421
The metabotropic glutamate receptor 8 agonist ( S ) - 3 , 4 - DCPG reverses motor deficits in prolonged but not acute models of Parkinson ' s disease .
 glutamate, ( S ) - 3 , 4 - DCPG
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 glutamate, ( S ) - 3 , 4 - DCPG