Search

The otolithic membrane is extremely fragile and is easily destroyed by post-mortem changes, tonic change, strong chemicals, et cetera. The routine technique of temporal bone preparation usually includes the use of a strong fixative and decalcifier; therefore, the structural preservation of this structure in histological slides is uncertain. An attempt was made to preserve the otolithic architecture as naturally as possible. In studying squirrel monkey temporal bones the results obtained with three different decalcifiers are compared. The best architectural preservation of the otolithic end organ was obtained after 10% formalin fixation, dehydration, celloidin embedding, and 10% EDTA decalcification. The morphological features of this end organ are discussed from the functional viewpoint. It is confirmed that, except for the otoconia, basically both otolith and semicircular canal end organs have almost similar components. (Author)

The study was undertaken to learn the incidence of unrecognized otological disease in young healthy squirrel monkeys (Saimiri sciureus) maintained under optimum laboratory conditions. No definite pathological changes were found in the middle ears of 20 out of 22 ears examined. Morphologically, all inner ear end organs appeared normal. All threshold caloric test values were within the normal range. No significant variance was noted among the trials. Six out of eleven squirrel monkeys were not susceptible to motion sickness on repeated trials in the Slow Rotation Room. Thus, the lack of susceptibility to motion sickness does not necessarily reflect pathologic suppression of semicircular canal function. (Author)

A study was made to determine the effects of vestibular damage or previous vestibular stimulation on the spontaneous activity of the rat during rotation. Unilateral destruction of the labyrinth through intratympanic injections of streptomycin sulfate decreased the sensitivity of unrestrained rats to rotation, as measured by the maintenance of high levels of spontaneous locomotor activity during rotation. Repeated exposure to rotation produced a similar threshold shift in undamaged rats. Normal control animals showed a marked decrement in activity while rotated. Rats were extremely resistant to streptomycin sulfate injected systemically; neither morphological damage to hair cells nor changes in the response to vestibular stimulation was found following a total dosage of 10,000 mg of the drug. The findings demonstrated that the spontaneous activity levels provide a sensitive behavioral measure of the effects of vestibular stimulation on the rat. (Author)

The size, length, and shape of the cochleas are compared in different mammalian species, with the use of graphic cochlear reconstructions. The ratio between the size of the cochlea and that of the skull generally decreases when the skull size increases. In other words, the size of the cochlea in small mammals is considerably larger. The number of cochlear turns increases when the cochlea protrudes into the well-pneumatized mastoid bulla instead of being embedded in the thick otic capsule. (Author)

The effects of prolonged caloric stimulation with hot (45C) or ice water have been studied upon eye movements, vestibulospinal, and segmental spinal activity. The results obtained under this variety of test conditions demonstrate that continuous irrigation with water of extreme temperatures evokes, in addition to the effects upon the position of the cupula by endolymphatic convection currents according to the theory of Barany, an initial excitatory thermal effect giving rise to an increased afferent firing which is followed by a paralyzing effect upon the vestibular sensori-neural structures. In order to localize more specifically the site of action of thermal stimulation, experiments were carried out upon labyrinthectomized squirrel monkeys and monkeys with the three semicircular canals plugged. These results, and those obtained by recording the cochlear microphonic and neural components to click stimulation during maximal cold and warm irrigation of the ear, indicate that the effect is upon the peripheral nerve fibers somewhere along their course from the ampulla to the internal auditory meatus. Earlier theories which have predicted this direct effect on the nerves are mentioned, but, for the present, without comment as to their respective importance in explaining paradoxical caloric reactions. (Author), Prepared in cooperation with National Aeronautics and Space Administration.

The squirrel monkey (saimiri sciuria) is probably one of the most useful experimental primates in recent days. They are small, not very difficult to handle, inexpensive primates, and good for all kinds of vestibular and cochlear functional experiments, behavioral conditioning, and so on. Since all inner ear sensory end organs are only purely mechanically stimulated in the vital bodies under natural circumstances, it is worthwhile to know the anatomical construction before performing any functional experimentation. For this purpose, the horizontal serial sections are excellant for acquiring good three-dimensional figures of the inner ear structures. All illustrations in this monograph will be limited within the usual anatomical (light-microscopical) structures, not extending to ultrastructures. Part I of this monograph includes a series of microphotographs of the horizontal serial sections under low magnification (about 20x). This series is the right ear viewing from superior. Part II includes higher magnification views of some important structures from this series and from the other animals, and some humans. Part III includes several bilateral temporal bone microphotographs (horizontal sections) of squirrel monkeys and cats. The modiolar angle and the posterior semicircular canal plane are clearly demonstrated in the series. (Author)

The ears of sixteen albino rats originating from three different suppliers were histologically examined. The specimens were prepared following the standard temporal bone preparation procedure. Spontaneous middle ear infection was found in 25% of the ears. When albino rats are used for otological experiments, it is necessary to have a large number of experimental animals as there is no precise method for detection of spontaneous ear infection of the rat in the vital status. Post-mortem histological investigation is the only reliable procedure available by which otological infections can be detected. (Author), Prepared in cooperation with National Aeronautics and Space Administration, Washington, D. C. Office of Advanced Research and Technology.

Streptomycin sulfate was injected to eight selected squirrel monkeys in sufficient dosage to cause suppression of canal function as indicated by the threshold caloric test, emesis in the Slow Rotation Room, and ataxia. The animals were sacrificed six months after the suppression and slides for light-microscopic investigation were prepared following the standard temporal bone preparation procedure. Pathological findings were confined largely to the cristae and organ of Corti, which were both involved in almost every case. Only very slight changes were observed in the maculae in a few instances; therefore, this drug has a place in vestibular studies requiring selective suppression of canal function. The clinical tests used were not reliable indicators of the pathophysiological state of the cristae but were fairly reliable indicators of normal function of these organs. With regard to emesis in the SRR and ataxia, the essentiality of normal function of the semicircular canals has been demonstrated. No such essentiality was demonstrated for the otolith organs in the present investigation. (Author)