3684
Adult rats had higher tissue serotonin content than adolescents in the prefrontal cortex , amygdala , and hippocampus , but the rate of serotonin synthesis was similar between age groups .
 Chemical: serotonin; 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; Chemical: serotonin