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.

EEG power densities (0.5-20 Hz) in different sleep-wake stages in rats.

Frontofrontal and frontoparietal EEG power densities (0.5-20 Hz) in waking, light and deep slow-wave sleep, transition-type sleep, and rapid-eye-movement (REM) sleep were investigated for 8 h during the light period in 16 male Wistar rats. The data indicate that as delta activity (0.5-4.5 Hz) increased from light to deep slow-wave sleep, the number of epochs per scoring epoch with high sigma activity (11-16 Hz) as well as power densities in the rest of the spectrum (5-20 Hz) including sigma frequencies also increased. This is in parallel with other rat studies but contrasts findings in humans, where EEG sigma activity is reported to decrease as sleep deepens. During the 8-h recording period, delta activity decreased whereas sigma activity increased.

Sleep/waking effects of a selective 5-HT1A receptor agonist given systemically as well as perfused in the dorsal raphe nucleus in rats.

Sleep/waking stages and behavior were studied following the selective 5-HT1A agonist 8-OH-DPAT given subcutaneously (s.c.) (0.010-0.375 mg/kg) as well as perfused continuously (10 microM) for 6 h into the dorsal raphe nucleus (DRN) using microdialysis. Given systemically, 8-OH-DPAT at 0.375 mg/kg s.c. induced 5-HT behavioral syndrome, increased waking to 149% and reduced slow wave sleep (SWS) to 86%, transition to 76% and rapid eye movement (REM) sleep to 73%. The effect on deep SWS (SWS-2) was biphasic, with an increase after 2 h. 8-OH-DPAT at 0.010 mg/kg did not have any vigilance effects. 8-OH-DPAT perfusion in DRN produced a fourfold increase in REM sleep compared to perfusion of artificial cerebrospinal fluid. This is consistent with the hypothesis that reduced 5-HT neurotransmission following 5-HT1A autoreceptor stimulation will disinhibit cholinergic REM-promoting mesopontine neurons and thereby lead to a REM sleep increase. The other sleep/waking stages were not significantly affected by 8-OH-DPAT perfusion in DRN.

The reliability and functional validity of visual and semiautomatic sleep/wake scoring in the Møll-Wistar rat.

The present paper has three major objectives: first, to document the reliability of a published criteria set for sleep/wake scoring in the rat; second, to develop a computer algorithm implementation of the criteria set; and third, to document the reliability and functional validity of the computer algorithm for sleep/wake scoring. The reliability of the visual criteria was assessed by letting two raters separately score 8 hours of polygraph records from the light period from five rats (14,040 10-second scoring epochs). Scored stages were waking, slow-wave sleep-1, slow-wave sleep-2, transition type sleep and rapid eye movement (REM) sleep. The visual criteria had good interrater reliability [Cohen's kappa (kappa) = 0.68], with 92.6% agreement on the waking/nonrapid eye movement (NREM) sleep/REM sleep distinction (kappa = 0.89). This indicated that the criteria allow separate raters to independently classify sleep/wake stages with very good agreement. An independent group of 10 rats was used for development of an algorithm for semiautomatic computer scoring. A close implementation of the visual criteria was chosen. The algorithm was based on power spectral densities from two electroencephalogram (EEG) leads and on electromyogram (EMG) activity. Five 2-second fast Fourier transform (FFT) epochs from each EEG/EMG lead per 10-second sleep/wake scoring epoch were used to take the spatial and temporal context into account. The same group of five rats used in visual scoring was used to appraise reliability of computerized scoring. The computer score was compared with the visual score for each rater. There was a lower agreement (kappa = 0.57 and 0.62 for the two raters) than in interrater visual scoring [percent agreement 87.7 and 89.1% (kappa = 0.82 and 0.84) in the waking/NREM sleep/REM sleep distinction]. Subsequently, the computer scores of the raters were compared. The interrater reliability was better than the interrater reliability for visual scoring (kappa = 0.75), with 92.4% agreement for the waking/NREM sleep/REM sleep distinction (kappa = 0.89). The computer scoring algorithm was applied to data from a third independent group of rats (n = 6) from an acoustical stimulus arousal threshold experiment, to assess the functional validity of the scoring directly with respect to arousal threshold. The computer algorithm scoring performed as well as the original visual sleep/wake stage scoring. This indicated that the lower intrarater reliability did not have a significant negative influence on the functional validity of the sleep/wake score.