment, there were no differences in the number of males showing circadian rhythm in the LL- and DD-groups. Most of the females in the LL-group showed a clear circadian rhythm under LL during the entire experiment. Thus, LL during lactation has a protective effect against the disruptive effect of LL on the circadian rhythm, although it is only clearly manifested in females.

Circadian locomotor rhythms in the cricket, Gryllodes sigillatus. I. Localization of the pacemaker and the photoreceptor.

Circadian locomotor rhythm and its underlying mechanism were investigated in the cricket, Gryllodes sigillatus. Adult male crickets showed a nocturnal locomotor rhythm peaking early in the dark phase of a light to dark cycle. This rhythm persisted under constant darkness (DD) with a free-running period averaging 23.1 +/- 0.3 hr. Although constant bright light made most animals arrhythmic, about 40% of the animals showed free-running rhythms with a period longer than 24 hr under constant dim light condition. On transfer to DD, all arrhythmic animals restored the locomotor rhythm. Bilateral optic nerve severance resulted in free-running of the rhythm even under light-dark cycles. The free-running period of the optic nerve severed animals was significantly longer than sham operated crickets in DD, suggesting that the compound eye plays some role in determining the free-running period. Removal of bilateral lamina-medulla portion of the optic lobe abolished the rhythm under DD. These results demonstrate that the photoreceptor for entrainment is the compound eye and the optic lobe is indispensable for persistence of the rhythm. However, 75% and 54% of the optic lobeless animals showed aberrant rhythms with a period very close to 24 hr under light and temperature cycles, respectively, suggesting that there are neural and/or humoral mechanisms for the aberrant rhythms outside of the optic lobe. Since ocelli removal did not affect the photoperiodically induced rhythm, it is likely that the photoreception for the rhythm is performed through an extraretinal photoreceptor.

Manifestation of circadian rhythm under constant light depends on lighting conditions during lactation

Adult rats transferred to continuous illumination (LL) show a disruption of circadian rhythms, although the mechanisms underlying this effect are not yet well known. In previous experiments, we found that when rats were born and raised under LL they showed an ultradian pattern during the first 10 days after weaning, but afterward they generated a circadian rhythm that was maintained until adulthood. It was not clear whether this evolution was attributable to the influence of the rhythm of the mother or to the effect of constant light. Here, we have studied the motor activity rhythm of young rats maintained under LL after weaning, taking into account the conditions to which they were exposed during lactation [LL or continuous darkness (DD)]. To check the possible effect of the rhythm of the dam, on the day of delivery some of the dams were blinded, others were subjected to a restricted feeding schedule of 3 h/day, and the others were used as controls. For each rat, the period of the circadian rhythm and the percentage of variance explained by this rhythm were calculated. Results show that all rats maintained under LL during lactation expressed a circadian rhythm in their motor activity. However, rats maintained under DD during lactation did not. This effect did not seem to be dependent on the type of dam. These results suggest that the rhythm of the dams does not affect the manifestation of the rhythm of the pups and that the expression of circadian rhythmicity under constant bright light depends on the lighting conditions under which the animals were maintained during lactation, which could affect the development of the circadian pacemaker or the retina.

Effects of daily injections of melatonin on locomotor activity rhythms in rats maintained under constant bright or dim light

It has been demonstrated that daily melatonin injections entrain free-running locomotor activity rhythms in rats kept in constant darkness, and synchronize disrupted circadian patterns of wheel-running activity under constant light. Contrary to these previous observations, our result did not show that daily injections of melatonin synchronize disrupted locomotor activity in rats maintained under constant bright light. On the other hand, daily treatment with melatonin entrained the intact free-running rhythm in rats kept in constant dim light. This entrainment took place only when the time of injection corresponded to the activity onset time, and similar results were obtained in blinded rats. Pinealectomy had no influences on either the free-running rhythm or melatonin-induced entrainment. To examine whether a behavioral feedback mechanism is involved in melatonin-induced entrainment, rats were immobilized for 3 h after each daily melatonin injections. This did not interfere with melatonin-induced entrainment. These results suggest that the mechanism underlying melatonin-induced entrainment of activity rhythms may be different from those in photic and behavioral entrainment.

Effects of Daily Injections of Melatonin on Locomotor Activity Rhythms in Rats Maintained Under Constant Bright or Dim Light

Effects of Daily Injections of Melatonin on Locomotor Activity Rhythms in Rats Maintained Under Constant Bright or Dim Light

Adverse effects of rotating schedules on the circadian rhythms of air medical crews

Air Medical Journal 14:2 April-June 1995 Introduction Observations of the rhythmic nature of animal behavior date back to the time of Aristotle, who noted swelling of sea urchin ovaries during the full moon.1 “Sleep movements” of plants also were noted by the ancient Greeks, who attributed the phenomena to the presence or absence of sunlight. Circadian rhythm (Latin: circa meaning about, and diem meaning a day) is defined as an inborn, genetically programmed, self-sustained rhythm in behavior, physiology and metabolism, developed over evolutionary time that enables living organisms to cope with the 24hour daily rotation of the planet.’ One of the first experiments designed to test circadian rhythms in plants was done in 1729 by de Mairan, who illustrated that plant leaves open in the daytime even when kept in total darkness.2 This was the first presentation of evidence of an endogenous biological clock that functioned in the absence of zeitgebers (German for “time givers” or clues to the time of day). The term “free running” has been used to describe a rhythm in behavior pattern, or resultant metabolic pattern, that continues in the absence of any exogenous clues.1 The concept of freerunning biological clocks was discovered in 1832 by de Candolle, who placed plants in constant bright light.2 After a few days, the leaves opened and closed on a 22-hour cycle. This display indicated that the plant had its own independent day length. Circadian rhythms have endogenous and exogenous components; the former is dependent on a clocklike mechanism, while the latter is driven by external time clues (zeitgebers).z The endogenous clock appears to be responsible for the free-running day length, and light/dark cycles have been shown to be important in adjusting the human circadian clock. Many species of invertebrates demonstrate that circadian clocks have evolved mechanisms by which they frequently are reset to keep pace with changes in the local environment, most notably by being sensitive to the intensity of light.3 Controlled experiments have shown that humans have a 25.1-hour circadian clock that is constant and predictable but entrained to the 24-hour day by environmental clues.294 Volunteers were studied by Weitzman and Czeisler in periods ranging from two weeks to six months, during which they were isolated from any zeitgebers. Subjects were permitted to eat and sleep at times of their own choosing, and after one week in the clue-free environment, they lagged behind their usual day/night schedules by almost eight hours. This implies that human internal clocks are reset on a daily basis.2 Forced changes in circadian rhythm produce sleep disruption and deprivation.2,5-7 The circadian system influences performance through its effects on metabolic functions and on quality of sleep. Its rhythmicity and consistency is crucial to the maintenance of normal levels of body function and performance. The most obvious change occurs in sleep patterns, where sleep becomes shortened and disrupted by the displacement of the circadian rhythm. Pilots undergoing a shift change may find themselves awake in the

The Pineal Gland: Photoreception and Coupling of Behavioral, Metabolic, and Cardiovascular Circadian Outputs

Although removal of the pineal gland has been shown to have very little effect on the mammalian circadian system in constant darkness (DD), several recent reports have suggested that the mammalian pineal gland may be more important for circadian organization in nocturnal rodents than was previously believed. Removal of the pineal gland (PINX) facilitates the disruptive effects of constant bright light on wheel-running rhythmicity. This suggests at least two possibilities for the role of the pineal gland in the mammalian circadian system. First, pinealectomized rats may perceive ambient light intensity to be brighter than do sham-operated (SHAM) rats. Second, the pineal gland, probably via its secretion of melatonin, may also be involved in coupling components of the circadian system. Coupling, as we see it, may occur at several levels of organization: (1) between retinohypothalamic afferents and suprachiasmatic nuclei (SCN) oscillatory neurons, (2) among multiple SCN oscillators, (3) between the SCN and their multiple outputs, and/or (4) among the multiple circadian outputs themselves. In this study we show that PINX rats free-run with a longer period in four different light intensities than do SHAM rats. Moreover, the rate of increase of tau is greater among PINX rats than among SHAM rats. This supports the first hypothesis. We also show that in PINX rats the circadian rhythms of wheel running, general activity, body temperature, and heart rate are all more disrupted in constant bright light than are those of SHAM rats, and each rhythmic output is disrupted in parallel. This supports the second hypothesis. Melatonin is probably not involved in coupling presynaptic elements of SCN afferents in the retinohypothalamic tract to pacemaking cells within the SCN, since enucleation has no effect on SCN 2-[125I]iodomelatonin (IMEL) binding. Together the data do not discount either of the two hypotheses but do restrict the possible levels at which the pineal gland is involved in coupling. These data also further support a growing body of literature indicating that the pineal gland and its hormone melatonin play a role in mammalian circadian organization.

Modelling the circadian system of the weta,Hemideina thoracica(Orthoptera: Stenopelmatidae)

The development of the current model of the circadian system of the nocturnal insect Hemideina thoracica is traced from a single feedback oscillator, to more complex interactions of two populations of oscillators. Each unit oscillator is based on a negative feedback system incorporating time‐delay and sensitivity to light and temperature. Individual oscillators are linked to one or more similar oscillators to form populations or networks of units. The components of each unit reflect functions which are physiologically relevant with respect to the biochemical evidence for circadian clocks. The single oscillator model accounts for many of the basic properties of the Hemideina locomotor rhythms, including temperature compensation, light and temperature entrainment and the effects of constant dim and bright light. The population concept enhances the model by explaining much of the spontaneous and induced lability of the free‐running rhythm. The single population model has been extended, and we now propose that there is more than one clock control centre in this insect. The overall pattern of temporal behaviour may result from the interaction of two major clock centres, one regulating, among other functions, the locomotor activity subsystem, and the other the control of cuticle deposition. The concept of feedback control of the clock system of this insect is based on the original circadian feedback model of Johnsson and Karlsson which they proposed for the rhythmic petal movements of the plant Kalanchoe blossfeldiana.

Constant light suppresses sleep and circadian rhythms in pigeons without consequent sleep rebound in darkness

Sleep patterns and circadian rhythms of body temperature, activity, body weight, and electroencephalographic (EEG) power spectra of pigeons were compared among three photic conditions: a 12:12-h light-dark cycle (LD), followed successively by constant bright (LL) and dim light (DD) periods. LL suppressed non-rapid-eye-movement and rapid eye movement sleep and circadian rhythms of the measured variables without producing increased drowsiness or other physiological or behavioral changes. Sleep patterns after LL-DD transitions also showed no evidence of prior sleep deprivation during LL. Sleep latency after LL-DD transitions was 93 min longer than after L-D transitions in LD. Total sleep and EEG slow wave activity during the first 24 h in DD did not differ from D in LD. Free-running circadian rhythms subsequently reappeared in DD after LL.

Orientation of pigeons exposed to constant light and released from familiar sites

It has been proposed that homing pigeons may use pilotage to orient home when released from familiar sites. To test this possibility, a group of pigeons was released from familiar locations after being exposed to a constant bright light. This treatment produced the loss of the circadian rhythmicity of general activity of the birds and thus presumably impaired their time-compensating sun compass mechanism. Experimental birds, both anosmic and olfactorily unimpaired, did not show any tendency to orient home, their bearing distributions being generally not different from random. Their homing performances were also affected. These results show that initail orientation of pigeons released from familiar sites entails the use of the sun compass even when the birds are released after a treatment that makes them arhythmic in their activity. The possibility that pilotage may play a role in the first part of the homing flight of pigeons remains to be demonstrated.

Pinealectomized rats entrain and phase-shift to melatonin injections in a dose-dependent manner.

Previous work has shown that daily injections of the pineal hormone melatonin (N-acetyl, 5-methoxytryptamine) entrain the free-running locomotor rhythms of rats held in constant darkness (with a median effective dose [ED50] of 5.45 +/- 1.33 micrograms/kg) and in constant bright light. The present experiments determined the dose-response characteristics of entrainment and phase shifting to daily and single melatonin injections in both sham-operated (SHAM) and pinealectomized (PINX) rats. The data indicated an ED50 of 332 +/- 53 ng/kg and 121 +/- 22 ng/kg for SHAM and PINX rats, respectively, during the entrainment experiment. The ED50's for the entrainment experiment were considerably lower than doses previously employed, and much lower than doses employed in reproductive and metabolic studies in rats and hamsters. The data indicated that no partial entrainment occurred; nor were there differences in phase angle, length of activity, or period among all effective doses. Next, a single injection of 1 mg/kg melatonin has previously been shown to cause a phase advance of approximately 45 min when administered at about circadian time (CT) 10. We found that both SHAM and PINX animals phase-advanced, in a dose-dependent manner to a single melatonin injection given at CT 10. The data for the phase-shifting experiment indicated an ED50 of 8.19 +/- 0.572 micrograms/kg and 2.16 +/- 0.326 micrograms/kg for SHAM and PINX animals, respectively, with an average phase advance of 40 min for both groups. Together, the data suggest that the presence of the pineal gland is not necessary for the effects of melatonin on the rat circadian system, and that PINX animals are marginally more sensitive to melatonin than their SHAM controls.

Melatonin infusions restore sleep suppressed by continuous bright light in pigeons

Constant bright light (LL) suppresses 24-h melatonin and many other behavioral and physiological rhythms in pigeons. LL also strongly suppresses sleep. Daily melatonin infusions in LL restore sleep to normal nocturnal levels of a light-dark cycle and continuous infusions sustain it for at least 10 days. Restoration of sleep in LL by melatonin indicates its key role in avian sleep mechanisms.

The formation of myeloid bodies in retinular cells of the pupal compound eyes of silkworm moths (Bombyx mori) exposed to a constant bright light

Numerous well-developed myeloid bodies are formed in the retinular cells of the compound eyes of pupae (cocoons were removed) of silkworm (Bombyx mori) irradiated with a constant bright light (10 000 lux). Such well-developed myeloid bodies are not usually observed in arthropod compound eyes, and they have been observed only in the retinular cells of lepidopterans reared with carotenoid-deficient diet. In this experiment silkworms were fed normal diet containing carotenoids, therefore the formation of myeloid bodies was caused by the abnormally strong illumination (10 000 lux). The fine structure and morphogenesis of myeloid bodies are discussed.

Endogenous rhythms in the succession of Sleep-wake stages inMicrocebus murinus

Sleep-wake stages were studied by means of EEG recordings in three female Microcebusmaintained under dim red light for 2 to 12 months and in a female maintained in constant bright light first for 1 month, then for 4 months. A circadian rhythm was apparent in all cases. In addition, the reduction of the alert-wake state in winter and its large increase in summer hints at a circannual rhythm.

Loss of the circadian rhythms of locomotor activity, food intake, and plasma melatonin concentration induced by constant bright light in the pigeon (Columba livia).

Locomotor activity and feeding activity were measured together with circulating levels of melatonin in pigeons which were exposed to constant bright light (LLbright, 2000 lux) following light-dark (LD) cycles. Although all the pigeons showed daily rhythms of locomotor activity, feeding activity, and melatonin levels under LD cycles, they lost all the rhythms in prolonged LLbright. Acute exposure to bright light (2000 lux) during darkness reduced plasma melatonin levels. The half-time for the suppression in melatonin levels was about 30 min after short-term light exposure. These results support the hypothesis that melatonin may control the circadian rhythms of locomotor activity and feeding activity in the pigeon.

Bright artificial light subsensitizes a central muscarinic mechanism

Supersensitivity of a muscarinic mechanism is implicated in the pathophysiology of depression. Bright artificial light is efficacious in the treatment of Seasonal Affective Disorder (SAD). We studied the effect of constant bright light (11, 500 lux) on the sensitivity of adult, male rats to oxotremorine, 1.5 mg/kg ip, using a repeated measures design. Oxotremorine challenges were proceeded by the injection of methylscopolamine, 1 mg/kg ip, by 30 minutes. Temperature was telemetrically measured every 10 minutes for 120 minutes starting 10 minutes after the injection of oxotremorine. Prior to and after 7 continuous days of exposure to bright light, the sample exhibited a hypothermic response of 2 if2.50 ± 0.48°C ( mean ± SEM) and 0.29 ± 0.31°C ( mean ± SEM), respectively (p < 0.0014). All 7 animals exhibited blunting to the thermic response to oxotremorine. Bright light also blocked the capacity of amitriptyline to supersensitize a central muscarinic mechanism. Exposure to light at an intensity of 300 lux for 7 days had no effect on the thermic response to oxotremorine. These data are consistent with the hypotheses that the biology of depression involves supersensitivity of central muscarinic mechanisms and that the effects of bright artificial light are not the consequence of shifting circadian rhythms.

A model for the study of the acute effects of melatonin in man.

The role of the pineal hormone melatonin in human physiology is uncertain. Previous studies correlated plasma melatonin levels with several physiological parameters or determined the responses to pharmacological doses of melatonin during daylight hours. We established an acute model that is more rigorously physiological. Constant nocturnal bright light in sleep-deprived normal men resulted in low plasma melatonin levels throughout the night, in contrast to sleep in the dark and dim light sleep deprivation nights. Subsequently, melatonin was infused during bright light exposure to approximate physiological levels. Plasma GH and PRL measurements in these four conditions revealed an effect of sleep deprivation independent of the presence or absence of melatonin. A subsample of these men had an intermediate level of melatonin suppression with 500 lux light intensity, relative to those during sleep and bright light. The results suggest that melatonin has no acute modulatory effect on the secretion of these two sleep-related hormones.

Effect of locus coeruleus and periventricular gray substance lesions on bright light-induced persistent estrous

To assess the relation between the suprachiasmatic nucleus and the locus coeruleus, persistent estrous was induced in female rats by exposure to constant bright light followed with electrolytic damage of the locus coeruleus. Locus coeruleus lesions resulted in a transient loss of persistent estrous indicated by sustained diestrous aspect of the vaginal smears. There was a direct correlation between duration of estrous loss and the amount of locus coeruleus damage. Simultaneous damage to the periventricular gray substance adjacent to the locus coeruleus prevented the suppression effects of locus coeruleus damage upon persistent estrous. These results suggest a physiological role of the locus coeruleus and periventricular gray substance in the modulation of the neuroendocrine control of ovarian function due to suprachiasmatic nucleus activity.

Dose-dependent entrainment of rat circadian rhythms by daily injection of melatonin.

Previous work in our laboratory has shown that daily injection of large doses of the pineal hormone melatonin entrains the free-running locomotor rhythms of rats held in constant darkness and synchronizes the disrupted patterns of rats maintained in constant bright light. The present experiments determined the dose-response characteristics of entrainment to daily melatonin injections and made preliminary biochemical estimates of blood melatonin levels and half-lives after two critical doses of the hormone. The data indicated that the median effective dose for melatonin as an entraining agent in free-running rats was 5.45 +/- 1.33 micrograms/kg, considerably lower than doses previously employed and lower than doses employed in reproductive and metabolic studies in rats and hamsters. The data further indicated that the response to melatonin was quantal; rats either entrained to melatonin or they did not. No "partial entrainment" was evident, nor were there differences in phase angle, activity, or period among all effective doses. Biochemical estimates of blood melatonin after either 1 mg/kg or 1 microgram/kg of melatonin indicated that all effective doses resulted in supraphysiological levels of blood melatonin, although doses of 1 microgram/kg resulted in blood levels that were within one order of magnitude of normal nighttime values. Together, the data suggest that the rat circadian system is sensitive to the pineal hormone melatonin at or below doses required to effect rodent reproduction. Whether this sensitivity reflects a role for the pineal gland in rat circadian organization, however, still remains to be determined.

Effects of light intensity on the circadian temperature and feeding rhythms in the squirrel monkey

The circadian rhythms of body temperature and feeding appear to be timed by separate pacemakers. Tonic administration of light has been used to investigate the response of the pacemaker timing behavioral rhythms; however, the response of the body temperature rhythm has not been similarly examined. This study investigates the circadian timing of the body temperature rhythm under conditions of different light intensity. We simultaneously recorded the patterns of both feeding and body temperature in squirrel monkeys free-running in an environment free of external time cues. In each lighting condition, the periods of the body temperature and feeding rhythms were identical. In constant bright light the rhythm periods were longer than when the animals were exposed to constant dim light. In addition, the variability of the periods was dependent on light intensity. The feeding rhythm period variance of animals in constant bright light was smaller than when in dim light. Conversely, the period of the free-running body temperature rhythm exhibited more variability in bright light than in dim light. Further, in each condition, there were changes in phase angle relationship between feeding and body temperature which were qualitatively similar to those observed in humans, although quantitatively smaller in magnitude. Thus, in the squirrel monkey, tonic light studies reveal that the mean circadian period of the body temperature and feeding rhythms are similar. However, changes in phase relationship, and differential rhythm period stabilities suggest differences in the period of the underlying, tightly coupled pacemakers.