Differential noradrenergic innervation of the gerbil superior colliculus in response to mistimed blue light in adolescence Restricted; Files Only
Troilo, Maxwell (Spring 2025)
Abstract
Blue-enriched light exposure impacts neural function in many adaptive ways, but mistimed exposure can negatively impact brain regions responsible for regulating arousal, attentiveness, and responses to visual stimuli. Previous research in our lab has demonstrated that exposure to mistimed blue light corresponds to increased social exploration and aggressive behaviors (Moon 2023). Intrinsically photosensitive retinal ganglion cells and normal retinal ganglion cells project information about blue light in the environment to multiple brain areas that process visual information, including the superior colliculus. The superior colliculus is a visual processing structure in the midbrain that receives direct visual input from the eyes as well as from higher cortical areas and produces motor responses to stimuli. For this reason, it is a relevant structure to investigate the effects of mistimed blue light exposure on the visual system. The superior colliculus is separated into distinct structural layers and functionally divided between the lateral and medial sides responsible for approach and avoidance behaviors, respectively. In addition, along the anterior-posterior axis of the SC, the anterior hemisphere of the structure processes visual input from the binocular field, while the posterior hemisphere processes information from the peripheral visual field. Moreover, noradrenergic innervation of the superior colliculus has an modulatory effect on the structure, which inhibits neural activity that shapes downstream motor responses. Given previous behavioral data (Moon 2023), we hypothesized that the lateral side of the superior colliculus from the evening-light and morning-light animals would demonstrate greater NE innervation density than the medial side. Because of the suppressive action of noradrenaline in the SC, higher density of NE innervation in the lateral side of the superior colliculus could contribute to increased threat-oriented approach behavior and aggressive responses. TH immunohistochemistry was used to visualize noradrenergic innervation of the superior colliculus, followed by photomicrography of 68 sampling boxes through the structure. TH innervation density was estimated via fiber counting of intersections through reticle squares arranged in a 3x3 grid for each sampling box. Results indicated that there were no significant effects of blue light exposure on the ratio of lateral:medial innervation density among the groups. However, further analysis demonstrated a significant effect of blue light exposure on the ratio of posterior:anterior superior colliculus innervation density. Previous research in mice has demonstrated that developmental differences in pursuit behavior are correlated with differences in cellular activity within the SC responsible for processing of the binocular visual field (Allen et al. 2022). Therefore, our finding suggests that the observed differences in behavior may be related to differential effects of blue light exposure on binocular vs. peripheral processing of visual stimuli, but further research is needed to investigate specific trends.
Table of Contents
Table of Contents
Introduction 1
Impact of the Day-Night Cycle on Human Activity Patterns: 2
Mongolian Gerbil: 2
Blue Light Exposure during Development: 4
Effects of Light on the Brain: 4
The Rodent Superior Colliculus: 5
Figure 1: Structural separation of the superior colliculus 6
Figure 2: Topographic organization of the superior colliculus to the visual field of rodents 7
Parabigeminal Nucleus Input: 8
Hypothesis: 9
Methods 9
Animals: 9
Light Exposure Intervention: 10
Figure 3: Experimental lighting conditions of the three groups of gerbils 11
Behavioral Testing of Gerbils: 11
Histology: 13
Sampling Guide and Counting: 14
Figure 4: Plate 35 of the Radtke gerbil brain atlas with the corresponding sampling guide. 15
Figure 5: SGS of the gerbil superior colliculus with the 3x3 sampling grid box superimposed above 16
Data Analysis: 16
Results 17
Medial:Lateral Innervation Density Ratio: 17
Figure 6: Average lateral:medial innervation density ratio across each experimental lighting condition. 17
Posterior:Anterior Innervation Density Ratio: 18
Figure 7: Average posterior:anterior innervation density ratio across each experimental lighting condition 19
Lateral:Medial Wall Innervation Density Ratio: 20
Figure 8: Average lateral:medial wall innervation density ratio across each experimental lighting condition. 21
Right:Left Hemisphere Innervation Density Ratio: 22
Figure 9: Average right:left hemisphere innervation density ratio across each experimental lighting condition 22
Discussion 23
Limitations: 28
Conclusion: 30
References 31
Appendices 38
A: Lateral and Medial SC Summary Statistics of Absolute Counts of Innervation 38
B: Anterior and Posterior SC Summary Statistics of Absolute Counts of Innervation 38
C: Summary Statistics of Absolute Counts of Innervation along Medial Wall of SC 38
D: Right and Left Hemisphere Summary Statistics of Absolute Counts of Innervation 39
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File download under embargo until 22 May 2027 | 2025-04-08 12:55:18 -0400 | File download under embargo until 22 May 2027 |
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