Successful use of S20098 and melatonin in an animal model of delayed sleep-phase syndrome (DSPS).

In human delayed sleep-phase syndrome (DSPS), sleep onset and wake times occur far later than normal. In the population, DSPS may be an important contributor to complaints of sleep onset insomnia. We previously reported an animal model of DSPS in laboratory rats in which the onset of nocturnal activity is delayed by several hours [negative phase angle difference (PAD)]. The effect of melatonin 1 mg/kg SC and S20098 (Servier) 1 and 3 mg/kg on the negative PAD was investigated over 22 days of injections. In comparison to control injections of dimethylsulfoxide (DMSO), both melatonin and S20098 over approximately 9 days phase advanced the onset of activity toward the onset of darkness. At cessation of injections, activity onset delayed over approximately 11 days back toward, but as a group did not reach the original PAD. This effect of melatonin on the phase angle of entrained rats is consistent with its effects on delayed sleep in humans. It is likely, therefore, that S20098 may be of use to ameliorate DSPS in humans.