On-line detection of extracellular levels of serotonin in dorsal raphe nucleus and frontal cortex over the sleep/wake cycle in the freely moving rat.
We used in vivo microdialysis coupled with polygraphic recording to monitor 5-hydroxytryptamine levels in the dorsal raphe nucleus and frontal cortex across waking, slow-wave sleep and rapid eye-movement sleep. Male Sprague-Dawley rats were prepared with electroencephalogram and electromyogram electrodes. Microdialysis probes were placed in dorsal raphe nucleus and/or frontal cortex. Dialysate samples were manually collected during polygraphically-defined behavioural states and the level of serotonin was assayed by means of microbore high-performance liquid chromatography separation and electrochemical detection. Samples from microdialysis probes histologically localized to the dorsal raphe nucleus and frontal cortex showed different levels of extracellular 5-hydroxytryptamine in waking, slow-wave sleep and rapid eye-movement sleep. In dorsal raphe nucleus the extracellular level of serotonin was highest in waking, decreased in slow-wave sleep to 69% and in rapid eye-movement sleep to 39% of waking mean level (waking 3.2 +/- 0.9; slow-wave sleep 2.2 +/- 0.8; rapid eye-movement sleep 1.3 +/- 0.4 fmol/sample). Mean extracellular levels of serotonin in frontal cortex displayed a similar pattern (waking 1.7 +/- 0.4; slow-wave sleep 1.0 +/- 0.3; rapid eye-movement 0.5 +/- 0.05 fmol/sample). In frontal cortex, rapid eye-movement sleep samples were only obtained in three animals. Our findings are consistent with previous results in cats, and suggest that in rats also, extracellular 5-hydroxytryptamine levels in dorsal raphe nucleus and frontal cortex across the sleep/wake cycle might reflect serotonergic neuronal activity. The findings stress the importance of controlling for behavioural state when investigating neurochemical correlates of serotonergic function.
Portas
C M
CM
Department of Physiology, University of Bergen, Norway.
Bjorvatn
B
B
Fagerland
S
S
Grønli
J
J
Mundal
V
V
Sørensen
E
E
Ursin
R
R
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004563:Electrochemistry / Q000379:methods; D005625:Frontal Lobe / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D008991:Monitoring, Physiologic / Q000379:methods*; D011903:Raphe Nuclei / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D012894:Sleep Stages / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology*
D012701:Serotonin