Sleep in Kcna2 knockout mice

Abstract

Background: Shaker codes for a Drosophila voltage-dependent potassium channel. Flies carrying Shaker null or hypomorphic mutations sleep 3-4 h/day instead of 8-14 h/day as their wild-type siblings do. Shaker-like channels are conserved across species but it is unknown whether they affect sleep in mammals. To address this issue, we studied sleep in Kcna2 knockout (KO) mice. Kcna2 codes for Kv1.2, the alpha subunit of a Shaker-like voltage-dependent potassium channel with high expression in the mammalian thalamocortical system.

Results: Continuous (24 h) electroencephalograph (EEG), electromyogram (EMG), and video recordings were used to measure sleep and waking in Kcna2 KO, heterozygous (HZ) and wild-type (WT) pups (P17) and HZ and WT adult mice (P67). Sleep stages were scored visually based on 4-s epochs. EEG power spectra (0-20 Hz) were calculated on consecutive 4-s epochs. KO pups die by P28 due to generalized seizures. At P17 seizures are either absent or very rare in KO pups (< 1% of the 24-h recording time), and abnormal EEG activity is only present during the seizure. KO pups have significantly less non-rapid eye movement (NREM) sleep (-23%) and significantly more waking (+21%) than HZ and WT siblings with no change in rapid eye movement (REM) sleep time. The decrease in NREM sleep is due to an increase in the number of waking episodes, with no change in number or duration of sleep episodes. Sleep patterns, daily amounts of sleep and waking, and the response to 6 h sleep deprivation are similar in HZ and WT adult mice.

Conclusion: Kv1.2, a mammalian homologue of Shaker, regulates neuronal excitability and affects NREM sleep.

Figure 1

Representative electroencephalographic (EEG) and electromyographic (EMG) recordings of non-fatal episodes of seizure occurring in two Kcna2 null pups during waking (upper two traces) and during REM sleep (lower two traces). The EEG shows some higher voltage, intermittent spikes (asterisks) followed by synchronized activity (9–10 Hz) with high-voltage spikes.

Figure 2

Hypnograms and sleep and waking patterns. Upper panel: representative 24-h hypnograms from a Kcna2 null (KO), heterozygous (HZ), and wild-type (WT) pup at P17. White and black bars indicate the light and dark period, respectively. W, waking; NREM, NREM sleep; REM, REM sleep. Middle and lower panels: 24-h sleep and waking patterns and 12-h sleep and waking amounts (mean ± SEM) in Kcna2 KO, HZ, and WT pups at P17. *, p < 0.05 (Tukey's test).

Figure 3

Number and duration (in min) of waking and NREM sleep episodes in Kcna2 KO, HZ, and WT pups at P17. Brief awakenings were defined as uninterrupted waking episodes shorter than 16 s and were computed per hour of total sleep *, p < 0.05 (Tukey's test).

Figure 4

Left panels: 24-h NREM and REM sleep EEG power density spectra (0–20 Hz) in Kcna2 KO, HZ, and WT pups at P17. The right panels show at higher magnification some of the frequency bands indicated on the left. The EEG power spectrum for each 0.5 Hz frequency bin is expressed as a percentage of the total (0–20 Hz) EEG power. Grey and black bars indicate differences between genotypes (p < 0.05, unpaired t test on log-transformed spectral values). Grey and black bars indicate frequency bins where EEG power in KO pups was highest and lowest among genotypes, respectively.

Figure 5

The 24-h sleep and waking patterns (upper panel) and 12-h sleep and waking amounts (lower panel) in Kcna2 adult HZ and WT mice. White and black bars indicate the light and dark period, respectively. Values are mean ± SEM.

Figure 6

Changes in NREM sleep duration and slow wave activity (SWA, 0.5–4.0 Hz) following 6 h of sleep deprivation (SD, during the first half of the light period) in Kcna2 adult HZ and WT mice. The asterisk in the upper WT panel indicates a significant increase in NREM sleep duration during the first 3 post-SD sleep relative to baseline (p < 0.05, paired t test). Middle panel, right: the amount of NREM sleep during the first 18 h after SD is expressed as a percentage of what was lost during the 6 h of SD. Lower panel: the asterisk indicates a significant increase in SWA during the first 3 h post-SD sleep relative to the corresponding baseline interval (p < 0.05, paired t test, both WT and HZ). All values are mean ± SEM.