21845
Cells in the CNS depend on paracrine / autocrine communication via several extracellular signaling molecules , such as , cytokines , growth factors , transmitters and free radical species to sense changes in microenvironment as well as to adapt to them .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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