Exposure to dim light at night during early development increases adult anxiety-like responses

May 27, 2014Physiology & behavior

Dim light at night during early growth increases anxiety-like behavior in adults

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Abstract

Mice exposed to dim light during early life exhibited increased anxiety-like behavior and fearful responses.

Early life exposure to dim light (~5 lux) was associated with increased anxiety-like behavior in mice.
Mice demonstrated heightened fearful responses in elevated plus maze and passive avoidance tests after dim light exposure.
Reduced growth rates were observed in mice exposed to dim light, although these rates normalized during adolescence.
mRNA expression of brain derived neurotrophic factor (BDNF) in the prefrontal cortex and hippocampus was not affected by early life light exposure.
Serum corticosterone concentrations at weaning were similar across groups, indicating no long-term physiological stress response from early life dim light exposure.
Behavioral effects were not observed in other tests, such as the open field or forced swim tests.

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Early experiences produce effects that may persist throughout life. Therefore, to understand adult phenotype, it is important to investigate the role of early environmental stimuli in adult behavior and health. Artificial light at night (LAN) is an increasingly common phenomenon throughout the world. However, animals, including humans, evolved under dark night conditions. Many studies have revealed affective, immune, and metabolic alterations provoked by aberrant light exposure and subsequent circadian disruption. Pups are receptive to entraining cues from the mother and then light early during development, raising the possibility that the early life light environment may influence subsequent behavior. Thus, to investigate potential influences of early life exposure to LAN on adult phenotype, we exposed mice to dim (~5 lux; full spectrum white light) or dark (~0 lux) nights pre- and/or postnatally. After weaning at 3 weeks of age, all mice were maintained in dark nights until adulthood (9 weeks of age) when behavior was assessed. Mice exposed to dim light in early life increased anxiety-like behavior and fearful responses on the elevated plus maze and passive avoidance tests. These mice also displayed reduced growth rates, which ultimately normalized during adolescence. mRNA expression of brain derived neurotrophic factor (BDNF), a neurotrophin previously linked to early life environment and adult phenotype, was not altered in the prefrontal cortex or hippocampus by early life LAN exposure. Serum corticosterone concentrations were similar between groups at weaning, suggesting that early life LAN does not elicit a long-term physiologic stress response. Dim light exposure did not influence behavior on the open field, novel object, sucrose anhedonia, or forced swim tests. Our data highlight the potential deleterious consequences of low levels of light during early life to development and subsequent behavior. Whether these changes are due to altered maternal behavior or persistent circadian abnormalities incurred by LAN remains to be determined.

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Exposure to dim light at night during early development increases adult anxiety-like responses

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