Development of spiral ganglion cells in mammalian cochlea

The development of the spiral ganglion in the cat, the rat, and the mouse was studied by electron microscopy, from fetal stages in the cat and from birth in the rodent. In the earliest stages, a single population of ganglion cells is present. Immature spiral ganglion neurons possess small perisomatic processes that seem to disappear with development, before the myelination ganglion cells are surrounded by one or two layers of Schwann cell processes. With maturation, the Schwann process increases in number around the perikaryon and its processes, which leads to the onset of myelination. The onset of myelination of the cell body processes is asynchronous. The perikaryon may be delayed in myelination by several days. Moreover, ganglion neurons from a given region of the cochlea do not myelinate simultaneously. The differentiation of two types of fibers in the intraganglionic spiral bundle and the first appearance of TII neurons occurs around birth in the cat and a few days after birth for the rat and the mouse. The distinction of TII cells is possible due to characteristic accumulation of neurofilamentous structures in the cytoplasm.     

The actin filament network associated to Sertoli cell ectoplasmic specializations

Junctional devices in Sertoli cells conform the blood-testis barrier and play a key role in maturation and differentiation of germ cells. The spacial distribution of ectoplasmic specializations of Sertoli cells was studied by beta-actin immunolabelling, using laser confocal and transmission electron microscopy. For confocal microscopy, beta-actin immunolabelling of ectoplasmic specializations was studied over the background of either prosaposin or glutaredoxin immunolabelling of the Sertoli cytoplasm. Labelling was found near the basal lamina, surrounding early spermatocytes (presumably in leptotene-zygotene) or at one of two levels in the seminiferous epithelium: (1) around deep infoldings of the Sertoli cell cytoplasm, in tubular stages before spermiation, and (2) in the superficial part of the seminiferous epithelium, in tubular stages after or during spermiation. For transmission electron microscopy, beta-actin immunolabelling of ectoplasmic specializations was also used. Ectoplasmic specializations were found at two different levels of the seminiferous epithelium. We also used freeze fracture to analyze the characteristics of tubulo-bulbar complexes, a known component of apical ectoplasmic specializations. Also, these different approaches allowed us to study the complex arrangement of the actin cytoskeleton of Sertoli cells branches, which surround germ cells in different stages of the spermatogenic cycle. Our results show a consistent labelling for beta-actin before, during and after the release of spermatozoa in the tubular lumen (spermiation) suggesting a significant role of the actin network in spermatic cell differentiation. In conclusion, significant interrelations among the beta-actin network, the junctional complexes of the blood-testis barrier and the ectoplasmic specializations were detected at different stages of the seminiferous cycle.     

Freeze-fracture organization of hair cell synapses in the sensory epithelium of guinea pig organ of Corti

The fine structure of both the afferent and efferent hair cell synapses in the sensory epithelium of guinea pig organ of Corti was examined by freeze-fracture electron microscopy. In the afferent synapse, barlike aggregates of intramembrane particles (IMPs) of about 10 nm in diameter were seen on the P-face of the afferent presynaptic membrane directly beneath the presynaptic dense projection which is located in the active zone of the presynaptic membrane. Small and large depressions have been seen on the presynaptic membrane. The former were observed in the proximity of the barlike aggregates, while the latter were observed some distance from the aggregate. In outer hair cells, IMPs of about 10 nm in diameter were seen on the P-face of the afferent postsynaptic membrane at a density of 3,000/μm². In the efferent synapse, many aggregates composed of from several to tens of large IMPs of 13 nm in diameter were observed on the presynaptic membrane. These aggregates were localized to small membrane depressions, which tended to be deeper as particle number per aggregate increased. Dense populations of IMPs of about 9 nm in diameter were observed on the P-face of the efferent postsynaptic membrane at a density of 4,000/μm². A fenestrated subsynaptic cistern completely covers the efferent postsynaptic membrane. Moreover, the subsynaptic cistern spans several efferent postsynaptic membranes when efferent synapses are gathered in a group. In the afferent and efferent synapses of hair cells, specializations of the synaptic membranes were represented by marked aggregates characteristic of IMPs. In the efferent synapse, IMP movement inside the synaptic membrane was proposed in relationship to retrival of synaptic vesicle membrane. Structural relationship between the subsynaptic cistern and efferent postsynaptic membrane was revealed.     

Trigeminal ganglion morphology in human fetus

The morphology of the trigeminal ganglion in human fetus was investigated by means of the tract‐tracing method using the lipophilic dye DiI‐C18‐(3) (1,1′‐double octadecane 3,3,3′3′‐tetramethyl indole carbonyl cyanine‐perchlorate), hematoxylin–eosin (HE) stain, and three‐dimensional computer reconstruction models. The trigeminal ganglion was flat in the dorsoventral direction, and DiI staining revealed that the trigeminal ganglion cells were somatotopically distributed in the ganglion in a way that reflected the mediolateral order of the three branches. Ganglion cells of the ophthalmic nerve were distributed in the anteromedial part of the trigeminal ganglion, those of the mandibular nerve were in the posterolateral part, and those of the maxillary nerve were localized in the intermediate part. DiI labeled both ganglion cells and nerve fibers in the trigeminal ganglion; the ganglion cells varied in size and appeared as round‐ or oval‐shaped, the neurites connected the cell soma, and some bipolar neurons were also observed. The number of embryonic trigeminal ganglion cells did not significantly change with gestational age, but the cell diameter, area, and perimeter significantly increased. The motor root leaves the pons, runs along the sensory root, passes the ventral surface of the ganglion, and finally runs together with the mandibular nerve. The findings reported here elucidate the morphology, development, and somatotopic organization of the trigeminal ganglion and reveal the trigeminal nerve motor root pathway along the trigeminal ganglion and mandibular nerve in the human fetus. Microsc. Res. Tech. 76:598–605, 2013. © 2013 Wiley Periodicals, Inc.     

Molecular ultrastructure of the urothelial surface: Insights from a combination of various microscopic techniques

The urothelium forms the blood–urine barrier, which depends on the complex organization of transmembrane proteins, uroplakins, in the apical plasma membrane of umbrella cells. Uroplakins compose 16 nm intramembrane particles, which are assembled into urothelial plaques. Here we present an integrated survey on the molecular ultrastructure of urothelial plaques in normal umbrella cells with advanced microscopic techniques. We analyzed the ultrastructure and performed measurements of urothelial plaques in the normal mouse urothelium. We used field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) on immunolabeled ultrathin sections (immuno‐TEM), and freeze‐fracture replicas (FRIL). We performed immunolabeling of uroplakins for scanning electron microscopy (immuno‐FESEM). All microscopic techniques revealed a variability of urothelial plaque diameters ranging from 332 to 1179 nm. All immunolabeling techniques confirmed the presence of uroplakins in urothelial plaques. FRIL showed the association of uroplakins with 16 nm intramembrane particles and their organization into plaques. Using different microscopic techniques and applied qualitative and quantitative evaluation, new insights into the urothelial apical surface molecular ultrastructure have emerged and may hopefully provide a timely impulse for many ongoing studies. The combination of various microscopic techniques used in this study shows how these techniques complement one another. The described advantages and disadvantages of each technique should be considered for future studies of molecular and structural membrane specializations in other cells and tissues. Microsc. Res. Tech. 77:896–901, 2014. © 2014 Wiley Periodicals, Inc.     

Serial reconstruction of inner hair cell afferent innervation using semithick sections

The afferent innervation pattern of inner hair cells in the apex of the guinea pig cochlea was studied using serial reconstruction of semithick (0.25–μm) sections and high-voltage electron microscopy (HVEM). This thickness produced a good compromise between the ability to resolve details of the synaptic contacts between the hair cells and sensory neurons and the number of sections required to reconstruct the nerve terminals within the receptor organ. The use of a goniometer allowed the sections to be tilted to angles optimum for viewing either the synaptic membrane specializations or the presynaptic bodies. Reasonably good images of 0.25-μm sections could be obtained using a conventional 120-keV microscope, but the images produced by the HVEM were clearly superior. The sensory nerve terminals and hair cells were reconstructed using a microcomputer-based computer-aided-design system. Nerve terminals with complex shapes could be successfully rendered as surface models viewed as stereo pairs. The advantages and limitations of the techniques used are discussed.     

Structure and function in the cerebral ganglion

Evidence is reviewed to evaluate whether the term "brain is justified in referring to the snail's cerebral ganglion. The focus of the review is terrestrial species, with particular attention given to the genus Helix. In accordance with a standard definition of "brain, the cerebral ganglion is found to be differentiated both structurally and functionally. It receives convergent sensory inputs from a variety of anterior sensory organs plus the posterior body wall. Its outputs comprise motor commands directed towards anterior muscle systems, e.g., the tentacles and the penis, as well as premotor commands directed towards executory centers in other ganglia, e.g., the buccal, visceral, and pedal ganglia. Of the three major divisions in the ganglion, the procerebrum and the mesocerebrum are the most differentiated, whereas the metacerebrum is the least differentiated. The specializations of the procerebrum for olfactory functions, and the mesocerebrum for reproductive functions, reflect the importance of adaptations for feeding and mating in the evolution of the Gastropoda.     

SNOM and AFM microscopy techniques to study the effect of non-ionizing radiation on the morphological and biochemical properties of human keratinocytes cell line (HaCaT)

In this study we have employed atomic force microscopy (AFM) and scanning near‐field optical microscopy (SNOM) techniques to study the effect of the interaction between human keratinocytes (HaCaT) and electromagnetic fields at low frequency. HaCaT cells were exposed to a sinusoidal magnetic field at a density of 50 Hz, 1 mT. AFM analysis revealed modification in shape and morphology in exposed cells with an increase in the areas of adhesion between cells. This latter finding was confirmed by SNOM indirect immunofluorescence analysis performed with a fluorescent antibody against the adhesion marker β4 integrin, which revealed an increase of β4 integrin segregation in the cell membrane of 50‐Hz exposed cells, suggesting that a higher percentage of these cells shows a modified pattern of this adhesion marker.     

Evaluation of fracture planes and cell morphology in complementary fractures of cultured cells in the frozen-hydrated state by field-emission secondary electron microscopy: feasibility for ion localization and fluorescence imaging studies

We have employed field-emission secondary electron microscopy (FESEM) for morphological evaluation of freeze-fractured frozen-hydrated renal epithelial LLC-PK₁ cells prepared with our simple cryogenic sandwich-fracture method that does not require any high-vacuum freeze-fracture instrumentation (Chandra et al. (1986) J. Microsc. 144 , 15–37). The cells fractured on the substrate side of the sandwich were matched one-to-one with their corresponding complementary fractured faces on the other side of the sandwich. The FESEM analysis of the frozen-hydrated cells revealed three types of fracture: (i) apical membrane fracture that produces groups of cells together on the substrate fractured at the ectoplasmic face of the plasma membrane; (ii) basal membrane fracture that produces basal plasma membrane-halves on the substrate; and (iii) cross-fracture that passes randomly through the cells. The ectoplasmic face (E-face) and protoplasmic face (P-face) of the membrane were recognized based on the density of intramembranous particles. Feasibility of fractured cells was shown for intracellular ion localization with ion microscopy, and fluorescence imaging with laser scanning confocal microscopy. Ion microscopy imaging of freeze-dried cells fractured at the apical membrane revealed well-preserved intracellular ionic composition of even the most diffusible ions (total concentrations of K⁺, Na⁺ and Ca⁺). Structurally damaged cells revealed lower K⁺ and higher Na⁺ and Ca⁺ contents than in well-preserved cells. Frozen-freeze-dried cells also allowed imaging of fluorescently labelled mitochondria with a laser scanning confocal microscope. Since these cells are prepared without washing away the nutrient medium or using any chemical pretreatment to affect their native chemical and structural makeup, the characterization of fracture faces introduces ideal sample types for chemical and morphological studies with ion and electron microscopes and other techniques such as laser scanning confocal microscopy, atomic force microscopy and near-field scanning optical microscopy.     

The distribution of histamine and serotonin in the barnacle's nervous system

The use of antisera directed against conjugates of histamine and serotonin has revealed the locations of neurons labeling for these transmitters in the nervous system of barnacles. Photoreceptors label for histamine but not serotonin and also satisfy a number of other criteria indicating that histamine is their neurotransmitter. Photoreceptors also take up radioactively labeled histamine but not serotonin. Within the barnacle's brain no somata are consistently found that label with antiserum against histamine, but one to three pairs of small cells, depending on species, label with antiserum against serotonin. The most impressive serotonin-like immunoreactivity in the brain, however, is in a pair of large fibers ascending through the circumesophageal connectives and ramifying extensively. Within the ventral ganglion, the only other ganglion in the barnacle, ten pairs of cells label with antiserum against histamine. These neurons are confined to the posterior portion of the ganglion but ramify extensively throughout the ganglion. Antiserum against serotonin labels about 15 cell pairs, depending on species, located throughout the ganglion. The positions of the arbors of many of these cells suggest that these amines have a role in modulating either the motor pathways underlying feeding or the visual pathways responsible for the detection of shadows.     

Cryofixation of vascular endothelium

Cryofixation refers to the immobilization of tissue components by the rapid removal of heat from the specimen, so that the structure is interred and stabilized in a natural embedding medium, namely, frozen (amorphous or microcrystalline) tissue water. Cryofixation is now often used as a complement to the more traditional fixation methods, especially when the cell structure is delicate or dynamic and may be inaccurately preserved by the slow selective action of chemical fixatives. Vascular endothelial cells are specialized for transcellular transport and for the regulation of blood flow and composition. The dynamic and labile subcellular organization of these cells, presumably reflecting these functional specializations, makes them ideal candidates for cryofixation. Several different types of endothelial cells were directly frozen at temperatures below 20 degrees Kelvin by pressing them against a liquid-helium-cooled block. These samples were subsequently processed for structural analysis by freeze-substitution. Detailed rationales, designs, and protocols are described for both freezing and freeze-substitution. Electron micrographs of cryofixed arterial and venous capillaries (rete mirabile of the American eel), iliac vein (rabbit), and cultured endothelium from the iliac vein (human) reveal that the organization of the characteristic intracellular membrane system of endothelial vesicles is qualitatively similar to that seen in chemically fixed endothelium, especially with regard to the interconnection of clusters of individual vesicles to form elaborate networks. The luminal and abluminal networks are not in communication, at least not in static images. Quantitatively, however, most directly frozen endothelial cells have far fewer vesicular profiles than comparable glutaraldehydefixed cells. The differences can be explained by presuming that the rapid action of cryofixation (approximately 1 msec) gives a more accurate picture of the vesicular network because it captures the transient structure of labile or dynamic membranes.     

Lysophosphatidylcholine acyltransferase 1 is involved in the regulation of exosome secretion and uptake in colorectal cancer cells

Lysophosphatidylcholine acyltransferase 1 (LPCAT1) is a phospholipid acyltransferase that promotes phospholipid synthesis and plasma membrane reconstruction. Exosomes play an important role in tumor metastasis. The release and uptake of exosomes are key steps of their functions and depend on plasma membrane fusion and plasma membrane receptors, respectively. The purpose of this study was to explore whether LPCAT1-induced plasma membrane remodeling would change the secretion and uptake behavior of exosomes in tumor cells. We first confirmed the abnormally high expression of LPCAT1 in colorectal cancer cells by quantitative real-time PCR (qPCR) and Western blot analysis. Then, SW620 cells were used as exosome source cells, and SW480 cells were used as exosome receiver cells. Exosomes from SW620 cells could effectively promote the migration of SW480 cells. When LPCAT1 expression was reduced via siRNA knockdown in the source cells, the secretion of exosomes was downregulated, thus weakening the pro-migratory effects of exosomes on target cells. Conversely, when LPCAT1 was knocked down in target cells, the uptake of exosomes in target cells also decreased sharply. These results undoubtedly revealed that LPCAT1 is functionally associated with the release and internalization of exosomes in colorectal cancer cells and could affect the paracrine effects of exosomes, preliminarily extending the classical metabolic function of LPCAT1 to exosome-related pathways.     

The similarity analysis of vibrating membrane with its applications

The similarity analysis is applied to the study of vibrating membrane with variable density. In this paper, the design of the eigenvalue problems of the vibrating mode (Helmholtz equation) by the infinitesimal transformation groups is exhibited.The exact similarity solutions of the eigenvalue problems of Helmholtz equation with variable weighting function under the spiral and inversion groups are constructed in the regions of spiral, concentric circles, eccentric circles, and upper-half plane with circle removed.The similitude and scaling law are also built under the study and manipulation of the differential equations that are known to govern the behavior of the eigenvalue problems of Helmholtz equation. Without the requirement of geometrically similitude or mapping, the eigenvalues of a complicated domain can be obtained directly from a given simple region through the scaling law and they are verified and checked by numerical calculation and the Rayleigh–Ritz method.     

Autoradiographic studies of selective amino acid uptake by neural and nonneural elements in the gerbil cochlea

The cochlea is well suited for studies of the uptake properties of auditory neurons and nonneuronal supporting cells. Probe concentrations of radioisotopically labeled amino acids, including putative neurotransmitters and their precursors, breakdown products, and blockers, can be introduced via the natural, fluid-filled channels of the inner ear. Uptake patterns can be mapped at cellular and intracellular levels using light and electron microscopic autoradiographic methods. The procedures for introduction of label, fixation, plastic embedment, and light and electron microscopic autoradiography are described with special reference to the cochlea. Labeling patterns observed with over 20 amino acids are summarized for hair cells, spiral ganglion neurons, efferents, and nonneural elements of the stria vascularis, limbus, and modiolus. Limitations on the interpretation of results and their implications for the general usefulness of the methods are discussed.     

Expression of TRPV4 in the zebrafish retina during development

The transient receptor potential (TRP) channels are involved in sensing mechanical/physical stimuli such as temperature, light, pressure, as well as chemical stimuli. Some TRP channels are present in the vertebrate retina, and the occurrence of the multifunctional channel TRP vanilloid 4 (TRPV4) has been reported in adult zebrafish. Here, we investigate the expression and distribution of TRPV4 in the retina of zebrafish during development using polymerase chain reaction (PCR), Western blot, and immunohistochemistry from 3 days post fertilization (dpf) until 100 dpf. TRPV4 was detected at the mRNA and protein levels in the eye of zebrafish at all ages sampled. Immunohistochemistry revealed the presence of TRPV4 in a population of the retinal cells identified as amacrine cells on the basis of their morphology and localization within the retina, as well as the co-localization of TRPV4 with calretinin. TRPV4 was first (3 dpf) found in the soma of cells localized in the inner nuclear and ganglion cell layers, and thereafter (10 dpf) also in the inner plexiform layer. The adult pattern of TRPV4 expression was achieved by 40 dpf the expression being restricted to the soma of some cells in the inner nuclear layer and ganglion cell layers. These data demonstrate the occurrence and developmental changes in the expression and localization of TRPV4 in the retina of zebrafish, and suggest a role of TRPV4 in the visual processing.     

Ultrastructure of the intercalated body,a novel organelle associated with fluid forming cells in the organ of Corti

The intercalated body is a newly discovered organelle in the inner and outer spiral sulcus cells of the mouse organ of Corti. The organelle was found in the cochleas of 14-day and older intact mice and in organs in culture of corresponding ages. The organelle consists of a stack of interconnected cisternae of endoplasmic reticulum and of membrane bound rodlets that are intercalated between, and run parallel to, the cisternae. The cisternal membranes are predominantly smooth, but some may display ribosomes. Most rodlets are from 1 to 2 μm long, about 0.1 μm wide, and contain electron dense material. Mitochondria are commonly associated with or incorporated into the organelle. Some electron micrographs suggest that the rodlets may originate from modified mitochondria. It is our impression that the formation of the organelle begins with the apposition of cisternae and mitochondria. Cisternal-associated mitochondria appear to constrict, elongate, and lose their inner membranes. In both the intact animal and in culture, the cells of the inner and outer spiral sulci display microvilli, apical junctional complexes, lateral intercellular spaces containing interdigitating cell processes, and appear to be involved in fluid formation. Moreover, in culture, the cells of inner and outer spiral sulci as well as some cells proliferating in the outgrowth zone participate in fluid formation, producing large fluid pockets. All these cells commonly contain intercalated bodies. It is possible that in the intact animal, as in culture, intercalated bodies may play a role in fluid regulation in the immediate vicinity of the hair cells.     

Agmatine pretreatment protects retinal ganglion cells (RGC-5 cell line) from oxidative stress <i>in vitro</i>

Agmatine, 2-(4-aminobutyl)guanidine, has been reported to have neuroprotective effects against various neuronal damages. In this study it was investigated whether agmatine pretreatment rescues the retinal ganglion cells from oxidative injury in vitro. After differentiation of transformed rat retinal ganglion cells (RGC-5 cell line) with staurosporine, agmatine (0.0 to 100.0 μM) pretreatment was performed for 2 hours. Subsequently, they were exposed to hydrogen peroxide (0.0 to 2.5 mM) as an oxidative stress. Cell viability was monitored for up to 48 hours with the lactate dehydrogenase (LDH) assay and apoptosis was examined by the terminal deoxynucleotide transferase-mediated terminal uridine deoxynucleotidyl transferase nick end-labeling (TUNEL) method. As a result, differentiated RGC-5 cells were found to have decreased viability after addition of hydrogen peroxide in a dose-dependent manner. This hydrogen peroxide induced cytotoxicity caused apoptosis characterized by DNA fragmentation. Agmatine pretreatment not only increased cell viability but also attenuated DNA fragmentation. In conclusion, agmatine pretreatment demonstrated neuroprotective effects against oxidative stress induced by hydrogen peroxide in differentiated RGC-5 cells in vitro. This suggests a novel therapeutic strategy rescuing retinal ganglion cells from death caused by oxidative injury     

Morphological observations of small granule-containing (Chromaffin) cells in the celiac ganglion of the guinea pig,with emphasis on cell contacts

Utilizing electron microscopic observation, several contacts between small, granule-containing cells (SGC) and postganglionic neurons (PGN) in the celiac ganglion of the guinea pig have been observed. A SGC in very close association with a PGN was seen to receive a distinct synaptic contact that contained many vesicles with dense cores. This contact was morphologically unlike cholinergic synapses previously reported on chromaffin cells. Because the SGC and PGN were clearly separated by a thin rim of satellite cell cytoplasm mutual to both cells, it is not known how or if the SGC would possibly exert a synaptic or paracrine effect on the PGN. Also, intraganglion SGC existed as large well-vascularized islands within the celiac ganglion. These intraganlion clusters sometimes contained more than 50 cells and perhaps could be considered to function as localized neuroendocrine components within the ganglion by secreting granule products into the nearby blood vessels for local or distant effects, although this certainly is not known. This work reports a unique synaptic ending upon a single-occurring SGC, which, in turn, closely approximates a ganglion neuron in a soma-somatic relationship. In addition, a very close association (but no actual contact) was observed between granule-containing processes, presumably emanating from the intraganglion clusters, and PGN. Whatever the function of ganglionic SGC may be, the exact relationship between SGC and PGN presumably would be of great interest and potential importance. © 1994 Wiley-Liss, Inc.     

Heat transfer and resistance characteristics of conical spiral tube bundle based on field synergy principle

Conical spiral tube bundle are universally used in heat transfer enhancement in heat exchangers.The heat transfer and resistance of the tube bundle are affected greatly by the conical structure,so the ...