Dim artificial light at night alters immediate early gene expression throughout the avian brain

Abstract

Artificial light at night (ALAN) is a pervasive pollutant that alters physiology and behavior. However, the underlying mechanisms triggering these alterations are unknown, as previous work shows that dim levels of ALAN may have a masking effect, bypassing the central clock. Light stimulates neuronal activity in numerous brain regions which could in turn activate downstream effectors regulating physiological response. In the present study, taking advantage of immediate early gene (IEG) expression as a proxy for neuronal activity, we determined the brain regions activated in response to ALAN. We exposed zebra finches to dim ALAN (1.5 lux) and analyzed 24 regions throughout the brain. We found that the overall expression of two different IEGs, cFos and ZENK, in birds exposed to ALAN were significantly different from birds inactive at night. Additionally, we found that ALAN-exposed birds had significantly different IEG expression from birds inactive at night and active during the day in several brain areas associated with vision, movement, learning and memory, pain processing, and hormone regulation. These results give insight into the mechanistic pathways responding to ALAN that underlie downstream, well-documented behavioral and physiological changes.

Keywords: Taeniopygia guttata; ZENK; cFos; light pollution; zebra finch.

Figure 1

Types of behavior 75 to 105 min before perfusion for birds exposed to ALAN and control birds collected during the day and night. A 30-min window of time 90 min before perfusion (75 to 105 min) was analyzed and broken down into four different behaviors: feeding (eating or drinking), grooming, hopping, and inactive. Shown are means ± 1 SE.

Figure 2

Immediate early gene expression of cFos and ZENK throughout the brain for birds exposed to ALAN, and control birds collected during subjective day and night. (A) Total cFos and ZENK expression, shown in percentages. Expression is significantly higher in the ALAN treatment group compared to the night controls but not the day controls. (B) cFos expression (percentage) comparing birds exposed to ALAN to control day and control night groups in three brain regions: posterior hyperpallium, anterior mesopallium dorsal, and entopallium. (C) ZENK expression (percentage) comparing birds exposed to ALAN to control day and control night groups in three brain regions: hippocampus, medial dorsal mesopallium, and entopallium. Displayed are representative brain regions from a priori hypotheses, please see Supplementary Figures S2, S3 for all brain regions. Shown are means ±1 SE. Significance stars: *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 3

Brain slices with cFos and ZENK staining in the anterior mesopallium dorsal. (A) A sagittal slice of a representative zebra finch brain 1 mm from the center, showing the anterior mesopallium dorsal. Blue is DAPI, green is cFos, and red is ZENK expression. (B) Images from the anterior mesopallium dorsal of cFos, ZENK, and the overlay of both with DAPI for a bird exposed to ALAN, a bird collected during the day (control day), and a bird collected at night (control night).