Evidence that only free serum tryptophan exchanges with the brain.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D008297:Male; D051381:Rats; D013997:Time Factors; D014364:Tryptophan / Q000097:blood / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D014443:Tyrosine; D014364:Tryptophan