Basic concepts and unique features of human circadian rhythms: implications for human health

Most physiological functions and behaviors exhibit a robust approximately 24-hour rhythmicity (circadian rhythm) in the real world. These rhythms persist under constant conditions, but the period is slightly longer than 24 hours, suggesting that circadian rhythms are endogenously driven by an internal, self-sustained oscillator. In mammals, including humans, the central circadian pacemaker is located in the hypothalamic suprachiasmatic nucleus. The primary zeitgeber for this pacemaker is bright sunlight, but nonphotic time cues also affect circadian rhythms. The human circadian system uniquely exhibits spontaneous internal desynchronization between the sleep-wake cycle and core body temperature rhythm under constant conditions and partial entrainment of the sleep-wake cycle in response to nonphotic time cues. Experimental and clinical studies of human circadian rhythms must take into account these unique features. This review covers the basic concepts and unique features of the human circadian system, the mechanisms underlying phase adjustment of the circadian rhythms by light and nonphotic time cues (eg, physical exercise), and the effects of eating behavior (eg, chewing frequency) on the circadian rhythm of glucose metabolism.

Obstacle avoidance in bumblebees is robust to changes in light intensity

Flying safely and avoiding obstacles in low light is crucial for the bumblebees that forage around dawn and dusk. Previous work has shown that bumblebees overcome the limitations of their visual system—typically adapted for bright sunlight—by increasing the time over which they sample photons. While this improves visual sensitivity, it decreases their capacity to resolve fast motion. This study investigates what effect this has on obstacle avoidance in flight, a task that requires the bees to reliably detect obstacles in the frontal visual field and to make a timely diversion to their flight path. In both bright and dim light, bumblebees avoided the 5 cm diameter obstacle at a consistent distance (22 cm) although in dim light they approached it more slowly from a distance of at least at least 80 cm. This suggests that bumblebees have an effective strategy for avoiding obstacles in all light conditions under which they are naturally active, and it is hypothesised that this is based on a time-to-contact prediction.

Advanced Ocular Lesions in Growing Calves with Avitaminosis A

A beef cattle farm was visited due to blindness in a group of 28 calves aged 10-12 months. According to farmer, the first blind calves were observed about 20 days before and no sign of lacrimation or corneal opacity was observed. He first noticed that 3 calves were disoriented, hitting on the pen walls and preferred to stand near the feed and water troughs. Gradually, more than half of calves of this group developed similar signs. The calves were fed ad libitum with wheat straw and a homemade concentrate mixture consisting of corn, wheat bran, soybean meal and a mixture of vitamins and trace minerals. The mixture was added at the concentrate feed at the 1/10 of the recommended dosage. At animals’ inspection it was revealed that 18 out of 28 had the ocular lesions presented in (Figures 1 and 2). They were characterized by bilateral exophthalmos with dilated pupils. The degree of exophthalmos varied among animals. The pupils were unresponsive even in bright sunlight and the menace response was absent. The observed ocular lesions are typical of a vitaminosis A in young calves [1-3]. Blindness and absence of the pupillary light reflex are the result of optic nerve necrosis caused by stenosis of the optic foramen due to failure of bone resorption and increase inosteoblastic activity [1-4]. Exophthalmos is always bilateral, with the most advanced cases showing a prominent eye with large area of sclera visible all around cornea. It is regarded that protruding eyes are the result of blindness alone since no macroscopic lesions are observed at retro bulbar tissues [3]. Such advanced lesions are not reversible [1-3]; so, it was recommended all the affected animals to be slaughtered. It was suggested the rest of the animals to be treated with injectable administration of vitamin A along with the inclusion of the mixture of vitamins and trace minerals at the appropriate dosage in the concentrates.

On the impact of seasonal solar activity on the progression of retinopathy of prematurity: preliminary research results

Purpose. To study the effect of bright sunlight on immature retina of a premature baby at different periods of solar activity.Material and methods. The study involved two groups of premature babies: 32 babies (64 eyes) in 2016 and 50 babies (100 eyes) in 2017. Both groups were tested using a retinal camera (RetCam Shuttle, USA) on the 3rd or 4th week after birth. In cases of threshold stages of retinopathy of prematurity (ROP) binocular ophthalmoscopy were performed. In such cases, laser coagulation of the retina was performed using "ALOD 01" (ALCOM Medica, Russia).Results. The greatest number of ROP with the greatest number of surgical interventions and adverse outcomes that required vitreoretinal surgery were revealed in the second seasonal period (May — August), which experienced the highest solar activity. In 2016, the amount of ROP cases diagnosed in this period amounted to 59 %, which is comparable with the corresponding amount revealed in 2017 (61.1 %).Conclusions. Stronger solar activity and its longer periods increase the risk of ROP; consequently, to prevent this pathology, the eyes of the newborn should be protected from the negative effects of daylight and artificial light, including that emitted by diagnostic equipment.

Associations between outdoor temperature and bright sunlight with metabolites in two population-based European cohorts

Context: Outdoor temperature and bright sunlight may directly and/or indirectly modulate systemic metabolism.Objective: We assessed the associations between outdoor temperature and bright sunlight duration with metabolomics.Design: meta-analysis of two cross-sectional studies.Setting: Two population-based European cohort studies.Patients or other participants: Non-diabetic individuals from the Oxford BioBank (OBB; N=6,368; mean age 47.0 years, males 44%) and the Netherlands Epidemiology of Obesity (NEO; N=5,916; mean age 55.6 years, males 43%) studies.Intervention(s): Data on mean outdoor bright sunlight and temperature collected from local weather stations in the week prior to blood sampling.Main Outcome Measure(s): Serum levels of 148 metabolites measured using NMR spectroscopy, including 14 lipoprotein subclasses.Statistical analyses: Multivariable linear regression analyses adjusted for age, sex, body mass index, season and either outdoor temperature or bright sunlight. Summary statistics from the OBB and NEO cohorts were combined using fixed-effect meta-analyses.Results: A higher mean outdoor temperature was associated with increased concentrations of lipoprotein (sub)particles and certain amino acids such as phenylalanine and leucine. In contrast, longer mean hours of bright sunlight were specifically associated with lower concentrations of very low density lipoprotein (sub)particles. The direction of effects was consistent between the OBB and NEO, although effect sizes were generally larger in the OBB.Conclusions: Increased bright sunlight duration is associated with an improved metabolic profile whilst higher outdoor temperature may adversely impact cardiometabolic health.

Learning to navigate – how desert ants calibrate their compass systems

Navigating through the environment is a challenging task that animals cope with on a daily basis. Many animal species have impressive capabilities to navigate in complex or even harsh environments. Cataglyphis desert ants are a famous example. These ants use a remarkable navigational repertoire to find their way home after far-reaching foraging trips. How do naïve ants calibrate their visual navigational systems? The ants perform stereotyped sequences of learning walks before switching from tasks inside the darkness of their nest, to foraging under bright sunlight. Here, naïve ants align nest-directed views using the earth’s magnetic field as a compass reference. Neuronal plasticity was mapped in two visual pathways to higher brain centers during this transition. Both their first exposure to light, and the performance of learning walks lead to distinct changes in synaptic circuits along both visual pathways, reflecting calibration and memory formation in the ants’ visual compass systems.

Contagious keratoconjuctivitis in goats due to Branhamella (Moraxella) ovis

Incidents of contagious kerato conjuctivitis in two flocks of goats in Chalkidiki Prefecture are described. The disease was only observed in young animals approximately two years of age. The early signs were excessive lacrimation, photophobia and blepharospasm, while the bright sunlight was revealed irritating for the affected eyes. Conjunctivitis and mucopurulent secretion was also observed at the late stage of the disease. Many animals with keratitis end up totally blind. The infection of the eyes was either lateral of bilateral. Branhamella ovis was isolated in almost pure culture, from lacrimal secretion in a large number of samples (32/35). The identification was based on the organism's morphology, cultural behaviour and biochemical reactions. The microbiological examination of the samples revealed only one kind of isolate. No other organisms that could cause similar clinical findings were isolated. Therefore, it was assumed that the etiological agent of the described cases was B.ovis. It is possible that certain environmental agents such as dust, flies or bright sunlight, that were present at that time of the year because of the prolonged summer, acted as predisposing factors. Although the disease exists in our country for years, it is the first time that the pathogen agent has been isolated and identified. A successful treatment was performed at the early stage of the disease by the topical application of antibiotics.