Differential effects of acute and repeat dosing with the H3 antagonist GSK189254 on the sleep-wake cycle and narcoleptic episodes in Ox-/- mice

Abstract

Background and purpose: Histamine H3 receptor antagonists are currently being evaluated in clinical trials for a number of central nervous system disorders including narcolepsy. These agents can increase wakefulness (W) in cats and rodents following acute administration, but their effects after repeat dosing have not been reported previously.

Experimental approach: EEG and EMG recordings were used to investigate the effects of acute and repeat administration of the novel H3 antagonist GSK189254 on the sleep-wake cycle in wild-type (Ox+/+) and orexin knockout (Ox-/-) mice, the latter being genetically susceptible to narcoleptic episodes. In addition, we investigated H3 and H1 receptor expression in this model using radioligand binding and autoradiography.

Key results: In Ox+/+ and Ox-/- mice, acute administration of GSK189254 (3 and 10 mg x kg(-1) p.o.) increased W and decreased slow wave and paradoxical sleep to a similar degree to modafinil (64 mg x kg(-1)), while it reduced narcoleptic episodes in Ox-/- mice. After twice daily dosing for 8 days, the effect of GSK189254 (10 mg x kg(-1)) on W in both Ox+/+ and Ox-/- mice was significantly reduced, while the effect on narcoleptic episodes in Ox-/- mice was significantly increased. Binding studies revealed no significant differences in H3 or H1 receptor expression between Ox+/+ and Ox-/- mice.

Conclusions and implications: These studies provide further evidence to support the potential use of H3 antagonists in the treatment of narcolepsy and excessive daytime sleepiness. Moreover, the differential effects observed on W and narcoleptic episodes following repeat dosing could have important implications in clinical studies.

Figure 1

Representative examples of hypnograms showing the sleep–wake cycle in (A) wild-type (Ox+/+) and (B) Ox−/− mice over a 5 h period in the lights-on phase. Arrows show where vehicle (placebo) and GSK189254 (3 and 10 mg·kg⁻¹) were administered. GSK189254 increased wakefulness (W) and decreased slow wave sleep (SWS) and paradoxical sleep (PS) in both Ox+/+ and Ox−/− mice compared with vehicle-treated mice.

Figure 2

Effects of acute and repeat administration of GSK189254 on mean duration (±SEM) of sleep–wake stages in a 4 h recording within the lights-on period in (A) wild-type (Ox+/+) and (B) Ox−/− mice (n= 14 per group). GSK189254 (3 and 10 mg·kg⁻¹) significantly increased wakefulness (W) and decreased slow wave sleep (SWS) and paradoxical sleep (PS) following acute dosing. Repeat administration of GSK189254 (10 mg·kg⁻¹, twice daily for 8 days) resulted in a reduction in effects on W, SWS and PS compared with acute dosing with 10 mg·kg⁻¹. *P < 0.05, t-test between groups (compared with vehicle-treated mice) after significant anova. #P < 0.05, t-test between groups (compared with acute 10 mg·kg⁻¹ dose group) after significant anova.

Figure 5

Cumulative effects of acute and repeat administration of GSK189254 and acute administration of modafinil on mean duration of sleep–wake stages over 12 h of the lights-off period in (A) wild-type (Ox+/+) and (B) Ox−/− mice (n= 14 per group). GSK189254 (3 and 10 mg·kg⁻¹) significantly increased wakefulness (W) and decreased slow wave sleep (SWS) and paradoxical sleep (PS) following acute dosing, as did modafinil (64 mg·kg⁻¹). Repeat administration of GSK189254 (10 mg·kg⁻¹, twice daily for 8 days) resulted in a reduction in effects on W, SWS and PS compared with acute dosing with 10 mg·kg⁻¹. *P < 0.05, t-test between groups (compared with vehicle-treated mice) after significant anova. #P < 0.05, t-test between groups (compared with acute 10 mg·kg⁻¹ dose group) after significant anova. There was no evidence of sleep rebound and effects of GSK189254 lasted for the 12 h duration of measurements.

Figure 3

Cumulative effects of acute and repeat administration of GSK189254 on mean duration of sleep–wake stages over 8 h of the lights-on period in (A) wild-type (Ox+/+) and (B) Ox−/− mice (n= 14 per group). GSK189254 (3 and 10 mg·kg⁻¹) significantly increased wakefulness (W) and decreased slow wave sleep (SWS) and paradoxical sleep (PS) following acute dosing. Repeat administration of GSK189254 (10 mg·kg⁻¹, twice daily for 8 days) resulted in a reduction in effects on W, SWS and PS compared with acute dosing with 10 mg·kg⁻¹. *P < 0.05, t-test between groups (compared with vehicle-treated mice) after significant anova. #P < 0.05, t-test between groups (compared with acute 10 mg·kg⁻¹ dose group) after significant anova. There was no evidence of sleep rebound and effects of GSK189254 lasted for the 8 h duration of measurements.

Figure 4

Effects of acute and repeat administration of GSK189254 on mean duration (±SEM) of sleep–wake stages in a 4 h recording within the lights-off period in (A) wild-type (Ox+/+) and (B) Ox−/− mice (n= 14 per group). GSK189254 (3 and 10 mg·kg⁻¹) significantly increased wakefulness (W) and decreased slow wave sleep (SWS) and paradoxical sleep (PS) following acute dosing. Repeat administration of GSK189254 (10 mg·kg⁻¹, twice daily for 8 days) had no effect on W, SWS and PS compared with acute dosing with 10 mg·kg⁻¹ on Ox+/+ mice. In Ox−/− mice, GSK189254 actually reduced W and increased SWS and PS, effects that were the reverse of those seen with acute dosing. *P < 0.05, t-test between groups (compared with vehicle-treated mice) after significant anova. #P < 0.05, t-test between groups (compared with acute 10 mg·kg⁻¹ dose group) after significant anova.

Figure 6

Effects of acute and repeat administration of GSK189254 and effect of acute administration of modafinil on narcoleptic attacks in Ox−/− mice in the lights-off period compared with vehicle-treated mice. (A) Mean (±SEM) number of narcoleptic episodes in the 4 h period after dosing. (B) Mean (±SEM) cumulative duration of narcoleptic attacks and (C) mean (±SEM) cumulative number of narcoleptic attacks over the 12 h lights-off period. *P < 0.05, t-test between groups (compared with vehicle-treated mice) after significant anova. #P < 0.05, t-test between groups (compared with acute 10 mg·kg⁻¹ dose group) after significant anova.

Figure 7

H₃ (left panels) and H₁ (right panels) receptor binding in Ox+/+ and Ox−/− mice measured using [³H]-GSK189254 and [³H]-mepyramine respectively, with real-time autoradiography. (A) Representative pseudo-coloured images of coronal half brain sections showing specific [³H]-GSK189254 and [³H]-mepyramine binding in cortex and hypothalamus of Ox+/+ and Ox−/− mice. Non-specific binding (NSB) for H₃ and H₁ was determined in the presence of 10 µmol·L⁻¹ imetit and 10 µmol·L⁻¹ chlorphenimramine respectively. Scale bars = 1 mm. (B) Quantitative histograms showing specific [³H]-GSK189254 and [³H]-mepyramine binding in cortex, hippocampus and hypothalamus of Ox+/+ and Ox−/− mice (mean ± SEM, n= 4 per group). No significant differences were observed between Ox+/+ and Ox−/− mice in any of these brain regions. (C) Saturation binding analysis for [³H]-GSK189254 to H₃ receptors and [³H]-mepyramine to H₁ receptors in whole brain of Ox+/+ and Ox−/− mice. Representative curves are shown. No significant differences were observed in mean B_max or K_D (n= 3–4 per group) as shown in Results section.