Hyperactivity and male-specific sleep deficits in the 16p11.2 deletion mouse model of autism

Abstract

Sleep disturbances and hyperactivity are prevalent in several neurodevelopmental disorders, including autism spectrum disorders (ASDs) and attention deficit-hyperactivity disorder (ADHD). Evidence from genome-wide association studies indicates that chromosomal copy number variations (CNVs) are associated with increased prevalence of these neurodevelopmental disorders. In particular, CNVs in chromosomal region 16p11.2 profoundly increase the risk for ASD and ADHD, disorders that are more common in males than females. We hypothesized that mice hemizygous for the 16p11.2 deletion (16p11.2 del/+) would exhibit sex-specific sleep and activity alterations. To test this hypothesis, we recorded activity patterns using infrared beam breaks in the home-cage of adult male and female 16p11.2 del/+ and wildtype (WT) littermates. In comparison to controls, we found that both male and female 16p11.2 del/+ mice exhibited robust home-cage hyperactivity. In additional experiments, sleep was assessed by polysomnography over a 24-hr period. 16p11.2 del/+ male, but not female mice, exhibited significantly more time awake and significantly less time in non-rapid-eye-movement (NREM) sleep during the 24-hr period than wildtype littermates. Analysis of bouts of sleep and wakefulness revealed that 16p11.2 del/+ males, but not females, spent a significantly greater proportion of wake time in long bouts of consolidated wakefulness (greater than 42 min in duration) compared to controls. These changes in hyperactivity, wake time, and wake time distribution in the males resemble sleep disturbances observed in human ASD and ADHD patients, suggesting that the 16p11.2 del/+ mouse model may be a useful genetic model for studying sleep and activity problems in human neurodevelopmental disorders. Autism Res 2016. © 2016 International Society for Autism Research, Wiley Periodicals, Inc. Autism Res 2017, 10: 572-584. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Keywords: 16p11.2 deletion; ADHD; autism; copy number variation; sex differences; sleep.

Figure 1.

16p11.2 del/+ mice are hyperactive throughout the diurnal cycle. (A and B) Infrared beam breaks in the XY (horizontal) and Z (vertical) (B) axis plotted for all four groups, in 1 hour bins, across the 24-hr day. Gray box indicates the dark (active) period. (C and D) 16p11.2 del/+ mice have significantly greater activity relative to wildtype littermates, irrespective of sex, in both the horizontal (C) and vertical (D) axes. (E and F) There are no significant differences between 16p11.2 del/+ and wildtype mice in elevated zero-maze time spent in open arms (E) or risk assessment (F). (G and H) There are no differences in open field total ambulation (G) or time spent in center (H) between 16p11.2 del/+ mice and wildtype controls. Mean 6 standard error of the mean (s.e.m.) * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001.

Figure 2.

Male 16p11.2 del/+ mice sleep less than wildtype littermates. (A–C) Male 16p11.2 del/+ mice are awake significantly more (A) and spend significantly less time in NREM sleep (B) than wildtype mice over the 24-hr period. The amount of REM sleep in male 16p11.2 del/+ mice was not significantly different from wildtype (C). (D) NREM sleep time expressed in 6 hr bins reveals that males have significantly less sleep during the last 6 hours of the light in comparison to wildtype littermates. Gray box indicates the dark period. (E–F) There are no significant differences in wake (E), NREM sleep (F and H), or REM sleep (G) time between 16p11.2 del/+ females and controls. Mean ± s.e.m. *P < 0.05, **P < 0.01.

Figure 3.

Male 16p11.2 del/+ mice spend a significantly higher proportion of wake time in prolonged bouts of wakefulness. Proportion of total wake time across the 24-hr period divided into bout lengths of 30s–80s, 80s–160s, 160s–320s, 320s–640s, 640s–1280s, 1280s– 2560s, and >2560s. (A) 16p11.2 del/+ male mice spend a significantly greater proportion of their wake time in long bouts of wakefulness (>2560s) and a significantly lower proportion of time in intermediate bouts of wakefulness (160s–1280s). (B and C) 16p11.2 del/+ males exhibit no differences in NREM (B) or REM (C) bout length distribution. (D–F) 16p11.2 del/+ female mice do not differ from wildtype littermates in distribution of wake (D), NREM (E), or REM (F) bout length. Mean ± s.e.m. *P < 0.05, **P < 0.01.

Figure 4.

Male 16p11.2 del/+ mice have increased alpha power during wake. (A) Male 16p11.2 del/+ mice have increased alpha power during wake (A, inset). (B–C) Male 16p11.2 del/+ mice have no differences in EEG power spectra during NREM sleep (B) or REM sleep (C). (D) Female 16p11.2 del/+ mice have increased beta power during wake (D, inset). (E) Female 16p11.2 del/+ mice have decreased low delta during NREM sleep (E, inset). (F) Female 16p11.2 del/+ mice have no differences in EEG power spectra during REM sleep (F). Mean ± s.e.m. *P < 0.05.