“…MAO may be histochemically visualized in tissues by tetrazolium salts and other methods [30,495,1333], and tetrazolium reduction has been sugg~sted as an additional measure of MAO activity in vitro [1285]. Using the tryptaminetetrazolium method, SHIMIZU and MORIKAVA [1105] demonstrated that with the exception of locus coeruleus and nucleus ambiguous, which display a MAO reaction already in late foetal life, the remaining portions of the rat brain are practically negative for MAO activity until new-born life, then rapidly reaching adult activity within 3 weeks after birth.…”