A few things to consider...
2-methyl-1,2,3,4-tetrahydro-beta-carboline has been detected as a minor component
in jungle spice according to Burnt's tests .
Now, the funny thing is, when reading about this substance, I found that in TIHKAL, in one of the proposed synthesis, Shulgin describes that "
There was thus obtained 0.40 g of dimethyltryptamine (DMT) with a mp 67-68 °C. The distillate contained about 3% of 2-Methyl-1,2,3,4-tetrahydro-b-carboline (parent peak mass 186, major peak mass 186) as an impurity which was lost upon recrystallization.". So there is the same substance in the same amount (around 3%) present.
So I was wondering if either mimosa's biosynthetic pathway of 2-MTHBC is similar to the synthetic pathway Shulgin took, or if maybe its an artifact that was generated in Burnt's tests due to the chemicals used.
In
this discussion in bluelight, seems one guy has also detected 2-MTHBC in mimosa (though most of the links/papers are dead in that thread now), but it seems the OP had used DCM for the extraction and in a comment someone says that "
If you used dichloromethane, it could be possible that the beta-carboline is an artifact produced by the extraction process. Dichloromethane in contact with aqueous alkali will cause a substitution recation to take place, the final product being formaldehyde. From what I remember, formaldehyde and acetaldehyde very easily react with tryptamines to form beta-carboline structures via Picter-Spengler reaction (the 2,3-double bond being the active methylene bond)." .
Though burnt's tests did not use DCM...
Another interesting paper I was asking Snozz if he could help me find the
full version of a study that shows that 2-methyl-1,2,3,4-tetrahydro-beta-carboline is also present in phalaris arundinacia (and interesting enough, the paper seems to state that there is an inverse relationship between the presence of gramine and of tryptamines/beta carbolines, but this is the subject of another thread I guess

)
2-methyl-1,2,3,4-tetrahydro-beta-carboline is a
normal metabolite of DMT in rats, I dont know if its also a metabolite of in human beings. It appears to be an
endogenously produced substance in rats too, regardless of dmt ingestion .. ?
As for all the discussion of neurotoxicity, we have to check what dosages are being talked about because so many normal things are neurotoxic in ridiculously high doses, and also the animal models arent always transferible to human beings.