11153
The difference in morphine - induced AC activation between the brainstem and the PAG contributes to the observed difference in tolerance between both morphine effects .
 Chemical: morphine; Chemical: morphine
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: morphine; Chemical: morphine