19808
Contribution of the m1 transmembrane helix and pre - m1 region to positive allosteric modulation and gating of N - methyl - d - aspartate receptors .
 N - methyl - d - aspartate
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 N - methyl - d - aspartate