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In a wide range of animals , uncontrollable stressful events can induce a condition called " learned helplessness . " In mammals it is associated with low general activity , poor learning , disorders of sleep and feeding , ulcers , and reduced immune status , as well as with increased serotonin in parts of the brain .
 Chemical: serotonin
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: serotonin