GABA and glutamate/aspartate amino acids are important neurotransmitters in the neuronal circuits involved in the vestibulo-ocular reflex. Vestibular nuclei are controled by Purkinje cells and opposite vestibular nuclei and affect oculomotor nuclei through GABAergic neurons. There are three types of GABA receptors that are targets of GABAergic nerves: GABAA, GABAB and GABAC receptors. GABAA and GABAB receptors are densely distributed in the cerebellum: GABAA receptor is distributed in cerebellar Purkinje cells, deep cerebellar nucleui and vestibular nucleui, and GABAB receptor is distributed in cerebellar Purkinje cells. GABAC receptor is specifically distributed in the retina. GABAA and GABAC receptors are members of the transmittergate channel superfamily and their compositions are determined by the formation of pentameric structures. GABAA receptor is composed of five kinds of subunit, α(α1-α6), β(β1-β4), γ(γ1-γ3), δand ρ, and possesses binding sites for benzodiazepines, barbiturates and neurosteroids. GABAB receptor is a G-protein coupled receptor, although the receptor is the first discovered receptor forming heterodimers in the Gprotein coupled receptors. The functions of GABAA and GABAB receptors in the neuronal circuits that are involved in the vestiburo-ocular reflex have been investigated by histological and electrophysiological studies, but the role of the receptors in the vestibular functions have not been studied.
Positional nystagmus is one of the valuable vestibular signs for the diagnosis of vertiginous diseases. However, the classification of positional nystagmus has been modified since Nylén's initial classification in 1950. In this paper we review the history and significance of the classification of positional nystagmus, and divide, experimental positional nystagmus of the past 50 years into that of peripheral and central origins. At present, positional nystagmus is generally classified into static and paroxysmal types. We indicate some problems in classifying positional nystagmus, such as observing conditions of nystagmus and the possibility of spontaneous nystagmus occurring, and also introduce a method for differentiating between static and paroxysmal positional nystagmus. Furthermore, with regard to typical positional nystagmus such as BPPV and its variants, static direction-changing positional nystagmus and downbeating positional nystagmus, we discuss the etiology, pathophysiology, and localization of lesions.
In this study the induction of c-fos, a protein product of proto-oncogene c-fos, was immunohistochemically examined in rat caudal brainstems in response to intense sound. One kHz of pure tone stimulation at 110 and 130 dB SPL was applied for 60 mins. In comparison with non-stimulated control rats, the brainstem of the soundstimulated rats showed c-fos protein in both the inside of the cochlear nucleus and the vestibular nucleus. In the vestibular nucleus, sound stimulation at 130 dB SPL led to widespread c-fos labeling in the medial, spinal and lateral vestibular nucleus compared with that at 110 dB SPL. The distribution of the primary vestibular afferent fiber projected from the saccule to the vestibular nucleus overlaped that of c-fos labeling neurons at 130 dB SPL, suggesting that the saccule is the origin of the c-fos labeling vestibular neurons produced in response to the intense sound.
From 1993 to 1997, 100 patients with sudden deafness who were admitted to Itabashi Hospital of Nihon University were classified into 3 groups: Group A, 32 patients with both vertigo and nystagmus; Group B, 19 with vertigo but no nystagmus; Group C, 49 with neither vertigo nor nystagmus. The rate of improvement was 22% for Group A, 47% for Group B, and 72% for Group C, showing a significant difference between each group. Eighty-Seven patients were examined by the caloric test using cold water. CP was observed in 29 patients (33%), 59% in Group A, 31% in Group B, and 13% in Group C. A significance was recognized between Group A and C. The improvement rate was significantly lower in the patients with CP than in those without CP.
Dizziness based on sympathetic nervous disturbances is primarily due to either vasovagal reflex (VVR) or an orthostatic degegulation. The head up tilt test is useful for a differential diagnosis of them but it is not useful for a clinical diagnosis. We report a case where an exercise test was used to clinically confirm dizziness due to VVR. A 13-year-old male visited our hospital complaining of recurring dizziness during exercise. He was examined by the pediatric department and underwent holter ECG, master ECG, brain MRI and head up tilt tests, but they were inconclusive. He was then examined in our department and we suspected VVR due to presenting symptoms and the negative clinical findings. Thus, an exercise test was performed to confirm our diagnosis. The subject steps up and down on a stair until they complain of sensations such as dizziness and nausea. Vital signs and the plasma adrenaline level are checked every 5 minutes during exercise and pre and post exercise. At 25 minutes he complained of dizziness, bradycardia, low blood pressure and a high plasma adrenaline level. The attack recurred with severe bradycardia (28/min) and a high plasma adrenaline level at 10 minutes after the test. We diagnosed it as a VVR attack. VVR is caused by excessive left ventricular contractions to adjust for blood volume retention in the legs while standing and/or sitting. The mechano-receptor also makes a paradoxical emission to the vagal nerve resulting in bradycardia, dizziness, and syncope. We recommend checking the plasma adrenaline level during VVR.
Impaired smooth pursuit eye movements may be corrected by saccades to repair visual errors during an eye tracking test (ETT). However, in this study, most of the cases that showed a saccadic pattern during ETT demonstrated smooth eye movements in a pendular rotation test (PRT) with the eyes open and fixed at the stand still target in lightness due to interaction between the visuoocular and vestibuloocular systems. The incidence and character of the two kinds of induced eye movements in horizontal ETT and PRT with the eyes open were investigated. Investigated were thirty one cases among out-patients in the Neuro-Otological Clinic of Kitasato University Hospital in 1996. All cases showed saccadic patterns in ETT, fulfilling the following criteria: each half period to the right and left containing three or more saccades with a maximum amplitude of four or more degrees. Only 3 cases or 10% of the 31 patients showed saccadic pattern in PRT with the eyes open. The saccadic index (S.I.) (maximum amplitude multiplied by the number of saccades) was calculated in each case. The combined SI of both directions was between 75.8 to 100.6 in the 3 cases who had saccadic pattern in PRT with the eyes open. VOR gains remained in the low range (0.40 to 0.57). However, cases who showed high S.I. in ETT, but had smooth pursuit eye movement in PRT with the eyes open showed a high VOR gain. We concluded that most cases of saccadic pattern in ETT showed smooth eye movements in PRT with the eyes open and fixed at the target due to a high VOR gain, but in 10% of cases no increase was recorded due to a failure of vestibular compensation.
Using an infrared charge-coupled device (CCD) camera for recording simple eye movement is widely accepted but since quantitative analysis of the video image produced is still difficult, we devised a new eye movement image analysis technique using a personal computer. The analysis was performed using the public domain NIH Image program (developed by the U.S. National Institutes of Health, http://rsb.info. nih.gov/nih-image/). The video image from an infrared CCD camera was captured at 30 frames per second in 320 × 240. Using the original macro, the X-Y center of the pupil was automatically analyzed, and the horizontal and vertical components were calculated. The merits of this technique are: (1) it is easy to use and very low-cost; (2) many types of infrared CCD cameras are available; (3) there are cross-applications to animal experiments; (4) it is possible to make a detailed analysis of eye movements such as the rotation axis of the eyeball.
We used the trapezoid rotation test to evaluate vestibular function in guinea pigs. Post-rotatory nystagmus (PRN) was recorded on videotape with an infrared chargecoupled device camera in the dark. We counted the number of PRN beats and calculated the PRN ratio as follows: PRN ratio=the number of PRN beats after rotation contralateral to the treated side/the number of PRN beats after rotation ipsilateral to the treated side. In the control study, we determined the 95% confidence interval for the PRN ratio to be 1.046 ± 0.461. Animals administrated with saline or polyethylene glycol 300 directly to the inner ear by osmotic pump showed no obvious PRN ratio abnormality, while animals, whose lateral semicircular canals were destructed surgically, showed a transient PRN ratio decrease at 3 days after treatment. We concluded that our method is simple and useful to evaluate vestibular function in animal models, furthermore, saline and polyethylene glycol can be used as safe vehicles when we administer various agents directly to the inner ear.