8406
The mechanism underlying such analgesia has been suggested to involve the interaction between the two separate but interconnected motivational systems " defense " and " pain . " To determine the developmental course of defense and nociception , these processes were analyzed during early ontogeny in rats .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
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