1983 Volume 33 Issue 5 Pages 1017-1025
The pharmacological actions, in vivo, of estazolam and haloxazolam were comparatively studied. Spontaneous discharges of spinal motoneurons in cats were markedly suppressed by estazolam (3 mg/kg, i.d.), but unaffected by similarly administered haloxazolam. The facilitatory effect of stimulation of the posterior hypothalamus on the γ-activity was suppressed by both haloxazolam and estazolam (3 mg/kg, p.o., for each). The stimulus threshold was raised 1.7 times by haloxazolam and 1.6 times by estazolam. The facilitation of the γ-activity induced by stimulation of the mesencephalic reticular formation was also depressed by both drugs. The stimulus threshold was raised 6 times by estazolam, but unchanged by haloxazolam. The spinal monosynaptic reflex was unaffected by haloxazolam, while its amplitude was depressed to a half by estazolam (3 mg/kg, p.o., for each). The facilitation of the monosynaptic reflex induced by conditioning stimulation was depressed by both drugs (3 mg/kg, p.o.), but estazolam showed a stronger suppressive action. The seizure-like responses of spinal motoneurons, which were induced by stimulation of the gastrocnemius nerve following strychnine administration, were unaffected by 30 mg/kg of haloxazolam, while they were suppressed by estazolam of the same dose. Thus, the results of all experiments in the present study indicate that estazolam blocks the descending activating functions of both α- and γ-motor systems, whereas the blockade by haloxazolam is limited only to the γ-system, and also that the suppressive actions of estazolam on both α- and γ-motor systems are stronger than that of haloxazolam.