day-12 embryos were incubated for 3-4 h in the presence of 5-ht or its precursors l-tryptophan ( l-trp ) or 5-hydroxytryptophan ( 5-htp ) , followed by fixation , sectioning and staining with a specific antiserum to 5-ht .
C0041249
tryptophan
C0000578
5-htp