[Spatial distribution of facial volumes. Ontogenetic and phylogenetic study with vestibular orientation]

On cephalic skeleton of Man and two species of chimpanzees, statistically considered during their growing, a sagittal area is measured in facial mass and total face. Barycenters are determined. This points describe, in vestibular axis, ontogenic curves with posterior concavity more important in Man. Remarkable relations exist between barycenters and several facial and mandibular points, and with those of frontal and parietal vault.

Vestibular inputs to the lateral tegmental field of the cat: potential role in autonomic control

The lateral tegmental field (LTF), which is comprised of the lateral reticular formation near the obex, is an important integrative area involved in cardiovascular control and the production of emesis. Using neuroanatomical and electrophysiological techniques, we tested the hypothesis that LTF neurons receive vestibular inputs; the neurons studied included those projecting into the subretrofacial rostral ventrolateral medulla (sRVLM), which contains cells that make direct connections with sympathetic preganglionic neurons. Injections of the anterograde tracer PHA-L into the medial and inferior vestibular nuclei produced labeled terminals in the LTF. Electrical stimulation of the vestibular nerve affected the firing rate of LTF neurons, including approximately one-third of those antidromically activated from the sRVLM. The response latencies ranged from 1.5 to 20 ms, suggesting that the neurons received both direct and polysynaptic vestibular inputs from the vestibular nuclei. The LTF may be involved in the production of vestibulosympathetic reflexes and vestibular-elicited vomiting.

Convergent evolution of the vestibular organ in the subterranean mole-rats, Cryptomys and Spalax, as compared with the aboveground rat, Rattus

The membranous labyrinth of the vestibular organ (examined in toto) in two unrelated species of subterranean rodents, Cryptomys sp. from Zambia and Spalax ehrenbergi from Israel, was in many parameters (streamline length, curvature radius, and cross-sectional area of the lumen) relatively or even absolutely (especially the cross-sectional area) larger than in the laboratory Norway rat. The mechanical sensitivity of the vestibular organ (estimated according to the mathematical model of Oman et al., [1987] Acta. Otolaryngol (Stockh.) 103:1-13) was similar in both subterranean rodent species and significantly higher than that in the laboratory rat. The most pronounced differences in morphometry and the resulting mechanical sensitivity between the subterranean forms and the rat occurred in the lateral (i.e., phylogenetically and ontogenetically most recent and presumably most plastic) semicircular duct. The area of the sensory epithelia, and density and total numbers of vestibular receptors, were estimated on surface specimens for both maculae and for all three cristae for all three species. While the density of hair cells in comparable sensory epithelia was similar in all three species, the sensory area and thus, also, the total receptor counts were significantly larger in both subterranean forms. The peripheral vestibular organ in subterranean rodents is, in comparison to a generalized aboveground dwelling form, i.e., the rat, progressively specialized, and in any case cannot be denoted as degenerate.

Cerebellovestibular projection from the posterior lobe cortex in the rabbit: an experimental study with the retrograde HRP method. I. Topographical relationships

The sources of corticovestibular projections from the cerebellar posterior lobe vermis and hemisphere in the rabbit were investigated by the retrograde horseradish peroxidase (HRP) tracing method. Following iontophoretic injections into various subdivisions of the vestibular nuclear complex (VNC), labelled Purkinje neurones were identified ipsilaterally in all vermal lobules (VI through IX) and some regions of the hemisphere. The results indicate that projection is profuse and directed to all four nuclei of VNC. The labelling suggests some topographical relationships between lobules and especially sublobules of the posterior lobe and individual nuclei of VNC. The major projection originates from lobules VI and IX. A moderate projection derives from lobule VIII whereas that from lobule VII is small. Projections from the hemisphere arise mainly from crus I and crus II of the ansiform lobule. Those from the copula pyramidis, lobule HV and the ventral paraflocculus are sparse. In the present study a topographical relationships were more precisely established than before because the technique revealed VNC afferents from individual sublobules of the cerebellar posterior lobe cortex.

Cerebellovestibular projection from the posterior lobe cortex in the rabbit: an experimental study with the retrograde HRP method. II. Zonal organization

The mediolateral distribution of neurones of origin of the corticovestibular projection from the cerebellar posterior lobe in the rabbit was studied with the retrograde horseradish peroxidase (HRP) tracing method. After iontophoretic injections confined to various subdivisions of the vestibular nuclear complex (VNC) labelled Purkinje neurones were found ipsilaterally in widespread mediolateral cortical regions of vermal lobules from VI to IX, as well as in crus I and crus II of the ansiform lobule, the copula pyramidis, lobule HV and the ventral paraflocculus. However, when projections from individual sublobules were examined, a clearly visible zonal pattern was found. Thus, Purkinje neurones projecting to VNC were arranged in longitudinal bands with medial and lateral boundaries quite well demarcated. These bands had a different width and were found to be located at different distances from the midline. The present findings constitute the first indication of a zonal organization of corticovestibular projections from individual sublobules of the cerebellar posterior lobe in the rabbit. This zonal arrangement of VNC afferents is discussed with the special emphasis on the cerebellar longitudinal zones and related to previous studies on other species.

Demonstration of intermediate filament proteins in the guinea pig vestibular labyrinth by a new, high-resolution cryotechnique

In order to establish the more precise localization of IFPs in the vestibular labyrinth we have developed an immunohistochemical method using semithin cryosections from guinea pig inner ear. The vestibular end organs were fixed by intralabyrinthine perfusion with formaldehyde and glutaraldehyde. Microdissection was performed, followed by decalcification in EDTA. After specimen embedding in gelatin, semithin cryosections (1 micron) were prepared. Prior to the immunohistochemical staining, a new antigen-unmasking treatment was performed. Monoclonal antibodies for cytokeratins (Cks), vimentin, neurofilament protein (NF), and glial fibrillary acidic protein (GFAP) were used and visualized with an indirect ABC method. In the guinea pig vestibular labyrinth, Cks8, 18 and 19 were present. Vimentin and NF were stained positively, GFAP negatively. These results are in accordance with our previous results in the human vestibular labyrinth except for Ck7. The high-resolution cryotechnique in combination with a new antigen-unmasking method may yield more, and more detailed information about the localization of IFPs in the vestibular region.

The volume protective natriuretic peptide system in the inner ear. Comparison between vestibular and cochlear compartments

It has been suggested that the family of natriuretic peptides (NP) has a protective role in volume overloading. Specific binding sites for atrial natriuretic peptide (ANP) and the kidney analog urodilatin (URO) were identified and quantified with computerized autoradiography and biochemical assay in the cryosection in the cochlear and vestibular (utricle/ampulla) tissue. Immunohistochemistry was used to identify and localize NP-like immunoreactive cells. Different levels of specific receptors between and within the inner ear compartments were detected. The presence of specific receptors for NP, as well as unequal distribution of NP-immunoreactivity between the compartments (in certain parts of the cochlea and the endolymphatic sac), may indicate a local autocrine and/or paracrine action of these peptide systems (presumably as a result of the integration of the different peptide effects), independent of their action via the more conventional systemic route, in addition to differences in response of the inner ear compartments to the load. The present results on specific binding of ANP and URO in the inner ear tissue may suggest physiological homology between the inner ear and the kidney. Moreover, a similar role of NP in these organs is suggested.

Choline acetyltransferase immunoreactivity in the human vestibular end-organs

Acetylcholine (ACh) is believed to play a major role in the efferent vestibular system in several animal models, however no information regarding the role of ACh in the human efferent vestibular system has been published. Post-embedding immunohistochemistry in a hydrophilic resin was used to investigate the choline acetyltransferase immunoreactivity (ChATi) and acetylcholinesterase (AChE) histochemistry in human vestibular end-organs. ChATi and AChE activity was found in numerous bouton-type terminals at the basal area of the vestibular hair cells. These terminals were found to contact type II vestibular hair cells and the afferent chalices surrounding type I hair cells. This study provides the first evidence that the human efferent vestibular axons and terminals are cholinergic.

Depression of the vestibulospinal reflex adaptation by intravermal microinjection of GABA-A and GABA-B agonists in the cat

In decerebrate cats the gain of the vestibulospinal reflex (VSR), elicited by sinusoidal roll tilt of the animal at 0.15 Hz, +/- 10 degrees, was tested every 10-15 min during and after a sustained (3 h) period of roll tilt of the head at the parameters indicated above, associated with synchronous roll tilt of the body at 0.15 Hz, +/- 12.5 degrees; this stimulus led to 2.5 degrees of neck rotation, which was thus out of phase with respect to head rotation. In this condition the gain of the VSR progressively increased during the first h of neck-vestibular stimulation, to reach a plateau level at the end of the third h of stimulation. This adaptive process was followed for at least 1 h after stimulation. Microinjection into the zone B of the cerebellar anterior vermis of the GABA-A agonist muscimol (0.25 microliter at 8 micrograms/microliter saline) producing only a slight or negligible depression of the VSR gain in non-adaptive conditions, prevented the occurrence of the adapted increase in gain of the VSR following a 3-h period of sustained head and neck rotation. In addition, intravermal injection of the GABA-A or the GABA-B agonist muscimol or baclofen, respectively, at the same dose indicated above supressed the adapted increase in gain occurring after a 3-h period of continuous neck-vestibular stimulation. The effective sites were located into the zone B of the cerebellar anterior vermis, from which the direct corticocerebellar projection to the lateral vestibular nucleus originates. In conclusion, the results seem to indicate that the adaptive increase in gain of the VSR which occurs in decerebrate cats depend upon plastic changes which affect the Purkinje cells of the cerebellar anterior vermis. These changes were in fact suppressed by GABAergic inhibition of these neurons. The demonstration that the effects of the GABA agonists occurred suddenly makes unlikely the hypothesis that the cerebellar anterior vermis represents either a relay for adaptive changes occurring before it (for instance in the inferior olive) or else the generator of error signals that elicit plasticity in target structures (as in the vestibular nuclei).

Vestibular rehabilitation improves daily life function

This article reviews recent research that addresses the functional outcomes of intervention for vestibular disorders. Vestibular impairments cause disequilibrium, blurred vision, disorientation, and vertigo. These sensory disturbances and motor impairments in turn cause dysfunction in many activities of daily living and in social interactions that traditional medical treatments do not address. The motor sequelae of some vestibular disorders can be treated successfully with programs of graded exercises and activities, the functional implications of which are described herein. The functional impairments caused by other vestibular disorders, which cannot be treated with graded activities, are also described. These disorders include bilateral vestibular loss caused by connective tissue disorders or by the use of ototoxic medications, tumors of the labyrinth or vestibular nerve, and Meniere's disease. Occupational therapy intervention for these conditions may involve providing adaptive equipment, teaching alternative strategies for performing activities of daily living, and psychological intervention for depression and anxiety.

Functional architecture of vestibular primary afferents from the posterior semicircular canal of a turtle, Pseudemys (Trachemys) scripta elegans

Physiological studies in many vertebrates indicate that vestibular primary afferents are not a homogeneous population. Such data raise the question of what structural mechanisms underlie these physiological differences and what functional role is played by afferents of each type. We have begun to answer these questions by characterizing the architecture of 110 afferents innervating the posterior canal of Pseudemys scripta. We emphasize their spatial organization because experimental evidence suggests that afferent physiological properties exhibit significant spatial heterogeneity. The sensory surface of the posterior canal comprises paired, triangular hemicristae, which are innervated by two afferent types. Bouton afferents (66% of total afferents) are found over the entire sensory surface. They differ significantly in the shape and size of their collecting areas, number of boutons, soma size, and axon diameter; this morphological variation is systematically related to the afferent's spatial position. In addition, multivariate analyses suggest that bouton afferents may comprise two subtypes: alpha afferents have delicate processes and are found throughout the crista; beta afferents are more robust and are concentrated preferentially toward the canal center. Calyx-bearing afferents comprise two morphological subtypes: dimorphs (13% of total afferents) bear calyceal and bouton endings; calyceal afferents (21%) bear calyceal endings only. Both types occur exclusively in an elliptical region near the center of each hemicrista; their morphology varies with radial distance from the center of this elliptical region. Our data provide evidence that in Pseudemys: (1) the classical vestibular afferent types (bouton, calyx, dimorph) are structurally heterogeneous, and (2) their spatial sampling characteristics are highly structured and distinctive for each type. These spatial patterns may shed light on regional differences in physiological profiles of vestibular afferents, and they raise questions about the role of this spatial heterogeneity in signaling head movement.

Morphological and electrophysiological consequences of unilateral pre- versus postganglionic vestibular lesions in the frog

The combined removal of the labyrinthine sense organs and of the ganglion of Scarpa on one side (postganglionic section) resulted in a degeneration of afferent fibres in the eighth nerve of the frog (Rana temporaria) within 2-4 days. If the eighth nerve was sectioned more peripherally (preganglionic section) and its distal part was removed together with the labyrinthine organs degeneration of afferent fibres was absent or restricted to very few fibres. Electrical stimulation of vestibular afferents in vitro evoked monosynaptic field potentials in the ipsilateral and via commissural fibres di- and polysynaptic field potentials in the contralateral vestibular nuclei. Afferent-evoked field potentials recorded on the intact side of chronic frogs (> or = 60 days) with a pre- or postganglionic lesion and afferent-evoked field potentials recorded on the operated side of chronic frogs with a preganglionic lesion had amplitudes that were very similar to those recorded in control frogs. Commissurally evoked field potentials recorded on the operated side of chronic frogs with pre- or postganglionic lesions were significantly increased (by about 90%) with respect to control amplitudes. In both groups the time-course of this increase was very similar, started between 15 and 30 days and saturated for survival periods longer than 60 days. Unilateral inactivation of vestibular afferents, but not degeneration, is the likely common denominator of the central process leading to the reported neural changes. A reactive supersensitivity of central vestibular neurons on the operated side for glutamate as a possible mechanism is unlikely, since converging afferent and commissural inputs are both glutamatergic and only one of them, the commissural input, was potentiated. Comparison of the time-courses of neural changes in the vestibular nuclei and postural recovery in the same individuals excludes a causal relation between both phenomena.

Immunolocalization of Na+, K(+)-ATPase, Ca(++)-ATPase, calcium-binding proteins, and carbonic anhydrase in the guinea pig inner ear

The distribution of Na+, K(+)-ATPase, Ca(++)-ATPase, carbonic anhydrase, and calcium-binding proteins were investigated immunohistochemically in paraffin sections of guinea pig inner ears. Marginal cells of the stria vascularis, type II fibrocytes of the spiral ligament, and cells in supralimbal and suprastrial regions, were positive for Na+, K(+)-ATPase. Type I fibrocytes of the spiral ligament were positive for Ca(++)-ATPase, carbonic anhydrase, calmodulin and osteopontin. In the vestibular system, dark cells were positive for Na+, K(+)-ATPase. However, these cells and subepithelial fibrocytes were negative for Ca(++)-ATPase, carbonic anhydrase, and the calcium-binding proteins. In the endolymphatic sac, epithelial cells in intermediate and distal portions were positive for Na+, K(+)-ATPase, but the reaction was less than that in the stria. The same endolymphatic sac cells that were positive for Na+, K(+)-ATPase were also positive for Ca(++)-ATPase and calcium-binding proteins, but negative for carbonic anhydrase. The presence of Ca(++)-ATPase and calcium-binding proteins in the type I fibrocytes of the spiral ligament suggests that these cells are involved in mediating Ca++ regulation. Lower levels of Na+, K(+)-ATPase and the co-existence of Ca(++)-ATPase and calcium-binding proteins in the epithelial cells of the endolymphatic sac indicate that these cells have a distinctive role in ion transport that is different from that of the cells of the stria vascularis and vestibular dark cells.

[The vestibular system: from structure to function]

The two vestibular receptors, right and left, hidden in the petrous part of the temporal bone with the cochlear receptors, receive information from angular and linear movements of the head and transform them into a nerve message sent to the nuclei of the brainstem, which are connected directly on the one hand to the oculomotor nuclei, at the origin of the oculovestibular reflex (induction of nystagmus), and on the other hand, to the spinal motor neurons, at the origin of the vestibulospinal reflex. These reflexes are associated with responses to visual and somaesthetic information for maintenance or return to the standing position, which characterises the function of equilibrium. Vertigo and disorders of balance reflect a conflict of information between these two labyrinths, or between the vestibular apparatus and the messages issued by other captors, and sometimes also dysfunction of central nervous system treatment of information or a lesion of the effector motor systems.

Cytoskeletal organization of the vestibular sensory epithelia: saponin perfusion method for observing intracellular structures by scanning electron microscopy

The cytoskeletal organization of the guinea pig vestibular sensory epithelial cells were investigated by the use of saponin perfusion method using scanning electron microscopy. The skeletal framework of a cell is composed of thin (actin or intermediate filaments) and thick filaments (microtubules). The membrane bound organelles such as nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, etc. were also well demonstrated. This made it possible to investigate the three-dimensional structures of cytoskeletons as well as their complex interactions with various membranes bound organelles. It is therefore suspected that this technique may provide us further information about distribution, topographic relationships, and the functional role of cytoskeletons.

Anatomical segregation of different adaptative processes within the vestibulocerebellum of the cat

Bilateral surgical lesions of the flocculus or the nodulo-uvular lobes were performed in the cat. Effects of these lesions on optokinetic and optokinetic afternystagmus OKAN), vestibulo-ocular reflex (VOR), visual suppression, and adaptation and habituation of VOR were studied using an identical experimental protocol. After flocculectomy, all these functions were impaired, except for habituation. Long-term postoperative recordings only revealed a recovery of the suppression of VOR, suggesting a limited contribution of the flocculus to this function. After nodulo-uvulectomy, only habituation and OKAN were modified. When the lesion was restricted to part of the uvula, OKAN duration was decreased. For other lesions involving the uvula together with the nodulus and/or the lobules VII-VIII,OKAN duration was increased. Habituation was lost after destruction of the nodulo-uvular lobes. When this latter structure was damaged, the retention component of habituation was selectively impaired, sparing the acquisition. Additional lesions outside the vestibulocerebellum appeared necessary to suppress the two components. Comparison of results obtained after flocculectomy and after nodulouvulectomy confirms and extends to non-primate species the concept of a "differential control" of adaptation and habituation by distinct vestibulocerebellar structures.

Morphometry of the vestibular organ in neonate and adult African mole-rats Cryptomys species

The dimensions (length and cross-sectional area) of the semicircular canal of the inner ear in Cryptomys (a rodent with long gestation, and altricial young with slow, extended postnatal growth) did not change after birth. This is further evidence for the relative morphometric postnatal stability of semicircular structures in mammals.

Morphology of the membrana limitans

The morphology of the membrana limitans (ML) was studied by light and electron microscopy to further understand its functional significance. The ML is a porous shield composed of a few to several layers of tightly packed fibrocytes that separate the perilymphatic space of the cochlea and saccule from that of the utricle and canal system. These fibrocytes are thinner on the side of the vestibule. They show many desmosomes and gap junctions and are interspersed with fibrils. The 3-dimensional reconstruction from celloidin sections shows that the ML, as it is viewed from the anterior side, is rectangular in shape, with various surface curvatures and an invagination toward the internal aperture of the vestibular aqueduct. Horseradish peroxidase, a tracer substance, placed on either side of the ML fails to pass to the opposite side. The ML and trabecular meshwork may be a factor contributing to differential sensitivity of cochlear and vestibular sensory cells in the presence of noxious substances.