The hypothalamic suprachiasmatic nucleus (SCN), the circadian pacemaker of the mammalian brain, integrates both environmental and endogenous information to modulate various physiological and behavioral processes. Both light and physical activity entrain SCN circadian rhythmicity, but the underlying molecular mechanisms for physical activity remain elusive. Repetitive neuronal stimulation results in accumulation of the stable transcription factor ΔFOSB, that has been implicated in long-term brain plasticity, altered neuronal excitability, and changes in behavior. In rodents, voluntary wheel running (VWR) mimics aspects of exercise training and increases ΔFOSB in several brain regions. Whether VWR also alters ΔFOSB in the SCN is unexplored. Here, young-adult male and female Wistar rats were housed sedentary or allowed to run for four weeks followed by quantification of ΔFOSB in the SCN. VWR lowered SCN ΔFOSB-positive cell numbers in males and females compared to sedentary housing. Total running distance did not correlate with ΔFOSB suppression. Analysis taking estrous cycle into account revealed that ΔFOSB-positive cell numbers were cyclic in sedentary females, being lowest during proestrus and highest during diestrus. Remarkably, this cyclicity was absent in runners, where ΔFOSB-positive cell numbers remained comparable to those observed during proestrus in sedentary controls. Finally, estradiol replacement following ovariectomy in sedentary females lowered SCN ΔFOSB-positive cell numbers. Thus, VWR and estrous cycle, via, at least in part, estradiol, modulate SCN ΔFOSB. Given its role in long-term plasticity and behavioral adaptations, ΔFOSB may provide a molecular link between VWR and/or estrous cycle and the output of the SCN and its related behavioral adaptations.

Circadian disruption is an important factor driving the current-day high prevalence of obesity and type-2 diabetes. While the impact of incorrect timing of caloric intake on circadian disruption is widely acknowlegded, the contribution of incorrect timing of physical activity remains relatively understudied. Here, we modeled the incorrect timing of physical activity in nightshift workers in male Wistar rats, by restricting running wheel access to the innate inactive (light) phase (LR). Controls included no wheel access (NR); access only during the innate active (dark) period (DR); or unrestricted (ad libitum) access (ALR). LR did not shift the phase of the muscle or liver clock, but dampened the muscle clock amplitude. As our previous study demonstrated that light-phase restricted feeding did shift the liver clock, but made the muscle clock arrhythmic, we next combined the time restriction of wheel and food access to either the light phase (LRLF) or dark phase (DRDF). LRLF produced a ∼12 h shift in the majority of clock gene rhythms in both skeletal muscle and liver. On the other hand, DRDF was most effective in reducing body weight and the accumulation of fat mass. Therefore, in order to shift the muscle clock in male Wistar rats, synergy between the timing of feeding and physical activity is necessary. These findings may contribute to further improve the design of lifestyle strategies that try to limit metabolic misalignment caused by circadian disruption.

Background/Objectives: N-lactoyl-phenylalanine (Lac-Phe), an exercise-induced metabolite, has been shown to reduce food intake, decrease body weight and adiposity, and improve glucose homeostasis without affecting energy expenditure. Until now, Lac-Phe has mainly been investigated in blood plasma, showing its appetite-suppressing effects. Interestingly, these beneficial effects were caused by a temporary increase in Lac-Phe levels after exercise. Second, despite the central role of the central nervous system in the homeostatic control of energy metabolism, little is known about the presence and function of Lac-Phe in the brain. The goal of this study is to investigate how Lac-Phe concentrations in the brain change during the 24 h light/dark cycle. Methods: We conducted an experiment in rats in which time-restricted running was combined with time-restricted feeding (TRF) of a high-calorie diet, after which Lac-Phe levels were measured in the hypothalamus and cortex using stable isotope dilution LC-MS/MS. Microglia were isolated from rat brains to study Lac-Phe-related gene expression. Results: We found that Lac-Phe levels changed over time within the 24 h light/dark cycle in the hypothalamus and/or cortex, even without exercise. Our study indicates that brain Lac-Phe is not only induced by exercise but also by high-calorie diet intake independent of exercise. Finally, we showed that microglial cells are cytosolic nonspecific dipeptidase 2 (CNDP2) positive and therefore able to produce Lac-Phe. Hereby, we identified SLC16A1 in microglia as a possible key mediator of Lac-Phe production. Conclusions: We conclude that high-calorie diet consumption induces Lac-Phe changes in the brain in a time-of-day manner independent of exercise. This study provides new knowledge on the presence and production of Lac-Phe in the brain. Further research is needed to elucidate the potential mechanism by which Lac-Phe reduces food intake and body weight by targeting appetite-suppressing neurons.

Excess caloric intake and insufficient physical activity are the two major drivers underlying the global obesity and type 2 diabetes mellitus epidemics. However, circadian misalignment of caloric intake and physical activity, as commonly experienced by nightshift workers, can also have detrimental effects on body weight and glucose homeostasis. We have previously reported that combined restriction of eating and voluntary wheel running to the inactive phase (i.e., a rat model for circadian misalignment) shifted liver and muscle clock rhythms by ~12 h and prevented the reduction in the amplitude of the muscle clock oscillation otherwise induced by light-phase feeding. Here, we extended on these findings and investigated how a high-fat diet (HFD) affects body composition and liver and muscle clock gene rhythms in male Wistar rats while restricting both eating and exercise to either the inactive or active phase. To do this, we used four experimental conditions: sedentary controls with no wheel access on a non-obesogenic diet (NR), sedentary controls with no wheel access on an HFD (NR-H), and two experimental groups on an HFD with simultaneous access to a running wheel and HFD time-restricted to either the light phase (light-run-light-fed + HFD, LRLF-H) or the dark phase (dark-run-dark-fed + HFD. DRDF-H). Consumption of an HFD did not alter the daily running distance of the time-restricted groups but did increase the running intensity in the LRLF-H group compared to a previously published LRLF chow fed group. However, no such increase was observed for the DRDF-H group. LRLF-H ameliorated light phase-induced disturbances in the soleus clock more effectively than under chow conditions and had a protective effect against HFD-induced changes in liver clock gene expression. Together with (our) previously published results, these data suggest that eating healthy and being active at the wrong time of the day can be as detrimental as eating unhealthy and being active at the right time of the day.