4162
Morphine - dependent and control rats in an oral free - choice protocol were treated with gamma - vinyl GABA ( GVG ) , 60 , 120 and 240 mg / kg IP , for 3 days over three successive periods .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 None