Quantifying Upper Motor Neurons in Rodent Model of Amyotrophic Lateral Sclerosis Open Access

Abstract

Amyotrophic Lateral Sclerosis (ALS), more commonly known as Lou Gehrig's disease, is an adult-onset neurodegenerative disorder in which there is a progressive loss of upper (brain) and lower (brainstem and spinal cord) motor neurons. Patients with ALS rapidly lose use of their extremities and become ventilator dependent, with 80% of patients dying within 3-5 years after diagnosis. Animal models have been used over the years to study the mechanisms of this disease as well as a way to test potential therapies. One of the most characterized models involves the over expression of the human SOD1 G93A gene, a mutation known to cause ALS. Currently, there is no data available that shows how the upper motor neurons--specifically rubrospinal and corticospinal motor neurons - compare in SOD1 G93A rats compared to wild-type animals. By injecting a retrograde tracer into the rubrospinal and corticospinal tracts, this study aims to quantify the upper motor neuron count in the red nucleus and motor cortex in both SOD1 G93A and wild-type animals to determine if there is a significant difference. Additionally, the motor neuron counts in the red nucleus will be compared by two methods: the tracer and cresyl violet staining to determine which is more accurate. Results indicate that despite accurate injections in 5 of 10 corticospinal tracts, the tracer did not reach the motor cortex. Rubrospinal tract injections were much less accurate, with only three animals presenting with tracer in the red nucleus. Additional brain areas also expressed tracers, further confirming the inaccuracy of injections. Further investigation with better accuracy, correct timing, and a larger sample size will be able to provide a better understanding of ALS; not only will it further validate the animal model replicating the clinical symptoms of human pathology but also becoming a resource that will allow investigation to determine if potential therapies are improving upper motor neuron survival rather than only behavioral improvements.

Table of Contents

1) Introduction..................................................................................................1

2) Methods.......................................................................................................6

a) Animals...............................................................................................6

b) Surgery...............................................................................................6

c) Tissue Collection...................................................................................7

d) Immunohistochemistry..........................................................................8

e) Imaging..............................................................................................8

f) Statistical Analysis................................................................................9

3) Results........................................................................................................9

a) No Microspheres Present in Motor Cortex.................................................9

b) Microspheres Can Reach Rubrospinal Neurons in the Red Nucleus................9

c) Difference in Rubrospinal Motor Neuron Counts between Retrogreen

Microspheres and Cresyl Violet Staining......................................................10

d) Microspheres Present in Additional Brain Regions.....................................10

4) Discussion...................................................................................................11

5) References..................................................................................................16

6) Figures.......................................................................................................19

a) Figure 1..............................................................................................19

b) Figure 2..............................................................................................20

c) Figure 3..............................................................................................21

d) Figure 4..............................................................................................22

e) Figure 5..............................................................................................23

f) Figure 6..............................................................................................23

7) Appendix A.................................................................................................24

About this Honors Thesis

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School	Emory College
Department	Neuroscience and Behavioral Biology
Degree	BS
Submission	Honors Thesis
Language	English
Research Field	Biology, Neuroscience
Keyword	Corticospinal Tract Retrograde Tracer Amyotrophic Lateral Sclerosis Rubrospinal Tract
Committee Chair / Thesis Advisor	Boulis, Nicholas, Emory University
Committee Members	Roesch, Leah Anderson, Emory University Hochman, Shawn, Emory University

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