4. Neurite Growth Research Project-JanPlan 2009

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Our results do not fully support our hypothesis.  Both of our DEET and Gingko Biloba additives resulted in a significantly different neurite growth than our controls (Figure 1).  It was expected that the Gingko Biloba additives would have a higher neurite growth than the control due to its chemical ability to prevent the free radicals from "stealing" electrons from the growing neurite membranes. However, DEET, a potentially toxic substance, had more neurite growth than Gingko Biloba, a health supplement. DEET and Ginkgo Biloba exhibit antagonistic properties of oxidation and antioxidation, respectively, and yet both led to a strong and significant stimulatory response.   This could mean that the oxidative influences of DEET are stimulatory and not inhibitory, which does not support our hypothesis.  Overall The reasons for the increased neurite growth of DEET is unknown however there is a very strong possibility that DEET simply increases neurite growth. Further studies are needed to discover the underlying mechanisms. However, in other studies it was found that acetylcholinesterase (AChE), the enzyme that catalyzes the reaction for the neurtransmitter acetylcholine (ACh) to be broken down into choline and acetic acid, enhances neurite growth and synapse development. This enzyme also functions to return an stimulated neuron to its resting state by inhibiting ACh. Hence, if AChE activity is suppressed by an inhibitor such as a pesticide like DEET, the concentration of ACh increases in the synapse causing over stimulation of neurons. This suggests that a potent dose of DEET could over stimulate neurons to a certain toxicity. Another study found that animals treated with DEET alone produced significant increases in cortical ACh receptor binding. In contrast, what we do know at this time is that DEET does indeed stimulate neuron growth, at least under the perimeters of this experiment. Therefore, there might be some undiscovered mechanism within the fiddler crabs that instead of inhibiting neurite growth it stimulates it. This experiment is highly worthy of further study due to the fact that other oxidative stressors, such as hydrogen peroxide, was found by previous Tilden studies to inhibit neurite growth.   Additionally, because both additives are made of a mixture of different chemicals, there could be many different unknown stimulating/inhibiting factors, which is why more research is needed on this subject. 

Figure 1. Neurite growth in neurons extracted from X-organs of _Uca pugliator_ as a function of cell culture additives. Controls were treated with normal culture medium, n=100; DEET n=79 and Ginko Biloba n=158.