3049
To investigate the validity of blood serotonin as a peripheral marker for central serotonin in this regard , we administered MDMA ( 20 mg / kg i . p . ) to rats and observed a parallel decrease in serotonin levels in the frontal cortex and blood at 2 h ( 63 % and 46 % respectively ) with some recovery evident at 8 h ( 42 % and 38 % ) and more so at 18 h ( 19 % and 24 % below control levels ) .
 Chemical: serotonin; Chemical: serotonin; Chemical: MDMA; 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; Chemical: MDMA; Chemical: serotonin