Key role of 5-HT1B receptors in the regulation of paradoxical sleep as evidenced in 5-HT1B knock-out mice

Abstract

The involvement of 5-HT1B receptors in the regulation of vigilance states was assessed by investigating the spontaneous sleep-waking cycles and the effects of 5-HT receptor ligands on sleep in knock-out (5-HT1B-/-) mice that do not express this receptor type. Both 5-HT1B-/- and wild-type 129/Sv mice exhibited a clear-cut diurnal sleep-wakefulness rhythm, but knock-out animals were characterized by higher amounts of paradoxical sleep and lower amounts of slow-wave sleep during the light phase and by a lack of paradoxical sleep rebound after deprivation. In wild-type mice, the 5-HT1B agonists CP 94253 (1-10 mg/kg, i.p.) and RU 24969 (0.25-2.0 mg/kg, i.p.) induced a dose-dependent reduction of paradoxical sleep during the 2-6 hr after injection, whereas the 5-HT1B/1D antagonist GR 127935 (0.1-1.0 mg/kg, i.p.) enhanced paradoxical sleep. In addition, pretreatment with GR 127935, but not with the 5-HT1A antagonist WAY 100635, prevented the effects of both 5-HT1B agonists. In contrast, none of the 5-HT1B receptor ligands, at the same doses as those used in wild-type mice, had any effect on sleep in 5-HT1B-/- mutants. Finally, the 5-HT1A agonist 8-OH-DPAT (0.2-1.2 mg/kg, s.c.) induced in both strains a reduction in the amount of paradoxical sleep. Altogether, these data indicate that 5-HT1B receptors participate in the regulation of paradoxical sleep in the mouse.

Fig. 1.

Diurnal variations of wakefulness (W), slow-wave sleep (SWS), and paradoxical sleep (PS) during 12 hr light/dark cycle (light on from 7:00 A.M. to 7:00 P.M.) in 5-HT_1B+/+ (open bars) and 5-HT_1B−/− (filled bars) mice. Data are expressed as min/3 hr (mean ± SEM of 7 and 8 animals, respectively). *p < 0.05, significantly different from the 5-HT_1B+/+ group; Student’s ttest.

Fig. 2.

Paradoxical sleep characteristics observed after a 12 hr PS deprivation performed during either the preceding dark period (left) or the preceding light period (right) in 5-HT_1B+/+ (open bars) and 5-HT_1B−/− (filled bars) mice. Top, PS amounts (mean ± SEM of 5 and 7 animals, respectively) are expressed as percent of the paired values obtained under control conditions (large platform).Bottom, Intrasleep PS latency observed at recovery is expressed as minutes (mean ± SEM) after control (C, large platform) or deprivation (D, small platform) conditions. *p < 0.05, significantly different from control conditions; paired Student’st test. °p < 0.05, significantly different from the 5-HT_1B+/+ group; Student’st test.

Fig. 3.

Effects of the 5-HT_1A/1B agonist RU 24969 at various doses on sleep and wakefulness in 5-HT_1B+/+ mice during the four successive 2 hr periods after injection. Results are expressed as min/2 hr (mean ± SEM of 8 animals; 6–8 tests for each dose). *p < 0.05, significantly different from baseline (open bars); paired Student’s t test.

Fig. 4.

Effects of RU 24969 (left) and CP 94253 (right) at various doses on PS in 5-HT_1B+/+ (open symbols) and 5-HT_1B−/− (filled symbols) mice during the 4 hr after injection in which an effect was observed. Results are expressed as minutes (mean ± SEM of 8 mice in each group for RU 24969 and 6 mice for CP 94253; 5–8 tests for each dose). *p < 0.05, significantly different from baseline (0 on abscissa); paired Student’st test. Complete set of data is available on request.

Fig. 5.

Effects of the 5-HT_1B/1D antagonist GR 127935 (hatched bars) on PS in 5-HT_1B+/+ (left) and 5-HT_1B−/− (right) mice during the four successive 2 hr periods after injection. Results are expressed as min/2 hr (mean ± SEM of 8 and 6 animals, respectively). *p < 0.05, significantly different from baseline (open bars); paired Student’s t test.

Fig. 6.

Effects of the 5-HT_1B/1D antagonist GR 127935 (hatched bars) on PS inhibition induced by RU 24969 (gray bars) or CP 94253 (black bars) in 5-HT_1B+/+ mice during the 2 hr period after injection in which an effect was observed. Results are expressed as minutes (mean ± SEM of 8 animals; 8 and 6 tests for each treatment, respectively). *p < 0.05, significantly different from baseline (open bar); paired Student’st test. Complete set of data is available on request.

Fig. 7.

A, Effects of the 5-HT_1A antagonist WAY 100635 (dotted bars) on the 8-OH-DPAT-induced inhibition of PS in 5-HT_1B+/+ (left) and 5-HT_1B−/− (right) mice during the 2 hr period after injection in which an effect was observed. Results are expressed as percent of baseline (mean ± SEM of 7 animals in each group; 6–7 tests for each dose). B, Effects of the 5-HT_1Aantagonist WAY 100635 (dotted bars) on the RU 24969-induced inhibition of PS in 5-HT_1B+/+ (left) and 5-HT_1B−/− (right) mice during the 4 hr after injection. Results are expressed as percentage of baseline (mean ± SEM of 7 and 9 animals, respectively; 4–5 tests for each dose). *p < 0.05, significantly different from baseline (open bars); paired Student’s t test. Complete set of data is available on request.