Abstract
The inhibitory effect of benzodiazepine-type agents such as 8-chloro-6-phenyl-4H-s-triazolo [4, 3a] [1, 4] benzodiazepine (D-40TA), diazepam and nitrazepam on the spinal and supraspinal polysynaptic reflexes was compared with that of mephenesin, methocarbamol, chlorzoxazone and chlormezanone in cats. Benzodiazepines did not depress the spinal and supraspinal polysynaptic reflexes or reflex potentials in the spinal and the gallamine-immobilized cats. In these respects, chlormezanone resembled benzodiazepines. On the other hand, mephenesin, methocarbamol and chlorzoxazone blocked these reflexes in all kinds of preparations such as the anesthetized, the spinal, the decerebrate and the gallamine-immobilized preparations. D-40TA depressed gamma rigidity at the dose below that necessary to depress alpha rigidity. Moreover, it inhibited more profoundly the tonic stretch reflex than the phasic one. Spontaneous and evoked discharges of the muscle spindle in the decerebrate cat were significantly depressed by D-40TA, while those of spinal cat were unaffected.
These results suggest that skeletal muscle relaxation by benzodiazepines including D-40TA is attributed to the primary depression of the brain stem reticular system and in turn the ascending inhibitory action via the gamma system on the spinal and supraspinal polysynaptic neurons. It should be stressed that the integrity of the connection between the brain stem and gamma system in the spinal cord and its related muscles is also required for eliciting the depression of supraspinal polysynaptic reflex by these agents. Mephenesin-type agents presumably inhibit directly the interneurons at the spinal and supraspinal levels.
