Light at night: effect on the daily clock, learning, memory, cognition, and expression of transcripts in different brain regions of rat.

Abstract

The rapid increase in urbanization is altering the natural composition of the day-night light ratio. The light/dark cycle regulates animal learning, memory, and mood swings. A study was conducted to examine the effect of different quantity and quality of light at night on the daily clock, learning, memory, cognition, and expression of transcripts in key learning centers. Treatment was similar for experiments one to three. Rats were exposed for 30days to 12h light and 12h dark with a night light of 2lx (dLAN group), 250lx (LL), or without night light (LD). In experiment one, after 28days, blood samples were collected and 2days later, animals were exposed to constant darkness. In experiment two, after 30days of treatment, animals were subjected to various tests involving learning, memory, and cognition. In experiment three, after 30days of treatment, animals were sampled, and transcript levels of brain-derived neurotrophic factor, tyrosine kinase, Growth-Associated Protein 43, Neurogranin, microRNA-132, cAMP Response Element-Binding Protein, Glycogen synthase kinase-3β, and Tumor necrosis factor α were measured in hippocampus, thalamus, and cortex tissues. In experiment four, animals were exposed to night light of 0.019W/m2 but of either red (640nm), green (540nm), or blue (450nm) wavelength for 30days, and similar tests were performed as mentioned in experiment 2. While in experiment five, after 30days of respective wavelength treatments, all animals were sampled for gene expression studies. Our results show that exposure to dLAN and LL affects the daily clock as reflected by altered melatonin secretion and locomotor activity, compromises the learning, memory, and cognitive ability, and alterations in the expression levels of transcripts in the hypothalamus, cortex, and thalamus. The effect is night light intensity dependent. Further, blue light at night has less drastic effects than green and red light. These results could be of the potential use of framing the policies for the use of light at night.