Mood regulator translated into Norse (9)
I believe the answer is:
serotonin
'mood regulator' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'translated into norse' is the wordplay.
'translated' indicates anagramming the letters.
'into'+'norse'='intonorse'
'intonorse' is an anagram of 'SEROTONIN'.
Can you help me to learn more?
(Other definitions for serotonin that I've seen before include "Neurotransmitter hormone, involved in depression say" , "Compound in the blood affecting sleep and depression - soon inert (anag)" , "Compound present in serum - ironstone (anag)" , "Neurotransmitter compound; soon inert (anag.)" , "Chemical compound in body" .)