[Effects of benzodiazepine derivatives on gamma-motor system in rats (author's transl)]

Effects of four benzodiazepine derivatives on gamma-activity were examined in the anesthetized rat. Diazepam and 5-(o-chlorophenyl)-1-methyl-7-nitro-1, 3-dihydro-2H-1, 4-benzodiazepin-2-one(ID-690) in a dose of 2.5 mg/kg (i.p.) showed depressant effects on gamma-activity. The depressant effects of 5.0 mg/kg (i.p.) lasted for more than 60 min. Nitrazepam had a slightly weaker effect than the above two drugs and the effect was evident after an administration of 5.0 mg/kg; the effect of 10 mg/kg(i.p.) lasted for more than 90 min. The effect of clonazepam was much weaker than effects of the other three drugs. A dose of 20 mg/kg(i.p.) was required to produce an obvious depressant action, and the effect appeared after a longer latency of about 20 min. ID 690 (5.0 mg/kg, i.p.) depressed the augmented response of the gamma-activity in response to pinna stimulation. The effect of diazepam on the augmented responses was observed with the same dose. In contrast, much higher doses of nitrazepam and clonazepam were required to induce an obvious depressant effect on the augmented gamma-activity. It is suggested that the difference in potency in depressing gamma-activity of these derivatives is one of the factors characterizing their pharmacological properties.