Three-Dimensional Analysis of Vestibular Efferent Neurons Innervating Semicircular Canals of the Gerbil

Purcell, I. M. and A. A. Perachio. Three-dimensional analysis of vestibular efferent neurons innervating semicircular canals of the gerbil. J. Neurophysiol. 78: 3234–3248, 1997. Anterograde labeling techniques were used to examine peripheral innervation patterns of vestibular efferent neurons in the crista ampullares of the gerbil. Vestibular efferent neurons were labeled by extracellular injections of biocytin or biotinylated dextran amine into the contralateral or ipsilateral dorsal subgroup of efferent cell bodies (group e) located dorsolateral to the facial nerve genu. Anterogradely labeled efferent terminal field varicosities consist mainly of boutons en passant with fewer of the terminal type. The bouton swellings are located predominately in apposition to the basolateral borders of the afferent calyces and type II hair cells, but several boutons were identified close to the hair cell apical border on both types. Three-dimensional reconstruction and morphological analysis of the terminal fields from these cells located in the sensory neuroepithelium of the anterior, horizontal, and posterior cristae were performed. We show that efferent neurons densely innervate each end organ in widespread terminal fields. Subepithelial bifurcations of parent axons were minimal, with extensive collateralization occurring after the axons penetrated the basement membrane of the neuroepithelium. Axonal branching ranged between the 6th and 27th orders and terminal field collecting area far exceeds that of the peripheral terminals of primary afferent neurons. The terminal fields of the efferent neurons display three morphologically heterogeneous types: central, peripheral, and planum. All cell types possess terminal fields displaying a high degree of anisotropy with orientations typically parallel to or within ±45° of the longitudinal axis if the crista. Terminal fields of the central and planum zones predominately project medially toward the transverse axis from the more laterally located penetration of the basement membrane by the parent axon. Peripheral zone terminal fields extend predominately toward the planum semilunatum. The innervation areas of efferent terminal fields display a trend from smallest to largest for the central, peripheral, and planum types, respectively. Neurons that innervate the central zone of the crista do not extend into the peripheral or planum regions. Conversely, those neurons with terminal fields in the peripheral or planum regions do not innervate the central zone of the sensory neuroepithelium. The central zone of the crista is innervated preferentially by efferent neurons with cell bodies located in the ipsilateral group e. The peripheral and planum zones of the crista are innervated preferentially by efferent neurons with cell bodies located in the contralateral group e. A model incorporating our anatomic observations is presented describing an ipsilateral closed-loop feedback between ipsilateral efferent neurons and the periphery and an open-loop feed-forward innervation from contralateral efferent neurons. A possible role for the vestibular efferent neurons in the modulation of semicircular canal afferent response dynamics is proposed.

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The vestibular nerve of the chinchilla. I. Peripheral innervation patterns in the horizontal and superior semicircular canals

Journal of Neurophysiology ◽

10.1152/jn.1988.60.1.167 ◽

1988 ◽

Vol 60 (1) ◽

pp. 167-181 ◽

Cited By ~ 139

Author(s):

C. Fernandez ◽

R. A. Baird ◽

J. M. Goldberg

Keyword(s):

Hair Cells ◽

Afferent Fiber ◽

Central Zone ◽

Semicircular Canals ◽

Peripheral Zone ◽

Sensory Epithelium ◽

Vestibular Nerve ◽

Fiber Types ◽

Peripheral Innervation ◽

Numerous Type

1. Afferent fibers supplying the horizontal and superior semicircular canals of the chinchilla were labeled by extracellular injections of horseradish peroxidase (HRP) into the vestibular nerve. The arborizations of labeled fibers within the sensory epithelium were reconstructed from serial sections of the crista. 2. The sensory epithelium of the crista can be divided into central, intermediate, and peripheral zones of approximately equal areas. The three zones can be distinguished in normal material by the density of hair cells and by the morphology of calyx endings. 3. Labeled fibers supply either the canalicular or the utricular side of the crista. Axons seldom bifurcate below the basement membrane and they begin dividing into their terminal arborizations almost immediately upon entering the sensory epithelium. The arborizations are compact, seldom extending more than 50 micron from the parent axon. 4. Both calyx and bouton endings were labeled. Calyces can be simple or complex. Simple calyces innervate individual hair cells, whereas complex calyces supply two to three adjacent hair cells. Complex calyces are commonly found only in the central zone. Simple calyces and boutons are located in all regions of the epithelium. Calyces emerge from the parent axon or one of its thick branches. Boutons, whether en passant or terminal, are always located on thin processes. 5. Fibers were classified as calyx, bouton, or dimorphic. The first type only has calyx endings, the second only has bouton endings, and the third has both kinds of endings. Dimorphic units make up some 70% of the labeled fibers, bouton units some 20%, and calyx units some 10%. The three fiber types differ in the diameters of their parent axons and in the regions of the crista they supply. Axon diameters are largest for calyx units and smallest for bouton units. Calyx units are concentrated in the central zone of the crista, whereas bouton units are largely confined to the peripheral zone. Dimorphic units are seen throughout the sensory epithelium. 6. Calyx units are almost always unbranched and end as simple calyces or, less often, as complex calyces. The terminal arbors of bouton units consist of fine processes containing 15-80 endings. Dimorphic units vary in complexity from fibers with a single calyx and a few boutons to those with one to four calyces and more than 50 boutons. 7. The results emphasize the importance of dimorphic units, which were the most numerous type of afferent fiber labeled in this study and were the only units found to innervate all regions of the sensory epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

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Morphological Identification of Physiologically Characterized Afferents Innervating the Turtle Posterior Crista

Journal of Neurophysiology ◽

10.1152/jn.2000.83.3.1202 ◽

2000 ◽

Vol 83 (3) ◽

pp. 1202-1223 ◽

Cited By ~ 44

Author(s):

Alan M. Brichta ◽

Jay M. Goldberg

Keyword(s):

Hair Cells ◽

Central Zone ◽

Peripheral Zone ◽

Morphological Identification ◽

Type I ◽

Type Ii ◽

Response Dynamics ◽

Multivariate Statistical ◽

Class B ◽

Longitudinal Position

The turtle posterior crista consists of two hemicristae. Each hemicrista extends from the planum semilunatum to the nonsensory torus and includes a central zone (CZ) surrounded by a peripheral zone (PZ). Type I and type II hair cells are found in the CZ and are innervated by calyx, dimorphic and bouton afferents. Only type II hair cells and bouton fibers are found in the PZ. Units were intraaxonally labeled in a half-head preparation. Bouton (B) units could be near the planum (BP), near the torus (BT), or in midportions of a hemicrista, including the PZ and CZ. Discharge properties of B units vary with longitudinal position in a hemicrista but not with morphological features of their peripheral terminations. BP units are regularly discharging and have small gains and small phase leads re angular head velocity. BT units are irregular and have large gains and large phase leads. BM units have intermediate properties. Calyx (C) and dimorphic (D) units have similar discharge properties and were placed into a single calyx-bearing (CD) category. While having an irregular discharge resembling BT units, CD units have gains and phases similar to those of BM units. Rather than any single discharge property, it is the relation between discharge regularity and either gain or phase that makes CD units distinctive. Multivariate statistical formulas were developed to infer a unit's morphological class (B or CD) and longitudinal position solely from its discharge properties. To verify the use of the formulas, discharge properties were compared for units recorded intraaxonally or extracellularly in the half-head or extracellularly in intact animals. Most B units have background rates of 10–30 spikes/s. The CD category was separated into CD-high and CD-low units with background rates above or below 5 spikes/s, respectively. CD-low units have lower gains and phases and are located nearer the planum than CD-high units. In their response dynamics over a frequency range from 0.01–3 Hz, BP units conform to an overdamped torsion-pendulum model. Other units show departures from the model, including high-frequency gain increases and phase leads. The longitudinal gradient in the physiology of turtle B units resembles a similar gradient in the anamniote crista. In many respects, turtle CD units have discharge properties resembling those of calyx-bearing units in the mammalian central zone.

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In situ investigation of the primary recrystallization of alpha titanium in HVEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100110313 ◽

1978 ◽

Vol 36 (1) ◽

pp. 634-635

Author(s):

S. Naka ◽

R. Penelle ◽

R. Valle

Keyword(s):

Dimensional Analysis ◽

Texture Evolution ◽

Cold Work ◽

Three Dimensional ◽

Primary Recrystallization ◽

Thin Foils ◽

In Situ Investigation ◽

Grain Growth Model ◽

Alpha Titanium

The in situ experimentation technique in HVEM seems to be particularly suitable to clarify the processes involved in recrystallization. The material under investigation was unidirectionally cold-rolled titanium of commercial purity. The problem was approached in two different ways. The three-dimensional analysis of textures was used to describe the texture evolution during the primary recrystallization. Observations of bulk-annealed specimens or thin foils annealed in the microscope were also made in order to provide information concerning the mechanisms involved in the formation of new grains. In contrast to the already published work on titanium, this investigation takes into consideration different values of the cold-work ratio, the temperature and the annealing time.Two different models are commonly used to explain the recrystallization textures i.e. the selective grain growth model (Beck) or the oriented nucleation model (Burgers). The three-dimensional analysis of both the rolling and recrystallization textures was performed to identify the mechanismsl involved in the recrystallization of titanium.

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