The guinea pig is a naturally-occurring animal model of insomnia. Therefore, it was of interest to determine, in this species, the effects on sleep and waking states of different hypnotic substances.

Accordingly, in the chronically-implanted adult and aged guinea pigs, we examined changes in NREM sleep, REM sleep, and wakefulness following the administration of eszopiclone and zolpidem.

Compared with naturally occurring sleep and wakefulness, the effects of eszopiclone were characterized by the induction of NREM sleep that occurred with a short latency, as well as long duration episodes of NREM sleep that were accompanied by an increase in delta power. The administration of zolpidem, compared with the responses produced by eszopiclone, resulted in shorter duration episodes of NREM sleep that arose at a longer latency; there was no change in delta power in conjunction with the administration of zolpidem. In addition, compared with zolpidem, lower doses of eszopiclone were required to induce the preceding effects.

We conclude that eszopiclone may have an advantage compared to zolpidem in producing homeostatic sleep on the basis of its ability to induce consolidated, long-duration episodes of NREM sleep. Since delta power has been suggested to reflect enhanced sleep-related memory and learning processes, we hypothesize that the increase in delta power that was induced by eszopiclone, which was not present following the administration of zolpidem, may facilitate memory and learning mechanisms during NREM sleep.

Support for this study provided by Sepracor Inc., Marlborough, MA.