Vestibular efferents contain peripherin.

Vestibular efferents have a common origin with the motoneurons of the facial nerve. In adults they share a number of common features, such as the same transmitter. Here we show using retrograde transport and immunohistochemistry, that the vestibular efferents, like facial motoneurons, contain peripherin. This supports the suggestion that peripherin-positive fibers at the apex of the cristae ampullaris are efferents.

Hair cell numbers do not decrease in the crista ampullaris of geriatric gerbils.

Among the geriatric population, dizziness and falling are serious problems. One system involved in balance that may change with age is the vestibular system. A common assertion is that the number of vestibular hair cells decreases as age increases. Our goal was to quantitate the number of hair cells in young and old gerbils and document the decrease. We used physical dissector design-based stereological procedures on serial 2-microm sections through the crista ampullaris. Between young and aged gerbils, there were no quantitative differences in the number, density, or types of hair cells or the length of the crista ampullaris. This lack of change in the number of hair cells suggests that the cause for vestibular dysfunction during aging must lie elsewhere.

Central distribution of vestibular afferents that innervate the anterior or lateral semicircular canal in the mongolian gerbil.

The central distribution of afferents that innervate the crista ampullaris of the anterior or lateral semicircular canals was determined in gerbils following the direct injection of tracers into one sensory neuroepithelia. Labeled somata were scattered throughout the superior ganglion. The central distribution of fibers demonstrated extensive overlap. The central branch of afferents innervating either canal was located in the rostral part of the nerve. Nerve fibers divided into ascending and descending branches. Ascending branch ramifications terminated in the superior vestibular nucleus, the magnocellular and parvicellular medial vestibular nuclei, and the cerebellum. Cerebellar terminal areas include the flocculus, nodulus and uvula. Descending branch ramifications terminated in the caudal medial, parvicellular medial and descending vestibular nuclei, and the nucleus prepositus hypoglossi. Lateral canal afferents terminated sparsely in nucleus cuneatus. The anterior canal had sparse innervation in the paratrigeminal and gigantocellular reticular formation. This study has shown many similarities in the central distribution of fibers that innervate the anterior and lateral canals and a few areas of segregated input. Projections outside the vestibular nuclei are more extensive than previously determined, including afferents to prepositus hypoglossi, cochlear nuclei, and reticular formation. Projections to the flocculus appear as numerous as those to the vermis.

Decreased expression of calretinin and calbindin in the labyrinth of old gerbils.

Calretinin and calbindin staining were compared in the vestibular periphery of old (35-48 months) and young (4-12 months) animals. Both stain calyx-only afferents; calbindin stains additional terminals in the apex [Brain Res. 928 (2002) 8-17]. In six of seven pairs of animals, calretinin and calbindin staining was diminished or absent in the old animals. These changes suggest that a reduction in certain calcium-binding proteins may be a characteristic of aging animals.

Central projections of the utricular nerve in the gerbil.

The central projections of primary afferent fibers in the utricular nerve, which convey linear head acceleration signals to neurons in the brainstem and cerebellum, are not completely defined. The purpose of this investigation was twofold: 1) to define the central projections of the gerbil utricular afferents by injecting horseradish peroxidase (HRP) and biotinylated dextran amine (BDA) into the utricular macula; and 2) to investigate the projections of individual utricular afferents by injecting HRP intracellularly into functionally identified utricular neurons. We found that utricular afferents in the gerbil projected to all divisions of the vestibular nuclear complex, except the dorsal lateral vestibular nucleus. In addition, terminals were observed in the interstitial nucleus of the eighth nerve, nucleus Y, external cuneate nucleus, and lobules I, IV, V, IX, and X of the cerebellar vermis. No projections appeared in the flocculus or paraflocculus. Fibers traversed the medial and intermediate cerebellar nuclei, but terminals appeared only occasionally. Individual utricular afferents collateralize extensively, projecting to much of the brainstem area innervated by the whole of the utricular nerve. This study did not produce complete filling of individual afferent collateral projections into the cerebellar cortex.

Molecular probes of the vestibular nerve. I. Peripheral termination patterns of calretinin, calbindin and peripherin containing fibers.

Vestibular afferents have different physiological properties that can be at least partially correlated with the morphology that the peripheral ending makes with type I and type II hair cells. If the location of the ending in the sensory epithelium is included, the correlations are further improved. It is also known that vestibular afferents can be immunohistochemically stained for a variety of different substances. We have concentrated on three of these markers, calretinin, calbindin and peripherin, because the sources of afferents to the vestibular nuclear complex that contain these substances are restricted, in two cases to the primary afferents. We demonstrate that calretinin is found only in the calyx-only afferents that are located at the apex of the cristae ampullaris and along the striola of the maculae. The area containing stained calyces is equal to or slightly smaller than the central zone of the cristae as defined by the Goldberg group [J. Neurophysiol. 60 (1988) 167]. Calbindin is also found in calyces at the apex of the cristae and along the striola of the otoliths. Examination of adjacent sections of all endorgans indicates that calbindin staining overlaps with calretinin, but is always several hair cells wider on each side. Peripherin also stains fibers in the neuroepithelium. The greatest density of staining is in the peripheral zone of the cristae, i.e. at the base and toward the planum semilunatum. We suggest that these substances are useful markers for specific sets of vestibular afferents.

Molecular probes of the vestibular nerve. II. Characterization of neurons in Scarpa's ganglion to determine separate populations within the nerve.

An unambiguous delineation of the exact numbers and/or proportions of calyx-only, dimorph, and bouton-only vestibular afferents is needed to continue studies concerning vestibular integration in the nervous system. Here, we take advantage of immunocytochemical properties of three groups of vestibular afferents. We utilize calretinin to delineate the calyx-only population, and peripherin to stain the bouton-only afferents. An additional subgroup of afferents that stain with calbindin, but not calretinin is also introduced. The size of the cells that stain with these markers was determined. Cells that are calbindin-positive overlap the sizes of Nissl-stained somata. Cells that stain with peripherin or calretinin are non-overlapping with calretinin cells being the largest and peripherin-positive cells the smallest. Twenty percent of the ganglion cells were peripherin positive, another 20% stained with calretinin antibodies, 30% stained with calbindin, and all cells in Scarpa's ganglion stained with parvalbumin. Most of the calretinin-positive cells also stained with calbindin. One-third of the calbindin-positive population stained only with calbindin. These studies indicate that the calyx- and bouton-only populations of vestibular afferents in gerbil comprise at least 40% of the nerve. In addition, at least 10% of the nerve also stains with calbindin and neither calretinin nor peripherin. Based on indirect evidence, we hypothesize that these are a subpopulation of dimorph afferents. This study has provided an anatomical instrument (in addition to intracellular physiological methods) to study separate populations of vestibular afferents.