8209
Therefore , we investigated the hippocampal gene expression of estrogen receptors alpha and beta ( ER alpha , beta ) in 8 - week - old , 12 - week - old and 24 - week - old male rats .
 Chemical: estrogen
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: estrogen