Dissociating the Effects of Light at Night from Circadian Misalignment in a Neurodevelopmental Disorder Mouse Model Using Ultradian Light-Dark Cycles.

Individuals with neurodevelopmental disorders (NDDs) often experience sleep disturbances and are frequently exposed to light during nighttime hours. Our previous studies using the knockout (KO) mouse model of NDDs demonstrated that nighttime light exposure increases behaviors such as excessive grooming, reduces social interactions, and disrupts daily locomotor rhythms. To further evaluate the effects of nighttime light exposure, we exposed wild-type (WT) and KO mice to an ultradian lighting cycle (T7), which alternates 3.5 hours of light and 3.5 hours of darkness. Circadian rhythms in activity, corticosterone levels, and clock gene expression are maintained under T7 lighting despite the presence of light during the usual night phase, whilst animals display increased depressive-like behaviors and reduce performance on the novel object recognition test. Based on these observations, we hypothesized that T7 lighting would mimic the impact of nighttime light exposure seen in standard light-dark cycles with dim light at night (DLaN). However, in this study, adult WT and KO mice held under the T7 cycle did not show the increased grooming behavior or reduced social interaction observed in KO mice exposed to DLaN. Regarding locomotor activity rhythms, the T7 cycle lengthened the circadian period and weakened the rhythm amplitude but did not abolish rhythmicity in either genotype. Finally, opposite to DLaN, neither the T7 cycle nor constant darkness (DD) elicited an increase in cFos expression in the basolateral amygdala in WT and KO mice. These results demonstrate that the adverse behavioral and neurobiological effects of nighttime light exposure in a model of a neurodevelopmental disorder depend on circadian disruption rather than light exposure alone, highlighting the importance of circadian stability as a protective factor in NDDS.