8351
Variations of dopamine ( DA ) levels induced by drugs of abuse or in the context of Parkinson ' s disease modulate the number of dendritic spines in medium spiny neurons ( MSNs ) of the striatum , showing that DA plays a major role in the structural plasticity of MSNs .
 dopamine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 dopamine