The Discovery and Synthesis of DSIP — the First Peptide Found to Induce Deep Sleep

The researchers isolated, sequenced, and synthesized the Delta Sleep-Inducing Peptide (DSIP) — a nine-amino-acid peptide (Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) from rabbit cerebral venous blood during electrical stimulation of sleep-promoting brain regions. When the synthetic DSIP was infused into rabbit brain ventricles at 6 nmol/kg, it increased delta wave EEG activity by 35% in both the neocortex and limbic cortex compared to controls. Only the alpha-aspartyl form was active; the beta-Asp isomer was inactive. None of the 8 other tested peptides (metabolic fragments and analogs) reproduced the effect.

DSIP was isolated from extracorporeal dialysate of cerebral venous blood in rabbits during electrical stimulation of the intralaminar thalamic area (a sleep-promoting brain region). The peptide was sequenced and synthesized, along with 5 metabolic fragments, 2 analogs, and 1 related tripeptide. All 9 synthetic peptides were infused intraventricularly in rabbits under double-blind conditions. EEG from frontal neocortex and limbic archicortex was analyzed by fast-Fourier transformation.

This 1978 paper represents the original characterization and synthesis of DSIP — the first peptide identified as a potential natural sleep-inducing molecule. It was a landmark in sleep neuroscience, suggesting that the brain produces specific peptide signals to initiate and maintain slow-wave sleep. The finding that only the exact sequence with the correct aspartyl configuration was active demonstrated remarkable molecular specificity.

DSIP was one of the earliest discoveries suggesting that sleep is regulated by specific peptide signals, not just neural circuits. It arrived during a golden age of neuropeptide discovery and helped establish the concept that the brain produces chemical sleep factors. While DSIP's clinical potential didn't pan out as hoped (reproducibility issues and delivery challenges), it paved the way for understanding other sleep-regulating peptides like orexin/hypocretin, whose absence causes narcolepsy. The orexin system, discovered two decades later, would prove far more clinically consequential.

This is a rabbit study using direct intraventricular infusion — the peptide was injected directly into the brain, bypassing the blood-brain barrier. Whether DSIP can reach the brain through peripheral administration is a separate question. The 35% delta increase, while statistically significant, is a moderate effect. Subsequent DSIP research has had mixed reproducibility, with some groups unable to replicate sleep-inducing effects.