Phase Shifting the ERG Amplitude Circadian Rhythm of Juvenile Crayfish by Caudal Monochromatic Illumination

The objective of the present work was to determine the physiological mechanisms underlying the synchronization of the ERG amplitude rhythm. Chronic ERG recordings were obtained from juvenile instars of crayfish. Changes on the ERG amplitude rhythm produced when 30 min blue light illuminated the telson were determined. The PRC obtained with these data showed advances in the early subjective night and delays in the late subjective night. These phase shiftings resemble the features of curves obtained by dark pulses in other species. The relation of this curve with PRCs generated in the crayfish and other animals species are discussed.     

Phase Shifting the ERG Amplitude Circadian Rhythm of Juvenile Crayfish by Caudal Monochromatic Illumination

The objective of the present work was to determine the physiological mechanisms underlying the synchronization of the ERG amplitude rhythm. Chronic ERG recordings were obtained from juvenile instars of crayfish. Changes on the ERG amplitude rhythm produced when 30 min blue light illuminated the telson were determined. The PRC obtained with these data showed advances in the early subjective night and delays in the late subjective night. These phase shiftings resemble the features of curves obtained by dark pulses in other species. The relation of this curve with PRCs generated in the crayfish and other animals species are discussed.     

Effects of Illumination on the Rabbits Eeg During the two Phases of its Circadian Rhythm

After exposure to a LD 12:12 regimen for several weeks, rabbits exhibit a programmed circadian rhythm in the RMS values of their occipital and frontal EEC's during 54-hr recordings in constant darkness. Illumination at levels of 80,160 and 230 Lx raises these RMS values in both phases of the rhythm. The induced rise is large in the phase with low RMS values and small in the other, whereas light-induced changes in spectral composition of the EEG's are slight in either phase. Bilateral optic nerve sectioning results in similar changes in properties of the EEG and in the amplitude of its rhythm. The results are discussed with reference to the influence exerted by steady illumination on the overall-level of retinal maintained “dark” discharge.     

Circadian Locomotor Activity Rhythm During Ontogeny in Crayfish Procambarus Clarkii

The characteristics of the circadian rhythm of locomotor activity in the crayfish Procambarus clarkii during ontogeny under constant darkness and light-dark (LD 12:12) conditions were studied in 132 juvenile crayfish, aged 10-140 days, divided in four groups. All animals were individually monitored with a motor activity recording system. Activity was quantitatively and qualitatively analyzed. All ages showed a circadian rhythm, although the probability of its appearance increased with age. Period values oscillated between 25.0 h in group I (2-4-week-old animals) and 24.3 h in group IV (16-20-week-old animals with more than 6 molts), but always with a high standard deviation. Groups II (5-10-week-old animals) and IV showed a statistically significant bimodal nonrandom synchrony of phases. The activity/ rest relationship diminishes as development progresses and is most uniform in group IV. We discuss the possibility that the pacemaker system responsible for this rhythm might be present from the moment of eclosion, but the coupling strength of this system with the effectors might change along development. The results presented in this work seem to indicate that the central pacemakers responsible for the activity and the ERG rhythm are not the same.     

Effect of Skeleton Photoperiods upon the Circadian Locomotor Activity Rhythm During Development in Crayfish Procambarus clarkii

This study was carried out to investigate the non-parametric effect of white light on the activity rhythm of the postembryonic stages of crayfish and to elucidate the characteristics and development of its entrainment mechanisms. Forty-five postembryonical instars of crayfish Procambarus clarkii, separated into three groups according to age and moult, were investigated. They were individually monitored with a motor activity recording system in constant photic conditions. For the three groups of animals, three trials with different skeleton photoperiod (SP) imitating LD 8:16, LD 12:12 and LD 20:4 were conducted, each followed by exposure to a period of constant darkness (DD). The locomotor activity rhythm and its entrainment ability were evaluated. All ages showed a circadian rhythm with a capability to synchronize to the different SP increasing with age. The three groups of crayfish analysed were generally synchronized by the dusk pulse, clustering the onset of activity close to the light pulses considered as dusk. The results presented in this study suggest the involvement of extraretinal pathways in the non-parametric entrainment of crayfish.     

Effect of Skeleton Photoperiods upon the Circadian Locomotor Activity Rhythm During Development in Crayfish Procambarus clarkii

This study was carried out to investigate the non-parametric effect of white light on the activity rhythm of the postembryonic stages of crayfish and to elucidate the characteristics and development of its entrainment mechanisms. Forty-five postembryonical instars of crayfish Procambarus clarkii, separated into three groups according to age and moult, were investigated. They were individually monitored with a motor activity recording system in constant photic conditions. For the three groups of animals, three trials with different skeleton photoperiod (SP) imitating LD 8:16, LD 12:12 and LD 20:4 were conducted, each followed by exposure to a period of constant darkness (DD). The locomotor activity rhythm and its entrainment ability were evaluated. All ages showed a circadian rhythm with a capability to synchronize to the different SP increasing with age. The three groups of crayfish analysed were generally synchronized by the dusk pulse, clustering the onset of activity close to the light pulses considered as dusk. The results presented in this study suggest the involvement of extraretinal pathways in the non-parametric entrainment of crayfish.     

Effects of Choline Depletion on the Circadian Rhythm in Neurospora crassa

One approach to identifying components of the circadian oscillator is to screen for clock defects in mutants with known biochemical lesions. The chol-1 mutant of Neurospora crassa is defective in the first methylation step of phosphatidylcholine synthesis, the conversion of phosphatidylethanolamine to phosphatidylmonomethylethanolamine, and requires choline for normal growth. Choline depletion of this mutant inhibits growth and lengthens the period of the rhythm of conidiation. On high levels of choline (above 20 µM), the growth rate and the period of the rhythm are normal. Below about 10 µM choline, the growth rate and period length depend on the choline concentration, and the period is about 58 h on minimal medium without choline. Choline depletion decreases period stability, and replicate cultures do not remain in phase due to variability in period within each culture. At intermediate levels of choline (around 10 µM) cultures are often arrhythmic. The choline requirement for growth can be met by the phosphatidylcholine precursors monomethylethanolamine and dimethylethanolamine, and these supplements also restore a normal period. Choline depletion of the chol-1 strain exaggerates the rhythm in growth rate previously reported in a chol + strain. Growth rate during formation of a conidial band (measured as forward advance of the mycelial front) is less than half of the maximum rate during non-conidiating interband formation. Choline-depleted cultures can be entrained to light/dark (LD) cycles with periods near to their free-running periods. Cultures on 10 µM choline (with a free-running period of about 25 h) can be entrained to a 24 h (12:12) LD cycle, but not to a 36 h (18:18) or 48 h (24:24) LD cycle. Cultures on 0.5 µM choline (free-running period of about 52 h) or minimal medium (free-running period of about 58 h) can be entrained to 18:18 and 24:24 LD cycles, but not a 12:12 cycle. The phase relationship of the conidiation rhythm to the zeitgeber for low-choline cultures in LD 24:24 is similar to high choline cultures in LD 12:12. Continuous light abolishes rhythmicity in choline-depleted cultures. These results may indicate a role for membrane phospholipids, and the metabolites of phosphatidylcholine in particular, in the control of the period of the circadian oscillator in Neurospora.     

Cerebroid Ganglion is the Presumptive Pacemaker of the Circadian Rhythm of Electrical Response to Light in the Crayfish

One of the most widely studied circadian rhythms in invertebrates is that of light responsiveness whose underlying mechanisms seem to involve different groups of oscillators which act as pacemakers. Although, in crayfish, there are clear circadian rhythms in the electroretinogram (ERG) amplitude, the precise location of the pacemaker system driving this rhythm is uncertain. Some data suggest that the circadian pacemaker could be located in a group of neurosecretory cells of the supraesophageal ganglion (the cerebroid ganglion or brain) and that the sinus gland plays a determinant role in the generation and expression of this rhythm through periodic release of pigment-dispersing hormone (PDH). The aim of this work is to examine the role of the brain in the expression of the ERG circadian activity. The hypothesis we test is that the electrical activity at the brain level has a circadian behavior in the firing pattern of spontaneous multiunit activity (MUA) and in visual evoked potentials (VEPs). The results indicate that there are robust circadian rhythms in both MUA, recorded from several regions of the brain, and in the averaged VEPs recorded from the protocerebrum area. These rhythms are 180° out of phase to one another. The rhythm of VEPs showed a main peak at midnight which was in close phase relationship with the ERG amplitude rhythm.     

Dim Nighttime Illumination Interacts With Parametric Effects of Bright Light to Increase the Stability of Circadian Rhythm Bifurcation in Hamsters

The endogenous circadian pacemaker of mammals is synchronized to the environmental day by the ambient cycle of relative light and dark. The present studies assessed the actions of light in a novel circadian entrainment paradigm where activity rhythms are bifurcated following exposure to a 24-h light:dark:light:dark (LDLD) cycle. Bifurcated entrainment under LDLD reflects the temporal dissociation of component oscillators that comprise the circadian system and is facilitated when daily scotophases are dimly lit rather than completely dark. Although bifurcation can be stably maintained in LDLD, it is quickly reversed under constant conditions. Here the authors examine whether dim scotophase illumination acts to maintain bifurcated entrainment under LDLD through potential interactions with the parametric actions of bright light during the two daily photophases. In three experiments, wheel-running rhythms of Syrian hamsters were bifurcated under LDLD with dimly lit scotophases, and after several weeks, dim scotophase illumination was either retained or extinguished. Additionally, “full” and “skeleton” photophases were employed under LDLD cycles with dimly lit or completely dark scotophases to distinguish parametric from nonparametric effects of bright light. Rhythm bifurcation was more stable in full versus skeleton LDLD cycles. Dim light facilitated the maintenance of bifurcated entrainment under full LDLD cycles but did not prevent the loss of rhythm bifurcation in skeleton LDLD cycles. These studies indicate that parametric actions of bright light maintain the bifurcated entrainment state; that dim scotophase illumination increases the stability of the bifurcated state; and that dim light interacts with the parametric effects of bright light to increase the stability of rhythm bifurcation under full LDLD cycles. A further understanding of the novel actions of dim light may lead to new strategies for understanding, preventing, and treating chronobiological disturbances. (Author correspondence: jevans@msm.edu)     

Effects of Choline Depletion on the Circadian Rhythm in Neurospora crassa

One approach to identifying components of the circadian oscillator is to screen for clock defects in mutants with known biochemical lesions. The chol-1 mutant of Neurospora crassa is defective in the first methylation step of phosphatidylcholine synthesis, the conversion of phosphatidylethanolamine to phosphatidylmonomethylethanolamine, and requires choline for normal growth. Choline depletion of this mutant inhibits growth and lengthens the period of the rhythm of conidiation. On high levels of choline (above 20 µM), the growth rate and the period of the rhythm are normal. Below about 10 µM choline, the growth rate and period length depend on the choline concentration, and the period is about 58 h on minimal medium without choline. Choline depletion decreases period stability, and replicate cultures do not remain in phase due to variability in period within each culture. At intermediate levels of choline (around 10 µM) cultures are often arrhythmic. The choline requirement for growth can be met by the phosphatidylcholine precursors monomethylethanolamine and dimethylethanolamine, and these supplements also restore a normal period. Choline depletion of the chol-1 strain exaggerates the rhythm in growth rate previously reported in a chol + strain. Growth rate during formation of a conidial band (measured as forward advance of the mycelial front) is less than half of the maximum rate during non-conidiating interband formation. Choline-depleted cultures can be entrained to light/dark (LD) cycles with periods near to their free-running periods. Cultures on 10 µM choline (with a free-running period of about 25 h) can be entrained to a 24 h (12:12) LD cycle, but not to a 36 h (18:18) or 48 h (24:24) LD cycle. Cultures on 0.5 µM choline (free-running period of about 52 h) or minimal medium (free-running period of about 58 h) can be entrained to 18:18 and 24:24 LD cycles, but not a 12:12 cycle. The phase relationship of the conidiation rhythm to the zeitgeber for low-choline cultures in LD 24:24 is similar to high choline cultures in LD 12:12. Continuous light abolishes rhythmicity in choline-depleted cultures. These results may indicate a role for membrane phospholipids, and the metabolites of phosphatidylcholine in particular, in the control of the period of the circadian oscillator in Neurospora .     

The Manifestation of the Motor Activity Circadian Rhythm of Blinded Rats Depends on the Lighting Conditions During Lactation

The purpose of this experiment was to examine the effect of different lighting conditions during lactation on the functioning of the circadian pacemaker in the adult rat in absence of the retinal input. We reared one group of rats under constant light (LL-rats) and the other under constant darkness (DD-rats). After weaning they were placed under light-dark cycles of 24h period for 29 days to eliminate the aftereffects of the previous lighting. All the animals were then binocularly enucleated and motor activity was recorded. Results reveal that, before and after the enucleation, the expression of the circadian rhythm was stronger in DD- than in the LL-rats. Our results indicate that lighting conditions during lactation modify the functioning of the circadian pacemaker.     

Effects of Temperature on the Circadian Conidiation Rhythm of Temperature-Sensitive Mutants of Neurospora crassa

Period lengths at different temperatures and phase responsecurves at a high temperature (35°C) of circadian conidiationrhythms were examined in 13 temperature-sensitive (un) strainsof Neurospora crassa. Two strains, un-16 and un-18, had longerperiod lengths than the wild-type strain even at permissivetemperatures. Period lengths of six strains, un-4, un-11, un-16,un-18, un-19 and un-22, changed differently from that of thewild-type strain at restrictive temperatures. However, the shapeof phase response curves for high temperature (35°C) for3 h was almost the same for all un strains and the wild-typestrain. We isolated 97 temperature-sensitive mutants with periodlengths from 19.2 to 24.8 h and determined the dependence ontemperature of the period length of the conidiation rhythm foreach mutant. The mutants could be divided into four differentgroups in terms of their responses to changes in temperature. (Received September 8, 1993; Accepted March 10, 1994)     

About the Existence of Circadian Activity in Cave Crayfish

Evidence of a circadian clock mechanism was found in the cave crayfish Procambarus cavernicola. Analysis of motor activity recorded in this species during 12 consecutive days in either free running (constant darkness, DD or constant light, LL) or entrainment conditions (12 h of light alternated with 12 h of darkness, 12 : 12 LD) showed a well recognized circadian rhythm. In this rhythm however, the absence of synchronization by periodical external signals was notorious. The comparison between the motor circadian rhythm in cave crayfish and epigeous crayfish Procambarus clarkii (these last studied during juvenile and adult stages), evidenced strong similitude between the motor circadian rhythm of cave crayfish and juvenile epigeous crayfish.     

Seasonal Rhythm of Red Pigment Concentrating Hormone in the Crayfish

The content of red pigment concentrating hormone (RPCH) in the eye-stalk of the crayfish Procambarus clarkii varies seasonally, with maximum values during the summer months and the lowest values in winter. The responsiveness of tegumentary chromatophores to synthetic RPCH varies concurrently. (Chronobiology International, 14(6), 639–645, 1997)     

Implicit Associations Have a Circadian Rhythm

The current study shows that people''s ability to inhibit implicit associations that run counter to their explicit views varies in a circadian pattern. The presence of this rhythmic variation suggests the involvement of a biological process in regulating automatic associations—specifically, with the current data, associations that form undesirable social biases. In 1998, Greenwald, McGhee, and Schwartz introduced the Implicit Association Test as a means of measuring individual differences in implicit cognition. The IAT is a powerful tool that has become widely used. Perhaps most visibly, studies employing the IAT demonstrate that people generally hold implicit biases against social groups, which often conflict with their explicitly held views. The IAT engages inhibitory processes similar to those inherent in self-control tasks. Because the latter processes are known to be resource-limited, we considered whether IAT scores might likewise be resource dependent. Analyzing IAT performance from over a million participants across all times of day, we found a clear circadian pattern in scores. This finding suggests that the IAT measures not only the strength of implicit associations, but also the effect of variations in the physiological resources available to inhibit their undesirable influences on explicit behavior.     

Circadian Rhythm in Pineal Methionine S-Adenosyltransferase

Abstract: The circadian rhythm of methionine S -adenosyltransferase, which catalyzes the formation of S -adenosylmethionine, a cosubstrate for melatonin in the pineal gland, follows the pattern of hydroxyindole- O -methyltransferase. Around the middle of the dark period, methionine S -adenosyltransferase and hydroxyindole- O -methyltransferase appear to be elevated by 2.5- and 1.5-fold, respectively, and tend to fall back during the light period.     

Circadian Rhythm in Serum Iron Levels

This study was aimed at assessing the circadian rhythm of serum iron levels in Chinese healthy subjects. The project was conducted in 19 healthy, Chinese male subjects following a 4-day diet equilibration. Blood samples were collected on day 5 at 0800, 1000, 1200, 1400, 1600, 1800, 2000, and 2400 hours to determine endogenous serum iron concentrations. Iron concentrations were determined using an inductively coupled plasma mass spectrometry. Iron concentration was decreased from morning to afternoon. The minimum value of iron level was 1,987 μg/L at 2000 hours while the maximum was 2,229 μg/L at 1000 hours, and 2,278 μg/L at 1400 hours, respectively, the amplitude was 291 μg/L. This study indicates that when assessing the bioequivalence of iron formulations, baseline levels of iron (obtained before dosing) should not be subtracted simply from the amount obtained on the drug dosing day to yield the net effect of iron formulation administration. More valid methods to optimize the design of such bioequivalence studies should be taken into consideration.     

The Circadian Rhythm of Body Temperature of the Horse

Rectal temperature of 10 female adult horses was recorded every 2 h for 10 consecutive days under a natural winter photoperiod (9 h of light and 15 h of darkness per day). A robust daily rhythm of body temperature was observed in all animals. The rhythm had a mean level of 38.3°C and a range of excursion of 1.0°C. Temperature started its daily ascent at dawn each day and reached a maximum 14 hours later. Body temperature of 5 of the horses was studied for 10 more days under constant illumination. The rhythm persisted under this condition, although with a slightly longer period of 24.2 h, which confirms the endogenous nature of the rhythm. Despite the fact that the body size of the horse is several orders of magnitude greater than that of rodents, the various parameters of the body temperature rhythm of the horse are similar to those of several species of rodents previously studied.