Delta sleep-inducing peptide was first discovered in 1974 by the Swiss Schoenenberger-Monnier group who isolated it from the cerebral venous blood of rabbits in an induced state of sleep. It was primarily believed to be involved in sleep regulation due to its apparent ability to induce slow-wave sleep in rabbits, but studies on the subject have been contradictory.
Delta-sleep-inducimng peptide (DSIP)-like aterial has been found in human breast milk
Delta-sleep-inducing peptide, abbreviated DSIP, is a neuropeptide that when infused into the mesodiencephalic ventricle of recipient rabbits induces spindle and delta EEG activity and reduced motor activities. Many roles for DSIP have been suggested following research carried out using peptide analogues with a greater molecular stability and through measuring DSIP-like immunological (DSIP-LI) response by injecting DSIP antiserum and antibodies. Its aminoacid sequence is Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu. However, the gene is unknown, raising serious questions regarding the actual existence of this peptide in nature.