Sleep/wake dependent changes in cortical glucose concentrations

摘要

Most of the energy in the brain comes from glucose and supports glutamatergic activity. The firing rate of cortical glutamatergic neurons, as well as cortical extracellular glutamate levels, increase with time spent awake and decline throughout non rapid eye movement sleep, raising the question whether glucose levels reflect behavioral state and sleep/wake history. Here chronic (2-3 days) electroencephalographic recordings in the rat cerebral cortex were coupled with fixed-potential amperometry to monitor the extracellular concentration of glucose ([gluc]) on a second-by-second basis across the spontaneous sleep-wake cycle and in response to 3 h of sleep deprivation. [Gluc] progressively increased during non rapid eye movement sleep and declined during rapid eye movement sleep, while during wake an early decline in [gluc] was followed by an increase 8-15 min after awakening. There was a significant time of day effect during the dark phase, when rats are mostly awake, with [gluc] being significantly lower during the last 3-4 h of the night relative to the first 3-4 h. Moreover, the duration of the early phase of [gluc] decline during wake was longer after prolonged wake than after consolidated sleep. Thus, the sleep/wake history may affect the levels of glucose available to the brain upon awakening. The brain overwhelmingly relies on glucose to meet its energy needs, which are higher in wake and REM sleep than in NREM sleep, but it remains unclear how the extracellular concentration of glucose [gluc] changes during sleep and wake. Using fixed-potential amperometry we find that in rat cerebral cortex [gluc] increases progressively during NREM sleep, decreases progressively during REM sleep, and initially declines (~8 min) before increasing during wake. Surprisingly, the early glucose decline upon awakening is longer after prolonged wake than after consolidated sleep, suggesting that sleep/wake history may affect brain glucose availability.