title: Effect of sleep and sleep deprivation on serotonergic neurotransmission in the hippocampus: a combined in vivo microdialysis/EEG study in rats.
abstract: Brainstem serotonergic neurotransmission is implicated in sleep regulation. However, the role of serotonin (5-HT) in forebrain regions in sleep-wake mechanisms is still unclear. Here, we have investigated, using a combined in vivo microdialysis/electroencephalogram method, the relationship between hippocampal 5-HT levels and sleep-wake behaviour in the rat. A clear-cut relationship was found between hippocampal 5-HT levels and vigilance state. The highest levels of 5-HT were observed during wakefulness, whereas a progressive decrease of 5-HT going from nonrapid eye movement sleep to rapid eye movement sleep was found. Sleep deprivation (SD) causes a transient enhancement of mood in depressed patients. Given the putative role of 5-HT in the aetiology of depression and the therapeutical efficacy of selective serotonin reuptake inhibitors in this illness, we also studied hippocampal 5-HT during 4 h of SD and during the subsequent recovery period. During the whole SD period, 5-HT levels were elevated substantially when compared to 5-HT levels during basal wakefulness. However, no changes in 5-HT levels and the relationship between hippocampal 5-HT and vigilance state were found during the subsequent recovery period. As SD is a potentially stressful experience and glucocorticoids are involved in the regulation of serotonergic neurotransmission and sleep, we investigated the effects of SD on free corticosterone levels. SD caused a marked rise in free corticosterone levels. However, the effects of SD on 5-HT seem not to be mediated by this hormone, because adrenalectomy did not affect the rise in hippocampal 5-HT during SD. We hypothesize that the elevated hippocampal 5-HT levels during SD may participate in the transient mood enhancing properties of forced wakefulness observed in depressed patients.
authors.affiliation: Max Planck Institute of Psychiatry, Section of Neurochemistry, Kraepelinstrasse 2, D-80804 Munich, Germany.
authors.forename: Rosana G
authors.initials: RG
authors.lastname: Peñalva
authors.forename: Marike
authors.initials: M
authors.lastname: Lancel
authors.forename: Cornelia
authors.initials: C
authors.lastname: Flachskamm
authors.forename: Johannes M H M
authors.initials: JM
authors.lastname: Reul
authors.forename: Florian
authors.initials: F
authors.lastname: Holsboer
authors.forename: Astrid C E
authors.initials: AC
authors.lastname: Linthorst
mesh_terms: D000315:Adrenalectomy / Q000706:statistics & numerical data; D000818:Animals; D003345:Corticosterone / Q000378:metabolism; D004569:Electroencephalography / Q000379:methods; D005110:Extracellular Space / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D017551:Microdialysis / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism*; D012890:Sleep / Q000502:physiology*; D012892:Sleep Deprivation / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology
chemical_list: D012701:Serotonin; D003345:Corticosterone