21835
To investigate the effects of naltrexone and BTX - A on neuronal activation in spinal cord , c - Fos expression was immunohistochemically examined in a model of formalin - induced pain .
 Chemical: naltrexone; Chemical: formalin
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: naltrexone; Chemical: formalin