In a cat study, giving the synthetic peptide DSIP directly into the brain after a long period without REM sleep didn't change how long the cats slept overall, but it did make them spend less time awake and in light sleep, and more time in deep, delta-rich sleep. This effect was seen when the animals were most sleepy after being deprived of REM sleep.

The effect of synthetic delta sleep inducing peptide (DSIP) on sleep was investigated in cat. DSIP (7 nmol/kg was administered intracerebroventricularly to cats deprived of paradoxical sleep (PS) for 72 h and immediately after termination of PS deprivation an injection of either Ringer or DSIP solution was given. Eight h of recovery sleep was then recorded. DSIP failed to affect the duration of slow-wave sleep, PS and total sleep time. There was, however, significant decrease of wakefulness and light slow-wave sleep (S1) while deep slow-wave sleep (S2) was significantly increased. There was also no change in the latency to the first episode of S2 sleep and PS. Thus, we conclude that DSIP altered the relative amounts of S1 and S2 sleep, causing more S2 (delta) sleep at the time when pressure for sleep was at its highest due to prior sleep deprivation.