Constant Light Environment Research Articles

Effect of Experimental Parameters on the Electrochemical Current during Scanning Electrochemical Microscopy of Living Cells

Scanning Electrochemical Microscopy (SECM) is gaining popularity for its application to live cell imaging to monitor electrochemical processes occurring at the interface of living cells and electrodes. [1] Although many studies have been reported varying the instrumental parameters and using various probe designs, [2] the influence of experimental parameters on the electrochemical current must not be neglected, in order to generate reliable results. Our work explores parameters, such as temperature, light exposure and cell media during the SECM analysis of Adenocarcinoma Cervical cancer (HeLa) cells. The experimental and numerical studies with temperature variation revealed that temperature changes of 2ᵒC influence the reaction kinetics of single living cells. [3] Further, it was observed during light exposure that the electrochemical current becomes stabilized after 20 minutes of constant light environment compared to dark, where the standard deviation of the electrochemical current showed an increase in trend overtime. Furthermore, electrochemical current responses of HeLa cells in Phosphate Buffered Solution (PBS), Dubelcco’s Modified Eagle Medium (DMEM) and DMEM with 10% Fetal Bovine Serum (FBS) is being explored. These results will help to understand the origin of potential electrochemical current changes and the ideal experimental conditions to perform SECM measurements with living cells.[1] I. Beaulieu, S. Kuss, J. Mauzeroll, M. Geissler, Biological scanning electrochemical microscopy and its application to live cell studies, Anal. Chem. 83 (2011) 1485–1492. https://doi.org/10.1021/ac101906a.[2] D. Polcari, P. Dauphin-Ducharme, J. Mauzeroll, Scanning Electrochemical Microscopy: A Comprehensive Review of Experimental Parameters from 1989 to 2015, Chem. Rev. 116 (2016) 13234–13278. https://doi.org/10.1021/acs.chemrev.6b00067.[3] N. Thomas, D. Lima, D. Trinh, S. Kuss, Temperature Effect on the Electrochemical Current Response during Scanning Electrochemical Microscopy of Living Cells, Anal Chem. 95 (2023) 17962-17967. https://doi.org/10.1021/acs.analchem.3c03716

Fragmented day-night cycle induces reduced light avoidance, excessive weight gain during early development, and binge-like eating during adulthood in mice

Fragmented day-night (FDN) cycles are environments in which multiple periods of light and dark alternate across a 24 h period. Exposure to FDN cycles disrupts circadian rhythms, resulting in period lengthening and alterations to mood in mice. A constant light environment, which also induces period lengthening, is linked to mood and metabolic disturbances and disruption to the development of the circadian clock. This study aims to determine how exposure to the FDN cycle impacts development in mice, with the hypothesis that there would be similar and adverse effects as observed in constant light conditions. Our study used CD-1 mice reared under the FDN cycle compared to the commonly used 12 h light: 12 h dark consolidated day-night cycle. During the first week of development, mouse pups reared under the FDN cycle gained bodyweight at a faster rate and did not avoid aberrant light exposure in comparison to 12:12 LD reared mouse pups. Developmental exposure to the FDN cycle lasted two weeks, and then mice were transferred to the 12:12 LD cycle, where after 2 weeks, bodyweight was similar between FDN reared and 12:12 LD reared mice at 1-month and 2-months old. When re-exposed to the FDN cycle during adulthood, FDN reared pups exhibited binge-like eating behaviors and reduced light avoidance. This study shows that the unnatural distribution of light and dark across the 24 h day can cause disruptions during early development that can reappear during adulthood when placed in the same stressful light-dark environment as adults.

Expression patterns of iron regulatory proteins after intense light exposure in a cone-dominated retina.

Iron is implicated in ocular diseases such as in age-related macular degeneration. Light is also considered as a pathological factor in this disease. Earlier, two studies reported the influence of constant light environment on the pattern of expressions of iron-handling proteins. Here, we aimed to see the influence of light in 12-h light-12-h dark (12L:12D) cycles on the expression of iron-handling proteins in chick retina. Chicks were exposed to 400 lx (control) and 5000 lx (experimental) light at 12L:12D cycles and sacrificed at variable timepoints. Retinal ferrous ion (Fe2+) level, ultrastructural changes, lipid peroxidation level, immunolocalization and expression patterns of iron-handling proteins were analysed after light exposure. Both total Fe2+ level (p = 0.0004) and lipid peroxidation (p = 0.002) significantly increased at 12-, 48- and 168-h timepoint (for Fe2+) and 48- and 168-h timepoint (for lipid peroxidation), and there were degenerative retinal changes after 168 h of light exposure. Intense light exposure led to an increase in the levels of transferrin and transferrin receptor-1 (at 168-h) and ferroportin-1, whereas the levels of ferritins, hephaestin, (at 24-, 48- and 168-h timepoint) and ceruloplasmin (at 168-h timepoint) were decreased. These changes in iron-handling proteins after light exposure are likely due to a disturbance in the iron storage pool evident from decreased ferritin levels, which would result in increased intracellular Fe2+ levels. To counteract this, Fe2+ is released into the extracellular space, an observation supported by increased expression of ferroportin-1. Ceruloplasmin was able to convert Fe2+ into Fe3+ until 48 h of light exposure, but its decreased expression with time (at 168-h timepoint) resulted in increased extracellular Fe2+ that might have caused oxidative stress and retinal cell damage.

Constant light environment suppresses maturation and reduces complexity of new born neuron processes in the hippocampus and caudal nidopallium of a diurnal corvid: Implication for impairment of the learning and cognitive performance.

Periodic day-night environment shapes the temporal pattern in the behaviour and physiology (e.g. 24-h activity-rest and sleep-wake cycles) and the advanced brain function, such as learning, memory and decision making. In a previous study, we showed the abolition of 24-h rhythm in the activity-rest pattern, and an attenuated cognitive performance in diurnal Indian house crows (Corvus splendens) under constant light (no-night; LL) environment. Present study extended this, and investigated LL-induced effects on the neurogenesis (birth, maturation and neurite complexity of new born neurons) in the hippocampus and caudal nidopallium, the brain regions directly associated with learning and cognition in birds. We performed immunohistochemistry of doublecortin (DCX; a neurogenesis marker) and tyrosine hydroxylase (TH, a key enzyme of the dopamine biosynthesis) in the brain section containing hippocampus or caudal nidopallium of Indian house crows exposed for 2 weeks to LL, with controls maintained under 12L:12D. As expected, crows showed arrhythmicity with a significantly reduced rest period in the 24-h activity-rest pattern, and a decreased cognitive performance when tested for the spatial and pattern association learning tasks under LL. Importantly, there was a significant decrease in DCX-immunoreactive (ir) cells and, as shown by Sholl analysis, in the complexity of DCX-ir neurites in both, the hippocampus and caudal nidopallium of crows under LL, as compared to those under 12L:12D. The anatomical proximity of DCX-ir neurons with TH-ir fibers suggested a functional association of the new born hippocampal and caudal nidopallial neurons with the learning, and perhaps cognition in Indian house crows. These results give insights into possible impact of the loss of night on brain health and functions in an emerging ecosystem in which other diurnal species including humans may be inadvertently exposed to an illuminated night, such as in an overly lighted metropolitan urban habitat.

A shadow detector for photosynthesis efficiency

Plants tolerate large variations in the intensity of the light environment by controlling the efficiency of solar to chemical energy conversion. To do this, plants have a mechanism to detect the intensity, duration, and change in light as they experience moving shadows, flickering light, and cloud cover. Sugars are the primary products of CO2 fixation, a metabolic pathway that is rate limited by this solar energy conversion. We propose that sugar is a signal encoding information about the intensity, duration and change in the light environment. We previously showed that the Arabidopsis heterotrimeric G protein complex including its receptor-like Regulator of G signaling protein, AtRGS1, detects both the concentration and the exposure time of sugars (Fu et al., 2014. Cell 156: 1084–1095). This unique property, designated dose-duration reciprocity, is a behavior that emerges from the system architecture / system motif. Here, we show that another property of the signaling system is to detect large changes in light while at the same time, filtering types of fluctuation in light that do not affect photosynthesis efficiency. When AtRGS1 is genetically ablated, photosynthesis efficiency is reduced in a changing- but not a constant-light environment. Mathematical modeling revealed that information about changes in the light environment is encoded in the amount of free AtRGS1 that becomes compartmentalized following stimulation. We propose that this property determines when to adjust photosynthetic efficiency in an environment where light intensity changes abruptly caused by moving shadows on top of a background of light changing gradually from sun rise to sun set and fluctuating light such as that caused by fluttering leaves.

Differential activation and tyrosine hydroxylase distribution in the hippocampal, pallial and midbrain brain regions in response to cognitive performance in Indian house crows exposed to abrupt light environment

Disruption of the cyclic feature of the day-night environment can cause negative effects on daily activity and advanced brain functions such as learning, memory and decision-making behaviour. These functions in songbirds, including corvids, involve the hippocampus, pallium and midbrain, as revealed by ZENK (a neuronal activation marker) and tyrosine hydroxylase (TH) expressions. TH is rate-limiting marker enzyme of the biosynthesis of dopamine, widely implicated in learning and memory. Here, we measured ZENK and TH immunoreactivity in the hippocampal, pallial and midbrain regions in response to cognitive performance (learning-memory retrieval) tests in Indian house crows (Corvus splendens) exposed to constant light environment (LL) with controls on 12h light:12h darkness. Along with the decay of circadian rhythm in activity behaviour, LL caused a significant decline in the cognitive performance. There was also a decrease under LL in the activity of neurons in the hippocampus, medial and central caudal nidopallium, and hyperpallium apicale, which are widely distributed with TH-immunoreactive fibres. Further, under LL, TH- immunoreactive neurons were reduced in number in midbrain dopamine synthesis sites, the venteral tegmental area (VTA) and substantia nigra (SN), with a negative correlation of co-localized ZENK/TH- immunoreactive cells on errors during the association tasks. These results show decreased activity of learning and memory neural systems, and underscore the role of dopamine in reduced cognitive performance of diurnal corvids with disrupted circadian rhythms under an abrupt light environment.

Circadian clocks and pregnancy.

The recognition that 24-h rhythmic processes (“circadian”) underlie many endocrine functions has added a fascinating new temporal dimension to our appreciation of their complexity. Research from various laboratories has revealed circadian gene expression in multiple tissues in the reproductive system of non-pregnant and pregnant mammals. However, many questions regarding role of circadian clocks in the female reproductive system remain unresolved. This Research Topic on Circadian Clocks and Pregnancy brings together a broad and innovative group of researchers to discuss, evaluate, and summarize the key aspects of circadian function as it relates to all aspects of pregnancy from ovulation and implantation to fetal development and parturition. In the initial review, Ditisheim et al. (1) address preeclampsia, a pregnancy-related disease that involves an imbalance of angiogenic factors, which leads to abnormal placentation, marked systemic inflammatory responses, and hypertension. One particularly relevant feature of this disease is the loss of the nocturnal decrease in arterial blood pressure. The authors assess the question of whether disruption of circadian function may represent an occupational risk factor for preeclampsia and make the case that while this condition should be considered a major public health concern, the evidence for shift work increasing the risk of preeclampsia is not yet persuasive enough to draw any solid conclusions. Using a DNA microarray approach, Tasaki et al. (2) analyzed gene expression in uterine endometrial stromal cells during the implantation stage in the rat. In particular, they focused on the evaluation of genes compromising the circadian clockwork as well as downstream clock-controlled genes, since mutations in the former are known to associate with implantation failure and other reproductive defects. Among their findings was evidence for the clock gene Bmal1 controlling inhibin-β, IGF-1, and other endometrial genes. They also developed the hypothesis that alterations in the circadian system during decidualization are important for regulating the expression of genes vital for the formation of the placenta. In his review, Sellix (3) highlights our current understanding of circadian clock functions in the female reproductive system as it relates to the timing of gonadotropin secretion at ovulation and the timing of parturition. He proposes that the neuroendocrine-reproductive axis should be considered a partnership of synchronized and cooperative oscillators whose disruption can help to explain some forms of fertility disorders. In their contribution, Gamble et al. (4) examine the importance of circadian clocks for successful pregnancy. It is well known that shift work increases the risk of miscarriages, preterm birth, low birth weights, etc. These authors identify key gaps in our knowledge of circadian clock function in reproductive physiology and offer useful strategies for better understanding how shift work-induced circadian misalignment leads to reproductive dysfunctions. The complex relationship between cholesterol metabolism, estrogens, and female reproductive cycles is reviewed by Urlep and Rozman (5). For example, various genes in the cholesterol and steroidogenic pathway are rhythmic and are regulated by clock genes. Conversely, the central circadian clock in the suprachiasmatic nuclei (SCN) expresses the estrogen receptor, ERβ, which is also under clock gene control. Thus, perturbations in clock gene expression can have profound effects at multiple levels of the neuroendocrine-reproductive axis. Watanabe et al. (6) address the growing recognition that circadian rhythms during pregnancy have important consequences on fetal development. In their interesting clinical trials, they have determined that preterm babies (week 31 of pregnancy) already have pupillary reflexes and that exposure of these infants to a regular light/dark cycle (as opposed to the more common constant light environment of neonatal units) promotes more daytime activity and body growth. In other words, the direct use of natural circadian cycles of light and dark would appear to offer the preterm infant a surrogate rhythmic environment more conducive to optimal postnatal development, underscoring the importance of the circadian system during pregnancy. While it has long been recognized that female reproductive cycles are under the control of the central circadian clock in the SCN, only in the last few years have the specific details of this hypothalamic regulation been clarified. Miller and Takahashi (7) provide a lucid overview of the contributions of circadian vasopressin signals to the kisspeptin neurons that regulate hypothalamic GnRH secretion as well as the VIP regulation of pituitary prolactin rhythms. They also make a compelling case for the effects of clock gene mutations on pregnancy having important similarities to the impact of senescence on reproductive abnormalities. As documented by this Research Topic, the study of cellular circadian clocks on reproductive systems is still fertile territory for endocrinologists, cell biologists, and clinicians alike. It has great potential for providing testable hypotheses and unified explanations for disparate processes, such as blood pressure and gene expression rhythms, effects of shift work and artificial lighting on fetal development, hormonal rhythms and fertility, etc. An exciting era awaits!

Effects of a constant light environment on hippocampal system in mice

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Effects of a constant light environment on hippocampal neurogenesis and memory in mice

Because the environmental light–dark cycle is a key factor involved in modulating circadian rhythm in mammals, disruption of cyclic light conditions has a variety of effects on physiology and behavior. In the hippocampus, neurogenesis, which continues to occur throughout life, has been reported to exhibit circadian variation under cyclic light–dark conditions. In the present study, we examined whether a constant light environment affected hippocampal neurogenesis in mice. Half of the animals were exposed to continuous light conditions (L/L group), while the other half remained under normal cyclic light–dark conditions (L/D group). In the L/L group, the number of BrdU-labeled cells (proliferating cells) and that of BrdU and class III β-tubulin double-labeled cells (newborn neurons) in the granule cell layer were significantly decreased compared with the L/D group. Because hippocampal neurogenesis is involved in memory and learning, we also investigated the effects on performance in water maze tasks to assess spatial learning. Exposure to L/L treatment for 3 weeks impaired spatial learning task performance, although there was no difference in the open field behaviors between the groups. These findings demonstrate that the constant light conditions impaired hippocampal neurogenesis as well as cognitive performance, and suggest an important role for the cyclic light–dark environment in appropriate maintenance of the hippocampal system.

DAILY VARIATION OF CONSTITUTIVELY ACTIVATED NUCLEAR FACTOR KAPPA B (NFKB) IN RAT PINEAL GLAND

In mammals, the production of melatonin by the pineal gland is mainly controlled by the suprachiasmatic nuclei (SCN), the master clock of the circadian system. We have previously shown that agents involved in inflammatory responses, such as cytokines and corticosterone, modulate pineal melatonin synthesis. The nuclear transcription factor NFKB, detected by our group in the rat pineal gland, modulates this effect. Here, we evaluated a putative constitutive role for the pineal gland NFKB pathway. Male rats were kept under 12 h:12 h light-dark (LD) cycle or under constant darkness (DD) condition. Nuclear NFKB was quantified by electrophoretic mobility shift assay on pineal glands obtained from animals killed throughout the day at different times. Nuclear content of NFKB presented a daily rhythm only in LD-entrained animals. During the light phase, the amount of NFKB increased continuously, and a sharp drop occurred when lights were turned off. Animals maintained in a constant light environment until ZT 18 showed diurnal levels of nuclear NFKB at ZT15 and ZT18. Propranolol (20 mg/kg, i.p., ZT 11) treatment, which inhibits nocturnal sympathetic input, impaired nocturnal decrease of NFKB only at ZT18. A similar effect was observed in free-running animals, which secreted less nocturnal melatonin. Because melatonin reduces constitutive NFKB activation in cultured pineal glands, we propose that this indolamine regulates this transcription factor pathway in the rat pineal gland, but not at the LD transition. The controversial results regarding the inhibition of pineal function by constant light or blocking sympathetic neurotransmission are discussed according to the hypothesis that the prompt effect of lights-off is not mediated by noradrenaline, which otherwise contributes to maintaining low levels of nuclear NFKB at night. In summary, we report here a novel transcription factor in the pineal gland, which exhibits a constitutive rhythm dependent on environmental photic information. (Author correspondence: rpmarkus@usp.br)

DIEL VERTICAL MIGRATION BY JUVENILE SOCKEYE SALMON: EMPIRICAL EVIDENCE FOR THE ANTIPREDATION WINDOW

Diel vertical migration (DVM) is a widespread phenomenon in aquatic organisms, yet the adaptive significance of this behavior is still unclear. In particular, diel vertical migration by juvenile sockeye salmon (Oncorhynchus nerka) has received considerable attention. We studied how changes in the light environment affect juvenile sockeye DVM in Alaskan lakes through changes in foraging rates and predation risk. Using hydroacoustics to track temporal changes in fish distribution, we found clear patterns of DVM and a strong, significant correlation between the mean depth of the sockeye and the amount of light at the lake surface. However, we could not detect diel changes in the depth distribution of fish large enough to be sockeye predators. Given a lack of diel vertical migration in the zooplankton community, it appears that juvenile sockeye were not simply tracking their food supply. Calculations of the in situ light experienced by individual juvenile sockeye suggested that they migrate to maintain a constant light environment. This light environment allowed the sockeye to exploit an antipredation window whereby they could forage on zooplankton while reducing the odds of visual detection by their predators. Furthermore, this antipredation window was continuous in early summer, but was split into two discrete time periods during the crepuscular hours in late summer. These data support the hypothesis that changes in habitat use by juvenile sockeye salmon reflect a dynamic strategy to minimize the ratio of predation risk to foraging gain that changes dramatically over the course of diel cycles in pelagic ecosystems.

Entrainment of Eclosion Rhythm in Drosophila melanogaster Populations Reared for More Than 700 Generations in Constant Light Environment

In this paper, we report the results of our extensive study on eclosion rhythm of four independent populations of Drosophila melanogaster that were reared in constant light (LL) environment of the laboratory for more than 700 generations. The eclosion rhythm of these flies was assayed under LL, constant darkness (DD) and three periodic light‐dark (LD) cycles (T20, T24, and T28). The percentage of vials from each population that exhibited circadian rhythm of eclosion in DD and in LL (intensity of approximately 100 lux) was about 90% and 18%, respectively. The mean free‐running period (τ) of eclosion rhythm in DD was 22.85 ± 0.87 h (mean ± SD). Eclosion rhythm of these flies entrained to all the three periodic LD cycles, and the phase relationship (ψ) of the peak of eclosion with respect to “lights‐on” of the LD cycle was significantly different in the three periodic light regimes (T20, T24, and T28). The results thus clearly demonstrate that these flies have preserved the ability to exhibit circadian rhythm of eclosion and the ability to entrain to a wide range of periodic LD cycles even after being in an aperiodic environment for several hundred generations. This suggests that circadian clocks may have intrinsic adaptive value accrued perhaps from coordinating internal metabolic cycles in constant conditions, and that the entrainment mechanisms of circadian clocks are possibly an integral part of the clockwork.

A BINOCULAR STEREOVISION SYSTEM FOR TRANSPLANT GROWTH VARIABLES ANALYSIS

Plug transplant production technology has been widely used in the plant production industry and is continuing to expand in scale. In order to achieve optimal control of the environment for a population of transplants growing in multi–cell plug trays, frequent measurement of the population.s structural and functional properties is required. A binocular stereovision system incorporating two digital cameras and two computers was developed, based on a pixel stereological algorithm, to analyze the aggregate growth variables of a plug tray of transplants. Three–dimensional (3–D) color images of the transplant population were reconstructed from pairs of digital two–dimensional (2–D) color images taken under a constant light environment. Sweet potato (Ipomoea batatas (L.) Lam.) was used as a test plant. Average height, leaf area, projected leaf area, and mass volume of the transplant population were calculated at a pixel level by extracting four user–selected colors. Image analysis took 2 to 3 min for each transplant population measurement. The aggregate growth variables of the transplant population calculated from image analysis correlated closely with corresponding average height, leaf area, and fresh and dry masses determined from destructive measurements. The binocular stereovision system using the pixel stereological algorithm successfully estimated the values of the transplant growth variables. This image analysis method has the potential to automatically provide necessary aggregate transplant physical properties for identifying growth responses to various environmental conditions. This technique will in turn lead to the selection of optimum environmental conditions for transplant growth.

Diurnal Regulation of Leaf Blade Elongation in Rice by CO2 (Is it Related to Sucrose-Phosphate Synthase Activity?).

The relationship between leaf blade elongation rates (LER) and sucrose-phosphate synthase (SPS) activity was investigated at different times during ontogeny of rice (Oryza sativa L. cv Jarrah) grown in flooded soil at either 350 or 700 [mu]L CO2 L-1. High CO2 concentrations increased LER of expanding blades and in vivo activity (Vlimiting) SPS activity of expanded blades during the early vegetative stage (21 d after planting [DAP]), when tiller number was small and growing blades were strong carbohydrate sinks. Despite a constant light environment, there was a distinct diurnal pattern in LER, Vlimiting SPS activity, and concentration of soluble sugars, with an increase in the early part of the light period and a decrease later in the light period. The strong correlation (r = 0.65) between LER and Vlimiting SPS activity over the diurnal cycle indicated that SPS activity played an important role in controlling blade growth. The higher Vlimiting SPS activity at elevated CO2 at 21 DAP was caused by an increase in the activation state of the enzyme rather than an increase in Vmax. Fructose and glucose accumulated to a greater extent than sucrose at high CO2 and may have been utilized for synthesis of cell-wall components, contributing to higher specific leaf weight. By the mid-tillering stage (42 DAP), CO2 enrichment enhanced Vlimiting and Vmax activities of source blades. Nevertheless, LER was depressed by high CO2, probably because tillers were stronger carbohydrate sinks than growing blades.

Effect of life in a constant light environment on the course of hypertension in Dahl rats

An important goal for biobehavioral scientists is to evaluate treatments that might extend life in the presence and absence of disease. The prototypic example of such a treatment is food restriction. Importantly, we have shown that exposure to a life-long environment of constant light extends life in hamsters with severe, life-threatening heart disease. The purpose of this experiment was to determine whether constant light would also extend the life of rats with an inherited form of hypertension. Constant light neither delayed the progression of hypertension nor extended life in this model. These data suggest that constant light may have a more limited use as an experimental therapeutic modality to extend life as compared to food restriction.

Empires of Time: Calendars, Clocks, and Cultures by Anthony F. Aveni

Book Reviews Empires of Time: Calendars, Clocks, and Cultures. By Anthony F. Aveni. New York: Basic Books, 1989. Pp. ix + 371; illustrations, notes, index. $24.95. Empires of Time is less about technology and technique than about culture. It deals with what we might call cosmic time, the time of the gods and the links between human societies and the heavens. It says much more about calendars than about clocks, much more about longer periods than about the hours and minutes of everyday life. Anthony Aveni is professor of astronomy and anthropology in Colgate University, but his heart and the heart of this book lie on the side of anthropology. We learn, to begin with, about natural bio­ rhythms, of animals and plants as well as people: about fruit flies that emerge from their pupal case at the same time of day, even if they have been subjected to a constant light environment for generations; about oysters that open their shells for a longer period of time when the sea is high than when it is low (and not because of water pressure, for they continue this pattern long after being removed from their ocean home and then adjust it to the appropriate times for their new location, as though there were an ocean there). The most astonishing example is the lowly potato. According to Aveni, experimental biologists have charted its metabolism by measuring the rate at which it uses oxygen. They removed the sprouting eyes and sealed them away from changes in light, temperature, pressure, and humidity; even so, the eyes kept the same cycle as before, apparently reflecting not only the position of the sun but also seasonal changes and barometric variations. According to these researchers, the potato eyes responded not only to current pressures but to barometric pressures two days later. After this chapter of surprises, Aveni takes us into the world of men, back to prehistoric cave dwellers who may or may not have counted days and calculated lunations; to the ancient Greeks and Hebrews and the builders of Stonehenge, whose intentions have also been the subject of imaginative if not fanciful conjecture; to the definition of nature’s and man’s cycles—the year, the week, the days, in short the calendar. The second half of the book is given over to others—most of it to the peoples of pre-Columbian America: Mayas, Aztecs, Incas. The discussion ends with a brief chapter on China, rather out of place, and an epilogue on the meaning of these attempts Permission to reprint a review printed in this section may be obtained only from the reviewer. 596 TECHNOLOGY AND CULTURE Book Reviews 597 to make sense of the heavens for the uses of this earth. Aveni sees these attempts as a response to a universal need that even our Western civilization is not exempt from: the need to find regularities in nature that mark (help us predict) the critical points in our own lives—time to sow, time to reap, time to hunker down, time to reemerge. The function of the calendar in each of these earlier civilizations is to establish control or compensate for the lack of it. Aveni also notes the political aspect: that the effect, if not the intent, of calendrical development and time standards is control of the society as well as of nature and the cosmos; that in ancient societies, for example, esoteric temporal knowledge monopolized by a small hieratic elite was an aspect and tool of domination by its possessors. But bad as these societies were, we are worse: “Today the rigid control of human time is still powered largely by the business of making money in a highly industrialized, technological world. . . . Since time must be controlled minute by minute, second by second, in our complicated world, we universalize it so all can march in lockstep. Just as, to survive, we develop systems of population control, crop control, and control in the distribution of wealth, so, too, we have perfected time control” (p. 335). Aveni is one of those—and they are legion— who feel that we in the West have become prisoners of time, have cut ourselves off from natural...

Growth and Development Temperature Influences Level of Tolerance to High Light Stress

The influence of growth and development temperature on the relative tolerance of photosynthetic tissue to high light stress at chilling temperatures was investigated. Two tuber-bearing potato species, Solanum tuberosum L. cv Red Pontiac and Solanum commersonii were grown for 4 weeks, at either 12 or 24 degrees C with 12 hours of about 375 micromoles per second per square meter of photosynthetically active radiation. Paired leaf discs were cut from directly across the midvein of leaflets of comparable developmental stage and light environment from each species at each growth temperature treatment. One disc of each pair was exposed to 1 degrees C and about 1000 micromoles per second per square meter photosynthetically active radiation for 4 hours, and the other disc was held at 1 degrees C in total darkness for the same duration. Photosynthetic tissue of S. tuberosum, developed at 12 degrees C, was much more tolerant to high light and low temperature stress than tissue developed under 24 degrees C conditions. Following the high light treatment, 24 degrees C-grown S. tuberosum tissue demonstrated light-limited and light-saturated rates that were approximately 50% of their paired dark controls. In contrast, the 12 degrees C-grown tissue from S. tuberosum that was subjected to the light stress showed only a 18 and 6% reduction in light-limited and light-saturated rates of photosynthetic oxygen evolution, respectively. Tissue from 24 degrees C-grown S. commersonii was much less sensitive to the light stress than was tissue from S. tuberosum grown under the same conditions. The results presented here demonstrate that: (a) acclimation of S. tuberosum to lower temperature growth conditions with a constant light environment, results in the increased capacity of photosynthetic tissue to tolerate high light stress at chilling temperature and (b) following growth and development at relatively high temperatures S. commersonii, a frost- and heat-tolerant wild species, has a much greater tolerance to the high light stress at chilling temperature than does S. tuberosum cv Red Pontiac, a frost-sensitive cultivated species.

Circadian rhythm of vasopressin levels in cerebrospinal fluid of the fetus: effect of continuous light.

We have measured the concentrations of vasopressin in sequential samples of cerebrospinal fluid (CSF) obtained from fetal lambs between 108 and 130 days gestation. There was a clear and significant (F = 4.46; P less than 0.005) rhythm in vasopressin concentrations in the CSF of nine fetuses, characterized by a mean trough value of 19.4 +/- 6.4 pg/ml (mean +/- SD) at 0200 h and a peak value of 41.1 +/- 28.0 pg/ml at 1400 h. The mean cycle length was 23.2 +/- 1.7 h, with the majority (greater than 80%) of peak concentrations found during daylight hours. There were no concurrent fluctuations in concentrations of vasopressin in plasma or Na, K, Cl, or osmolality in CSF. To examine the relationship between environmental cycles of light and darkness and rhythm of vasopressin concentrations in CSF, pregnant animals were maintained in a constant light environment. In the five fetuses of ewes maintained under these conditions, the rhythm of vasopressin in CSF was markedly damped or not apparent (F = 1.50; P greater than 0.15). These results demonstrate that prominent circadian rhythm of vasopressin in the CSF of the fetus in utero. Despite the fact that the fetus is sequestered from direct influences of the environment, exposure of the pregnant ewe to constant light disrupts the fetal pacemaker that generates the circadian rhythm of vasopressin in CSF. Studies of this rhythm in the fetal lamb, therefore, provide a means to examine the mechanisms of entrainment and assess prenatal influences on circadian organization of the fetus.

Seesaw signal processing in pineal cells: homologous sensitization of adrenergic stimulation of cyclic GMP accompanies homologous desensitization of beta-adrenergic stimulation of cyclic AMP.

Studies of the adrenergic regulation of cyclic GMP in the pineal gland show that (-)-norepinephrine stimulates cyclic GMP primarily in pineal cells, rather than in nerve endings as previously thought. The response exhibits the interesting and unusual characteristic of homologous sensitization: It is maintained by neural stimulation and disappears gradually as a consequence of depressed neural stimulation, due to denervation or decentralization of the superior cervical ganglia or to constant light. The response is restored in intact animals that had been in a constant-light environment when they are returned to a normal light cycle and in ganglionectomized animals by norepinephrine treatment. These findings are especially interesting because the pineal adrenergic--cyclic AMP stimulus--response system exhibits homologous desensitization. The occurrence of homologous sensitization of a cyclic GMP response and desensitization of a cyclic AMP response, which we term seesaw signal processing, in the same tissue or cell has intriguing implications. It provides a mechanism through which the qualitative nature of a multicomponent response can be modified. Such a mechanism could play a role in signal processing by neural or neuroendocrine tissues that release two or more extracellular messages.

The Ultrastructure of the Gerbil Pineal Gland Under Normal and Experimental Conditions

Multilayered concretions (corpora arenacea), which have been found in the pineal gland of numerous species, may be indicative of the intensity of the secretory processes of the pineal gland. Concretions in the pineal gland of the gerbil (Meriones unguiculatus) occur by the age of 2 months and are a consistent feature in the adult animal. We feel the gerbil pineal provides a good system for examining pineal calcification under controlled conditions.The ultrastructure of the pineal gland of the gerbil was examined in 1 to 18 month old gerbils which had been maintained in a controlled light environment (LD 14:10). Other gerbils used for this study had been maintained either in constant light environment, had been superior cervical ganglionectomized, or had been blinded by bilateral optic enucleation.