4460
Indeed , after a single oral dose , the role of the mu - receptor agonist component of the antinociceptive effect of tramadol appears to be minor , with most of the analgesic effect being attributable to nonopioid properties of the parent compound .
 GENE: mu - receptor
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
 GENE: mu - receptor