Nifedipine blocks effects of triazolam injected into the dorsal raphe nucleus on sleep.

In previous studies, the author has reported both in vitro and in vivo sleep studies in which there were complex interactions between benzodiazepine hypnotics and the dihydropyridine calcium channel blocker nifedipine. The author has also reported that microinjections of triazolam into the dorsal raphe nucleus of the rat result in enhancement of wakefulness. In the present study, nifedipine and triazolam were coadministered into this site. As previously was observed, triazolam produced a dose-dependent increase in sleep latency and a decrease in total sleep, primarily by reducing non-rapid-eye-movement sleep. Nifedipine had no effect on sleep when given by itself but prevented the alterations in sleep by triazolam. These various sleep effects were not associated with alterations in core temperature. These data are consistent with the view that aspect of the sleep-altering activity of triazolam involves interaction with voltage-dependent calcium channel activity.