We investigated extracellular 5-hydroxytryptamine (5-HT) levels in rat hippocampus during different stages of the sleep-waking cycle using in vivo microdialysis. The extracellular 5-HT level was highest in active waking (AW) and, when compared to AW, 5-HT level was progressively lower in quiet waking (QW; 78%), quiet sleep (QS; 50%) and REM (which we termed active sleep (AS); 40%). Functional implications of AS related-decreased 5-HT in the hippocampus are discussed.
Copyright 1999 Elsevier Science B.V.