Diurnal rhythms of urine volume and electrolyte excretion in healthy young men under differing intensities of daytime light exposure.

In humans, most renal functions, including urine volume and electrolyte excretions, have a circadian rhythm. Light is a strong circadian entrainment factor and daytime-light exposure is known to affect the circadian rhythm of rectal temperature (RT). The effects of daytime-light exposure on the diurnal rhythm of urinary excretion have yet to be clarified. The aim of this study was to clarify whether and how daytime exposure to bright-light affects urinary excretions. Twenty-one healthy men (21-27 years old) participated in a 4-day study involving daytime (08:00-18:00 h) exposure to two light conditions, Dim (< 50 lx) and Bright (~ 2500 lx), in a random order. During the experiment, RT was measured continuously. Urine samples were collected every 3 ~ 4 h. Compared to the Dim condition, under the Bright condition, the RT nadir time was 45 min earlier (p = 0.017) and sodium (Na), chloride (Cl), and uric acid (UA) excretion and urine volumes were greater (all p < 0.001), from 11:00 h to 13:00 h without a difference in total daily urine volume. The present results suggest that daytime bright light exposure can induce a phase shift advance in urine volume and urinary Na, Cl, and UA excretion rhythms.

Response of brain-derived neurotrophic factor to combining cognitive and physical exercise.

PURPOSE: Brain-derived neurotrophic factor (BDNF) is well known for its potential to promote brain plasticity. It has been proposed that combining cognitive and physical exercise (CCPE) may have the potential to generate more synergistic benefits in cognitive function than either cognitive exercise (CE) or physical exercise (PE) alone. The purpose of this study was to examine acute responses of peripheral BDNF levels and cognitive performance to CE, PE, and CCPE. METHODS: Thirteen healthy adult men participated in four experimental sessions; a 30-min CE, a 30-min cycling PE at an intensity of 60% peak oxygen uptake, a 30-min CCPE at the same intensity as PE, and a 30-min session of complete rest. Plasma BDNF levels and cognitive performance were measured before and after each session. RESULTS: Both PE and CCPE significantly increased plasma BDNF levels (p < .05). CE led to no significant increase (p ≥ .05), and there was no significant difference in peripheral BDNF levels between PE and CCPE (p ≥ .05). No session induced a significant change in cognitive performance (p ≥ .05). CONCLUSIONS: Our study suggests that CE and PE have different responses of peripheral BDNF levels and that CCPE had no additional or synergistic effect on peripheral BDNF levels compared with PE alone. This study offers further insights into the potential mechanisms underlying the respective roles of CE, PE, and CCPE for peripheral BDNF levels and cognitive performance.

Effect of Neuromuscular Electrical Stimulation on Brain-derived Neurotrophic Factor.

Brain-derived neurotrophic factor (BDNF) has been considered an essential mediator responsible for the beneficial effects of physical activity in preventing cognitive impairment. This study aimed at examining the effects of a single bout of neuromuscular electrical stimulation (NMES) on levels of BDNF in the plasma and on cognitive performance in healthy adult men. Thirteen healthy adult men participated in three experimental sessions. The first session was 30 min of NMES to both legs, the second was 30 min of cycling exercise at the intensity of 60% peak oxygen uptake, and the third was 30 min of complete rest. Blood was examined for plasma BDNF levels and glucose concentrations, and cognitive performance tests were performed before and after each session. A single bout of NMES significantly increased plasma BDNF levels (p<0.05), which were equivalent to the amount of plasma BDNF released during the exercise session (p>0.05). However, there were no significant changes in cognitive performance between the sessions (p>0.05). The present study found that a single bout of NMES significantly increased plasma BDNF to levels normally present during moderate voluntary exercise. Therefore, NMES could serve as an alternative method of exercise, and might shed light on individuals for whom voluntary physical exercise is contraindicated.