Study of development of ciliary folds and Zinn's zonules in Rana temporaria L. by means of scanning electron microscopy]

The development of ciliary folds and zonul of Zinn has been studied in the eyes of the common frog Rana temporaria L. by means of scanning electron microscopy. The development of ciliary folds begins at the stage 45 by the flexure of the external layer in the ciliary zone. At the stage 46 this process involves the internal layer and the folds become two-layered. The zonules of Zinn form before the folds of internal layer of the ciliary epithelium begin to form as separate bundles of fibers. At the stage 45 they are already distinct. Later the ciliary filaments fold in 2 felt-like layers -- zonula which pass from the equatorial lens zone and attach near orbiculum ciliaris. In the place of attachment the margin of zonul repeats the relief of folds, thus attaching to their whole surface, and individual filaments go farther, to orbiculum ciliaris. All these processes take place in they eye prior to the beginning of metamorphosis.     

The eye muscles and their innervation in the gobiid fishTridentiger trigonocephalus

The morphology and innervation of the six oculomotor muscles in the gobiid fishTridentiger trigonocephalus are described. Every rectus muscle is composed of two types of muscle fibres. Muscles attach onto the cartilaginous or fibrous sclerotica. Oblique muscles attach onto the ethmoidal plate; recti muscles attach onto the parasphenoid or a thick fibrous membrane. There is no myodome. The common oculomotor nerve is composed of four bundles, the trochlear and the externus of two. The two kinds of fibres of the lateral rectus and the two distinct bundles of the nerve VI suggest a possible homology between this muscle in fishes and the lateral rectus+retractor bulbi in mammals.     

The polarisation of hair cells from the ear of the European bass (Dicentrarchus labrax)

The polarisation of ciliary bundles on the macula of the saccule in the European bass (Dicentrarchus labrax L) has been studied using a scanning electron microscope (SEM). These data show that D. labrax possesses ciliary bundles arranged in four dichotomous quadrants with a standard orientation, comparable to hearing generalists from the order Perciformes. The spacing between ciliary bundles was investigated in three size classes of fish, with the results indicating that the addition of receptor cells in the ear of D. labrax continues for at least the first 2 years of development. The lengths of the kinocilia from ciliary bundles in each quadrant of the macula were also studied, and found to be of uniform length. In addition, we look at the internal structure of the afferent using transmission electron microscopy (TEM), revealing the nucleated cell body and peripheral nerve fibres of the saccule consistent with other TEM examinations of saccular ultrastructure. This information is required to gain an insight into the inner ear of D. labrax, as part of a larger study of the morphology and physiology of the hearing systems of both vertebrate and invertebrate marine animals.     

Functional morphology of the crista ampullaris: with special interests in sensory hairs and cupula: a review.

The functional significance of the ciliary interconnections and cupula has been reviewed. The ciliary interconnecting systems are divided into 2 types, i.e. side links and tip links. The side links acts to maintain the regular distance between the cilia thereby keeping the geometrical arrangement of the entire sensory hair bundle intact as well as to prevent close contact between neighbouring cilia. The tip links, stretching upwards from the tips of the shorter stereocilia to their taller neighbouring shafts, are actually involved in mechanoelectrical transduction. The cupula is composed of the cupula and subcupular meshwork. The subcupular meshwork consists of long branching filaments cross-bridged to one another. The cupula would function as a rigid plate and equally distribute the shear force of the cupula to all the ciliary bundles. The subcupular meshwork may play a role in the transmission of the shear strain force of the cupula to the ciliary bundle and may also exert an additional damping effect in order to prevent unwanted vibrations.     

A fibrous membrane suspends the multifocal lens in the eyes of lampreys and African lungfishes

The sharpness and thus information content of the retinal image in the eye depends on the optical quality of the lens and its accurate positioning in the eye. Multifocal lenses create well‐focused color images and are present in the eyes of all vertebrate groups studied to date (mammals, reptiles including birds, amphibians, and ray‐finned fishes) and occur even in lampreys, i.e., the most basal vertebrates with well‐developed eyes. Results from photoretinoscopy obtained in this study indicate that the Dipnoi (lungfishes), i.e., the closest piscine relatives to tetrapods, also possess multifocal lenses. Suspension of the lens is complex and sophisticated in teleosts (bony fishes) and tetrapods. We studied lens suspension using light and electron microscopy in one species of lamprey (Lampetra fluviatilis) and two species of African lungfish (Protopterus aethiopicus aethiopicus and Protopterus annectens annectens). A fibrous and highly transparent membrane suspends the lens in both of these phylogenetically widely separated vertebrate groups. The membrane attaches to the lens approximately along the lens equator, from where it extends to the ora retinalis. The material forming the membrane is similar in ultrastructure to microfibrils in the zonule fibers of tetrapods. The membrane, possibly in conjunction with the cornea, iris, and vitreous body, seems suitable for keeping the lens in the correct position for well‐focused imaging. Suspension of the lens by a multitude of zonule fibers in tetrapods may have evolved from a suspensory membrane similar to that in extant African lungfishes, a structure that seems to have appeared first in the lamprey‐like ancestors of allextant vertebrates. J. Morphol. 271:980–989, 2010. © 2010 Wiley‐Liss, Inc.     

Adrenergic Nerves in the Avian Eye and Ciliary Ganglion

Summary The distribution of adrenergic fibres to the eye and to the ciliary ganglion was studied in pigeons, chicken and ducks with the aid of the sensitive and highly specific fluorescence method of Falck and Hillarp. In some animals the intensity of the fluorescence was increased by treating the animals with Nialamide and 1-DOPA. The cornea contained no adrenergic fibres except at the limbus, where a plexus of adrenergic varicose fibres was seen, partly associated with vessels. In the chamber angle, adrenergic varicose fibres were common in the loose connective tissue covering the canal of Schlemm. The canal of Schlemm was supplied by only few adrenergic fibres, but such fibres appeared along the intrascleral aqueous drainage vessels. In the iris, adrenergic varicose fibres appeared immediately in front of the posterior layer of pigment cells, strongly indicating the presence of a dilator homologous with that seen in mammals. The frontal third of the stroma contained several adrenergic varicose fibres, many of which seemed to lack association with any vessel. Varicose adrenergic fibres were also sparsely seen in the striated muscle of the iris. The ciliary processes contained many adrenergic varicose fibres, at least part of which seemed to be associated with the ciliary epithelium. The striated muscles of the ciliary body contained adrenergic varicose fibres along the vessels only. The retina contained adrenergic varicose fibres in three layers in the inner plexiform layer. Adrenergic ganglion cells of two sizes were detected in the inner nuclear layer. The retinal vessels had no adrenergic nerve fibres. The pecten was also devoid of adrenergic nerve fibres, except along the vessels close to the papilla. The optic nerve contained adrenergic varicose nerve fibres along vessels only. In the ciliary ganglion, varicose adrenergic fibres appeared at the small ganglion cells, often forming baskets of synaptic character.Acknowledgements. The work has been supported by the United States Public Health Service (grant NB 06701-01), by the Swedish Medical Research Council (project B 67-12 X-712-02 A) and by the Faculty of Medicine, University of Lund, Sweden.     

Scanning electron microscopy of the zonular fibers in the rat eye

Summary The three-dimensional arrangement of the zonular fibers of Zinn and their ultrastructure was studied with the aid of scanning and transmission electron microscopy.Most of the thicker zonular fibers are arranged in straight bundles between the ciliary body and the lens, while the thinner fibers form a complex three-dimensional network interconnecting all the zonular fibers. These do originate from the limiting membrane covering the ciliary body. The zonular fibers are subdivided close to lens and form a complicated network on the surface of the lens capsule, i. e. the zonular lamella. The latter consists of a dense network of fibers and is from a structural point of view closely related to the zonular fibers and not to the lens capsule.The zonular fibers are continuous with those in the vitreous body close to the ciliary body but never in the lenticular two thirds of the zonular fibers or in the retrolental area.The ground substance is possible to demonstrate in freeze-dried specimens by scanning electron microscopy. It appeared granular or amorphous and coated the zonular fibers. It does not form membranes or fill all available space in contrast to its properties in the vitreous body. The many structural similarities between the zonular fibers and the vitreous body indicate perhaps a common origin.Supported by grants from Magnus Bergwalls Stiftelse and the Swedish Medical Research Council (B70-12 X -2543-02, B71-12 X -2543-03).     

Spine-scale reorientation inApedinella radians (Pedinellales,Chrysophyceae): the microarchitecture and immunocytochemistry of the associated cytoskeleton

Summary Motile unicells ofApedinella radians have the extraordinary ability to instantaneously reorient six elongate spine-scales located on the cell surface. Extracellular striated fibrous connectors (termed microligaments) attach spine-scales to discrete regions of the plasma membrane underlain by intricate cytoplasmic plaques. A complex cytoskeleton is associated with the plaques and appears responsible for spine-scale movement. Three cytoskeletal proteins have thus far been identified by immunofluorescence using anti-tubulin, anti-actin, and anti-centrin. The three-dimensional configuration of the cytoskeleton has been established and consists of filamentous bundles of actin and centrin which form stellate systems interconnecting the plaques. Additionally, there is a network of microtubular triads which originate on the surface of the nuclear envelope and subtend the plasma membrane and also support several tentacular protrusions. It is proposed that contraction of the actin and/or centrin filamentous bundles is responsible for the reorientation of the spine-scales.     

The architecture of the flagellar apparatus ofPrymnesium patellifera (Prymnesiophyta)

The flagellar apparatus of the small prymnesiophytePrymnesium patellifera has been analysed and a reconstruction is presented. Externally, the cell carries two sub-equal flagella and a short non-coiling haptonema. Within the cell, there are four microtubular roots and a number of fibrous bands, the latter interconnecting the two basal bodies and the haptonema base. One of the roots (r1) consists of a sheet of up to 25 microtubules originating close to the proximal extremity of the haptonema base, but the other three roots are composed of between 1 and 4 microtubules only. Distally, a large striated fibrous auxiliary connecting root extends across the anterior part of the cell linking root r1 and a mitochondrial profile on the opposite side of the cell. The arrangement of the components of the flagellar apparatus ofP. patellifera is commensurate with the general pattern found in many prymnesiophytes other than members of the Pavlovales, but there are a number of differences in detail from the other species described hitherto.     

Dynamic mechanism of visual accommodation in teleosts: structure of the lens muscle and its nerve control

The accommodatory system was examined in two teleosts (mackerel and bass). The fine structure and innervation of the lens muscle is presented to characterize the muscle organization. The neural pathway involved in the dynamic accommodation was examined by analysing the fibre spectrum of the ciliary nerve, and the nerve that controls the lens-muscle activity was studied by means of electrical stimulation. The lens muscle is composed of smooth-muscle cells, which contain numerous mitochondria. Many synaptic endings are also found on the muscle cells; these synaptic endings contain many agranular vesicles. From the results of the fibre analysis, it was found that the nerve that controls the lens muscle contains less than 100 myelinated nerve fibres in both fish: the electrical stimulation experiments demonstrate that the muscle is controlled by oculomotor (parasympathetic) nerve fibres. Ultrastructural features of the lens muscle and its nerve control resemble those of the mammalian ciliary muscle. The teleostean lens muscle is classified as a multi-unit smooth muscle.     

Arrangement of accessory cells and nematocytes bearing mastigophores in the tentacles of the cubozoan Chironex fleckeri

Nematocytes containing microbasic mastigophores are intimately associated with accessory cells in the epidermis of Chironex fleckeri. Large microbasic mastigophores may be surrounded by seven to nine such cells. Each accessory cell possesses an apical portion containing secretory droplets and a basal portion which carries a radially oriented fibre linking the cell to the underlying mesogloea. The fibre is capable of projecting and retracting the accessory cell. Junctional complexes occur between accessory cells and the apical regions of neighbouring mastigophores. Each nematocyte bearing a mastigophore contains a triggering apparatus consisting of a cnidocil surrounded by microvilli. This apparatus protrudes from an invagination in the apical region of the nematocyte and is exposed when the mastigophore is in the fire-ready position. A basket of filaments which make contact with microvilli surrounds the apical end of the nematocyst like a collar. The basket is linked via fibrous bundles which envelop the mastigophore to radially oriented fibres basally. These fibres are capable of projecting and retracting the mastigophore and its associated triggering apparatus. Up to nine such fibres were observed to be associated with a single large microbasic mastigophore. Microtubules averaging 25 nm in diameter and linked via cross bridges to electrondense material were detected in the radial fibres of both nematocytes and accessory cells. Retraction of the accessory cells and projection of nematocytes result in mastigophores being brought to the firing line and in the exposure of the cnidocil apparatus.     

Ultrastructure of the ocular ciliary epithelium of the common frog

The ultrastructure of the adult frog ciliary epithelium cells has definite regional differences. Cells of ciliary epithelium folds near the iris display morphological features characterizing its barrier and secretory functions which lead to the formation of aqueous humor. These are junctional complexes with tight junctions (zonula occludents) in the apical parts of contacting sides of cells of the inner leaf: a great quantity of mitochondria, ribosomes and various vesicles, well developed endoplasmic reticulum in the cytoplasm, much folded basal surface, gap junctions between cells of external and internal leaflets. In the mammalian inner epithelial layer different cell junctions are known to be arranged in a fixed spatial fashion. Unlike, in the frog's epithelium both zonula adherent and desmosomes may be found in any sequence. Tight junctions are formed during metamorphosis, on the place of focal junctions, whereas gap junctions, referred to earlier as "extended", start functioning between cells just on the very early stages of eye morphogenesis (Dabagyan et al., 1979). The epithelium of the posterior part of the ciliary fold and pars plana of the ciliary body have, in addition, the number of morphological sign indicating the cell involvement in the accomodational function of any eye (i. e. a majority of desmosomes binding all cells together and of zonulae adherentes, well developed intracellular skeleton of tonofilament bundles). These features are characteristic of the whole distal part of ciliary epithelium rather than of the place of attachment of zonula fiber only.     

Anti-tubulin labeling reveals ampullary neuron ciliary bundles in opisthobranch larvae and a new putative neural structure associated with the apical ganglion

This investigation examines tubulin labeling associated with the apical ganglion in a variety of planktotrophic and lecithotrophic opisthobranch larvae. Emphasis is on the ampullary neurons, in which ciliary bundles within the ampulla are strongly labeled. The larvae of all but one species have five ampullary neurons and their associated ciliary bundles. The anaspid Phyllaplysia taylori, a species with direct development and an encapsulated veliger stage, has only four ampullary neurons. The cilia-containing ampulla extends to the pretrochal surface via a long, narrow canal that opens to the external environment through a very small pore (0.1 microm diameter). Cilia within the canal were never observed to project beyond the opening of the apical pore. The ampullary canals extend toward and are grouped with the ciliary tuft cells and remain in this location as planktotrophic larvae feed and grow. If, as has been reported, the ciliary tuft is motile, the pores may be continually bathed in fresh seawater. Such an arrangement would increase sensitivity to environmental chemical stimuli if the suggested chemosensory function of these neurons is correct. In general, ciliary bundles of newly hatched veligers are smaller in planktotrophic larvae than in lecithotrophic larvae. In planktotrophic larvae of Melibe leonina, the ciliary bundles increase in length and width as the veligers feed and grow. This may be related to an increase in sensitivity for whatever sensory function these neurons fulfill. An unexpected tubulin-labeled structure, tentatively called the apical nerve, was also found to be associated with the apical ganglion. This putative nerve extends from the region of the visceral organs to a position either within or adjacent to the apical ganglion. One function of the apical nerve might be to convey the stimulus resulting from metamorphic induction to the visceral organs.     

Anatomy of the external anal sphincter in man

The anatomy of the external anal sphincter was studied in 20 adult human cadavers of both sexes by dissection and histological examination. The external anal sphincter is not naturally divided into layers or laminae. The lowermost muscle bundles differ from the main part in being completely surrounded by thick fibrous tissue septa derived form the longitudinal anal coat. The perineal branch of S4 supplies the posterior third, the inferior haemorrhoidal nerves supply the anterior two thirds. All fibres of the sphincter retain their skeletal attachment to the anococcygeal ligament to the coccyx. Some fibres cross the median plane to be continuous with the transversus perinei of the opposite side. A cleft was displayed separating the lower border of the levator ani muscle from the upper border of the external anal sphincter. The muscle bundles of the sphincter are arranged circumferentially in one continuous circle and not in loops. Fibres from the anterior border of the levator ani muscle extend to cover and blend with the outer surface of the external sphincter in their way to the anococcygeal ligament.     

The innervation of mammalian bronchial smooth muscle: the localization of catecholamines and cholinesterases

Synopsis A study has been made of the innervation of the bronchial tree in five mammals. The results show that in most species a dual innervation of catecholamine-containing and acetylcholinesterase-positive fibres exists, and that the acetylcholinesterase-containing fibres greatly outnumber those containing catecholamines. Acetylcholinesterase-positive fibres are also found in the bronchioles although catecholamine-containing fibres are absent. The pig was the only mammal in which fibres were observed in the mucosa.The presence of fibres in the bronchial vasculature has also been demonstrated. Evidence is given for the presence of catecholamine-containing cells in the parasympathetic ganglia of the bronchus. A method for the demonstration of catecholamines and cholinesterases on adjacent sections of tissue is described in full.     

Electron microscopic study of the intestinal epithelium of Saccoglossus mereschkowskii (Enteropneusta, Hemichordata)

Epithelium of the hepatic region of the intestine in Saccoglossus mereschkowskii, a representative of enteropneusts (Enteropneusta, Hemichordata) standing at the base of Chordata, has been investigated using electron microscope. The ultrastructure of ciliated and granular epithelial cells, elements of the intraepithelial nerve layer, and intercellular junctions have been characterized. The data concerning details of the organization of the ciliary apparatus and rootlets system are presented. It is justified the presence of complicated supporting construction of cilia which performs a mechanical stabilizing function and possibly also provide synchronization of ciliary movements. The presence of cilia with two centrioles is considered as an adaptation to high functional load on ciliary apparatus. Well developed bundles of myofilaments are found in the cytoplasm of the basal portions of ciliary cells that characterizes these cells as myoepithelial. The features indicating the role of ciliary cells in absorption are described. The capability of these cells to balloon-like secretion is considered. Data on the accumulation of food reserves in the form of lipid droplets and glycogen in the cell cytoplasm are presented. Ciliated cells are characterized by their function as ciliated secretory-absorptive myoepithelial cells. Based on the location of secretory granules both in the apical and basal portions of granular cells, an exocrine-endocrine function of these cells has been suggested. Typical endocrine cells in the intestinal epithelium of S. mereschkowskii are absent. Several types of granules in the nerve fibers cytoplasm are described. Junctions between the nerve fibers and basal portions of ciliary and granular epithelial cells are found. Nerve regulation of contractile and secretory functions of epithelial cells is supposed. The presence of the regulatory nerve-endocrine system that includes receptor cells of open type, secretory endocrine-like cells and nerve elements of nerve layer is supposed in the intestinal epithelium of enteropneusts.     

Functional morphology of the adrenergic innervation and adrenocontaining structures of the lymphoid organs

Topography of adrenergic neural fibres and adrenodependent structures in lymphoid organs of some mammals (rat, cat, dog, guinea-pig, golden hamster) has been studied by means of Falck's method with other histochemical methods applied simultaneously. In thymus, spleen, tonsils, lymph nodes and appendix adrenergic innervation is performed at the expense of adventitial vascular plexus and some neural fibres directed towards the organs' parenchyma. In the parenchyma of the lymphoid organs some fluorescent interfollicular macrophages and intrafollicular cells with serotonin and catecholamines in their cytoplasm were detected spectroscopically. These two types of cells respond differently to increasing amount of free amines in the organism. Orthochromic mast cells and elastic fibres also possess fluoresent properties which are connected with the presence of serotonin and catecholamines in the lymphoid organs.     

Dominant inhibition of lens placode formation in mice

The lens in the vertebrate eye has been shown to be critical for proper differentiation of the surrounding ocular tissues including the cornea, iris and ciliary body. In mice, previous investigators have assayed the consequences of molecular ablation of the lens. However, in these studies, lens ablation was initiated (and completed) after the cornea, retina, iris and ciliary body had initiated their differentiation programs thereby precluding analysis of the early role of the lens in fate determination of these tissues. In the present study, we have ablated the lens precursor cells of the surface ectoderm by generation of transgenic mice that express an attenuated version of diphtheria toxin (Tox176) linked to a modified Pax6 promoter that is active in the lens ectodermal precursors. In these mice, lens precursor cells fail to express Sox2, Prox1 and αA-crystallin and die before the formation of a lens placode. The Tox176 mice also showed profound alterations in the corneal differentiation program. The corneal epithelium displayed histological features of the skin, and expressed markers of skin differentiation such as Keratin 1 and 10 instead of Keratin 12, a marker of corneal epithelial differentiation. In the Tox176 mice, in the absence of the lens, extensive folding of the retina was seen. However, differentiation of the major cell types in the retina including the ganglion, amacrine, bipolar and horizontal cells was not affected. Unexpectedly, ectopic placement of the retinal pigmented epithelium was seen between the folds of the retina. Initial specification of the presumptive ciliary body and iris at the anterior margins of the retina was not altered in the Tox176 mice but their subsequent differentiation was blocked. Lacrimal and Harderian glands, which are derived from the Pax6-expressing surface ectodermal precursors, also failed to differentiate. These results suggest that, in mice, specification of the retina, ciliary body and iris occurs at the very outset of eye development and independent of the lens. In addition, our results also suggest that the lens cells of the surface ectoderm may be critical for the proper differentiation of the corneal epithelium.     

Filament arrangements in negatively stained cultured cells: the organization of actin

Treatment of spread, cultured cells with Triton X-100 followed by negative staining reveals the organization of the unextracted intracellular filamentous elements: actin, microtubules and the 100 angstrom filaments. The present report describes the organization of the actin-like filaments in human skin fibroblasts and mouse 3 T 3 cells. As shown in earlier studies, the cytoplasmic stress fibres were seen to be composed of bundles of colinear actin-like filaments. In addition to these large stress fibres much smaller bundles of thin filaments as well as randomly oriented thin filaments were also observed. A thick bundle of thin filaments, 0.2 microm to 0.5 microm in diameter, was found to delimit the concave cell edges most prominent in well-spread stationary cells. The leading edge and ruffled border of human skin fibroblasts appeared as a broad web, of meshwork of diagonally oriented thin filaments interconnecting radiating, linear bundles of thin filaments about 0.1 microm in diameter. These bundles corresponding to the microspikes described earlier ranged from about 1.5 microm in length and were separated by 1 microm to 3 microm laterally. The leading edge of 3 T 3 cells showed a similar organization but with fewer radiating thin filament bundles. Both the filaments in the bundles and in the meshwork formed arrowhead complexes with smooth muscle myosin subfragment - 1 which were unipolar and directed towards the main body of the cell. The findings are discussed in relation to the mechanisms of non-muscle cell motility.