Electron microscopic observations were made of the vestibular epithelial linings at various stages during the development from embryo to adult. The dark cells of the vestibular labyrinth have structural features which suggest that they play a significant role in the active transport of electrolytes in the vestibular labyrinth. They have a complicated folded membrane system resting on a basement membrane which re-sembles the cells of the distal convoluted tubules of the kidney and other sites of fluid secre-tion. ATP-ase can be histochemically demonstrated on the surface of these folded mem-branes. During maturation of the inner ear the dark cells develop in stages from a simple cubordal epithelium.
Light and electron microscopy was used to study the developing and adult sensory epithelia in the vestibular labyrinth in mammals. The ultrastructure of two different types of vestibular sensory cells, type I and II was first reported by Wersall, the innervation of these cells was thoroughly described. Type I sensory cells are directly innervated by only one nerve fiber (chalice). This same chalice nerve may also innervate a neighbouring type I sensory cell. Some type II sensory cells are innervated by the chalice nerve as well as bouton shaped nerve endings. Some type II sensory cells have only bouton shaped nerve endings. Type II sensory cells have direct contact with efferent nerve endings while there is no direct contact between efferent nerve endings and type I sensory cell. Here the efferent nerve fibers form synaptic contacts with the nerve chalice or the afferent dendrite. Thus, the innervation of the vestibular sensory cells is complicate and thorough. (Fig. 2) The sensory cells can be differentiated from simple cylindrical cells when their nerve endings make synaptic contact. The afferent nerve endings in type II sensory cells first appear, then the efferent innervation in type II sensory cells and nerve chalice formation in the type I sensory cells occurrs at birth.
The response of unitary discharges of the vestibular nuclei to caloric stimulation and lateral tilt was studied in the encephale isolé preparation of unanesthetized and pentobarbital anesthetized cats. The mean frequency of the spontaneous discharges in the vestibular nuclei was significantly higher in the unanesthetized cats than in the pentobarbital anesthetized ones. The responses of 32 vestibular neurons to both cold and warm stimulation in the pentobarbital anesthetized animals were classified into the following three types: the increased, in which the frequency of the unitary discharges was increased by both caloric stimulations, the decreased, in which the frequency was decreased by both caloric stimulations and the refractory in which the frequency did not change with either caloric stimulation. In the unanesthetized animals, the response of 232 vestibular neurons was classified into the following five types, increased, decreased, reversed type-I in which the frequency of the unitary discharges was decreased by cold stimulation and increased by warm stimulation, reversed type-II in which the frequency was increased by cold stimulation and decreased by warm stimulation, and the refractory type. The reversed type of the vestibular neurons was observed only in the unanesthetized animals. Responses of the lateral tilt of 93 vestibular neurons were classified into 5 types; increased, decreased, reversed type-I (increase in the unitary discharge rate with ipsilateral and decrease with contralateral tilt), reversed type-II (decrease with ipsilateral and increase with contralateral tilt), and refractory type. The decreased type of neuron was the predominant pattern in the responses of the lateral tilt (60.2%). Two main types of neurons were localized in the vestibular nuclei: those increasing the frequency in response to ipsilateral tilt selectively, and the other increaseing the frequency in response to caloric stimulation with cold water.
Using isolated semicircular canals of frogs and a stimulator which induced a current of fluid within the ampulla, the electrical response of each three ampullar receptors were tested. The adaptation time of isolated posterior ampullar receptors was also measured and the action of several ototoxic drugs on the ampullar receptors on the isolated posterior semicircular canal of the frog and the intracellular rest potential from the posterior semicircular canal crista were investigated.
SEM observation was reported on the morphology of the crista ampullares of the semicircular canals and on the structure of the cupula, the sensory epithelia and the planum semilunatum in several kinds of animals.
For studying surface areas of the vestibular sensory epithelia, the silver reaction method and succinic dehydrogenase staining were successfully used to demonstrate the over-all view of each sensory epithelium. In the central part of the sensory epithelium of the crista ampullaris, larger sensory cells were often found while in the peripheral regions, smaller sensory cells were observed as they appeared on the surface of the sensory epithelium. Cell density was greater in peripheral areas than in the central region. About two-thirds of all sensory cells in the striola were type I cells. Outside the striola, type I sensory cells included approx 45 per cent of the cells while type II was found among all the remainder. Larger sensory cells of type I which were found in the striola were usually innervated by common nerve chalices, however these cells in the striola contained more succinic dehydrogenase activity than smaller cells located both in the striola and in other peripheral areas of the macula.
Histochemical studies of the vestibular labyrinth were performed. The cupula and otolithic membrane showed strong PAS reaction, Alcian blue reaction and metachromatic reaction of toluidin blue. These findings suggest that sulphomucopolysaccharides are an important chemical constituent of the cupula and otolithic membrane. Marked succinic acid dehydrogenase activity and cytochrome oxidase activity were found in the vestibular sensory cells. These enzyme activities were stronger in Type 1 cells than in Type 2. The sensory cells in the striola of the macula utriculi and macula sacculi showed stronger activities than peripherally located sensory cells. It is assumed that the encrgy requirements of sensory cells are mainly provided by carbohydrate metabolism. Strong ATP-ase activity was found in the sensory hairs, especially in the kinocilium. The role of the cupula, otolithic membrane and sensory hairs in the stimulation transmitting mechanism was discussed according to histochemical findings.
Surface structure of the cellular elements of the pigeon crista ampullaris was studied using a scanning electron microscope. The vertical and the lateral cristae ampullares were markedly different from each other mostly due to the presence of two prominent humps in the middle of the vertical cristae, the eminentia cruciata. Studied were the hair cells on the cristae, three types of cells on the eminentia cruciata, two types on the slope of the cristae, two types on the planum semilunatum and those on the ampullary wall.
1) A simple improvement to a clinical turning chair is given. 2) A method of rotatory stimulation of the vestibular receptors has been worked out which allows the measurement of the threshold of ocular nystagmus in humans. 3) The stimulating technique consists of an initial acceleration of short duration followed by a long lasting deceleration without a pause between the two. 4) Nystagmus is recorded electrically during and after the rotation. The nystagmic response appears immediately after the beginning of the rotation and then subsides. After a while a reversed nystagmus (opposite in direction to the preceding nystagmus) appears. 5) Theoretical formula of the cupula-endolymph displacement based on the general theory of the cupular mechanism established by Steinhausen, van Egmond, et al. are given subject to the conditions of stimulus. 6) The threshold of ocular nystagmus during rotatory stimulation can be computed by measurement of parameters such as initial angular velocity, durations of acceleration and deceleration and the time of appearance of the reversed nystagmus. 7) Average values of the threshold (expressed by the angular deviation of the cupula-endolymph system) are:0.84° for clockwise rotation and 0.86° for counterclockwise rotation. 8) The fiducial limits are also given: 0.70°-0.88° and 0.82°-0.90° respectively. 9) The most important advantage of this method is its application to clinical investigations.The method also indicates numerous possibilities for quantitative determination of vestibular dysfunctin in a manner not dissimilar to audiometry in auditory function.