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We report here that mRNA expression of the mu - opioid receptor in the ventral tegmental area ( VTA ) at weaning was 1 . 4 - fold ( males ) and 1 . 9 - fold ( females ) lower in offspring of junk - food ( JF ) - fed rat dams than in offspring of dams fed a standard rodent diet ( control ) ( P < 0 . 05 ) .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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