11146
Mechanisms of tolerance were investigated using binding studies to mu - opioid receptors ( MOR ) and adenylate cyclase ( AC ) activity measurement in homogenates of cell membranes from the periaqueductal gray region ( PAG ) and brainstem .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None