Comparative study on the effects of haloxazolam and estazolam, new sleep inducing drugs, on the .ALPHA.- and .GAMMA.-motor systems.

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 gamma-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 gamma-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 alpha- and gamma-motor systems, whereas the blockade by haloxazolam is limited only to the gamma-system, and also that the suppressive actions of estazolam on both alpha- and gamma-motor systems are stronger than that of haloxazolam.