Inducible nitric oxide synthase and AMP-activated protein kinase in basal forebrain during prolonged waking

Maternal dietary restriction alters offspring's sleep homeostasis

Nutritional state in the gestation period influences fetal growth and development. We hypothesized that undernutrition during gestation would affect offspring sleep architecture and/or homeostasis. Pregnant female mice were assigned to either control (fed ad libitum; AD) or 50% dietary restriction (DR) groups from gestation day 12 to parturition. After parturition, dams were fed AD chow. After weaning, the pups were also fed AD into adulthood. At adulthood (aged 8-9 weeks), we carried out sleep recordings. Although offspring mice displayed a significantly reduced body weight at birth, their weights recovered three days after birth. Enhancement of electroencephalogram (EEG) slow wave activity (SWA) during non-rapid eye movement (NREM) sleep was observed in the DR mice over a 24-hour period without changing the diurnal pattern or amounts of wake, NREM, or rapid eye movement (REM) sleep. In addition, DR mice also displayed an enhancement of EEG-SWA rebound after a 6-hour sleep deprivation and a higher threshold for waking in the face of external stimuli. DR adult offspring mice exhibited small but significant increases in the expression of hypothalamic peroxisome proliferator-activated receptor α (Pparα) and brain-specific carnitine palmitoyltransferase 1 (Cpt1c) mRNA, two genes involved in lipid metabolism. Undernutrition during pregnancy may influence sleep homeostasis, with offspring exhibiting greater sleep pressure.

Refeeding after a 24-hour fasting deepens NREM sleep in a time-dependent manner

Sleep/wake cycle is regulated by a variety of neuropeptides in the hypothalamus, a brain region that also regulates energy homeostasis and feeding behavior. Since circadian rhythms are affected by energy metabolism and feeding condition, we investigated whether changes in feeding regimen would influence sleep/wake parameters and body temperature. We monitored sleep and body temperature across three days of baseline (day 1), fasting (day 2), and refeeding (day 3) conditions under ordinary ambient temperature and employed different refeeding schedules. Refeeding at ZT1 following the 24-h fasting enhanced EEG delta power in NREM sleep. However, when the time of refeeding was set at either ZT7 or ZT12, the enhancement of EEG delta power was attenuated. The amount of NREM sleep was not largely affected by a 24-h fasting started at ZT1, although fasting that started at ZT12 changed the temporal distribution of NREM sleep. Hypothalamic nNOS mRNA level was increased both before and after refeeding at ZT1 compared with control condition, while there was no significant change in mice refed at ZT7. Level of NPY mRNA in the arcuate nucleus was increased before the refeeding only at ZT1. These results suggest that refeeding after a 24-h fasting makes NREM sleep deeper in a time-dependent manner.

Basal forebrain lactate release and promotion of cortical arousal during prolonged waking is attenuated in aging

The wake-promoting basal forebrain (BF) is critically involved in sustaining cortical arousal. In the present study, we investigated how aging affects the capacity of the BF to cope with continuous activation during prolonged waking. Increased neuronal activity induces lactate release in the activated brain area, and BF stimulation increases cortical arousal. We used in vivo microdialysis to measure lactate levels in the BF, and electroencephalography (EEG) to measure cortical arousal, during 3 h sleep deprivation (SD) in three age groups of rats. Lactate increased during SD in young but not in aged (middle-aged and old) rats. The increase in high-frequency (HF) EEG theta power (7-9 Hz), a marker of cortical arousal and active waking, was attenuated in the aged. Furthermore, a positive correlation between BF lactate release and HF EEG theta increase was found in young but not in aged rats. We hypothesized that these age-related attenuations result from reduced capacity of the BF to respond to increased neuronal activation. This was tested by stimulating the BF with glutamate receptor agonist NMDA. Whereas BF stimulation increased waking in young and old rats, lactate increase and the HF EEG theta increase were attenuated in the old. Also, the homeostatic increase in sleep intensity after SD was attenuated in aged rats. Our results suggest that an age-related attenuation in BF function reduces cortical arousal during prolonged waking. As the quality of waking is important in regulating the subsequent sleep, reduced cortical arousal during SD may contribute to the age-related reduction in sleep intensity.