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Objectives Healthy age-related cognitive changes are highly heterogeneous across individuals. This variability is increasingly explained through the lens of spontaneous fluctuations of brain activity, now considered a powerful index of age-related changes. However, brain activity is a biological process modulated by circadian rhythms, and how these fluctuations evolve throughout the day is under investigation. Methods We analyzed data from 101 healthy late middle-aged participants from the Cognitive Fitness in Aging study (68 women and 33 men; aged 50–69 years). Participants completed 5 electroencephalographic (EEG) recordings of spontaneous resting-state activity on the same day. We used weighted phase-lag index (wPLI) analyses as an index of the functional synchrony between brain regions couplings, and we computed daily global PLI fluctuation rates of the 5 recordings to assess the association with cognitive performance and β-amyloid and tau/neuroinflammation pathological markers. Results We found that theta and gamma daily fluctuations in the salience-control executive internetwork (SN-CEN) are associated with distinct mechanisms underlying cognitive heterogeneity in aging. Higher levels of SN-CEN theta daily fluctuations appear to be deleterious for memory performance and were associated with higher tau/neuroinflammation rates. In contrast, higher levels of gamma daily fluctuations are positively associated with executive performance and were associated with lower rate of β-amyloid deposition. Discussion Thus, accounting for daily EEG fluctuations of brain activity contributes to a better understanding of subtle brain changes underlying individuals' cognitive performance in healthy aging. Results also provide arguments for considering the time of day when assessing cognition for old adults in a clinical context. [ABSTRACT FROM AUTHOR]

A mathematical model of the hypothalamic-pituitary-adrenal (HPA) axis with cholesterol as a dynamical variable was derived to investigate the effects of cholesterol, the primary precursor of all steroid hormones, on the ultradian and circadian HPA axis activity. To develop the model, the parameter space was systematically examined by stoichiometric network analysis to identify conditions for ultradian oscillations, determine conditions under which dynamic transitions, i.e. bifurcations occur and identify bifurcation types. The bifurcations were further characterized using numerical simulations. Model predictions agree well with empirical findings reported in the literature, indicating that cholesterol levels may critically affect the global dynamics of the HPA axis. The proposed model provides a base for better understanding of experimental observations, it may be used as a tool for designing experiments and offers useful insights into the characteristics of basic dynamic regulatory mechanisms that, when impaired, may lead to the development of some modern-lifestyle-associated diseases. [ABSTRACT FROM AUTHOR]

The network of molecular components thought to regulate pollen tube growth presents an almost bewildering array of potential interactions. Damineli et al. (2017) have developed novel tools to help define the relationships between the kinetics of these proposed regulators and growth. They highlight both the insights and the challenges that extracting cause and effect from complex regulatory networks brings [ABSTRACT FROM AUTHOR]

Water availability is a major limiting factor on plant growth and productivity. Considering that Eucalyptus spp. are among the few plant species able to produce both isoprene and monoterpenes, experiments were designed to investigate the response of isoprene emission and isoprenoid concentrations in Eucalyptus citriodora saplings exposed to decreasing fraction of transpirable soil water (FTSW). In particular, this study aimed to assess: (a) the kinetic of water stress-induced variations in photosynthesis, isoprene emission, and leaf isoprenoid concentrations during progressive soil water shortage as a function of FTSW; (b) the ultradian control of isoprene emission and photosynthesis under limited soil water availability; and (c) the optimum temperature sensitivity of isoprene emission and photosynthesis under severe water stress. The optimum temperature for isoprene emission did not change under progressive soil water deficit. However, water stress induced a reallocation of carbon through the MEP/DOXP pathway resulting in a qualitative change of the stored isoprenoids. The ultradian trend of isoprene emission was also unaffected under water stress, and a similar ultradian trend of stomatal and mesophyll conductances was also observed, highlighting a tight coordination between diffusion limitations to photosynthesis during water stress. The kinetics of photosynthetic parameters and isoprene emission in response to decreasing FTSW in E. citriodora are strikingly similar to those measured in other plant functional types. These findings may be useful to refine the algorithms employed in process-based models aiming to precisely up-scale carbon assimilation and isoprenoid emissions at regional and global scales. [ABSTRACT FROM AUTHOR]

BackgroundAbnormal circadian variation of blood pressure (BP) increases cardiovascular risk. In this study, we examined the influence of angiotensin AT1A receptors on circadian BP variation, and specifically on its behavioral activity-related and -unrelated components.MethodsBP and locomotor activity were recorded by radiotelemetry in AT1A-receptor knockout mice (AT1A−/−) and their wild-type controls (AT1A+/+) placed on a normal-salt diet (NSD) or high-salt diet (HSD, 3.1% Na).ResultsThe 24-h BP was lower in AT1A−/− than AT1A+/+ mice on a NSD (92 ± 2 and 118 ± 2 mm Hg, respectively), whereas the day–night BP difference (ΔDNBP) was similar between groups (11 ± 2 and 12 ± 1 mm Hg, respectively). HSD increased BP by 20 ± 2 mm Hg and ΔDNBP by 7 ± 1 mm Hg in AT1A−/− mice, without affecting these parameters much in AT1A+/+ mice. The ΔDNBP increase in AT1A−/− mice was caused by nondipping BP during the inactive late-dark period. Conversely, BP rise associated with circadian behavioral activation during the early dark period was not altered by HSD in AT1A−/− mice. The BP change associated with spontaneous ultradian activity–inactivity bouts was also similar between strains on HSD as was the BP rise associated with induced (cage-switch) behavioral activity. Ganglionic or α1-adrenergic blockade decreased BP in both strains; HSD did not affect this response in AT1A−/−, but abolished it in AT1A+/+ mice.ConclusionsAT1A-receptor deficiency, when combined with HSD, can increase circadian BP difference in mice. This increase is mediated principally by activity-unrelated factors, such as the nonsuppressibility of basal resting sympathetic tone by HSD, thus suggesting a form of salt-/volume-dependent hypertension.American Journal of Hypertension 2010; doi:10.1038/ajh.2010.12 [ABSTRACT FROM AUTHOR]

In this article, we have developed a simple mathematical model that captures the vital mechanisms of the hypothalamic-pituitary-adrenal (HPA) axis self-regulatory activities. For this, a system of three-component non-linear delay differential equations has been proposed and analysed to observe the ultradian and circadian variabilities of the hormone secretion of the HPA axis in normal subjects. Our analysis reveals that a feedback mechanism is sufficient to show the ultradian variability of the hormone secretion pattern but fails to show the circadian variability. A central nervous system-driven pulse generator coupled with the primary feedback mechanism can exhibit the ultradian as well as circadian variability in the hormone secretion of the HPA axis. The model can also predict different dynamics of the normal HPA axis following physiological changes (viz. adrenalectomy and hypophysectomy) and pathological changes (viz. infusion of different hormones). [ABSTRACT FROM AUTHOR]

While the general steps of fatty acid (FA) biosynthesis are well understood, the individual enzymes involved in the elongation of long chain saturated and polyunsaturated FA (PUFA) are largely unknown. Recent research indicates that these enzymes might be of considerable physiological importance for human health. We use Caenorhabditis elegans to study FA elongation activities and associated abnormal phenotypes. In this article we report that the predicted C. elegans F11E6.5/ELO-2 is a functional enzyme with the FA elongation activity. It is responsible for the elongation of palmitic acid and is involved in PUFA biosynthesis. RNAi-mediated suppression of ELO-2 causes an accumulation of palmitate and an associated decrease in the PUFA fraction in triacylglycerides and phospholipid classes. This imbalance in the FA composition results in multiple phenotypic defects such as slow growth, small body size, reproductive defects, and changes in rhythmic behavior. ELO-2 cooperates with the previously reported ELO-1 in 20-carbon PUFA production, and at least one of the enzymes must function to provide normal growth and development in C. elegans. The presented data indicate that suppression of a single enzyme of the FA elongation machinery is enough to affect various organs and systems in worms. This effect resembles syndromic disorders in humans. [ABSTRACT FROM AUTHOR]

The effects of night shift schedules on circadian time structure of blood pressure were studied in seven healthy young subjects by continuous monitoring of blood pressure every 30 min for 72 h. In the control experiment, subjects were instructed to sleep at regular times with the light off at 00.00 h and the light on at 07.00 h. In the shift experiment, they were instructed to go to bed at 06.00 h and wake up at 11.00 h. The circadian rhythm of blood pressure rapidly phase delayed by 3.5 h in the second night shift day as a group phenomenon. Individual differences in changes in power spectral patterns of blood pressure were found in the night shift schedule. Ultradian rhythmicity of blood pressure was more pronounced in three subjects, whereas the circadian rhythmicity was maintained in four subjects. These findings held when the adaptation to shift work was taken into account. [ABSTRACT FROM PUBLISHER]

Using the method of experience sampling, we studied the fluctuations in thought generation and cognitive control strength during the wakeful hours of the day, centered around episodes of mind wandering. Thought generation, measured in terms of the number of thoughts that concurrently occupy the mind at sampling time, goes through regular 4–6 h cycles, suggesting the mind operates with an alternation of focused and multitasking modes. Cognitive control strength rises and falls in relative coordination with thought generation, implying that both are occasionally misaligned. This happens, in particular, when cognitive control suddenly drops after having been keeping up with a cycle of thought generation. When this drop occurs while the thought generation cycle is still up, mind wandering appears. As cognitive control quickly resumes before returning to intermediate values, the thought generation cycle begins to fall again, and the mind wandering episode comes to an end. Implications regarding the role of long-term regulation in mind-wandering processes are discussed. [ABSTRACT FROM AUTHOR]