Fine structure of the epidermis of the optic tentacle in a slug, Limax flavus L.

The epidermis at the tip of the optic tentacle in Limax flavus is constructed of columnar epithelial cells, distal processes of nerve cells, and scattered processes of the collar cells. The epithelial cells extend stout microvilli called plasmatic processes by Wright perpendicularly from the free surface. Each plasmic process branches into a few terminal twigs embedded in a fuzzy filamentous substance. Most nerve cells have their nuclei under the basal lamina. The distal processes of these nerve cells reach the free surface and send long microvilli to form the spongy layer under a filamentous covering. At the side surface of the tentacle the epithelial cells are cuboidal or squamous and the neural elements are fewer. Here, no spongy layer is formed; and the collar cell processes are replaced by the lateral cell processes. Peculiar secretion granules are contained in the lateral and collar cell processes as well as in their cell bodies situated beneath the basal lamina.     

Role of fixed parenchyma cells in blastema formation of the planarian Dugesia japonica.

Observations of fixed parenchyma cells using electron microscopy were carried out in an attempt to understand the morphogenetic process of blastema formation in regenerating planarians. Fixed parenchyma cells could be found throughout one-day blastemata. In the mid-blastema region where migrating regenerative cells build up a compact cell aggregate, long and slender cytoplasmic processes of the fixed parenchyma cells were seen occupying spaces among regenerative cells. A characteristic feature of such processes was orderly arranged microtubules. Ruthenium red staining revealed thickened portions of cell coats on these processes and occasional formation of gap junctions between the cytoplasmic process of the fixed parenchyma cell and the regenerative cell undergoing migration. Colchicine treatment (M/1,000) caused detachment of the cytoplasmic processes from the regenerative cells. Microtubules within such processes became depolymerized. As a result, directional migration of regenerative cells was inhibited by colchicine treatment. To determine the extracellular site of fibronectin, immunoelectron microscopy was performed in one-day blastema. Immunogold labeling was detected at the surface area of fixed parenchyma cells and regenerative cells. In particular the reactivity was conspicuous at the cytoplasmic process of the fixed parenchyma cells. These observations suggest that the cytoplasmic processes of fixed parenchyma cell are related to directional movement of regenerative cells by providing a contact guidance system. The biological implications of this system are discussed in relation to the extracellular matrix components.     

Morphology and synaptic connectivity of nitric oxide synthase-immunoreactive neurons in the guinea pig retina

Immunocytochemical methods with an antiserum against neuronal nitric oxide synthase (NOS) were applied to identify the morphology and synaptic connectivity of NOS-like immunoreactive neurons in the guinea pig retina. In the present study, two types of amacrine cells were labeled with anti-NOS antisera. Type 1 cells had large somata located in the inner nuclear layer (INL) with long, sparsely branched processes ramifying mainly in stratum 3 of the inner plexiform layer (IPL). The somata of type 2 cells (smaller diameters) were located in the INL. Some displaced amacrine cells in the ganglion cell layer were labeled. The soma size of the displaced amacrine cells was similar to that of the type 2 amacrine cells. However, processes originating from type 2 amacrine cells and displaced amacrine cells stratified mainly in strata 1 and 5, respectively. Some cone bipolar cells were weakly NOS-immunoreactive. The synaptic connectivity of NOS-like immunoreactive amacrine cells was identified in the IPL by electron microscopy. NOS-labeled amacrine cell processes received synaptic input from other amacrine cell processes and bipolar cell axon terminals in all strata of the IPL. The most frequent postsynaptic targets of NOS-immunoreactive amacrine cells were other amacrine cell processes. Cone bipolar cells were postsynaptic to NOS-labeled amacrine cells in all strata of the IPL. Labeled amacrine cells synapsing onto ganglion cells were found only in sublamina b. A few synaptic contacts were observed between labeled cell processes. In the outer plexiform layer, dendrites of labeled bipolar cells made basal contact with cone pedicles or formed a synaptic triad opposed to a synaptic ribbon of cone pedicles.     

Cell surface effects of human immunodeficiency virus

Cell killing by human immunodeficiency virus (HIV) is thought to contribute to many of the defects of the acquired immunodeficiency syndrome (AIDS). Two types of cytopathology are observed in HIV-infected cultured cells: cell-cell fusion and killing of single cells. Both killing processes appear to involve cell surface effects of HIV. A model is proposed for the HIV-mediated cell surface processes which could result in cell-cell fusion and single cell killing. The purpose of this model is to define the potential roles of individual viral envelope and cell surface molecules in cell killing processes and to identify alternative routes to the establishment of persistently-infected cells. Elucidation of HIV-induced cell surface effects may provide the basis for a rational approach to the design of antiviral agents which are selective for HIV-infected cells.     

In vivo observations of terminal Schwann cells at normal, denervated, and reinnervated mouse neuromuscular junctions

We found a low-molecular-mass, fluorescent dye, Calcein blue am ester (CB), that labels terminal Schwann cells at neuromuscular junctions in vivo without damaging them. This dye was used to follow terminal Schwann cells at neuromuscular junctions in the mouse sternomastoid muscle over periods of days to months. Terminal Schwann cell bodies and processes were stable in their spatial distribution over these intervals, with processes that in most junctions were precisely aligned with motor nerve terminal branches. Three days after nerve cut, the extensive processes elaborated by terminal Schwann cells in denervated muscle were labeled by CB. The number and length of CB-labeled terminal Schwann cell processes decreased between 3 days and 1 month after denervation, suggesting that terminal Schwann cell processes are only transiently maintained in the absence of innervation. During reinnervation after nerve crush, however, terminal Schwann cell processes were extended in advance of axon sprouts, and these processes persisted until reinnervation was completed. By viewing the same junctions twice during reinnervation, we directly observed that axon sprouts used existing Schwann cell processes and chains of cell bodies as substrates for outgrowth. Thus, CB can be used to monitor the dynamic behavior of terminal Schwann cells, whose interactions with motor axons and their terminals are important for junction homeostasis and repair.     

Phenotypic expression of photoreceptor and endocrine cell properties by cultured pineal cells of the newborn rat

Pineal glands of newborn rats were dissociated and maintained under cell culture conditions. The phenotypic expression of both photoreceptor and endocrine cell properties was investigated using immunohistochemical techniques (specific antibodies against opsin or serotonin). After one week in culture, a number of small round cells appeared on top of a sheet of flat epithelium. Among those cells, opsin-like immunoreactive cells were observed. These cells showed a neuron-like morphology with neuritic processes and often formed rosettes. Immunoreactivity was found on the plasma membrane of both the soma and cell processes. Serotonin-like immunoreactive cells were also differentiated in culture with two different morphological types of cells being found. One type resembled cultured serotonin-containing amacrine cells of the retina, and the other type had a flat, polygonal shape similar to that of pinealocytes. Both types of immunoreactive cells possessed fine neuritic processes. These results indicated that cell culture of rat pineal gland cells allowed expression of some properties, such as opsin synthesis and neuron-like morphology with long neuritic processes, that were not expressed in the intact rat pineal gland.     

Light- and electron-microscopic analysis of neuropeptide Y-immunoreactive amacrine cells in the guinea pig retina

We investigated the morphology and synaptic connections of neuropeptide Y (NPY)-containing neurons in the guinea pig retina by immunocytochemistry, using antisera against NPY. Specific NPY immunoreactivity was localized to a population of wide-field and regularly spaced amacrine cells with processes ramifying mainly in stratum 1 of the inner plexiform layer (IPL). Double-label immunohistochemistry demonstrated that all NPY-immunoreactive cells possessed glutamic acid decarboxylase 65 immunoreactivity. The synaptic connectivity of NPY-immunoreactive amacrine cells was identified in the IPL by electron microscopy. The NPY-labeled amacrine cell processes received synaptic input from other amacrine cell processes and bipolar cell axon terminals in stratum 1 of the IPL. The most frequent postsynaptic targets of NPY-immunoreactive amacrine cells were other amacrine cell processes. Synaptic outputs to bipolar cells were also observed in a small number of cases. This finding suggests that NPY-containing amacrine cells may influence inner retinal circuitry in stratum 1 of the IPL, thus mediating visual processing.     

Light and electron microscopic localization of ATPase in normal and degenerating testes of Syrian hamsters.

The distribution of Mg++-activated ATPase was determined with light and electron microscopy in normal and degenerating seminferous tubules. In the normal animals ATPase was localized in the interface between spermatids and Sertoli cells, in association with the cytoplasmic filaments contained within Sertoli cell processes, and in the lymphatic endothelium. ATPase activity increased in degenerating tubules as observed by light microscopy. Electron microscopic investigations of the degenerating tubules which contained only spermatogonia and Sertoli cells revealed reaction product on the outer surface of the Sertoli cell processes and within the interface between adjacent Sertoli cells. Reactaction product was also observed in the Sertoli cell processes between the cytoplasmic filaments and the cell membrane. Where filaments were absent in Sertoli cell processes, no reaction product was observed. These electron microscopic studies indicate that the increase in ATPase activity in testicular degeneration is probably a relative increase due to a loss of the germinal elements of the tubular epithelium and subsequent apposition of the Sertoli cell processes. We speculate that the ATPase activity localized within the Sertoli cell processes may be involved in providing an energy source for filament motility.     

Intercellular contacts of astroglial cells in vitro in the presence of PGE2. SEM, TEM and immunocytochemical studies

The investigations were performed on 32 tumors of the CNS of fibrillary and gemistocyte type of astrocytoma from which the cultures were derived. The dissociated culture was used and the cells were seeded direct on glass. The MEM was supplemented with calf serum and embryonal extract. The cells maintained in culture for 21 days. They developed multiple or single long and delicate processes which originated a network of relative high density. SEM observations indicate that the cell established intercellular connections through spikes and surfaces of the processes and cell bodies. TEM studies have shown that the cell to cell connections are very tight but the contacts between the cell processes are similar to those described by DUFFY as punctate connections. The addition of PGE2 does not disturb the reconstruction of intercellular communication. The estimation of GFAP antigenicity of the investigated cells proved their astrocytic origin and revealed that the intermediate fibres are in the cell processes, and in the location of the contacts between cells.     

Penaeid (Penaeus japonicus) lymphoid cells replicate by cell division in vitro

Penaeid cell culture has gained much attention as a potential model to facilitate researches on the characterization of the virus and to develop more sophisticated and improved diagnostic procedures for use in the aquaculture industry. However, to date, cell division processes of cultured penaeid cells have not been found, which is suggested as one of the reasons that block the establishment of the continuous penaeid cell lines. We reported here the cell division processes of cultured lymphoid cells of Penaeus japonicus. The culture medium used was based on M199 and was modified by supplementing saline components. Cultures were incubated at 25 degrees C, and 5% CO2 was supplemented. In primary cultured lymphoid cells, dividing cells in different shapes were found. Cell division processes of 12 dividing lymphoid cells were tracked. After cell division, their daughter cells turned into fibroblast-like or epithelioid cells. These results proved that the culture conditions used were suitable for lymphoid cells of I japonicus to proliferate in vitro and that cultured lymphoid cells still had the ability to carry out cell division. These findings would give light to the establishment of continuous penaeid cell lines and would also provide us with the knowledge of cell division processes of the penaeid.     

Migration Behavior of Granule Cell Neurons in Cerebellar Cultures I. A PKH26 Labeling Study in Microexplant and Organotypic Cultures

Granule cells were dissociated from early postnatal mouse cerebella and labeled with a fluorescent dye probe PKH26. Small number of the labeled cells were mixed with cerebellar cortical microexplant cultures or transplanted into cerebellar cortical organotypic explants, and their time-dependent morphological changes during cultures were examined with fluorescence microscopy. Granule cell neurons first extended asymmetrical short bipolar processes in both cultures, and migrated actively in microexplant cultures. After elongation of symmetrically bipolar long and thin neurites, they sprouted short thick processes from cell bodies and migrated perpendicular to neurite bundles that were devoid of glia in microexplant cultures, or migrated vertically inward into the internal granular layer in the organotypic explant. During such migrations, they extended short thick processes in front and thin processes behind the cell body. The latter processes were connected to thin long neurites with T- or Y-shaped junctions in both cultures. Finally, they extended many short thick processes from cell bodies in both cultures. Such behaviors of granule cell neurons in microexplant cultures were, thus, similar to those in organotypic explant cultures despite of the absence of Bergmann glial cells. These migration patterns may be closely related to migration of granule cells in histogenesis of the cerebellar cortex.     

The epitheliomuscular cell of hydra: Its fine structure, three-dimensional architecture and relation to morphogenesis

Ectodermal epitheliomuscular cells of Hydra attenuata were studied by transmission and scanning electron microscopy, and a three-dimensional model was constructed. These cells are cuboidal to columnar, and each cell has one muscle process arising from the basal portion of the oral-facing surface and one from the aboralsurface. Adjacent epitheliomuscular cells are joined apicolaterally by septate junctions. Numerous gap junctions occur between adjacent epitheliomuscular cells and are irregularly distributed along the lateral and basal aspects. Finger-like interdigitations and specialized folds (couplers) also occur along the basal and lateral aspects and interlock adjacent epitheliomuscular cells. In the basal portion of these cells, myofilaments are aggregated into myonemes which are oriented in the oral-aboral axis of the polyp. Myonemes dominate the cytoplasm of muscle processes. Myofilaments are also aggregated in the basal cytoplasm of the cell body when the cell body is in contact with the mesoglea but are sparse or absent when the cell body rests upon other muscle processes. Epitheliomuscular cells and associated muscle processes rest upon other processes and the mesoglea and show variations in these relations. A muscle process and associated cell may rest upon another process; the process may then extend under the preceding process and cell body. This configuration, and variations, present a woven or braided network of muscle processes which collectively form a sheet of muscle on the mesoglea. The interdigitations, couplers and gap junctions between epitheliomuscular cells and the woven network of muscle processes present a cytological basis for the observations that the ectoderm in hydra behaves as a coherent sheet along the body column.     

The microanatomy of the compound eye of Munida irrasa (Decapoda: Galatheidae)

The compound eye of Munida irrasa differs in several respects from the typical decapod eye. The proximal pigment is found only in retinula cells. The eccentric cell is extremely large and expanded to fill the interstices of the crystalline tract area; thus, a typical "clear-zone" is absent. Six retinula cells course distally to screen two sides of the crystalline cone. There are approximately 12,500 ommatidia in each compound eye. There are several similarities to the typical decapod eye. Each ommatidium is composed of a typical cornea, corneagenous cells, crystalline cone cells, crystalline cone, crystalline cone tract and eight retinula cells. Distal pigment cells are present and surround the crystalline cone. The distal processes of the retinula cells also contain pigment. The retinula cell processes penetrate the basement membrane as fascicles composed of processes from adjacent retinulae.     

Fine structure of taste buds in the barbel of the catfish,Ictalurus punctatus

Summary Taste buds occur in the epithelium of the catfish barbel along its entire length. Two major cell types, light and dark cells, occupy the upper two-thirds of the taste bud. A third cell type, the basal cell, lies on the basal lamina and is essentially separated from the light and dark cells by a plexus of unmyelinated nerve fibers. The dark cells have branching processes, both apically and basally whereas the light cells have a single apical process and many basal processes. The apical processes of dark cells contain secretory granules, while the apical processes of light cells contain an abundant agranular endoplasmic reticulum. Light cell nuclei contain bundles of 10 nm filaments, often arranged in the shape of a cup or ring, but nucleoli are rarely seen. It is suggested that this morphology indicates a low degree of RNA synthesis by light cells. The basal cells contain large numbers of vesicles, about 60 nm in diameter, which are sometimes seen in clumps in relation to an adjacent nerve fiber in a configuration resembling a synapse. Curiously, although basal cells present a large surface to the basal lamina, there are no hemidesmosomes. This suggests that the basal cell does not originate from the epidermis.Supported by grant#NS-06181 from the National Institute of Neurological Diseases and Stroke, U.S. Public Health Service     

Studies on the gastrulation of amphibian embryos: Ultrastructure of the migrating cells of anurans

Summary In order to investigate the ultrastructure of the migrating cells in anuran gastrulae, three anurans, which belong to three different genera, were observed with transmission electron microscopy supported by light microscopy of the 1 m sections and scanning electron microscopy. Fine filopodial cell processes, as well as cell processes probably flattened against the inner surface of the blastocoel wall, were formed by the migrating cells. Blebs and lobopodial cell processes were frequently observed inBufo, sometimes inXenopus, but not observed inRana. Microfilaments were observed in the cell processes. Focal close contacts, probably having adhesive properties, were made between the migrating cells and the inner surface of the blastocoel wall. These observations suggest that the cells migrate along the inner surface of the blastocoel wall by forming filopodia and pseudopodia flattened against the wall. The role of the blebs and lobopodial cell processes requires more investigation.     

The morphology and coupling of Aplysia bag cells within the abdominal ganglion and in cell culture

The bag cells in the abdominal ganglion of Aplysia californica control egg-laying behavior by releasing a polypeptide (ELH) during an afterdischarge of synchronous action potentials. We have used intracellular injection of Lucifer Yellow to study the morphology and interconnections of the bag cells. These neurosecretory cells are typically multipolar and their processes extend in all directions out from the bag cell clusters into the surrounding connective tissue, where they branch in a complex manner. In some of the dye injection experiments, dye transfer from the injected cell to neighboring cells was observed. Freeze fracture of the bag cell clusters and their surrounding connective tissue revealed numerous gap junctions on bag cell processes within the clusters as well as on more distal processes. We have also examined the morphology and coupling between bag cells in primary culture. As in the intact ganglion, bag cells in culture were found to be multipolar. All pairs of bag cells whose somata or processes had formed contacts in culture were electrically coupled. The strongest coupling was observed between pairs of cells whose somata appeared closely apposed. In these cases transfer of Lucifer Yellow between cells could also be observed. It is therefore likely that the synchrony of bag cell action potentials during a bag cell afterdischarge is a result of coupling between individual cells in the bag cell cluster.     

Electron microscopy of the esophageal ganglion complex of the gastropod pulmonate Triodopsis divesta. I. Ultrastructure of the epineurium

The epineurium of the esophageal complex of the gastropod pulmonate Triodopsis divesta was examined by electron microscopy. The epineurium consists of two main regions: an inner dense fibrous region adjacent to the avascular neural tissue of the ganglion and an outer cellular region comprised of a variety of cell types embedded in a connective tissue matrix. The dense fibrous region contains smooth muscle cells and associated nerve processes and is invested on the neural side by thin processes of glial cells. The outer highly cellular region contains smooth muscle cells, nerve processes, wandering cells (amebocytes), globular cells, and myoepithelial cells comprising the walls of the vascular system. In addition, a cell type not previously identified in other gastropod epineuria is present. These cells resemble neurosecretory cells. The morphology and structural interrelationships of these various constituents are presented and the possible functions of individual cell types and the epineurium in general are discussed in relation to information available on other molluscs.     

Light- and electron-microscopic study of substance P-immunoreactive neurons in the guinea pig retina

Substance P (SP) immunoreactivity in the guinea pig retina was studied by light and electron microscopy. The morphology and distribution of SP-immunoreactive neurons was defined by light microscopy. The SP-immunoreactive neurons formed one population of amacrine cells whose cell bodies were located in the proximal row of the inner nuclear layer. A single dendrite emerged from each soma and descended through the inner plexiform layer toward the ganglion cell layer. SP-immunoreactive processes ramified mainly in strata 4 and 5 of the inner plexiform layer. SP-immunoreactive amacrine cells were present at a higher density in the central region around the optic nerve head and at a lower density in the peripheral region of the retina. The synaptic connectivity of SP-immunoreactive amacrine cells was identified by electron microscopy. SP-labeled amacrine cell processes received synaptic inputs from other amacrine cell processes in all strata of the inner plexiform layer and from bipolar cell axon terminals in sublamina b of the same layer. The most frequent postsynaptic targets of SP-immunoreactive amacrine cells were the somata of ganglion cells and their dendrites in sublamina b of the inner plexiform layer. Amacrine cell processes were also postsynaptic to SP-immunoreactive neurons in this sublamina. No synaptic outputs onto the bipolar cells were observed.     

Ultrastructural localisation of alkaline phosphatase in the intertubular tissue of the testis in the domestic fowl

Alkaline phosphatase activity in the intertubular tissue of the testes of the domestic fowl was examined using an ultracytochemical technique based on the lead capture method. In the interstitial tissue, the Leydig cells, transitional cells and the fibroblasts displayed enzyme activity on their cell membranes. Vacuoles located in the transitional cells were lined by reaction products of enzyme activity, whereas the vacuoles representing extracted lipid droplets and present mainly in the Leydig cells were free of enzyme activity. In the peritubular tissue the cell processes of fibroblasts showed enzyme activity on the cell membranes and in pinocytotic vesicles. Cell processes lying adjacent to blood vessels showed pronounced activity. In the blood vessel itself some activity was present in the basement membrane and the endothelium. The surface of the red blood cell showed moderate activity. The possible role of alkaline phosphatase in the transfer of hormone from the Leydig cells to the seminiferous tubules and from the seminiferous tubules to the interstitium is discussed. The myoid cells and their processes were devoid of enzyme activity.     

The microtubule plus end-binding protein EB1 is involved in Sertoli cell plasticity in testicular seminiferous tubules

Sertoli cells of testis belong to a unique type of polarized epithelial cells and are essential for spermatogenesis. They form the blood-testis barrier at the base of seminiferous tubule. Their numerous long, microtubule-rich processes extend inward and associate with developing germ cells to sustain germ cell growth and differentiation. How Sertoli cells develop and maintain their elaborate processes has been an intriguing question. Here we showed that, by microinjecting lentiviral preparations into mouse testes of 29 days postpartum, we were able to specifically label individual Sertoli cells with GFP, thus achieving a clear view of their natural configurations together with associated germ cells in situ. Moreover, compared to other microtubule plus end-tracking proteins such as CLIP-170 and p150(Glued), EB1 was highly expressed in Sertoli cells and located along microtubule bundles in Sertoli cell processes. Stable overexpression of a GFP-tagged dominant-negative EB1 mutant disrupted microtubule organizations in cultured Sertoli cells. Furthermore, its overexpression in testis Sertoli cells altered their shapes. Sertoli cells in situ became rod-like, with decreased basal and lateral cell processes. Seminiferous tubule circularity and germ cell number were also reduced. These data indicate a requirement of proper microtubule arrays for Sertoli cell plasticity and function in testis.