ABSTRACT
Sleep seems essential to proper functioning of the prefrontal cortex (PFC). The role of different neurotransmitters has been studied, mainly the catecholamines and serotonin. Less attention has been paid to the amino acid transmitters and histamine. Here, we focus on the activity of these molecules in the PFC during sleep and sleep deprivation (SD). We determined extracellular concentrations of histamine and 8 amino acids in the medial PFC before, during and after SD. Additionally, we systematically reviewed the literature on studies reporting microdialysis measurements relating to sleep throughout the brain. In our experiment, median concentrations of glutamate were higher during SD than during baseline (p = 0.013) and higher during the dark-active than during the resting phase (p = 0.003). Glutamine was higher during post-SD recovery than during baseline (p = 0.010). For other compounds, no differences were observed between light and dark circadian phase, and between sleep deprivation, recovery and baseline. We retrieved 13 papers reporting on one or more of the molecules of interest during naturally occurring sleep, 2 during sleep deprivation and 2 during both. Only two studies targeted PFC. Histamine was low during sleep, but high during sleep deprivation and wakefulness, irrespective of brain area. Glu (k = 11) and GABA (k = 8) concentrations in different brain areas were reported to peak during sleep or wakefulness or to lack state-dependency. Aspartate, glycine, asparagine and taurine were less often studied (1-2 times), but peaked exclusively during sleep. Sleep deprivation increased glutamate and GABA exclusively in the cortex. Further studies are needed for drawing solid conclusions.
ABSTRACT
Disruption of the monoaminergic system, e.g. by sleep deprivation (SD), seems to promote certain diseases. Assessment of monoamine levels over the circadian cycle, during different sleep stages and during SD is instrumental to understand the molecular dynamics during and after SD. To provide a complete overview of all available evidence, we performed a systematic review. A comprehensive search was performed for microdialysis and certain monoamines (dopamine, serotonin, noradrenaline, adrenaline), certain monoamine metabolites (3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA)) and a precursor (5-hydroxytryptophan (5-HTP)) in PubMed and EMBASE. After screening of the search results by two independent reviewers, 94 publications were included. All results were tabulated and described qualitatively. Network-meta analyses (NMAs) were performed to compare noradrenaline and serotonin concentrations between sleep stages. We further present experimental monoamine data from the medial prefrontal cortical (mPFC). Monoamine levels varied with brain region and circadian cycle. During sleep, monoamine levels generally decreased compared to wake. These qualitative observations were supported by the NMAs: noradrenaline and serotonin levels decreased from wakefulness to slow wave sleep and decreased further during Rapid Eye Movement sleep. In contrast, monoamine levels generally increased during SD, and sometimes remained high even during subsequent recovery. Decreases during or after SD were only reported for serotonin. In our experiment, SD did not affect any of the mPFC monoamine levels. Concluding, monoamine levels vary over the light-dark cycle and between sleep stages. SD modifies the patterns, with effects sometimes lasting beyond the SD period.
