Enhancing effect of cerebral blood volume by mild exercise in healthy young men: a near-infrared spectroscopy study.

A mechanism by which exercise improves brain function may be attributed to increase in cerebral blood volume (CBV) with physical activity. However, the exact exercise intensity that influences CBV is still uncertain. To clarify this issue, 10 healthy young male participants were asked to perform a graded cycling exercise to the point of exhaustion while their prefrontal cortex CBVs are being monitored using near-infrared spectroscopy. Overall responsive cerebral oxygenation showed a non-linear pattern with three distinct phases. The CBV-threshold (CBVT), an event where rapid oxygenation takes place, occurred at approximately 42% of the V O2max. The CBVT preceded the lactate threshold (LT), which was at approximately 55% of the V O2max. The V O2max was not predictive of the CBVT in among the subjects. Our results indicate that oxygenation of the prefrontal cortex increases during graded cycling even at exercise intensities below the LT, suggesting the potential role of mild exercise in enhancing CBV.

Sleep is increased in mice with obesity induced by high-fat food.

Excessive daytime sleepiness has been associated with obesity in humans. However, experimental studies on sleep in obese animals are scarce and the results are not consistent. To test the hypothesis that obesity is associated with increased sleep, we examined the effects of obesity, induced by high-fat food, on sleep in mice. We first determined baseline sleep in adult C57BL/6 mice (6 months of age). In the following 6 weeks, the experimental mice (n = 12) were switched to high-fat food, in which fat provided 59% of calories, and the control mice (n = 11) were continuously fed with regular lab chows, in which fat provided 16% of calories. The body weights increased steadily in the high-fat group, but maintained constant in the controls. Wakefulness was reduced when assessed after 2, 4, and 6 weeks of high-fat feeding. Concurrently, there were large increases (about 80-100 min/day) in non-rapid eye movement sleep (NREMS). Rapid eye movement sleep (REMS) was not altered. The numbers of NREMS and REMS episodes were increased, whereas the duration of waking episodes was reduced, mainly during the dark period. These alterations in sleep were not observed in the controls. In the high-fat group, the increases of body weight, but not the amounts of energy intake, were negatively correlated with the change in the amounts of wakefulness and positively correlated with the change in the amounts of NREMS. These results indicate that the obese animals have increased sleep pressure and difficulties in maintaining wakefulness during the active phase.

Activation of A1 and A2 noradrenergic neurons in response to running in the rat.

Since running accompanied with blood lactate accumulation stimulates the release of adrenocorticotropic hormone (ACTH), running above the lactate threshold (LT) acts as stress (running stress). To examine whether A1/A2 noradrenergic neurons that project to the hypothalamus activate under running stress, c-Fos immunohistochemistry was used to compare the effects of running with or without stress response on A1/A2 noradrenergic neurons. Blood lactate and plasma ACTH concentrations significantly increased in the running stress group, but not in the running without stress response and control groups, confirming different physiological impacts between different intensity of running with or without stress. Running stress markedly increased c-Fos accumulation in the A1/A2 noradrenergic neurons. Running without stress response also induced a significant increase in c-Fos expression in the A1/A2 noradrenergic neurons, and the percentage of the increase was smaller than that of running stress. The extent of c-Fos expression in the A1/A2 noradrenergic neurons correlates with exercise intensity, signifying that this neuronal activation is running speed-dependent. We thus suggest that A1/A2 noradrenergic neurons are activated in response to not only running stress, but also to other physiological running, enhanced by non-stressful running. These findings will be helpful in studies of specific neurocircuits and in identifying their functions in response to running at different intensities.

Interleukin-6 levels fluctuate with the light-dark cycle in the brain and peripheral tissues in rats.

Interleukin-6 (IL-6) has been implicated in excessive daytime sleepiness (EDS) in humans, and exogenous IL-6 also induces sleep alterations both in humans and rats. The IL-6 levels in human blood vary with the light-dark cycle with IL-6 levels being high during the dark period and low during the light period, whereas in the pituitary of rats the IL-6 levels are elevated during the light period compared to the dark period. However, it is unknown whether IL-6 in the brain is affected by the light-dark cycle. We hypothesized that IL-6 levels in the brain are regulated by the light-dark cycles and are elevated during the period that is predominantly occupied by sleep. To test this hypothesis, we measured IL-6 levels in the brain, blood, and adipose tissue of rats across light-dark cycle every 4 h. IL-6 levels were significantly higher during the light period than during the dark period in the cortex, hippocampus and hypothalamus. In the brainstem, IL-6 levels did not significantly vary across the light-dark cycles. IL-6 levels in the blood and adipose tissues were also significantly higher during the light period than during the dark period. IL-6 levels were positively correlated between the blood and adipose tissue, between hypothalamus and blood, and between the hypothalamus and hippocampus. These observations suggest that IL-6 levels vary across the light-dark cycle among different tissues and that IL-6 levels are elevated both centrally and peripherally during the period predominantly occupied by sleep but decreased during the period that primarily consists of wakefulness.

Increased c-fos gene expression in alpha motoneurons in rat loaded hindlimb muscles with inclined locomotion.

The potential usefulness of c-fos gene expression as an indicator of the activity level of spinal alpha motoneurons was examined in loaded locomotive rats. The motor pools of the plantaris (PL) and soleus muscles (SOL), mainly composed respectively of fast- and slow-twitch muscle fibers, were investigated in rats under locomotion at 25 m/min on a 20% incline. We first labeled motoneurons with a retrograde tracer, Nuclear Yellow (NY), and then quantified the c-fos mRNA expression level in the NY-labeled alpha motoneurons by means of in situ hybridization. Electromyographic (EMG) activities were also recorded. The c-fos expression level per alpha motoneuron showed a greater increase in the PL (75%) than in the SOL motor pool (38%). EMG activities also showed a greater increase in the PL (159%) than in the SOL (43%). Taken together, these results suggest that c-fos expression levels in alpha motoneurons are associated with the activity levels of their corresponding muscle. This cytochemical method for identifying the c-fos expression level has potential for use as a tool for estimating the activity level of large populations of alpha motoneurons in unrestricted animals.