20371
These results cannot be explained by a direct interaction of sigma 1 ligands with mu - opioid receptors or adaptive changes of mu - receptors in sigma 1 - KO mice , given that [ ( 3 ) H ] DAMGO binding in forebrain , spinal cord , and hind - paw skin membranes was unaltered in mutant mice , and none of the sigma 1 drugs tested bound to mu - opioid receptors .
 Chemical: [ ( 3 ) H ] DAMGO
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: [ ( 3 ) H ] DAMGO