the only reason I think dopamine is in the peels is because i was reading research papers and many of them happened to be on banana, and the liquid-chromatograms showed retention times indicating that there was the amine present. It dosen't really matter though I just thought it was interesting. I found it in the paper:

Riggin, R.M.; McCarthy, M.J.; Kissinger, P.T. "Identification of Salsolinol a Major Dopamine Metabolite in Banana", J. Agric. Food. Chem. Vol. 24. No 1.1975. P 189-191.

I read on the net that dopamine injections would boost the mesc. content of a cactus.