The Impairments of Ca2+-dependent Hyperpolarization Pathway Altered NREM Sleep Duration in Mice

抄録

During NREM sleep, as known as slow-wave sleep (SWS), an EEG mostly displays high-amplitude low-frequency fluctuations, which are generated by synchronized slow oscillations of the cortical neuron membrane potential. During waking, an EEG exhibits low-amplitude high-frequency fluctuations, which are generated by the irregular firings of cortical neurons. These two states are mutually exclusive in a normal brain, and their ratio is homeostatically regulated. However, it is still challenging to bridge the gap between electrophysiological dynamics (i.e. SWS firing pattern) and the homeostatic dynamics (i.e. sleep duration).

A simple computational model predicted that the Ca2+-dependent hyperpolarization pathway may play a role in generating the SWS firing pattern. From this prediction, we hypothesized that Ca2+-dependent hyperpolarization pathway also plays a role in the regulation of sleep duration.

To validate the hypothesis, we comprehensively generated the KO mice by the Triple-CRISPR methods, which allow us to obtain biallelic-KO mice in one-generation, and analyzed these sleep phenotypes by the respiration-based non-invasive sleep phenotyping system to screen for important molecules for sleep duration. We found that impaired Ca2+-dependent K+ channels (Kcnn2 and Kcnn3), voltage-gated Ca2+ channels (Cacna1g and Cacna1h), or NMDA receptors decrease sleep duration, while impaired plasma membrane Ca2+ ATPase (Atp2b3) increases sleep duration in mice. Interestingly, impaired Ca2+/calmodulin-dependent kinases (Camk2a and Camk2b) decrease sleep duration. To analyze detailed sleep phenotypes of genetically- or pharmacologically-impaired mice, we conducted the EEG/EMG recording of these mice. As a result, the observed sleep phenotypes of these mice were largely attributed to the significant change of NREM sleep (SWS) duration.

Based on these results, we propose a hypothesis that the Ca2+-dependent hyperpolarization pathway underlies the regulation of NREM sleep duration by the active-dependent modification (e.g., phosphorylation) to its components.