13803
Treatment with ultra - low doses of the nonselective opioid antagonist ( - ) - naloxone or its inactive enantiomer ( + ) - naloxone blocks this excitatory effect and enhances Gi - coupling .
 Chemical: ( - ) - naloxone; Chemical: ( + ) - naloxone
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: ( - ) - naloxone; Chemical: ( + ) - naloxone