Effect of diazepam on vestibular compensation in squirrel monkeys

The effect of the chronic administration of diazepam on vestibular compensation (post-unilateral labyrinthectomy) was studied in squirrel monkeys. An intramuscular injection of diazepam (2 mg/kg) was given daily for a period of 4 weeks post-operatively. After daily injection, reduction of the slow-phase eye velocity ( SPEV ) of spontaneous nystagmus and enhancement of locomotor body dysequilibrium were found in the early post-operative stage. However, these pharmacological effects decreased gradually and almost no remarkable effect was found about 3 weeks after surgery. When compared to control animals, no marked differences was found in SPEV reduction of spontaneous nystagmus in injected animals during the vestibular compensation period. Platform runway tests showed that the average number of calendar days needed to regain the pre-operative level of locomotor balance function in the group injected with diazepam was even less than that of the control group. Thus, post-operative daily diazepam injections did not retard the vestibular compensation. The possible neural mechanism responsible for this phenomenon is discussed.