Effects of Photoperiod and Blue Light Exposure on Thyroid Hormone Regulation in Male Wistar Rats (Rattus norvegicus) Afdhal Tisyan(a*), Lulu Lusianti Fitri(a), Karlia Meitha(a)
School of Life Sciences and Technology, Bandung Institute of Technology, Ganesha Street No.10, Bandung 40132, Indonesia
*tisyan.bong[at]gmail.com
Abstract
Blue light (bl) is a nonvisual stimulus to the biological clock center in the suprachiasmatic nucleus (SCN). SCN generates metabolic rate change, which is regulated centrally by thyroid hormone (TH) in the hypothalamus and peripherally in adipose tissue through the deiodination mechanism. The purpose of the present study was to analyze the differences in the photoperiodic response under bl exposure by examining total circulated TH and deiodinase expression levels in rats. The physiological response was tested on neutral photoperiod (12L:12D) without bl exposure- short (8L:16D, SD) and long (16L:8D, LD) photoperiod treatment which consists of a group without bl exposure and bl interruption in the middle of the light phase (n = 6/group). The results revealed that blue light exposure suppressed the expression of DIO2 in the hypothalamus of SD rats and iBAT of LD rats, as well as suppression of DIO3 expression in the hypothalamus of LD rats. Lower DIO2 levels in iBAT supported higher body mass of LD rats. SD rats exhibited milder stress behavior than LD, whereas, under exposure to bl, LD rats showed more stress suppression than non-bl LD rats. Our data suggest that bl exposure positively affected the body mass of LD rats. Conversely, SD rats with a more negative energy balance showed lower body mass and high compensation of food intake. In conclusion, blue light suppressed stress levels notably in long photoperiod compared to non-exposure to blue light, and low-stress behavior was found to contribute to higher body mass.
Keywords: blue light- brown adipose tissue- hypothalamus- photoperiod- thyroid hormone
