Neuroligin 3 R451C mutation alters electroencephalography spectral activity in an animal model of autism spectrum disorders

Abstract

Human studies demonstrate that sleep impairment is a concurrent comorbidity of autism spectrum disorders (ASD), but its etiology remains largely uncertain. One of the prominent theories of ASD suggests that an imbalance in synaptic excitation/inhibition may contribute to various aspects of ASD, including sleep impairments. Following the identification of Nlgn3^R451C mutation in patients with ASD, its effects on synaptic transmission and social behaviours have been examined extensively in the mouse model. However, the contributory role of this mutation to sleep impairments in ASD remains unknown. In this study, we showed that Nlgn3^R451C knock-in mice, an established genetic model for ASD, exhibited normal duration and distribution of sleep/wake states but significantly altered electroencephalography (EEG) power spectral profiles for wake and sleep.

Keywords: Autism; EEG; NREM; Nlgn3 R451C mouse model; REM; Sleep deficit.

Fig. 1

Representative traces of EEG-EMG recordings in a WT mouse. For each mouse, continuous recordings for 48 h were done (top 2 channels: EEG; bottom 2 channels: EMG). The top EEG channel is from left frontal electrode recording with reference to cerebellum. The second EEG channel is from right parietal electrode recording with reference to cerebellum. a Wake EEG is predominated by oscillations greater or equal to theta oscillations (≥5 Hz) with varying amplitude and is irregular in comparison to NREM and REM sleep. b, c NREM sleep is predominated by either high amplitude delta waves (<4 Hz) or mixed high amplitude theta/delta waves in the EEG channels and low muscle activity. The mixed high amplitude theta/delta waves in our mice often occur before transitioning into REM sleep. d REM sleep is characterized by regular low amplitude theta waves (≥7 Hz) in the EEG channels associated with muscle atonia. Every gridline marks 1 s in duration. The amplitude scale for EEG is 100 μV and the amplitude scale for EMG is 300 μV

Fig. 2

Total sleep-wake time in Nlgn3^R451C mutant mice. Proportion of total time spent in each vigilance state during the 12-h light and 12-h dark periods in WT (n = 7) and Nlgn3^R451C mice (KI, n = 7). Student t-test was used for this set of analysis. Both WT and Nlgn3^R451C mice spent more time in NREM and REM sleep during the light period than they did during the dark period. Nlgn3^R451C mice did not significantly alter the time that the mice spent in wake (a), NREM sleep (c), and REM sleep (e) during light period (all p >0.15. Nlgn3^R451C mice did not significantly alter the time that the mice spent in wake (b), NREM sleep (d), and REM (f) sleep during dark period (all p >0.28)

Fig. 3

Time-of-day profile of vigilance states in WT and Nlgn3^R451C mutant mice. The distribution profile of each vigilance state across the entire recording. Nlgn3^R451C mutant mice exhibited a trend of less NREM sleep than WT (p = 0.051) (b), while the two groups did not differ from each other for wakefulness (a) and REM sleep (c) (genotype: both > 0.11)

Fig. 4

Sleep-wake episodes in Nlgn3^R451C mutant mice. Total number of episodes and the mean episode duration for each vigilance state were compared between WT (n = 7) and Nlgn3^R451C mice (KI, n = 7) using student t-test. Episode number of each state and their mean episode duration were separately assessed in the light (a, c, e, g, i, and k) or dark phase (b, d, f, h, j, and l). Nlgn3^R451C mutation did not result in significant alteration in the number of episodes (all p >0.45) nor the mean episode duration (all p >0.13) of wake (a to d), NREM (e to h), and REM sleep (i to l) in the light period or the dark period

Fig. 5

Power spectral profiles of WT and Nlgn3^R451C mutant mice. The power of the individual frequency band (1 Hz bins) was normalized by expressing it as % of the average of total power (1-56 Hz for all epochs). Repeated measure two-way ANOVA using “genotype” and “frequency” as factors revealed significant genotype-frequency interaction for NREM sleep (F = 2.856, p <0.001). The NREM (B) spectral profile of Nlgn3^R451C (KI) mice differed significantly between 2-8 Hz from WT mice (WT, n = 7; KI, n = 7; all p <0.05). More specifically, Nlgn3^R451C mice had reduced powers between 2-8 Hz during NREM sleep (b) in comparison to WT mice. No significant genotype effect or genotype-frequency interactions were found for wake (a) and REM (c) states

Fig. 6

Altered power spectral profiles in Nlgn3^R451C mutant mice. The power of the individual frequency band was normalized by expressing it as % of the mean of total power (1-56 Hz for all epochs). The mean normalized power of each 3-h interval (of both days) is displayed over the 24-h period. “Genotype” and “time” were used as factors to examine their effects on delta, theta, alpha, sigma, and beta powers in each behavioural vigilance state (only data with significant genotype effect are displayed here). During wakefulness, Nlgn3^R451C (KI) mice exhibited significantly higher sigma (a) and beta (b) powers than WT mice (p <0.05). During NREM sleep, Nlgn3^R451C mice showed suppressed delta (c), theta (d), and alpha (e) powers than WT mice (p <0.05). During REM sleep, Nlgn3^R451C mice exhibited significantly lower alpha (f) and higher beta (g) powers than WT (p <0.05). No significant interactions between genotype and time were found (all p >0.05)