Effects of different light intensities in the morning on dim light melatonin onset

The present study evaluated the effects of exposure to light intensity in the morning on dim light melatonin onset (DLMO). The tested light intensities were 750 lux, 150 lux, 3000 lux, 6000 lux and 12,000 lux (horizontal illuminance at cornea), using commercial 5000 K fluorescent lamps. Eleven healthy males aged 21-31 participated in 2-day experiments for each light condition. On the first experimental day (day 1), subjects were exposed to dim light (<30 lux) for 3 h in the morning (09:00-12:00). On the same day, saliva samples were taken in dim light (<30 lux) every 30 min from 21:00 to 01:00 to determine the DLMO phase. The subjects were allowed to sleep from 01:00 to 08:00. On the second experimental day (day 2), the subjects were exposed to experimental light conditions for 3 h in the morning. The experimental schedule after light exposure was the same as on day 1. On comparing day 2 with day 1, significant phase advances of DLMO were obtained at 3000 lux, 6000 lux and 12,000 lux. These findings indicate that exposure to a necessary intensity from an ordinary light source, such as a fluorescent lamp, in the morning within one day affects melatonin secretion.     

Effects of constant light on the rhythm of adult locomotor activity in the blowfly, Calliphora vicina

Abstract. Females of the blowfly, Calliphora vicina , showed an increase in the free-running period (γ) of their locomotor activity rhythm when transferred from continuous darkness (DD) to continuous 'dim' light (LL) at an irradiance below about 0.03 Wm^-2. Transfer to LL of this intensity also caused a reduction in the duration of the active phase (α) of the cycle. Transfer to 'bright' light (>0.03 Wm²), however, lead to arrhythmicity. Data suggest that constant light of this intensity does not 'stop' the circadian pacemaker but imposes behavioural arrhythmicity at a more superficial level.     

Splitting of the circadian rhythm of activity in hamsters: Effects of exposure to constant darkness and subsequent re-exposure to constant light

Summary The circadian rhythm of wheel running behavior was observed to dissociate into two distinct components (i.e. split) within 30 to 110 days in 56% of male hamsters exposed to constant light (Figs. 1–2). Splitting was abolished in all 16 animals that were transferred from constant light (LL) to constant darkness (DD) within 1–4 days of DD, and the components of the re-fused activity rhythm assumed a phase relationship that is characteristic of hamsters maintained in DD (Figs. 3–5). Re-fusion of the split activity rhythm was accompanied by a change in period (); in 14 animals increased while in the other 2 animals decreased after transfer to DD.After 10–30 days in DD, the hamsters were transferred back into LL at various time points throughout the circadian cycle. A few of these animals went through two or three LL to DD to LL transitions. The effect of re-exposure to LL was dependent on the phase relationship between the transition into LL and the activity rhythm. A rapid (i.e. 1–4 days) induction of splitting was observed in 7 of 9 cases when hamsters were transferred into LL 4–5 h after the onset of activity (Fig. 5). In the other 2 animals, the activity pattern was ultradian or aperiodic for 20 to 50 days before eventually coalescing into a split activity pattern. In contrast, transfer of animals (n = 13) from DD to LL at other circadian times did not result in the rapid induction of splitting and the activity rhythm continued to free-run with a single bout of activity (Fig. 5). Importantly, a transfer from DD to LL 4–5 h after the onset of activity did not induce splitting if the hamsters had not shown a split activity rhythm during a previous exposure to LL (n=10; Fig. 6).These studies indicate that transfer of split hamsters from LL to DD results in the rapid re-establishment of the normal phase relationship between the two circadian oscillators which underlie the two components of activity during splitting. In addition, there appears to be a history-dependent effect of splitting which renders the circadian system susceptible to becoming split again. The rapid re-initiation of the split condition upon transfer from DD to LL at only a specific circadian time is discussed in terms of the phase response curve for this species.Abbreviation PRC phase response curve This investigation was supported by NIH grants HD-09885 and HD-12622 from the National Institute of Child Health and Human Development and by a grant from the Whitehall FoundationRecipient of Research Career Development Award K04 HD-00249 from the National Institute of Child Health and Human Development     

Effects of photoperiod on rat motor activity rhythm at the lower limit of entrainment

The experiment described here studied the rat motor activity pattern as a function of the photoperiod of circadian light-dark cycles in the limits of entrainment (22-and 23-h periods). In most cases, the overt rhythm showed 2 circadian components: 1 that followed the external LD cycle and a 2nd rhythm that was free run. The expression of these components was directly dependent on the photoperiod, and there was a gradual transition in the manifestation of 1 or the other. The component with a period equal to that of the external cycle was more manifested under long photoperiods, while the other 1 was more expressed during short photoperiods. Also, the period of the free-running component was longer under T22 than T23. For each period, the free-running component was longer under a longer photoperiod. At first sight, the presence of these 2 components in most of the rats might appear to be due to the fact that in the limits of entrainment, some rats do not entrain and thus show a free-running rhythm plus masking. However, the gradation observed in the different patterns of the overt motor activity rhythm, especially those patterns related to the different balance between the 2 components and the length of the period of the free-running component under LD as a function of the photoperiod, suggests that the circadian system can be functionally dissociated.     

Effect of short-term constant light or constant darkness on the nyctohemeral rhythm of type-II iodothyronine 5'-deiodinase activity in rat anterior pituitary and pineal

Type-II iodothyronine 5'-deiodinase activity (5'-D) in both anterior pituitary and pineal was significantly elevated at 2400 h, approximately 0.5- and 20-fold higher than the noon value, respectively. The nocturnal rise in both organs was abolished by 6 h additional light. Short-term constant darkness did not alter 5'-D rhythmicity in either organ. These data suggest that environmental lighting plays an important role in the control of the 5'-D nyctohemeral rhythm in both anterior pituitary and pineal.     

Synchronization by light of the circadian rhythm of motor activity in the crayfish

Abstract

We have studied the pattern for resetting the circadian rhythm in the spontaneous motor activity of the crayfish. Spontaneous motor activity was recorded continously at a constant temperature and under free running conditions in complete darkness. The effect of single light pulses applied at different circadian times, on the circadian rhythm of motor activity was measured in both transient stage and steady state. The results led us to construct a phase‐transition curve and phase‐response curve which were analyzed to obtain information about the oscillators which underlie the circadian rhythm of motor activity.     

Circadian rhythm of acute phase proteins under the influence of bright/dim light during the daytime

We investigated the influence of two different light intensities, dim (100 lx) and bright (5000 lx), during the daytime on the circadian rhythms of selected acute phase proteins of C-reactive protein (CRP), alpha1-acid glycoprotein (AGP), alpha1-antichymotrypsin (ACT), transfferin (TF), alpha2-macroglobulin (alpha2-m), haptoglobin (HP), and ceruloplasmin (CP). Serum samples were collected from 7 healthy volunteers at 4 h intervals during two separate single 24 h spans during which they were exposed to the respective light intensity conditions. A circadian rhythm was detected only in ACT concentration in the bright light condition. The concentration of ACT, a positive acute phase protein (APP), increased (significantly significant differences in the ACT concentration were detected at 14:00 and 22:00 h) and AGP showed a tendency to be higher under the daytime bright compared to dim light conditions. There were no significant differences between the time point means under daytime dim and bright light conditions for alpha2-M, AGP, Tf, Cp, or Hp. The findings suggest that some, but not all, APP may be influenced by the environmental light intensity.     

Melatonin administration modifies circadian motor activity under constant light depending on the lighting conditions during suckling

Early lighting conditions have been described to produce long-term effects on circadian behavior, which may also influence the response to agents acting on the circadian system. It has been suggested that melatonin (MEL) may act on the circadian pacemaker and as a scavenger of reactive oxygen and nitrogen species. Here, we studied the oxidative and behavioral changes caused by prolonged exposure to constant light (LL) in groups of rats that differed in MEL administration and in lighting conditions during suckling. The rats were exposed to either a light–dark cycle (LD) or LL. At 40 days old, rats were treated for 2 weeks with a daily subcutaneous injection of MEL (10?mg/kg body weight) or a vehicle at activity onset. Blood samples were taken before and after treatment, to determine catalase (CAT) activity and nitrite level in plasma. As expected, LL-reared rats showed a more stable motor activity circadian rhythm than LD rats. MEL treatment produced more reactivity in LD- than in LL rats, and was also able to alter the phase of the rhythm in LD rats. There were no significant differences in nitrite levels or CAT activity between the groups, although both variables increased with time. Finally, we also tested depressive signs by means of sucrose consumption, and anhedonia was found in LD males treated with MEL. The results suggest that the lighting conditions in early infancy are important for the long-term functionality of the circadian system, including rhythm manifestation, responses to MEL and mood alterations.     

Acute phase proteins, body temperature and urinary melatonin under the influence of bright and dim light intensities during the daytime

Concentrations of five acute phase proteins: C-reactive protein (CRP), alpha 1-antichymotrypsin (ACT), transferin (Tf), alpha 2-macroglobulin (alpha 2-M) and haptoglobin (Hp) as well as glycosylation profiles of alpha 1-antichymotrypsin (ACT) were studied in sera samples with 7 healthy volunteers under the influence of two different light intensities during the daytime dim (100 lx) and bright (3000 lx) light. Concentration of transferin (negative proteins) under the influence of bright light during the daytime decreased significantly. Other proteins have the tendency to increase (positive proteins) under the influence of daytime bright light. The microheterogeneity of ACT did not change under the influence of different light intensities. Melatonin and rectal temperature were also measured simultaneously. Rectal temperature decreased to be lower during the first half of the night and urinary melatonin secretion rate increased to be higher during the night when the subjects spent time under the bright light during the day. Thus, it is concluded that the diurnal bright light exposure may activate some parameters of acute phase proteins, increase nocturnal melatonin secretion and accelerate a fall of rectal temperature during first half period of night sleep.     

Effect of constant light on the circadian rhythm in locomotor activity in intact or eyelids-removed rats

According to the Aschoff's role, exposure to continuous light (LL) results in the elongation of the free-running period of the rat circadian rhythm. However, the LL may not always mean the constant intensity of the light for the suprachiasmatic nucleus, since the rat may regulate the contrast of the illumination by their eyelids which are closed during the sleep phase. In this study, the surgical removal of the eyelids under the LL caused arrhythmicity of the locomotor activity in 7 of 10 rats. The remaining 3 rats maintained the free-running rhythm after the removal of the eyelids. These results suggest that constant light may affect the free-running rhythm of the rat with or without eyelids in the different manner.     

The effect of carbachol on the phase of free-running locomotor activity rhythm under constant darkness (DD) and constant light (LL) in mice.

Carbachol chronically and peripherally administered, depending on the circadian time, caused a phase shift in the free-running locomotor activity rhythm, resynchronized the rhythm, or had a masking effect of this rhythm in mice. In the discussion it is stressed that the drug affects the rhythmicity of this activity, probably by acting on the mechanism of suprachiasmatic nuclei.     

Effect of light on the development of the circadian rhythm of motor activity in the mouse

In previous experiments, we found that rats raised in constant light (LL) manifested a more robust circadian rhythm of motor activity in LL and showed longer phase shifts after a light pulse in constant darkness (DD) than those raised under constant darkness. In addition, we observed that the effects produced by constant light differed depending on the time of postnatal development in which it was given. These results suggest that both sensitivity to light and the functioning of the circadian pacemaker of the rat could be affected by the environmental conditions experienced during postembryonic development. Thus, the present experiment aimed to study whether postnatal exposure to light could also affect the circadian system of the mouse. Three groups of mice were formed: One group was raised under constant darkness during lactation (DD group), the second under constant light (LL group), and the third under light-dark cycles (LD group). After lactation, the three groups were submitted first to constant light of high intensity, then to LD cycles, and finally to constant darkness. In the DD stage, a light pulse was given. Finally, mice were submitted to constant light of low intensity. We observed that the circadian rhythm of the DD group was more disturbed under constant light than the rhythm of the LL group, and that, when light intensity increased, the period of the rhythm of the DD group lengthened more than that of the LL group. No significant differences among the groups were found in the phase shift induced by the light pulse. Therefore, it appears that DD mice are more sensitive to light than their LL counterparts. However, at present there is no evidence to affirm that the light environment experienced by the mouse during postnatal development affects the circadian pacemaker. (Chronobiology International, 18(4), 683-696, 2001)     

Daily exercise facilitates phase delays of circadian melatonin rhythm in very dim light

Shift workers and transmeridian travelers are exposed to abnormal work-rest cycles, inducing a change in the phase relationship between the sleep-wake cycle and the endogenous circadian timing system. Misalignment of circadian phase is associated with sleep disruption and deterioration of alertness and cognitive performance. Exercise has been investigated as a behavioral countermeasure to facilitate circadian adaptation. In contrast to previous studies where results might have been confounded by ambient light exposure, this investigation was conducted under strictly controlled very dim light (standing approximately 0.65 lux; angle of gaze) conditions to minimize the phase-resetting effects of light. Eighteen young, fit males completed a 15-day randomized clinical trial in which circadian phase was measured in a constant routine before and after exposure to a week of nightly bouts of exercise or a nonexercise control condition after a 9-h delay in the sleep-wake schedule. Plasma samples collected every 30-60 min were analyzed for melatonin to determine circadian phase. Subjects who completed three 45-min bouts of cycle ergometry each night showed a significantly greater shift in the dim light melatonin onset (DLMO(25%)), dim light melatonin offset, and midpoint of the melatonin profile compared with nonexercising controls (Student t-test; P < 0.05). The magnitude of phase delay induced by the exercise intervention was significantly dependent on the relative timing of the exercise after the preintervention DLMO(25%) (r = -0.73, P < 0.05) such that the closer to the DLMO(25%), the greater the phase shift. These data suggest that exercise may help to facilitate circadian adaptation to schedules requiring a delay in the sleep-wake cycle.     

Locomotor activity rhythm in four wrasse species under varying light conditions

Under controlled laboratory conditions, the locomotor activity rhythms of four species of wrasses (Suezichthys gracilis, Thalassoma cupido, Labroides dimidiatus andCirrhilabrus temminckii) were individually examined using an actograph with infra-red photo-electric switches in a dark room at temperatures of 21.3–24.3°C, for 7 to 14 days. The locomotor activity ofS. gracilis occurred mostly during the light period under a light-dark cycle regimen (LD 12:12; 06:00-18:00 light, 18:00-06:00 dark). The locomotor activity commenced at the beginning of the light period and continued until a little before the beginning of dark period. The diel activity rhythm of this species synchronizes with LD. Under constant illumination (LL) this species shows distinct free-running activity rhythms varying in length from 23 hrs. 39 min. to 23 hrs. 47 min. Therefore,S. gracilis appears to have a circadian rhythm under LL. However, in constant darkness (DD), the activity of this species was greatly suppressed. All the fish showed no activity rhythms in DD conditions. After DD, the fish showed the diel activity rhythm with the resumption of LD, but this activity began shortly after the beginning of light period. The fish required several days to synchronize with the activity in the light period. Therefore,S. gracilis appeared to continue the circadian rhythm under DD. InT. cupido, the locomotor activity commenced somewhat earlier than the beginning of the light period and continued until the beginning of the dark period under LD. The diel activity rhythm of this species synchronizes with LD. Under LL, four of the five specimens of this species tested showed free-running activity rhythms for the first 5 days or longer varying in length from 22 hrs. 54 min. to 23 hrs. 39 min. Although the activity of this species was suppressed under DD, two of five fish showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 38 min. to 23 hrs. 50 min. under DD. Therefore, it was ascertained thatT. cupido has a circadian rhythm. InL. dimidiatus, the locomotor activity rhythm under LD resembled that observed inT. cupido. The diel activity rhythm of this species synchronizes with LD. Under LL, four of seven of this species showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 07 min. to 25 hrs. 48 min. Although the activity of this species was suppressed under DD, three of five fish showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 36 min. to 23 hrs. 41 min. under DD. Therefore, it was ascertained thatL. dimidiatus has a circadian rhythm. Almost all locomotor activity of C.temminckii occurred during the light period under LD. The diel activity rhythm of this species coincides with LD. Under LL, two of four of this species showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 32 min. to 23 hrs. 45 min. Although the activity of this species was suppressed under DD, one of the four fish showed free-running activity rhythms throughout the experimental period. The length of the free-running period was 23 hrs. 21 min. under DD. Therefore,C. temminckii appeared to have a circadian rhythm. According to field observations,S. gracilis burrows and lies in the sandy bottom whileT. cupido, L. dimidiatus, andC. temminckii hide and rest in spaces among piles of boulders or in crevices of rocks during the night. It seems that the differences in nocturnal behavior among the four species of wrasses mentioned above are closely related to the intensity of endogenous factors in their locomotor activity rhythms.     

Effects of ovariectomy and constant light on responsiveness to estrogen in the rat

The hypothesis that the responsiveness of sexual behavior and LH secretion to exogenous gonadal steroid treatment is dependent on the endogenous steroid environment existing prior to treatment was tested in female rats. The major finding was that estrogen was more effective in stimulating lordosis behavior when treatment was commenced immediately after ovariectomy than when it was delayed for 6 weeks. This indicates that the sensitivity of behavior regulating mechanisms in the female rat declines after removal of the “activating” hormones, as previously reported for testosterone in the male. Similar results were obtained in groups of animals whose pattern of steroid secretion prior to ovariectomy had been changed by 2 months' exposure to constant light. The constant illumination itself showed no significant effect on behavioral responsiveness in spayed estrogen-treated rats. Results are also reported for plasma LH determinations and uterine weights in each of the experiments. Plasma LH levels were found to be lower under conditions of constant as compared to cycling light, both in spayed untreated and spayed estrogen-treated animals.     

The dim light melatonin onset, melatonin assays and biological rhythm research in humans

The most useful marker for human circadian phase position is the dim light melatonin onset (DLMO). This is optimally obtained by sampling blood or saliva in the evening at intervals of 30 min or less. Ambient light intensity should not exceed 30-50 lx. For many years, the DLMO was determined mainly with the 'gold standard' GCMS technique for measuring melatonin in human plasma. However, new and improved RIAs now provide the requisite sensitivity and accuracy (specificity) for detecting the time that low daytime levels begin to increase in the evening: the lower the operational threshold for the DLMO, the more reliable it is as a phase marker.