16893
RATIONALE : The head - twitch response ( HTR ) is a rapid side - to - side rotational head movement that occurs in rats and mice after administration of serotonergic hallucinogens and other 5 - HT ( 2A ) agonists .
 Chemical: 5 - HT
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: 5 - HT