ANXIETY-LIKE BEHAVIOUR STUDY IN ADULT RAT STRESS MODEL INDUCED BY LIGHT DOMINANT EXPOSURE IN CIRCADIAN RHYTHM DISRUPTION

Abstract

The breakdown of biobehavioural adaptive mechanisms with stress response and vulnerability may result from circadian rhythm disruption driven by an internal timing system that enables numerous fundamental features from gene expression to behaviour. Previous study showed the difference length of the exposure in circadian cycle caused behaviour abnormality. However, the light dominant exposure as a stressor in circadian disruption affects behaviour still remain unclear. Using a rat model, we investigated the stress-related mechanisms susceptible to chrono disruption manifested in anxiety-like behaviour. We evaluated the effect of light-dominant exposure of adult male rats to white light-emitting diodes (LED) with 300 lux light intensity. The experimental groups consisted of three conditioned light-dominant exposures. Group 1 (16 h light: 8h dark); Group 2 (20 h light: 4 h dark); Group 3 (24 h light) compared to the control group (12 h light: 12 h dark) in 4 weeks of intense light exposure. By the end of the exposure time, we assessed their behaviour using Open Field Test instruments. Additionally, body weight and food consumption amounts were measured by the end of each week to indicate the effect of chrono disruption on the eating behaviour of the rats. ANOVA and Tukey post-hoc test were applied to determine the significant value among the groups of the treatments. Behaviour study revealed that 24-hour light exposure showed increased time spent in the centre and total travelled distance, which showed less anxiety than all groups. Meanwhile, rats exposed to 20h light had the lowest activity to interact with the recognized and novel object, which indicates anxiety toward the stimulus. Similarly, 20h light exposure rats showed the least interaction with the social partner and increased duration and frequency of grooming, which exhibited anxiety-like behaviour. Other than that, 24-hour light exposure showed less anxiety, indicated by increased social interaction and decreased grooming time. In body weight change, there was no significant difference (P >0.05) between all groups; meanwhile, the 24-hour light exposure showed the lowest food consumption. The disruption of circadian rhythm by exposure to chronic light induces stress and anxiety by altering serotonin regulation in the brain. The light dominant exposure lengthens the inactive phase of the rat’ s biological clock that influence serotonin release which is the highest serotonin release is during the active phase under circadian control. Decreased serotonergic activity has been implicated in anxiety and depression. The low serotonin activity might inhibit melatonin hormone release as the essential factor in sleep regulation, which underlies the circadian rhythm. Therefore, light-dominant exposure to rats has marked an anxiety-like behaviour on the circadian rhythm dysregulation.