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<p>In order to develop a better understanding of the role environmental toxicants
may play in the onset and progression of neurodegenerative diseases, it has become
increasingly important to optimize sensitive methods for quickly screening toxicants
to determine their ability to disrupt neuronal function. The model organism Caenorhabditis
elegans can help with this effort. This species has an integrated nervous system producing
behavioral function, allows for easy access for molecular studies, has a rapid lifespan,
and is an inexpensive model. This project focuses on the development and optimization
of a low-cost efficient behavioral tool for the identification of environmental toxicants
with actions that disrupt dopamine function in the nematode C. elegans. Several dopamine-mediated
locomotory behaviors, Area Exploration, Body Bends, and Reversals, as well as Swimming-Induced
Paralysis and Learned 2-Nonanone Avoidance, were compared to determine the best behavioral
method for screening purposes. These behavioral endpoints were also compared to morphological
scoring of neurodegeneration in the dopamine neurons. We found that in adult worms,
Area Exploration is more advantageous than the other behavioral methods for identifying
DA-deficient locomotion and is comparable to neuromorphological scoring outputs. For
larval stage worms, locomotion was an unreliable endpoint, and neuronal scoring appeared
to be the best method. We compared the commonly used dat-1p::GFP reporter strains
BY200 and BZ555, and we further characterized the dopamine-deficient strains, cat-2
e1112 and cat-2 n4547. We found that BY200 and BZ555 have differential responses in
DA-targeted neurodegeneration using the model toxicant 6-hydroxydopamine, with BY200
appearing to have somewhat increased sensitivity to treatment. In contrast to published
results, we found that the cat-2 strains slowed on food almost as much as N2s. Rather
than being null mutants, both showed decreased levels of cat-2 mRNA and DA content,
with cat-2 e1112 having the greatest reduction in DA content in comparison to N2.
Ultimately, we concluded that while behavioral analysis is a promising endpoint, it
is probably best used as a quick screening tool, with follow-up studies assessing
affects to neuron morphology. A more informative readout of toxicant effects to the
DA system would be best accomplished using a combination of the assays outlined in
this project. We offer a table at the conclusion of this study comparing strengths,
limitations, costs, and equipment needs for the methods of analysis of the dopaminergic
system in C. elegans undertaken in this project.</p>
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