Origin of the iris sphincter muscle in chick embryo

The origin of the iridial sphincter muscle in chick embryo was investigated by means of immunohistochemistry. Desmin immunoreactive cells are shown in the mesenchymal stroma overlying the anterior epithelial layer of the iris in 4 1/2-day chick embryos. In 9-11-day chick embryos also some cells of the posterior epithelium near the pupillary margin, and of the iridial lamella show a slighter desmin-immunoreactivity. This finding agrees with a double origin of the iridial sphincter muscle: an early mesenchymal one and a later epithelial other.     

Projection of statocyst sensory neurons associated with crescent hairs in the crayfish Procambarus clarkii Girard

Summary Both smooth muscle and striated muscle are present in the iris of the chick embryo. The two types of musculature form mixed clusters which include undifferentiated cells and many nerve fibres, but they are structurally quite distinct and have different origins. The smooth musculature originates around the 10th day from a laminar invagination (iridial lamella) of the posterior epithelium, and is therefore an ectodermal derivative. The striated musculature appears slightly later than the smooth musculature and originates from undifferentiated cells which are regarded as mesenchymal. After the 15th day in ovo the smooth musculature stops growing; its cells become confined to an area very near the pupillary margin and many develop pigment granules in the sarcoplasm. Many smooth muscle cells seem to undergo regressive changes; however, cells with the typical appearance of visceral muscle cells are still present in the iris of 3-month-old chickens. High density of innervation and vasculari/ation, wide range of striated muscle fibre diameters, presence of lipid vacuoles and of large clusters of mitochondria in the striated fibres, occurrence of peripheral couplings of the sarcoplasmic reticulum, and presence of numerous fibroblast processes in the interstices between fibres, characterize the sphincter pupillae of the mature iris.This work was supported by grants from the Medical Research Council and the Central Research Fund of the University of London     

Cytoskeleton in neuroectodermally derived epithelial and muscle cells of the human iris and ciliary body.

The cytoskeleton of epithelial and muscle cells of the human iris and ciliary body was analyzed by immunohistochemistry in three morphologically normal formalin-fixed, paraffin-embedded eyes and in 34 eyes containing a uveal melanoma. Both layers of the iris epithelium reacted with monoclonal antibodies (MAb) V9 and Vim 3B4 to vimentin, whereas the ciliary epithelia additionally reacted with MAb CAM 5.2, CK5, KS-B17.2, and CY-90, recognizing cytokeratins 8 and 18. The same cytokeratin MAb labeled the retinal pigment epithelium, which lacked vimentin. The muscle portion of the anterior iris epithelium, which forms the dilator muscle, as well as the sphincter and ciliary muscles, reacted with MAb DE-U-10 to desmin and 1A4 to alpha-smooth muscle actin. The dilator and ciliary muscles also reacted with V9 and Vim 3B4 to vimentin, and some dilator fibers were weakly immunopositive for cytokeratin 8 and 18 with CY-90 and CAM 5.2. The antigenic profile of iris and ciliary epithelia infiltrated by melanoma cells remained unchanged. The intraocular epithelia, which are developmentally related but differ in function, and the intraocular muscles, which differ in origin but are functionally related, have distinct cytoskeletal profiles and may provide insights into the functional significance of intermediate filament expression.     

Histophysiological studies on the corpus allatum of Leucophaea maderae

Summary On the basis of the occurrence, at the light microscopic level, of alkaline and acid phosphatases, the pigment epithelium covering the posterior surface of the iris in the albino rabbit can be divided into two zones not previously described, viz. a central zone close to the pupil, approximately corresponding to the area occupied by the iridic sphincter muscle, and a peripheral zone extending to the ciliary body. The central zone which is in intimate relation with the lens was found to have a high content of both phosphatases. At the fine structural level it exhibits a marked pinocytotic activity in the epithelium at the interdigitations between adjacent cells. Electron microscopy revealed that acid phosphatase is localized to the walls of the pinocytotic vesicles. Alkaline phosphatase is in evidence at the surface membrane folds and at microvillous processes between the epithelial cells and the adjoining muscle cells. Unlike the distribution of the acid phosphatase, that of the alkaline phosphatase does not differ fundamentally in the two zones at the fine structural level.In a series of dehydrogenases studied, staining with a view to succinic-, isocitric- and glucose-6-phosphate dehydrogenases revealed an evenly distributed content of enzyme throughout the epithelium. As to the lactic- and -hydroxybutyric dehydrogenases, contents seem to be lower in the pupillary than in the peripheral zone.     

Immunohistochemical demonstration of neurotensin and tyrosine hydroxylase in iris nerves of the rabbit eye

Summary In previous studies we have provided evidence that intracameral administration of neurotensin (NT), an endogenous tridecapeptide, produces strong miosis in the rabbit. The presence of NT immunoreactivity was investigated in rabbit iris whole mounts by light microscopic immunohistochemistry, and its distribution in the iris compared to that, of tyrosine hydroxylase (TH). A few scattered NT-positive cell bodies were localized in the dilator muscle. Both, the NT cell bodies and processes appeared parallel to the muscle cells. Extensive branching of NT-containing cell processes was observed in connection with the sphincter muscle. These NT-positive fibers formed a dense, randomly oriented network throughout the sphincter muscle cells. The distribution of TH immunoreactivity was similar to that of NT-positive cell processes, except that no TH-positive cell bodies were detected in any of the iris structures examined. Moderate branching of TH-positive fibers was observed in the dilator and sphincter iris muscles. These findings provide neuroanatomical support for an important role of NT in pupillary physiology. Its similar topographical distribution with TH suggests that NT and dopamine may be co-localized, as it has already been described in brain.     

Immunohistochemical demonstration of neurotensin and tyrosine hydroxylase in iris nerves of the rabbit eye

In previous studies we have provided evidence that intracameral administration of neurotensin (NT), an endogenous tridecapeptide, produces strong miosis in the rabbit. The presence of NT immunoreactivity was investigated in rabbit iris whole mounts by light microscopic immunohistochemistry, and its distribution in the iris compared to that, of tyrosine hydroxylase (TH). A few scattered NT-positive cell bodies were localized in the dilator muscle. Both, the NT cell bodies and processes appeared parallel to the muscle cells. Extensive branching of NT-containing cell processes was observed in connection with the sphincter muscle. These NT-positive fibers formed a dense, randomly oriented network throughout the sphincter muscle cells. The distribution of TH immunoreactivity was similar to that of NT-positive cell processes, except that no TH-positive cell bodies were detected in any of the iris structures examined. Moderate branching of TH-positive fibers was observed in the dilator and sphincter iris muscles. These findings provide neuroanatomical support for an important role of NT in pupillary physiology. Its similar topographical distribution with TH suggests that NT and dopamine may be co-localized, as it has already been described in brain.     

Expression of the HB9 homeobox gene concomitant with proliferation accompanying epidermal stratification during development of chick embryonic tarsometatarsal skin

A homeobox gene, HB9, has been isolated from the tarsometatarsal skin of 13-day-old chick embryos using a degenerate RT-PCR-based screening method. In situ hybridization analysis revealed that, during development of chick embryonic skin, the HB9 gene was expressed in epidermal basal cells of the placodes, but not in those of interplacodes, and in the dermal cells under the placodes at 9 days before addition of an intermediate layer by proliferation of the basal cells in the placodes. With the onset of epidermal stratification, the direction of the basal cell mitosis changed, with the axis becoming vertical to the epidermal surface. Placodes and interplacodes form outer and inner scales, respectively, after they have elongated distally (Tanaka S, Kato Y (1983b) J Exp Zool 225: 271–283). During scale ridge elongation at 12–15 days, HB9 was strongly expressed in the epidermis of the outer scale face, where the cell proliferation is more active than in the epidermis of the inner scale face; hence, stratification of the outer scale face is more prominent than that of the inner scale face. After 16 days, when mitotic activity in the epidermal basal cells decreases and the thickness of the epidermis is maintained at a constant level, the HB9 expression decreases with the onset of epidermal keratinization. These results suggest that HB9 may be involved in the proliferation of the epidermal basal cells that accompanies epidermal stratification.     

Development of smooth and skeletal muscle cells in the iris of the domestic duck,chick and quail

Summary Embryonic development of the avian iris muscle was studied by light and electron microscopy in order to clarify the origin of the iridial skeletal muscle cells. In normal development of the domestic duck, chick, and quail, the muscle bundles appearing in the iris at stage 35 consisted solely of smooth muscle cells. Undifferentiated cells appeared at stage 36, and finally skeletal muscle cells were observed at stage 37. This sequence suggests that stromal mesenchymal cells migrate into the muscle bundles to become skeletal muscle cells.Tissue culture of whole indes removed from duck embryos at stages 30 through 34 produced skeletal muscle cells while culture of isolated iridial epithelia removed at stages 31 and 32 did not. Removal of the midbrain region of duck embryos at stage 10 frequently produced severe disorganization of the eye concomitant with craniofacial deformities typical of a neural crest mesenchymal defect. These severely disorganized eyes were devoid of iridial skeletal muscle cells. These results also suggest mesenchymal origin of iridial skeletal muscle cells.     

Formation of neuroblastic layers in chicken retinospheroids: the fibre layer of Chievitz secludes AChE-positive cells from mitotic cells

Summary The significance of the classical subdivision of the retinal primitive neuroepithelium into an outer and an inner neuroblastic layer by the transient fibre layer of Chievitz (LOC) is little understood. We examine here the formation of neuroblastic layers by regenerating fully laminated retinospheroids from dissociated cells of the embryonic chick eye margin in rotary culture. By tracing cellular processes with the fibre-specific F11-antibody in retinospheroids, we occasionally find, in addition to an outer and an inner plexiform layer, a cell-free F11-positive LOC homologue, subdividing the inner nuclear layer. Moreover, we demonstrate that the LOC precisely separates postmitotic AChE-positive cells of the inner retina from an AChE-negative outer part holding all BrdU-labelled mitotic cells. These in vitro data suggest that the inner neuroblastic layer is exclusively composed of AChE-positive cells, thus representing a primary differentiation zone of the retina.     

On the fine structure of the Octopus iris

Summary The Octopus iris is composed of five different layers: A, the external epithelium; B, the chromatophore layer; C, the iridocyte layer; D, the layer of muscles and collagen strands; E, the pigment epithelium. The nerves innervating the sphincter and the chromatophore muscles are identified and their neuromuscular junction is described. The motor endings of chromatophore nerves have an additional ending in presynaptic position which probably functions as a modifier of neuromuscular transmission. The chromatophores are naked and exhibit a tubular channel system between plasmalemma and pigment container which looks similar to the T-system of muscle cells.The financial support of this investigation by the Swiss National Foundation is gratefully acknowledged.     

Immunoreactivity of the septins SEPT4, SEPT5, and SEPT8 in the human eye.

We aimed to examine the distribution of SEPT4, SEPT5, and SEPT8 in the human eye. For each septin, five to six normal human eyes were examined by immunohistochemical staining of paraffin sections using polyclonal antibodies against SEPT4, SEPT5, and SEPT8 and an avidin biotin complex immunodetection system. SEPT4 immunoreactivity (IR) was detected primarily in the epithelium of cornea, lens, and nonpigmented ciliary epithelium; in the endothelium of cornea and vessels of iris and retina; and in the retinal nerve fiber layer, the outer plexiform layer, the outer segments of the photoreceptor cells, the inner limiting membrane of the optic nerve head, and optic nerve axons. SEPT5-IR was present in corneal endothelial cells, iris tissue, nonpigmented ciliary epithelium, and epithelial cells of the lens. SEPT8-IR almost paralleled that of SEPT4, except for a lower SEPT8-IR of the outer photoreceptor segments and a positive staining of the meningothelial cell nests in the subarachnoidal space of the bulbar segment of the orbital optic nerve. In conclusion, SEPT4, SEPT5, and SEPT8 are expressed in various ocular tissues, each revealing a distinct expression pattern. Both physiological and potential pathophysiological role of septins in the human eye deserve further investigation.     

Occurrence and regional distribution of striated muscle fibers in the rat pineal gland

Summary In a total of 96 rat pineals studied 31 were found to contain striated muscle fibers or their precursors. The muscle fibers were most frequently present in the stalk region and more frequently found in the left than in the right hemisphere. Size measurements revealed that the lengths of pineal muscle cell nuclei differ only slightly from those of the sphincter muscle of the iris. However, the yellowish appearance of pineal muscle cell nuclei under darkfield investigation, a phenomenon observed in all muscular tissues of mesenchymal origin and connective tissue cells, may support the hypothesis that pineal musculature is of mesenchymal rather than ectodermal origin.Supported by a grant (Vo 135/4) of the Deutsche Forschungsgemeinschaft within the Schwerpunktprogramm Neuroendokrinologie     

Fine structure of the photosensitive iris of the toad, Bufo marinus

The iris of the toad Bufo marinus is directly photosensitive and will constrict in response to light striking only the iris. This is true even when the iris is isolated from the rest of the eye, and therefore from reflex neuronal influences initiated in the retina. This autonomous response is probably mediated by the sphincter pupillae muscle, since no specialized photoreceptors are present in the iris, nor does the sphincter exhibit any specializations likely to subserve a purely photoreceptive function. The photosensitive sphincter appears typical of smooth muscle and, like mammalian sphincters, possesses many intercellular junctions. The iris possesses a well-developed neuronal plexus with fibers projecting into the sphincter muscle layer. Nerve terminals contain small, agranular (30-70nm) and large, dense-cored (80-120nm) vesicles. No consistent postsynaptic specializations are seen on any cells of the iris, including the cells of the sphincter muscle. The anterior pigment epithelial cells of the iris appear specialized and resemble the myoepithelial dilator muscle described by Kelly and Arnold ('72) for the iris of rats.     

Expression of monocarboxylate transporters in rat ocular tissues

The aim of the present study was to determine the distribution of monocarboxylate transporter (MCT) subtypes 1-4 in the various structures of the rat eye by using a combination of conventional and real-time RT-PCR, immunoblotting, and immunohistochemistry. Retinal samples expressed mRNAs encoding all four MCTs. MCT1 immunoreactivity was observed in photoreceptor inner segments, Müller cells, retinal capillaries, and the two plexiform layers. MCT2 labeling was concentrated in the inner and outer plexiform layers. MCT4 immunolabeling was present only in the inner retina, particularly in putative Müller cells, and the plexiform layers. No MCT3 labeling could be observed. The retinal pigment epithelium (RPE)/choroid expressed high levels of MCT1 and MCT3 mRNAs but lower levels of MCT2 and MCT4 mRNAs. MCT1 was localized to the apical and MCT3 to the basal membrane of the RPE, whereas MCT2 staining was faint. Although MCT1-MCT4 mRNAs were all detectable in iris and ciliary body samples, only MCT1 and MCT2 proteins were expressed. These were present in the iris epithelium and the nonpigmented epithelium of the ciliary processes. MCT4 was localized to the smooth muscle lining of large vessels in the iris-ciliary body and choroid. In the cornea, MCT1 and MCT2 mRNAs and proteins were detectable in the epithelium and endothelium, whereas evidence was found for the presence of MCT4 and, to a lesser extent, MCT1 in the lens epithelium. The unique distribution of MCT subtypes in the eye is indicative of the pivotal role that these transporters play in the maintenance of ocular function. retina; eye; immunohistochemistry; polymerase chain reaction     

Musculature of the penial complex: A new criterion in unravelling the phylogeny of Hygrophila (Gastropoda: Pulmonata)

The taxonomy of freshwater pulmonates (Hygrophila) has been in a fluid state warranting the search for new morphological criteria that may show congruence with molecular phylogenetic data. We examined the muscle arrangement in the penial complex (penis and penis sheath) of most major groups of freshwater pulmonates to explore to which extent the copulatory musculature can serve as a source of phylogenetic information for Hygrophila. The penises of Acroloxus lacustris (Acroloxidae), Radix auricularia (Lymnaeidae), and Physella acuta (Physidae) posses inner and outer layers of circular muscles and an intermediate layer of longitudinal muscles. The inner and outer muscle layers in the penis of Biomphalaria glabrata consist of circular muscles, but this species has two intermediate longitudinal layers separated by a lacunar space, which is crossed by radial and transverse fibers. The muscular wall of the penis of Planorbella duryi is composed of transverse and longitudinal fibers, with circular muscles as the outer layer. In Planorbidae, the penial musculature consists of inner and outer layers of longitudinal muscles and an intermediate layer of radial muscles. The penis sheath shows more variation in muscle patterns: its muscular wall has two layers in A. lacustris, P. acuta, and P. duryi, three layers in R. auricularia and Planorbinae and four layers in B. glabrata. To trace the evolution of the penial musculature, we mapped the muscle characters on a molecular phylogeny constructed from the concatenated 18S and mtCOI data set. The most convincing synapomorphies were found for Planorbinae (inner and outer penis layers of longitudinal muscles, three-layered wall of the penis sheath). A larger clade coinciding with Planorbidae is defined by the presence of radial muscles and two longitudinal layers in the penis. The comparative analysis of the penial musculature appears to be a promising tool in unraveling the phylogeny of Hygrophila.     

Macrophage mobilization and morphology during lens regeneration from the iris epithelium in newts: studies with correlated scanning and transmission electron microscopy

The lens was removed from both eyes of adult newts (Notophthalmus viridescens), and the eyes were fixed in Karnovsky's fixative every 2 days 0-20 days after operation. Anterior half-eyes were prepared by standard procedures for scanning electron microscopy of the surface. Before fixation, the posterior iris surface was cleaned of adhering vitreous mechanically with forceps or by treatment with bovine testicular hyaluronidase or with hyaluronidase and collagenase. Some specimens were cryofractured in buffer or ethanol transverse to the mid-dorsal iris, and the fractured surface viewed with scanning electron microscopy (SEM). Cells with various combinations of ridges, blebs, filopodia, and lamellipodia were observed adhering to the posterior surface of the iris by 6 days after lentectomy. These cells, which exhibited the surface characteristics of macrophages, became more numerous in specimens fixed after longer intervals. Invasion of the iris epithelium was observed in a cryofractured specimen. After observations with SEM, selected specimens were embedded in plastic and sectioned for study with transmission electron microscopy (TEM). The cells on the iris surface had the cytological characteristics of macrophages, and other macrophages were located within the iris epithelium. In specimens fixed 16 or more days after lentectomy, a bulging lens vesicle was regenerating from the dorsal pupillary margin of the iris. Macrophages were absent or few on the surface of this developing lens but remained scattered over the adjoining iris. Roles that might be played by these macrophages during the transdifferentiation of iris epithelium into lens are discussed.     

Neurobiology of Polyorchis. II. Structure of effector systems

The gross and fine morphology of the major effector systems in the anthomedusan, Polyorchis penicillatus, is described and discussed in relation to the known physiological and behavioral properties of these systems. Swimming is controlled by an anastomosing network of giant neurons within the inner nerve ring and radial nerves. Although these neurons may be coupled by gap junctions it is likely that they form a syncytium. The photosensitivity of the “giants” is attributed to reflexive membranes within the cytoplasm. Giant neurons act as both the pre- and postsynaptic cell when forming synapses with other neurons of the inner nerve ring. Neuromuscular synapses between “giants” and the striated swimming muscle are found around the margin and along the radii. Swimming muscle cells are connected laterally by gap junctions and end-to-end by desmosomes which are sometimes elaborated with extra-thick filaments. Unstriated sphincter and radial muscles, the major muscles associated with crumpling, are both greatly folded over mesogloeal ridges and have processes that cross the mesogloea to contact the ring and radial canals, respectively. Synapses or other sites that might be responsible for exciting these muscles during crumpling have not been found. The ability of the endodermal lamella and canals to propagate action potentials can be accounted for by the numerous gap junctions that are seen in these tissues. The precise location where excitation is transferred to the nervous system to initiate crumpling is not known but epithelial bridges crossing the mesogloea are likely routes. Synapses between neurons originating in the outer nerve ring and tentacle longitudinal muscle can account for the control of tentacle length. Neurons of the outer nerve ring also synapse onto velar, radial fibers and the sphincter muscle. The inner and outer nerve rings have nervous connections. The organisation of the outer nerve ring and the arrangement of nerves within the endodermal plexus is described. A diagram showing the major connections and interactions of components of the effector systems is presented.     

Uptake of circulating hyaluronic acid by the rat liver

Summary The present study deals with the localization and development of S-100 protein-like immunoreactivity in the retina, ciliary body and iris of human fetuses. In the retina, numerous astrocytes, densely distributed in the nerve-fiber layer and ganglion-cell layer, were stained strongly with the S-100 antiserum. The first immunoreactive astrocytes occurred at the posterior pole of the retina and spread gradually outward and toward the ora serrata with increasing age. Müller cells were not immunoreactive for S-100 during development, except in the retina of the latest fetus examined. S-100 immunoreactivity was also found in the nonpigmented ciliary epithelium and posterior epithelium of the iris, both of which are developed from the inner wall of the optic cup. On the other hand, the pigmented epithelium extending from retina to iris, derived from the outer layer of the optic cup, was free of S-100 immunoreactivity.     

Submicroscopic structure of the membranous labyrinth

Summary Investigations were performed by light and electron microscope on the submicroscopic structure of the epithelium of Corti's organ in the white rat.Morphological and structural differences between the inner hair cells and the outer hair cells are revealed.The inner hair cells are closely inter-related with the inner supporting cells and have a polyhedral shape, whereas the outer hair cells look like cylinders and are surrounded by an intraepithelial fluid.The structural peculiarities consist of differences in the dimensions of the hairs, in the arrangement of cytoplasmic organoids and in the aspect of the receptoneural junction. In both sensory hair cells 4 zones of different structure can be distinguished from the surface inwards: apical zone, intermediate zone, perinuclear zone and receptoneuronal junction. The functional value of these different zones is discussed and compared with what has been demonstrated in other receptors.The pillar cells and the Deiters' cells are supporting cells which have a filamentous skeleton, composed of submicroscopic individual filaments. These filaments have a diameter of about 215 Å and present some analogies with the tonofilaments of the stratified squamous epithelium. The filaments are arranged differently in the pillar cells and in the Deiters' cells. Possible functional differences between these patterns are discussed.The reticular membrane is not an extracellular cuticle. It consists of intracellular cementitious material (like the terminal bars of the epithelial cells).The Hensen's and Claudius cells, the Böttcher's cells, the inner supporting cells, the inner and outer spiral sulcus cells are regular prismatic cells with few endoplasmic organoids and without filaments.This work is dedicated to the memory of the late Prof. L. Pietrantoni.