DSIP (Delta Sleep-Inducing Peptide / Emideltide)

Identity a naturally occurring nonapeptide (9 amino acids, ~849 Da; < 40 aa → peptide), amphiphilic, notable for crossing the blood-brain barrier and being unusually absorbed via the gut. Found in small amounts in brain, pituitary, gut, blood and breast milk. Unusually, it has no identified receptor, and the gene has not been found — a basic-biology gap that matters when reading the "mechanism." ## Development & history - Isolated in 1974 (characterised in PNAS 1977) by the Swiss group Guido Schoenenberger and Marcel Monnier at the University of Basel, from the cerebral venous blood of rabbits in an electrically-induced sleep state. Infused into other rabbits, the peptide increased delta-frequency (deep-sleep) EEG activity — which is exactly how it got its name.

• The mystery: decades later, no DSIP receptor or precursor gene has been identified in rabbits, and BLAST searches align the sequence with a hypothetical Amycolatopsis coloradensis protein — raising the possibility that DSIP may be of bacterial origin. In other words, the compound's fundamental biology is still unsettled. ## Mechanism (as proposed), and it is not approved anywhere. The name is more definitive than the data.