Early Light Phase Research Articles

Early morning bright light phase advances the human circadian pacemaker within one day

One day after a single exposure to bright light from 03.00 to 09.00 h the morning declines in the serum melatonin concentration were phase-advanced in all subjects relative to pre-exposure patterns by 1.2–2.6 h. The evening melatonin rise was phase-advanced in 5 out of 6 subjects by 0.6–2.2 h. The data suggest that an underlying human circadian pacemaker controlling the melatonin rhythm may be phase-advanced within one day; however, the evening melatonin rise and the morning decline do not necessarily phase-shift by the same amount.

Hypothalamic neuronal histamine modulates ad libitum feeding by rats

Manipulating histamine endogenously, its effects on brain functions were assessed in rats. α-Fluoromethylhistidine (FMH), an inhibitor of histamine synthesis, elicited feeding ( P < 0.01) after intra-third cerebroventricular infusion at the early light phase when hypothalamic histamine was normally highest. No periprandial drinking was observed. The effect of FMH was attenuated, and thioperamide, an antagonist of auto-inhibitory effects on both histamine synthesis and release at presynaptic H 3-receptor, conversely suppressed food intake ( P < 0.05), when these probes were carried out during the minimum histamine level early in the dark period. Bilateral microinfusion of FMH into the ventromedial hypothalamus (VMH) and the paraventricular nucleus (PVN) selectively induced feeding, but the infusion into the remaining sites of the hypothalamus had no effect. These data show that neuronal histamine plays a physiological role in feeding suppression through the VMH and the PVN in the rat.

Synthesis and Degradation of Carbonic Anhydrase in a Synchronized Culture of Chlamydomonas reinhardtii

The biosynthesis and degradation of carbonic anhydrase (CA; EC 4.3.1.1) was investigated during the course of synchronous culture of the unicellular green alga Chlamydomonas reinhardtii, carried out under a regime of 12 h of light and 12 h of darkness with bubbling of ordinary air. The enzymatic activity increased linearly during the light phase. A coordinate increase in the level of the 35-kDa mature CA polypeptide was demonstrated by immunostaining after poly-acrylamide gel electrophoresis and Western blotting. Pulse-labeling with [14C]arginine followed by immunoprecipitation showed that the biosynthesis of the CA polypeptide is very active in the early light phase and rapidly decreases after the middle of the light phase, indicating that the bio-synthetic activity does not reflect the quantity of enzyme protein or the level of enzymatic activity. The 42-kDa precursor but not the 35-kDa mature polypeptide was synthesized in the dark. The 35-kDa polypeptide, pulse-labeled at the beginning of the light phase, was gradually degraded throughout the light phase while it appeard to be stable in the dark. These results suggest that the messenger RNA coding for CA is present but its translation is limited in the dark. Normal translation of mRNA and processing of the precursor to yield the holoenzyme may both require light.

Amiloride effect on diurnal cyclic Na and K excretion in rats

Amiloride was administered to rats during the peak and minimum of Na and K diurnal rhythmic excretion (i.e., during early dark phase and early light phase). In rats receiving a normal-K diet (2.34 meq/day) amiloride decreased K excretion from 186 to 37 mueq/h (dark phase) and from 31 to 4 mueq/h (light phase). Amiloride increased Na excretion from 91 to 344 mueq/h (dark phase) and from 35 to 164 mueq/h (light phase). Rats receiving a high-K diet (10.4 meq/day) showed a higher diurnal peak and minimum for K excretion. During high-K intake, amiloride decreased K excretion from 787 to 191 mueq/h (dark phase) and from 197 to 40 mueq/h (light phase) and increased Na excretion from 237 to 891 mueq/h (dark phase) and from 31 to 222 mueq/h (light phase). Whenever given, amiloride reduced K excretion to approximately 20% of control excretion. It is concluded that rhythmic changes in amiloride-sensitive distal transport are largely, but not entirely, responsible for the diurnal K cycle, but do not cause the concurrent Na cycle. Thus the diurnal cycles in Na and K are expressed through changes in different transport mechanisms. In rats maintained on a high-K diet there is an increase in rhythmic K secretion and Na reabsorption by amiloride-sensitive transport. To maintain Na excretion unchanged, Na reabsorption must be correspondingly depressed at an amiloride-insensitive site.

Metamorphic rate in Rana pipiens larvae treated with thyroxine or prolactin at different times in the light/dark cycle

Premetamorphic Rana pipiens tadpoles at Stages V to VIII on a 12L/12D cycle with photoperiod from 0800 to 2000 hr were treated with 30 μg/liter thyroxine (T 4) by immersion for various daily 8-hr spans, or by daily intraperitoneal injection at different times with 0.1 to 10 μg T 4 or 10μg prolactin (PRL), in order to see if the rate of metamorphosis varied with the time of hormone treatment. T 4 was most effective in promoting tail resorption and hindlimb growth and development if tadpoles were immersed at least partly in the light or if the hormone was injected late in the dark or in the early or mid light phase. T 4 was least effective in accelerating metamorphosis when immersion was totally in the dark or injection early in the dark. PRL antagonized metamorphosis just as well at any time of the day except that tail fin growth was faster when PRL was administered early in the dark. The findings show circadian variations in target tissue responsiveness to exogenous T 4 that depend on the occurrence of light during T 4 immersion or following T 4 injection. The data suggest rhythmicity in the secretion of endogenous T 4 in the tadpole and a diurnal effect on T 4 utilization by target cells.

Circadian rhythm in the light response of rat retinal disk-shedding and autophagy

Under a light-dark cycle, disk-shedding and autophagy in the rat retina peak in the early and mid light phase, respectively. Under constant conditions, disk-shedding and autophagy responses after light stimulation were elicited at different time points of a 24-h cycle. The greatest magnitude of response occurred in the late dark and early light phase. Thus there is a circadian variation of the light response of important metabolic parameters in the mammalian retina. Inhibition of dopamine synthesis during the early light phase caused a significant dampening of the light responses of both disk-shedding and autophagy.

Similarities in feeding behavior of chronic methamphetamine treated and withdrawn rats to VMH lesioned rats

During chronic methamphetamine (M) administration and after drug withdrawal, total daily food intake, water consumption and body weight increase was measured. Additionally, food intake in the early light phase provided an index of normal circadian rhythmicity. A parallel development of tolerance to the anorexic effect of M and increased feeding in the early light phase occured. A further abnormal behavior of both chronic M-treated and withdrawn rats was the lack of preference reversal when given free access to concentrated vs. diluted glucose solutions. Both disturbed circadian feeding rhythmicity and inhibition of the glucose preference reversal are found in rats with ventromedial hypothalamic (VMH) lesions. Reduced food intake and diminished body weight increase is a characteristic of lateral hypothalamic lesions. By analogy, chronic M-treatment could be considered to induce a functional state similar to lesions of the medial and lateral hypothalamus, each with a different time course.

Scheduled feeding and 24-hour rhythms of N-acetylserotonin and melatonin in rats.

Male rats, kept under a lighting condition of 14-h light, 10-h dark, were subjected to scheduled feeding regimens. Food was available either in the early light phase or the early dark phase. The 24-h rhythms of serum corticosterone and of N-acetylserotonin (NAS) and melatonin (MT) in the pineal and serum were determined. It was found that whereas serum corticosterone and NAS rhythms responded to the feeding schedules, the rhythms of pineal NAS and of serum and pineal MT remained synchronized with the light-dark cycle. These findings indicated that the pineal was not the major source of circulating NAS. Whereas environmental lighting was the dominant "Zeitgeber" for the NAS rhythms in the pineal and the MT rhythms in the pineal and serum, for serum NAS rhythm, food presentation was the stronger Zeitgeber.

Influence of photoperiod on the time of birth in the rat. IV. Effects of an imposed feeding rhythm.

In order to study the respective effects of photoperiod and feeding rhythm on the time of birth in rats, the onset of fetus expulsion was determined in six experimental groups. Under the standard light regime (14L-10D; lights-on at 6 a.m.), rats caged alone or in threes and fed ad libitum (groups C and 3C) gave birth over two preferential periods, the first during the late light phase of day 22 of gestation and the second during the early light phase of day 23. Under the same conditions, rats fed during a restricted period (from 9 a.m. to 11 a.m.) from day 8 of gestation (groups PF and 3PF) gave birth during a single period, starting just before and spreading over the first half of the night separating the last two days of gestation. The number of rats per cage affected birth distribution slightly, but an inverse effect was observed between the feeding regime and the social group constituted by mating (group 3C vs 3PF). Most births occurred after lights-on at day 23 of gestation when the rats were caged alone, fed ad libitum and submitted to a progressive shift in the light phase (group BC). This shift was realized by daily advancing dawn and dusk every day by 15 min from day 8 of gestation. Under these conditions, food restriction from 9 a.m. to 11 a.m. (group BC-PF) resulted in an intermediate distribution between groups BC and PF. The data show that time of birth in rats can be modulated by two different biological entrainers, photoperiod and feeding rhythm and that time of birth, in a given case, is determined by the interactions between these two factors.

Stress-induced increase of pineal n-acetyltransferase activity in intact rats

Adult male rats were killed immediately following a 20 min ether stress at 01:00, 07:00 or 19:00 h (lights on 06:00–20:00 h). Compared to unstressed controls sacrificed at the same times, ether-stressed animals exhibited a 4-fold rise in pineal N-acetyltransferase activity at 07:00 h but not at the other time points. Measurement of [ 3H]epinephrine uptake in rat pineals suggests that this early light phase NAT response does not result from decreased neuronal uptake of circulating catecholamine.

Mineral ion fluxes in slices of acidified and de-acidified leaves of the CAM plant Bryophyllum daigremontianum

Summary Acidified leaves (high levels of malic acid) of the CAM plant Bryophyllum daigremontianum were harvested at the end of the dark phase or during the early light phase, de-acidified leaves (low levels of malic acid) were obtained towards the end of the light phase. Slices of acidified leaves loose large amounts of H + and malate to solutions of low potential osmotic pressure (π*). This loss is reduced by increasing π* of the medium up to 5 Atm. 86 Rb and 36 Cl uptake are independent of H + and malate levels, H and malate fluxes, and π* up to 5 Atm. K + and Cl − net fluxes in acidified leaf slices are much smaller than changes of H+ levels in the tissue, even when the external KCl concentration is as high as 50 mM. K + , Na + , and Cl − levels in acidified leaf tissue are much smaller than H + and malate 2− levels. There is no significant diurnal variation of K + , Na + , and Cl − levels in leaf cells of intact plants. It is concluded i) that the effect of π* of the medium on H + and malate net effluxes is specific; ii) that there is no negative feedback of malic acid in the vacuoles on K + and Cl − uptake; iii) that the oscillations of malic acid levels in leaf cells of the CAM plant B. daigremontianum are independent of potassium (by contrast to other oscillatory systems known from the literature).

The Effect of Light on the Synthesis of Mitochondrial Enzymes in Division-synchronized Euglena Cultures

The development of the mitochondrial enzymes fumarase and succinate dehydrogenase has been followed in Euglena cultures division-synchronized by 14-hour light periods alternating with 12-hour dark periods. The activity of both enzymes was unaltered over the light phase, doubled in early dark phase, and thereafter remained constant over the rest of the cycle. The increase in enzyme activity in early dark phase probably represented de novo enzyme synthesis because it was prevented by the addition of cycloheximide at a concentration known to inhibit protein synthesis on Euglena cytoplasmic ribosomes.When division-synchronized cultures were darkened in early light phase, a doubling of both fumarase and succinate dehydrogenase activity resulted, showing that light was repressing enzyme synthesis. The addition of acetate did not have a similar effect to darkening cultures: enzyme activity being unaltered over the light phase of the cycle. Enzyme expression was also unaffected by the addition of 3-(3,4 dichlorophenyl)-1,1-dimethylurea, a potent inhibitor of photosynthetic carbon dioxide fixation. The addition of 6-methylpurine (an inhibitor of transcription) at the beginning of the light phase inhibited enzyme increase in early dark phase, but when added at a later stage of the light phase (hour 8), increase in enzyme activity in early dark phase was unaffected. We concluded that transcription for these enzymes occurs in early light phase but light exerts a post-transcriptional control so that enzyme synthesis does not result until cells enter the dark phase of the cell cycle.

Biosystematic studies onMaianthemum (Liliaceae-polygonatae)

The photosynthetic activity of the foliage of aMaianthemum species, i.e.,M. dilatatum under changing light and temperature regimes in the typical temperate woodland environment was investigated in Ohodaira, Nikko, located at an altitude of ca. 1300 m above sea level, and its adaptive significance was discussed in relation to the ecological life history of this species. It was revealed thatM. dilatatum from the broad-leaved deciduous forest floor displays a very characteristic photosynthetic behaviour which has thus far not been reported for any other forest floor plants.M. dilatatum sprouts at the early spring light phase and efficiently performs photosynthesis under this prevernal light condition; a considerably high saturation light intensity of approximately 20–25 klux results in an unusually high net photosynthetic rate (ca. 30 mgCO2/dm2/hr) as a forest floor plant. However, in the subsequent period, at the end of June and July, a rather drastic decrease was observed in the photosynthetic rate in response to the reduction of the light intensity on the forest floor. Also,M. dilatatum showed a broad photosynthetic optimum over a wide thermal range from 10 to 30 C at the prevernal stage. This is another interesting functional characteristic of this temperate woodland herb.

The Regulation of Glycolate Metabolism in Division Synchronized Cultures of Euglena

Phosphoglycolate and phosphoglycerate phosphatases and glycolate dehydrogenase activities were determined in division synchronized Euglena gracilis strain Z cultures. Phosphoglycolate phosphatase activity remained nearly constant in the light but doubled in the dark, whereas phosphoglycerate phosphatase activity decreased by half in the light and increased 4-fold over the dark phase of the cycle. Glycolate dehydrogenase activity assayed by dye reduction increased over the light and remained constant during the dark phase, but when determined by the phenylhydrazone method, an assay dependent upon the presence of a natural hydrogen acceptor, activity decreased in the dark phase. The acceptor decayed in the dark in all cell-free extracts and 3-(3,4-dichlorophenyl)-1, 1-dimethylurea inhibited light regeneration.Enzyme activity regulated flow of carbon via the glycolate pathway; with cells at end of light phase and early dark phase, high levels of glycolate dehydrogenase activity were accompanied by an early and rapid labeling of glycerate. Degradation of early samples gave uniformly labeled glycolate and glycerate while phosphoglycerate was predominantly carboxyl labeled. At these stages in the division cycle, glycerate was formed from glycolate via the glycolate pathway, all the enzymes of the pathway being recorded in Euglena. In contrast to cells from end of dark phase and early light phase, times of maximum phosphoglycerate phosphatase activity, glycerate was predominantly carboxyl labeled as was phosphoglycerate, but glycolate was still uniformly labeled.Glycolate excretion varied over the cycle, being maximal at end of dark phase, decreasing throughout the light phase until not detectable in early dark phase. When alpha-hydroxy-2-pyridinemethanesulfonate was used as a measure of glycolate biosynthesis, sufficient glycolate dehydrogenase was present to oxidize the glycolate produced at all stages over the cycle.