Abraham Haim

Light at night increases body mass by shifting the time of food intake

The global increase in the prevalence of obesity and metabolic disorders coincides with the increase of exposure to light at night (LAN) and shift work. Circadian regulation of energy homeostasis is controlled by an endogenous biological clock that is synchronized by light information. To promote optimal adaptive functioning, the circadian clock prepares individuals for predictable events such as food availability and sleep, and disruption of clock function causes circadian and metabolic disturbances. To determine whether a causal relationship exists between nighttime light exposure and obesity, we examined the effects of LAN on body mass in male mice. Mice housed in either bright (LL) or dim (DM) LAN have significantly increased body mass and reduced glucose tolerance compared with mice in a standard (LD) light/dark cycle, despite equivalent levels of caloric intake and total daily activity output. Furthermore, the timing of food consumption by DM and LL mice differs from that in LD mice. Nocturnal rodents typically eat substantially more food at night; however, DM mice consume 55.5% of their food during the light phase, as compared with 36.5% in LD mice. Restricting food consumption to the active phase in DM mice prevents body mass gain. These results suggest that low levels of light at night disrupt the timing of food intake and other metabolic signals, leading to excess weight gain. These data are relevant to the coincidence between increasing use of light at night and obesity in humans.

Light at Night Co‐distributes with Incident Breast but not Lung Cancer in the Female Population of Israel

Recent studies of shift‐working women have reported that excessive exposure to light at night (LAN) may be a risk factor for breast cancer. However, no studies have yet attempted to examine the co‐distribution of LAN and breast cancer incidence on a population level with the goal to assess the coherence of these earlier findings with population trends. Coherence is one of Hills “criteria” (actually, viewpoints) for an inference of causality. Nighttime satellite images were used to estimate LAN levels in 147 communities in Israel. Multiple regression analysis was performed to investigate the association between LAN and breast cancer incidence rates and, as a test of the specificity of our method, lung cancer incidence rates in women across localities under the prediction of a link with breast cancer but not lung cancer. After adjusting for several variables available on a population level, such as ethnic makeup, birth rate, population density, and local income level, a strong positive association between LAN intensity and breast cancer rate was revealed (p<0.05), and this association strengthened (p<0.01) when only statistically significant factors were filtered out by stepwise regression analysis. Concurrently, no association was found between LAN intensity and lung cancer rate. These results provide coherence of the previously reported case‐control and cohort studies with the co‐distribution of LAN and breast cancer on a population basis. The analysis yielded an estimated 73% higher breast cancer incidence in the highest LAN exposed communities compared to the lowest LAN exposed communities.

GLOBAL CO-DISTRIBUTION OF LIGHT AT NIGHT (LAN) AND CANCERS OF PROSTATE, COLON, AND LUNG IN MEN

The incidence rates of cancers in men differ by countries of the world. We compared the incidence rates of three of the most common cancers (prostate, lung, and colon) in men residing in 164 different countries with the population‐weighted light at night (LAN) exposure and with several developmental and environmental indicators, including per capita income, percent urban population, and electricity consumption. The estimate of per capita LAN exposure was a novel aspect of this study. Both ordinary least squares (OLS) and spatial error (SE) regression models were used in the analysis. We found a significant positive association between population exposure to LAN and incidence rates of prostate cancer, but no such association with lung cancer or colon cancer. The prostate cancer result is consistent with a biological theory and a limited number of previous studies of circadian disruption and risk. The LAN‐prostate cancer connection is postulated to be due to suppression of melatonin and/or disruption of clock gene function. An analysis holding other variables at average values across the 164 countries yielded a risk of prostate cancer in the highest LAN‐exposed countries 110% higher than in the lowest LAN exposed countries. This observed association is a necessary condition for a potentially large effect of LAN on risk of prostate cancer. However, it is not sufficient due to potential confounding by factors that increase the risk of prostate cancer and are also associated with LAN among the studied countries.

Seasonal Thermogenic Acclimation of Diurnally and Nocturnally Active Desert Spiny Mice

Diurnally active golden spiny mice (Acomys russatus) and nocturnal common spiny mice (Acomys cahirinus) coexist in hot rocky deserts of Israel. Diurnal and nocturnal activities expose these species to different climatic conditions. Nonshivering thermogenesis (NST) capacity of individuals of both species immediately upon removal from the field exhibited seasonal changes, with no significant interspecific difference. Colony‐reared mice of either species transferred in the laboratory from long to short photoperiod increased NST capacity, though to a lesser extent than observed in the seasonal acclimatization. The underlying biochemical mechanisms of short photoperiod acclimation differed between the species. In both Cytochrome‐c oxidase (Cox) activity was higher in short as compared to long photoperiod. In short‐photoperiod‐acclimated A. cahirinus uncoupling protein (UCP) content in brown adipose tissue (BAT) was significantly higher than in long photoperiod, while in A. russatus there was no significant change. In A. russatus there was a significant increase in lipoprotein lipase (LPL) activity in BAT in short‐photoperiod‐acclimated individuals, while in A. cahirinus LPL activity was high under both acclimations. The low LPL activity in brown adipose tissue of desert‐adapted A. russatus may facilitate lipid uptake in white adipose tissue, an advantage in desert conditions where food is scarce and irregularly distributed in space and time.

Inter- and intraindividual variation in daily energy expenditure of the pouched mouse (Saccostomus campestris)

1. We measured the simultaneous energy expenditure of five male and six female pouched mice (Saccostomus campestris), over 3 consecutive days, using the doubly labelled water (DLW) technique. The aim was to assess the interindividual scaling of daily energy demands and also the repeatability of measures of daily energy expenditure when using doubly labelled water. 2. Individual mice were housed in cages, given free access to food and water and were kept in a natural photoperiod (February at 26°S) at a mean temperature of 26.5°C (daily range 25-28°C). 3. Males were significantly heavier than the females, as is typical in this species. Mean energy expenditure (Watts) (single-pool model) over 3 days, across individuals, was positively related to body mass (reduced major axis scaling exponent b = 1.96) and to change in body mass over the 3 days

Nighttime light level co-distributes with breast cancer incidence worldwide

Breast cancer incidence varies widely among countries of the world for largely unknown reasons. We investigated whether country-level light at night (LAN) is associated with incidence. We compared incidence rates of five common cancers in women (breast, lung, colorectal, larynx, and liver), observed in 164 countries of the world from the GLOBOCAN database, with population-weighted country-level LAN, and with several developmental and environmental indicators, including fertility rate, per capita income, percent of urban population, and electricity consumption. Two types of regression models were used in the analysis: Ordinary Least Squares and Spatial Errors. We found a significant positive association between population LAN level and incidence rates of breast cancer. There was no such an association between LAN level and colorectal, larynx, liver, and lung cancers. A sensitivity test, holding other variables at their average values, yielded a 30–50% higher risk of breast cancer in the highest LAN exposed countries compared to the lowest LAN exposed countries. The possibility that under-reporting from the registries in the low-resource, and also low-LAN, countries created a spurious association was evaluated in several ways and shown not to account for the results. These findings provide coherence of the previously reported case–control and cohort studies with the co-distribution of LAN and breast cancer in entire populations.

Melatonin as an antioxidant and its semi-lunar rhythm in green macroalga Ulva sp.

The presence and role of melatonin in plants are still under debate owing to difficulties of identification and quantification. Accordingly, although it has been frequently proposed that melatonin acts as an antioxidant in phototrophic organisms, experimental data on its physiological role are scarce. This study describes the use of a rapid and simple new method for quantification of melatonin in the marine macroalga Ulva sp., organisms routinely exposed to tide-related environmental stresses and known for their high tolerance to abiotic conditions. The method was used here to show that exposure to oxidative stress-inducing environmental conditions (elevated temperature and heavy metals) induced a rise in melatonin level in the algae. Addition of exogenous melatonin alleviated the algae from cadmium-induced stress. Interestingly, although the algae were taken from a culture growing free floating and kept under constant photoperiod and water level, they exhibited a semi-lunar rhythm of melatonin levels that correlated with predicted spring tides. The correlation can probably be interpreted as reflecting preparation for predicted low tides, when the algae are exposed to increasing temperature, desiccation, and salinity, all known to induce oxidative stress. Given the simplicity of the described method it can easily be adapted for the study of melatonin in many other phototrophic organisms. These results provide, for the first time, experimental data that support both an antioxidant role for melatonin and its semi-lunar rhythm in macroalgae.

Dim light at night provokes depression-like behaviors and reduces CA1 dendritic spine density in female hamsters

The prevalence of major depression has increased in recent decades; however, the underlying causes of this phenomenon remain unspecified. One environmental change that has coincided with elevated rates of depression is increased exposure to artificial light at night. Shift workers and others chronically exposed to light at night are at increased risk of mood disorders, suggesting that nighttime illumination may influence brain mechanisms mediating affect. We tested the hypothesis that exposure to dim light at night may impact affective responses and alter morphology of hippocampal neurons. Ovariectomized adult female Siberian hamsters (Phodopus sungorus) were housed for 8 weeks in either a light/dark cycle (LD) or a light/dim light cycle (DM), and then behavior was assayed. DM-hamsters displayed more depression-like responses in the forced swim and the sucrose anhedonia tests compared with LD-hamsters. Conversely, in the elevated plus maze DM-hamsters reduced anxiety-like behaviors. Brains from the same animals were processed using the Golgi-Cox method and hippocampal neurons within CA1, CA3, and the dentate gyrus were analyzed for morphological characteristics. In CA1, DM-hamsters significantly reduced dendritic spine density on both apical and basilar dendrites, an effect which was not mediated by baseline cortisol, as concentrations were equivalent between groups. These results demonstrate dim light at night is sufficient to reduce synaptic spine connections to CA1. Importantly, the present results suggest that night-time low level illumination, comparable to levels that are pervasive in North America and Europe, may contribute to the increasing prevalence of mood disorders.

The ecological significance of resting metabolic rate and non-shivering thermogenesis for rodents

Abstract 1. 1. Resting metabolic rates (RMR) lower than those expected for body mass according to allometric equations have been recorded for species of rodents inhabiting arid and semi-arid environments. Such a phenomenon was also noted in non-arid rodent species which are adapted to various modes of life. Non-shivering thermogenesis (NST) is an important mechanism for heart production in small cold-acclimated mammals. 2. 2. The aim of this study was to try to assess the ecological significance of NST by comparing various parameters concerning NST, RMR and overall minimal thermal conductance. The analysis was carried out on data obtained from 21 species, 4 chromosomal types of Spalax ehrenbergi and 2 different populations of Acomys russatus . The studied species were from Israel and South Africa. 3. 3. The analysis revealed that RMR is an adaptive parameter and has an allometric relation with body mass. It depends on habitat and time of activity. Species which have low RMR values show high values of NST.

On the Use of the Time Axis for Ecological Separation: Diel Rhythms as an Evolutionary Constraint

Temporal partitioning as a mechanism of coexistence among competitors has seldom been explored and is considered uncommon (Schoener 1986). Understanding ecological and evolutionary plasticity in use of the temporal niche axis is significant for assessing the potential for temporal partitioning and may be key to understanding the relative rarity of this phenomenon. Daily rhythms in mammalian physiology, hormone concentrations, biochemistry, and behavior are driven by an internal circadian clock that is entrained to the predictable 24-h change in light intensity (Heldmaier et al. 1989; Refinetti et al. 1992; Smith et al. 1998). Entrainment to this overriding cue (“zeitgeber”) allows mammals to choose the right time for a given response or activity without being easily misled by minor environmental disturbances (Aronson et al. 1993). Thus, a degree of rigidity to environmental nonphotic stimuli is built into the circadian system. However, under laboratory conditions, small mammals can be forced to shift their locomotor activity patterns by nonphotic stimuli (Mistlberger 1991; Cambras et al. 1993; Challet et al. 1997; Brinkhof et al. 1998), indicating that activity is not tightly controlled by the circadian clock