The effects of delta-sleep-inducing peptide (DSIP) on wakefulness and sleep patterns in the cat

The effect of a single injection of synthetic delta-sleep-inducing peptide (DSIP, 7 nmol/kg) into the lateral ventricle of 10 cats was investigated by monitoring the sleep-wake cycle during an 8 h period. A significant decrease in sleep latency and a significant increase in total sleep and in total slow wave sleep (SWS) was found following DSIP administration. The increase in sleep resulted exclusively from a significant increase in deep slow wave sleep (S 2), while light slow wave sleep (S 1) was significantly decreased. Neither the total amount of REM sleep, nor hourly values of REM sleep were affected by DSIP application. Additional measures of REM sleep, like REM sleep latency, mean episode number and mean episode length were not different from those found in control conditions. DSIP was immediately effective since the amount of S 2 increased to more than 50% in the first postinjection hour and the difference from the control value was highly significant. The increase in S 2 was maintained over 7 h, and disappeared by the eighth hour. The increase in S 2 was caused by a prolongation of S 2 episodes and not by their more frequent occurrence. The results obtained suggest a sleep-facilitating property of DSIP.