Observation of vestibular compensation after unilateral labyrinthectomy in a rat model of type I insulin-dependent diabetes mellitus

This study was aimed to explore the influence of diabetes duration on cervical vestibular-evoked myogenic potential (cVEMP) and vestibular compensation after unilateral labyrinth injury in streptozocin (STZ)-induced diabetic rats. SD male rats (with the weight of 300-350 g) were injected (55 mg/kg) with STZ intraperitoneally. At 4, 8 and 12 weeks after the induction of diabetes in model rats; cVEMP was detected by auditory evoked potential equipment (Audera V2.7, GSI, USA). Rats were anesthetized with 2% pentobarbital sodium (0.2 mL/100g i.p,). When recorded, the head of rat was lifted and moved forward and upward to achieve hyperextension of the neck muscles. cVEMP was detected before unilateral labyrinthectomy and four selected imbalance symptoms for scoring (head deflection, limb outreach, forced annular motion or roll and nystagmus) were recorded at different time points after surgery. The cVEMP results indicated that there were no significant difference in N1 latency periods (ms) in the Week 4 and Week 8 groups compared with that in the control group (P > 0.05), while the N1 latency period was significantly increased in the Week 12 group (P < 0.01). There were no significant difference in the amplitude between P1-N1 of cVEMP in the control group and diabetes groups (P > 0.05). There was no significant difference in the stimulation threshold and P1 latency period (ms) of the Week 4 and control groups (P > 0.05), while those of the Week 8 (P < 0.05) and Week 12 (P < 0.01) groups were significantly increased. There were no significant difference in the imbalance symptom scores in the Week 4 and Week 8 groups compared with those in the control group (P > 0.05), while the scores were significantly higher in the Week 12 group at 12 h after surgery or later (P < 0.05). These results suggested that the rate of abnormal cVEMP (increased stimulation threshold and extended wave latency) increased with the duration of diabetes course or uncontrolled blood glucose, although there was no significant difference in wave amplitude. Furthermore, longer diabetes course had a negative influence on vestibular compensation after unilateral labyrinthectomy, leading to extension of compensation time.