Circadian Rhythm

Diurnal activity is characteristic of many toad species, including Bufo granulosus from the Brazilian semi-arid biome called the Caatinga. Because of their patterns of activity, juvenile toads are exposed to hot and dehydrating conditions. Our investigation focuses on temperature and water relationships, and is based on the prediction that anuran diurnal activity in a semi-arid environment must be associated with morphological, physiological and behavioral traits enhancing thermal tolerances, capacity for performance at high temperatures and water balance. To test specific hypothesis related with this prediction, we investigated postmetamorphic B. granulosus and collected data on thermal tolerances and preferences, thermal safety margins, thermal dependence of locomotor behavior, thermal and kinetic properties of citrate synthase (CS), and skin morphophysiology. This information was compared with additional data from adult conspecifics and adult toads from sympatric species or from species from more moderate environments. We found that juvenile B. granulosus exhibit the highest critical maximum temperature reported for toads (44.2°C) and are well suited to move at high temperatures. However, and in contrast with juveniles of other Bufo species, they do not show thermal preferences in a gradient and appear to hydroregulate more than thermoregulate. The CS of adult and juvenile toads shows typical patterns of thermal sensibility, but the thermal stability of this enzyme is much higher in juveniles than in adult Bufo of any other species studied. The inguinal skin exhibits a complex folding pattern and seems highly specialized for capillary water uptake. Diurnal activity in juvenile B. granulosus is possible given high thermal tolerances, keen ability to detect and uptake water, and avoidance behaviors. Comparative Biochemistry and Physiology, Part A 147 (2007) 647 -657 www.elsevier.com/locate/cbpa ☆ This paper is part of the 3rd special issue of CBP dedicated to The Face of Latin American Comparative Biochemistry and Physiology organized by Marcelo Hermes-Lima (Brazil) and co-edited by Carlos Navas (Brazil), Rene Beleboni (Brazil), Rodrigo Stabeli (Brazil), Tania Zenteno-Savín (Mexico) and the editors of CBP. This issue is dedicated to the memory of two exceptional men, Peter L. Lutz, one of the pioneers of comparative and integrative physiology, and Cicero Lima, journalist, science lover and Hermes-Lima's dad.

It has been established that 4.4 to 20% of the general population suffers from a major depressive disorder (MDD), which is frequently associated with a dysregulation of normal sleep-wake mechanisms. Disturbances of circadian rhythms are a cardinal feature of psychiatric dysfunctions, including MDD, which tends to indicate that biological clocks may play a role in their pathophysiology. Thus, episodes of depression and mania or hypomania can arise as a consequence of the disruption of zeitgebers (time cues). In addition, the habit of sleeping at a time that is out of phase with the body's other biological rhythms is a common finding in depressed patients. In this review, we have covered a vast area, emerging from human and animal studies, which supports the link between sleep and depression. In doing so, this paper covers a broad range of distinct mechanisms that may underlie the link between sleep and depression. This review further highlights the mechanisms that may underlie such link (e.g. circadian rhythm alterations, melatonin, and neuroinflammatory dysregulation), as well as evidence for a link between sleep and depression (e.g. objective findings of sleep during depressive episodes, effects of phar-macotherapy, chronotherapy, comorbidity of obstructive sleep apnea and depression), are presented.

The possible effects of blue light during acute hypoxia and the circadian rhythm on several physiological and cognitive parameters were studied. Fifty-seven volunteers were randomly assigned to 2 groups: nocturnal (2200-0230 hours) or diurnal (0900-1330 hours) and exposed to acute hypoxia (4000 m simulated altitude) in a hypobaric chamber. The participants were illuminated by blue LEDs or common artificial light on 2 different days. During each session, arterial oxygen saturation (Spo2), blood pressure, heart rate variability, and cognitive parameters were measured at sea level, after reaching the simulated altitude of 4000 m, and after 3 hours at this altitude. The circadian rhythm caused significant differences in blood pressure and heart rate variability. A 4% to 9% decrease in waking nocturnal Spo2 under acute hypoxia was observed. Acute hypoxia also induced a significant reduction (4%-8%) in systolic pressure, slightly more marked (up to 13%) under blue lighting. Women had significantly increased systolic (4%) and diastolic (12%) pressures under acute hypoxia at night compared with daytime pressure; this was not observed in men. Some tendencies toward better cognitive performance (d2 attention test) were seen under blue illumination, although when considered together with physiological parameters and reaction time, there was no conclusive favorable effect of blue light on cognitive fatigue suppression after 3 hours of acute hypobaric hypoxia. It remains to be seen whether longer exposure to blue light under hypobaric hypoxic conditions would induce favorable effects against fatigue.

Sleep-wake abnormalities are common in patients with cirrhosis but their evaluation is time consuming and laborious. The aim of this study was to assess the validity of a simple Sleep Timing and Sleep Quality Screening questionnaire (STSQS) against an established sleep quality questionnaire and daily sleep diaries.

Purpose: To assess the relationship between nocturnal plasma melatonin and serum estradiol (E 2 ) and progesterone (P 4 ) levels in depressed pregnant women (DW) and matched healthy women (HW). Methods: We used analysis of variance (ANOVA) and linear regression analyses on data obtained from pregnant HW and DW. Results: Log E 2 and log P 4 were positively correlated with measures of melatonin quantity in HW ( p < 0.05) but not DW, controlling for age. Log E 2 and log P 4 were positively correlated with melatonin offset and duration in DW ( p < 0.01) but not HW. Conclusions: Pregnant DW may be less sensitive than HW to modulation of melatonin secretion by E 2 and P 4 . That melatonin timing measures are more sensitive to E 2 and P 4 variation in DW may reflect a circadian system more attuned to the need for realignment in DW than in HW. These altered sensitivities to reproductive hormones may reflect a biologic vulnerability that predisposes some pregnant women to depression.