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We found that networks derived from spinal cord are more sensitive to the toxin than those from frontal cortex ; a concentration of only 10nM produced statistically significant effects on activity from spinal cord networks whereas 50nM was required to alter activity in frontal cortex networks .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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