A late-appearing benzodiazepine-induced hypoactivity that is not reversed by a receptor antagonist.

The activity of rats in a holeboard test is reduced 30, 90, and 240 min after treatment with a single dose of lorazepam. The administration of a benzodiazepine antagonist (RO 15-1788) 20 min before the holeboard test (i.e., 10, 70, or 220 min after lorazepam administration) reverses the hypoactivity of animals tested 30 min after treatment with lorazepam, partially reverses the hypoactivity of animals tested 90 min after receiving lorazepam, but is without effect on the hypoactivity observed 240 min after treatment with the benzodiazepine. If, however, RO 15-1788 is given at the same time as lorazepam then it reverses the hypoactivity seen 4 h later. The results of these experiments demonstrate that a benzodiazepine can exert a behavioral effect at a time when it no longer appears to be acting at central benzodiazepine receptors.