The effect of Neuroligin-2 absence on sleep architecture and electroencephalographic activity in mice

Sleep disorders are comorbid with most psychiatric disorders, but the link between these is not well understood. Neuroligin-2 (NLGN2) is a cell adhesion molecule that plays roles in synapse formation and neurotransmission. Moreover, NLGN2 has been associated with psychiatric disorders, but its implication in sleep remains underexplored. In the present study, the effect of Nlgn2 knockout (Nlgn2^-/-) on sleep architecture and electroencephalographic (EEG) activity in mice has been investigated. The EEG and electromyogram (EMG) were recorded in Nlgn2^-/- mice and littermates for 24 h from which three vigilance states (i.e., wakefulness, rapid eye movement [REM] sleep, non-REM [NREM] sleep) were visually identified. Spectral analysis of the EEG was performed for the three states. Nlgn2^-/- mice showed more wakefulness and less NREM and REM sleep compared to wild-type (Nlgn2^+/+) mice, especially during the dark period. This was accompanied by changes in the number and duration of individual episodes of wakefulness and sleep, indexing changes in state consolidation, as well as widespread changes in EEG spectral activity in all states. Abnormal 'hypersynchronized' EEG events have also been observed predominantly in Nlgn2^-/- mice. These events were mainly observed during wakefulness and REM sleep. In addition, Nlgn2^-/- mice showed alterations in the daily time course of NREM sleep delta (1-4 Hz) activity, pointing to modifications in the dynamics of sleep homeostasis. These data suggest that NLGN2 participates in the regulation of sleep duration as well as EEG activity during wakefulness and sleep.