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We report here the synthesis and in vitro validation of a Gd ( III ) - based contrast agent designed to act as an MRI responsive probe for imaging the activity of the enzyme glutamic acid decarboxylase ( GAD ) present in neurons .
 Chemical: Gd ( III ); Chemical: glutamic acid
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: Gd ( III ); Chemical: glutamic acid