Artificial blue light exposure induces anxiety-like behaviour, alters recognition memory and modifies hippocampal morphology in adolescent rats

Abstract

Background: The constant artificial blue light exposure from electronic gadgets at night raises concerns about its impact on mood and brain functions. This study is designed to evaluate the effect of chronic exposure to artificial blue light from a light-emitting diode (LED) light on emotionality, locomotion, novel object recognition memory and hippocampal cytoarchitecture in adolescent rats. Materials and methods: Male albino Wistar rats were exposed to artificial blue light (450 – 495 nm, and 100 Lux) for 14 days from a LED
light source. Later, their emotionality, general locomotor behaviours and novel object recognition memory were tested by a computerised behavioural assessment system. After the behavioural assessments animals were euthanized to study the hippocampal cytoarchitecture by Nissl and Golgi-Cox staining. Results: In the open field test, latency to enter the centre zone was significantly increased in blue light-exposed animals compared to controls. Total entries to the centre zone and percentage of time spent in the centre zone
were slightly reduced in blue light-exposed animals. The mean speed of animals in the centre, total zone transitions, total distance travelled, and zone transitions were not different between the two groups. In the elevated plus maze test, entries to the open arm were significantly reduced in blue light exposed animals. Time spent and distance travelled on the open arm were slightly reduced in blue light-exposed animals. Entries to the closed arm and time spent in the closed arm were slightly increased but, the distance travelled in the closed arm was significantly reduced in the light-exposed group. The mean speed of light-exposed animals on the open arm, closed arm and centre were comparable in the two groups. Rearing duration and total zone transitions were slightly reduced but the total distance travelled was significantly reduced in the light exposed group. Novel object recognition was altered in the light exposed group as indicated by their negative discrimination index values. Hippocampal CA1 and CA3 regions demonstrated pyknotic cells and CA1 apical dendritic spine density was reduced in blue light exposed rats. Conclusion: Artificial blue light exposure induced anxiety-like behaviours, and significantly altered novel object recognition memory, but only mildly affected the general locomotor behaviours in adolescent rats. Moreover, it induced hippocampal cellular pyknosis and reduced cornu ammonis-1 (CA1) apical dendritic spine density in blue light exposed adolescent rats.