Salsolinol (SAL) is a dopamine-related compound first discovered in the 1970s. It was found in the urine of patients with Parkinson'splugin-autotooltip__plain plugin-autotooltip_bigParkinson's disease

Also known as Parkinson disease, Parkinson's, idiopathic Parkinsonism, primary Parkinsonism, PD, or paralysis agitans - is a degenerative disorder of the central nervous system resulting from the death of dopamine-containing cells in the, and was assumed to be a possible chemical marker for the disease. But only a few years later it was also found in healthy individuals - and subsequently in a wide range of foodstuffs, including bananas, cocoa and beer.

It's thought to have some kind of neurological role, but its origin in the human body, and its overall function (if any, as it may simply be a by-product) are currently unknown.

Further (technical) reading : Salsolinol: an Unintelligible and Double-Faced Molecule—Lessons Learned from In Vivo and In Vitro Experiments Neurotoxicity Research 33(2): 485–514.