The Role of Blue LED Light Exposure in Basolateral Amygdalar Serotonin Innervation and Anxiety-Like Behavior Open Access

Abstract

Blue LED light has been thought to impact affective behavior by activating intrinsically photosensitive retinal ganglion cells (ipRGCs). Past literature has suggested that frequent long-term activation of ipRGCs will continually over-activate anxiety networks in the limbic system leading to the development of anxiety psychopathologies. Literature has indicated that nocturnal blue light exposure negatively impacts mood, whereas diurnal blue light exposure has been used as a treatment modality for seasonal affective disorder (SAD). Additionally, long-term altered light has been correlated with differences in monoamine levels and behavioral changes. Thus, the present study aimed to see if this pattern holds true with blue light, specifically looking at serotonin the basolateral amygdala. Therefore, the present study aimed to investigate whether nocturnal or diurnal blue light exposure creates changes in both serotonin innervation in the basolateral amygdala and anxiety-like behavior. 

Adolescent Mongolian gerbils (Meriones uniguiculatus)  were either assigned blue LED light enrichment for four weeks, at morning or night where they received 12:12 hours of light and dark, with blue LED light enrichment turned on two hours before or after the colony lighting. Following, the gerbils underwent the Elevated Plus Maze (EPM) and Social Approach tasks. Once reaching adulthood, the gerbils were euthanized, and serotonin innervation of the basolateral amygdala was tested through immunohistochemistry using the SERT antibody. 

It was hypothesized that the gerbils who received evening light enrichment would show lower levels of social approach and greater time in the enclosed arms of the EPM levels, indicating anxiety-like phenotypes and behaviors. Additionally, it was expected that these gerbils would have a lower SERT density in the basolateral amygdala compared to gerbils with morning or no enrichment. Therefore, it was expected that the evening lighting conditions mimic behavioral and neurochemical changes similar of anxiety pathologies. 

There was not significant data suggesting that blue LED lighting during the adolescent development period is correlated with either serotonin innervation or anxiety-like behaviors. This may indicate that low levels of blue light do not actually cause detrimental harm, despite the common belief. This may suggest that there may be confounding variables that attribute to increased psychopathologies, and there may not be a direct mechanism involving iPRGCs. However, this interpretation should be considered preliminary due to the small sample size and the limited areas of interest and behavioral phenotypes studied. 

Table of Contents

Table of Contents

Introduction ………………………………………………………………   1

                  1.1.         Psychophysiological Impacts of Lighting

                  1.2.         The Amygdala’s Role in Affective Behavior 

                  1.3.         Serotonin System in the Central Nervous System

                  1.4.         Serotonin Transporter (SERT)

                  1.5.         The Mongolian Gerbil Model and Relevant Animal Behavior 

                  1.6.         Purpose of Present Study 

Methods ………………………………………………………………         11

                  2.1.         Animal Rearing and Conditions

                  2.2.         Behavioral Training and Testing 

                  2.3.         Neuroanatomical Analysis and Histological Processing 

                  2.4.         Scoring and Data Collection 

Results …………………………………………………………………… 15

                  3.1.         SERT Innervation Analyses

                  3.2.         Anxiety-Like Behavior Analyses 

                  3.3.         Exploratory Analyses 

Discussion ………………………………………………………………… 17

                  4.1.         General Discussion

                  4.2.         Limitations and Future Directions 

                  4.3.         Conclusion

References ………………………………………………………………… 22

Figures and Appendices  ………………………………………………………30

            

 

            

About this Honors Thesis

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School	Emory College
Department	Psychology
Subfield / Discipline	Neuroscience and Animal Behavior
Degree	B.A.
Submission	Honors Thesis
Language	English
Research Field	Psychology, Physiological
Keyword	serotonin anxiety psychopathology chronobiology Blue LED light exposure
Committee Chair / Thesis Advisor	Hillary Rodman , Emory University
Committee Members	Gillian Hue, Emory University Sarah Higinbotham , Emory University Elizabeth Kim , Emory University

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