Sleep-promoting effect following intracerebroventricular injection of a phosphorylated analogue of delta sleep-inducing peptide (DSIP-P) in rats

The effect of phosphorylated delta sleep-inducing peptide (DSIP-P) on sleep of rats was studied. DSIP-P (20 or 200 pmol/kg) was injected into the third cerebroventricle of male rats immediately before the onset of the dark period of a 12:12 h light-dark cycle. DSIP-P resulted in increases of slow-wave sleep (SWS) (17.3%, P less than 0.01) and paradoxical sleep (PS) (32.3%, P less than 0.05) during the subsequent dark period without shortening sleep latency in the dose of 200 pmol/kg. The SWS-promoting effect was carried over to the next light period. These changes returned to control levels on the second day. These results indicate that DSIP-P is a long-lasting sleep-promoting substance in rats.