Abstract
Abnormal activity of neurons in the brainstem vestibular nuclei is related to the onset of dizziness in hemodynamic vertebrobasilar insufficiency (VBI). In the present study, we compared the vestibular nuclei (VN) with the cochlear nuclei (CN) and the inner ear in terms of the reactions of brainstem and inner ear neurons and investigated the influence of ischemia on the VN in a vertebrobasilar insufficiency model. The following conclusions were obtained :
1. Comparison between the VN and CN
1) When the unilateral VA was occluded, the activity of ipsilateral VN neurons decreased, but the activity of CN neurons showed no change.
2) When the unilateral VA was occluded with hypotension, immunohistochemical staining of the dendrites decreased around the VN only, while staining CN neurons did not change. When the basilar artery was occluded with a trap, VN staining decreased more than that of CN.
3) As a result of unilateral VN occlusion, the ipsilateral caloric nystagmus decreased, but the ABR did not change. When hypotension was added, the former decreased more markedly, while the latency of the latter was prolonged.
2. Reaction of VN in ischemia models
1) The activity of ipsilateral VN neurons was decreased more by the unilateral VA occlusion plus hypotension than by unilateral VA occlusion alone. The severity of disturbance was greater in the presence of VA stenosis than with VA occlusion.
2) Release of glutamic acid in the VN did not change in the presence of the unilateral VA occlusion, but increased when hypotension was added.
3) The glucose utilization response in the VN following stimulation of the ipsilateral inner ear with cold water was inhibited by unilateral VA occlusion combined with hypotension.
3. Comparison between the VN area and the inner ear
1) When the unilateral VA was occluded, the activity of the ipsilateral VN neurons decreased, but the activity of neurons in the vestibular ganglion (VG) showed no change.
2) As a result of VA occlusion combined with hypotension, the caloric nystagmus test showed CP in all cases, but the ABR did not any change in the I wave.
3) In the absence of VA occlusion, control of blood flow was better in the brainstem than in the inner ear. However, in the presence of unilateral VA occlusion, control was more severely disturbed in the brainstem than in the inner ear.
4. The above experimental results showed that the VN is injured more easily than the CN or inner ear in the presence of VA occlusion plus hypotension. We conclude that the susceptibility of the VN to ischemia leads to the onset of dizziness in hemodynamic VBI.
