—Using either tryptophan or 5-hydroxytryptophan as the precursor, and examining the metabolites in whole rat brain and in brain regions of dog, the pattern of metabolites resembled that found under physiological conditions only after tryptophan administration. From these and other observations on the cerebral 5-hydroxyindoles the main conclusions are firstly, that there are regional differences within brain in storage, turnover or metabolic fate of 5-HT. Secondly, that the normal pathway appears to be well localized biochemically with linking of its succeeding steps, and thirdly, that turnover through the system is normally controlled by intracerebral tryptophan 5-hydroxylase in both rats and dogs although there are differences between the species in the cerebral metabolism of 5-HT.

The effects of precursor loading in the cerebral metabolism of 5‐hydroxyindoles

Monoamine oxidase inhibitors in South American hallucinogenic plants: tryptamine and beta-carboline constituents of ayahuasca.

Rhythmic activity induced by harmaline in the olivo-cerebello-bulbar system of the cat

http://www.psychonautdocs.com/docs/mckenna_aya.pdf

Bernard Witkop

Papers

Studies with reversible inhibitors of monoamine oxidase: Harmaline and related compounds

On the inability of tryptamine to serve as a precursor of serotonin.