2070
The effect appears to be mediated by central nicotine receptors , possibly located on dopaminergic neurons , and also requires the activation of both D1 and D2 dopamine receptors .
 nicotine, dopamine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 nicotine, dopamine