Sleep and sleep homeostasis in mice lacking the 5-HT2c receptor

Abstract

Studies in humans and rats indicate that serotonin (5-hydroxytryptamine, 5-HT) receptors are involved in mammalian sleep expression. We investigated the contribution of the 5-HT2c receptor to sleep expression by examining sleep patterns in mice bearing a targeted null mutation of this receptor. 5-HT2c receptor knock-out mice had more wakefulness, several abnormalities in rapid eye movement sleep expression and an enhanced response to sleep deprivation compared with wild-type control mice. These findings suggest that 5HT2c receptors may mediate several effects on sleep that have been ascribed to serotonin.

Figure 1

Vigilance state amounts and duration in wild-type (WT) and 5-HT2cR knock-out (KO) mice. A. Mean (± SEM) amounts (expressed as a % of total recording time (RT)) of nonREM sleep, REM sleep and wake are shown for the light phase (LP: 8 a.m.-8 p.m.) dark phase (DP: 8 p.m.-8 a.m.), and overall (O: 24 h) in the baseline period. B. Mean (± SEM) duration (in minutes (Min.)) of nonREM sleep, REM sleep, and wake bouts shown for the LP, DP portions and overall (O) of the baseline period. * Significant difference between the groups (GLM, SNK, p < .05).

Figure 2

Mean vigilance state EEG spectra in (A) wild-type (WT) and (B) 5-HT2cR knock-out (KO) mice. EEG spectral power in each vigilance state is expressed as a percentage of the mean power in all EEG frequencies averaged across all vigilance states (normalized power). There were no significant differences in EEG spectra in nonREM (N) sleep, REM (R) sleep, and wake (W) between the groups.

Figure 3

Effects of 6-h sleep deprivation (SD) on nonREM sleep EEG slow wave activity (SWA) in (A) wild-type (WT) and (B) 5-HT2cR KO mice. Mean (± SEM) nonREM sleep SWA values following sleep deprivation (POST-SD: circles) and in the PRE-SD period (squares) are expressed as a % of the mean 24-h nonREM SWA values obtained in the baseline day of sleep/wake recording. * Significant difference between PRE-SD and POST-SD values (5-HT2cR KO: PRE-SD vs. POST-SD × Hour: F = 4.42, p < .0001, SNK, p < .05; WT:PRE-SD vs. POST-SD × Hour: F = 2.11, p < .04, SNK, p < .05).