Accessory Cone Research Articles

The euphausiid compound eye ? a morphological re-investigation (Crustacea: Euphausiacea)

The ommatidia of the compund eye of the krill, Meganyctiphanes norvegica, are composed of the following cell types: corneagenous cells, main cone cells, accessory cone cells, distal pigment cells, and retinula cells. The corneagenous cells secrete the cuticular lenses, below which the crystalline cones are present. The bipartite crystalline cone is formed within the main cone cells, whereas the accessory cone cells invest the distal part of the cone and proceed proximally in the retina to the basement membrane. Six distal pigment cells are arranged around each ommatidium, though shared by adjacent ommatidia. The seven retinula cells form the rhabdom, and penetrate the basement membrane as axons. The basement membrane is formed by the conjoined extended prolongations from the accessory cone cells and sheets from the basal pigment cells.

Fine structure and convergent development of the Cirolana compound eye (Crustacea Isopoda)

Each sessile eye comprises about 60 ommatidia with large lenses (diameter 100–150 μm), spherical crystalline cones, and hypertrophied rhabdoms (diameter about 100 μm). The cones are formed by two main cone cells, and in addition two accessory cone cells are present. Seven retinula cells contribute to the rhabdom, which is fused distally and open proximally (separated rhabdomeres). A special cell type, previously designated ‘hyaline cells’ are shown to be reflecting pigment cells. These cells form a well-developed tapetal layer. Distal pigment cells screen neighbouring ommatidia. Further, the eye is delimited by two membranes homologous to the fenestrated and eye capsule membranes present in several other isopod groups. The hypertrophied rhabdoms and the elaborate tapetal layer separate the morphology of the Cirolana eye from that of other isopod eyes. These structural features makes the Cirolana eye a case of convergent development with several other deep water living crustaceans.

Ultrastructure of the eye of a euphausiid crustacean

The compound eye of the Antarctic euphausiid Euphausia superba is a spherical clear zone eye. The dioptric system consists of a hexagonally-faceted cornea, two corneagenous cells, two crystalline cone cells which form the bipartite crystalline cone, and two accessory cone cells. The dioptric system of each ommatidium is separated from that of adjacent ommatidia by six distal pigment cells and a basement membrane. The proximal tip of the crystalline cone is cupped by the distal ends of the seven retinula cells whose nuclei are arranged in a staggered array slightly distal to the middle of the clear zone. In the distal half of the clear zone, each narrow retinula cell column is surrounded by large proximal extensions of the six distal pigment cells. The pigment cells narrow more proximally and terminate at the proximal basement membrane. A specialized axial channel complex extends from the crystalline cone through the clear zone, and is continuous with a conical refractive element which caps the distal end of the rhabdom. The rhabdom is fused, and made up of alternating highly birefringent layers of orthogonally-oriented microvilli. It is surrounded by a narrow extra-cellular space which is continuous with the distal refractive element and a second conical refractive element at the proximal end of the rhabdom.

Clasping structure in the double cone of the retina of the turtle (Gyoclemys reevesii).

The double cone of the turtle retina was reconstructed three-dimensionally from electron micrographs of 400 serial sections. Cytoplasm of the accessory cone extends bilaterally to surround the principal cone incompletely. The cytoplasmic extensions are 0.1 microns in width and 2 microns in length at their longest portions. They arise at approximately the median portion of the ellipsoid (consisting of mitochondria) and terminate at the level of the outer limiting membrane. The possible function of these extensions as a clasping structure is discussed.

In vivo synthesis of glycogen by phosphorylase system.

Application of conventional histochemical techniques to the living chick retina demonstrates that phosphorylase can synthesize glycogen (polyglucose) in vivo, in the paraboloid of the accessory cone. Natural in vivo glycogen synthesis may therefore be due to glycogen synthetase and phosphorylase systems, although phosphorylase is normally regarded as a glycolytic enzyme.

The Fine Structure of the Compound Eyes of Shallow-Water Asellotes,Jaera albifronsLeach andAsellus aquaticusL. (Crustacea: Isopoda)

Both species have small sessile compound eyes. The dioptric apparatus of J. albifrons consists of a biconvex lens and a pyriform crystalline cone, the latter formed by two principal and two accessory cone cells. A. aquaticus has a reduced lens and a round cone formed by two to four principal cone cells with two to no accessory cone cells. Distal pigment cells and pigmented retinular cells lie between the ommatidia in J. albifrons. A. aquaticus has only the pigmented retinular cells. Both species have a fused, continuous (unhanded) rhabdom formed by eight retinular cells (R1—8), one of which (R8) is situated distally. The retinular cells R1—7 form, in J. albifrons, a cylinder-shaped middle portion with three microvillar directions (60° apart) and a proximal star-shaped portion. The entire rhabdom of A. aquaticus is star-shaped. Distal pigment-cell processes and basal cells form the fenestrated membrane in J. albifrons and “eye-cup cells” in A. aquaticus.

The Fine Structure of the Compound Eye ofTanais cavoliniiMilne-Edwards (Crustacea: Tanaidacea)

The compound (apposition) eyes of Tanais cavolinii are not well developed: the number of ommatidia is small and there are certain irregularities in structure. The refractive components are formed by the cornea and the cone. The latter is built up by two cone cells. In addition, there are two accessory cone cells confined to the distal part of the cone. The eight pigmented retinular cells extend from the cornea to the basement membrane. Proximal to the cone, they form a fused continuous rhabdom, which in cross section has a rectangular outline. In the middle part of the rhabdom, the microvilli are arranged perpendicular to the long axis of the rhabdom when seen in cross section. The microvilli outside of this area can be arranged either parallel or perpendicular to the microvilli of the middle part. Other irregularities occur in the ommatidium, e.g. the position of the retinular cell nuclei, which are found at different levels. Extensions from the cone cells fuse and form a mesh proximal to the rhabdom. Between the mesh and basal lamina is a basal cell type enveloping the proximal parts of the retinular cells and their axons. These cells also form the basal lamina, which delimits the compound eye from the haemocoel. No special pigment cells are present in the compound eye of Tanais cavolinii.

DIFFERENCES BETWEEN THE IN VITRO AND IN VIVO HISTOCHEMISTRY

Histochemical techniques for glycogen synthetase and phosphorylase were applied to the living chick retina. Polyglucose particles which were histochemically synthesized in the paraboloid of the accessory cone by either enzyme in vivo were larger in size and better stainable with lead citrate than those in vitro. The retina incubated in the medium in vitro showed swelling of the paraboloid. The cytoplasmic matrices of the paraboloid were expanded by overproduction of synthesized polyglucose particles, especially amorphous particles with a diameter of less than 100A. The enzymatic histochemical reaction is apt to appear more intense in vitro than in vivo.Compared with polyglucose particles synthesized in vitro by glycogen synthetase or phosphorylase, polyglucose particles histochemically synthesized in vivo showed a close resemblance to native glycogen particles. Although there is no difference between the fundamental findings of the in vivo and in vitro experiments in such areas as localization and distribution of enzyme activity, the in vivo histochemistry can give more accurate information about the living cell.

Paleoecological Significance of the Short-Tailed Shrew (Blarina), with a Systematic Discussion of Blarina ozarkensis

The parapatric distributions of Recent Blarina brevicauda brevicauda, B. b. kirtlandi , and B. b. carolinensis correspond to the subhumid microthermal, humid microthermal, and humid mesothermal climatic regions. Three late Pleistocene populations of Blarina can be equated with the extant “subspecies” B. b. brevicauda, B. b. kirtlandi , and B. b. carolinensis by means of statistical analysis of mandibular parameters. All three ecotypes are found together, distinct and sympatric, in the Pleistocene deposits of Cumberland, New Paris No. 4, and Peccary Caves, whereas Meyer Cave, Crankshaft Pit, Natural Chimneys, and Welsh Cave local faunas contain two distinct phena. Coexistence of these phena in the same deposit without apparent interbreeding suggests a specific rather than subspecific relationship. Sympatry of these phena during the Pleistocene suggests that a more equable climate existed during glacial time than at present and that sympatric phena of Blarina coexisted in partitioned niches that presently are not defined. Post-glacial continental climates subsequently divided the three phena into their existing parapatric distributions. Blarina brevicauda fossilis is synonymized with B. b, brevicauda. Blarina ozarkensis , an extinct species from the Conard Fissure, is distinguished from other species of Blarina by (1) the absence of the lingual accessory cone posterior to the protoconid on the first lower unicuspid of extant species; (2) the proportionally larger and more bulbous cingula of the third and fourth upper unicuspids, the second lower unicuspid, and the lower molars; (3) its reduced fifth upper unicuspid; (4) its reduced talonid of M3. The Conard Fissure population of B. ozarkensis is more variable than any modern population of Blarina examined.

Application of histochemistry to a living organ: polyglucose histochemically synthesized in the paraboloid of the chick accessory cone in vivo by phosphorylase and branching glycosyltransferase.

Histochemical application in a living animal was tested on the paraboloid of the accessory cone of the chick retina. After the anterior part of the eye had been cut with a Graefe's knife under ether anesthesia, the posterior part was filled with the medium for phosphorylase under exposure to light. The specimens were embedded for routine electron microscopy and the paraboloid of the accessory cone was observed by electron microscopy. Polyglucose particles were synthesized from glucose-l-phosphate in the paraboloid by the activities of phosphorylase and branching glycosyl transferase and found to be in the cytoplasmic matrices. These particles were larger in size and better stainable with lead citrate than those found in the paraboloid of the retina incubated in the medium in vitro by the conventional histochemical method. Overproduction of polyglucose particles was not found in the paraboloid of the retina incubated in the medium in vivo. These findings suggest that polyglucose particles synthesized in vivo have a close resemblance to native glycogen particles and that glycogen metabolism is regulated by the living cell. Glycolysis may not be related to the membranous structures. Therefore, application of enzyme histochemical techniques to the living organ can demonstrate more accurate morphological aspects of metabolism in the cell.

Polyglucose particles histochemically synthesized by glycogen synthetase activity in the living chick retina.

Electron histochemical techniques for glycogen synthetase has been applied to the living retina of the chick and the polyglucose particles synthesized from UDPG in the paraboloid of the accessory cone were compared with those synthesized by the conventional histochemical techniques. In the retina incubated in the medium for glycogen synthetase in vivo, synthesized polyglucose particles were located in the cytoplasmic matrices and most of the particles were less than 200 A in diameter. These particles were rather well stainable with lead citrate and filled the cytoplasmic matrices. However, the tubular structures were not flattened, but slightly dilated. Compared with polyglucose particles synthesized in vitro by glycogen synthetase, those demonstrated by the in vivo histochemical techniques showed closer resemblance to native glycogen particles in size and stainability with lead citrate. The polyglucose particles synthesized from UDPG by glycogen synthetase were apparently different from those synthesized from glucose-1-phosphate by phosphorylase and branching glycosyltransferase.

Colour receptors, and their synaptic connexions, in the retina of a cyprinid fish

Morphologically speaking, there are five kinds of cone cells in the retina of the rudd ( Scardinius erythrophthalmus ). But two of them, the principal elements of the double cones and the free principal cones, are probably functionally equivalent, while another, sparse, population of small ( oblique ) cones (which disappear in older fish), is unlikely to make a significant contribution to visual spectral sensitivity. Thus, principal and accessory cones (usually paired with one another), and single cones seem to be the three receptors which underlie the fish’s trichromacy. Photographic densitometry of individual cone cells was used to provide evidence that accessory cones contain a green-absorbing photopigment and the single cones a blue one. Other arguments are given in support of those identifications, and they also strongly suggest that principal cones contain the red-absorbing pigment. Golgi-impregnated bipolar cells were examined electron-microscopically to determine the specific patterns of synaptic connexion they make with these different, anatomically identifiable, colour cones and with the retinal rods. Three principal arrangements were distinguished (see figure 69, page 190). (1) Rod bipolar cells comprise two distinct morphological types, both of which connect exclusively to principal (red) cones as well as to the rods within the outlines of their dendritic fields. (2) Selective cone bipolar cells, more delicate neurons with considerably wider dendritic fields, connect (according to type) to one or other of the different colour cone populations. Examples analysed were specific for the accessory (green) or for the single (blue) cones; no bipolar cells were found connected only to red cones. (3) Mixed cone bipolars have the smallest dendritic fields, and connect to combinations of cones (for example, red and green, or green and blue, but not red and blue). They also have synaptic input (usually relatively sparse) from the rods. Cells were encountered connecting to all three cone types, but they were only partially analysed, and are not described at length. The light microscopic morphology of these bipolar cell types consistently reflects the detailed pattern of connexion each makes with the different receptor populations (just as the morphology of the cones reflects the spectral properties of their photopigment). But while their synaptic connectivity is generally highly specific for cone type, they do occasionally make anomalous connexions with the ‘wrong’ receptors. There is a high degree of divergence (page 85) at the receptor-bipolar synapses, and the different kinds of cones each characteristically connect to different numbers of bipolar cells. Principal (red) cones, which are the most numerous, individually connect to more bipolars than cones of other types, whose characteristic synaptic divergence is likewise related to the frequency with which they occur in the retina. However, rods, which are much more numerous than cones, do not conform with this generalization. The selectivity with which the synaptic terminals of the different cones are connected together by their invaginating basal processes was also examined. These processes link neighbouring synaptic terminals of differently coloured cones: specifically, principal (red) cone basal processes invaginate accessory (green) cone pedicles, and vice versa. Single (blue) cone basal processes connect only to accessory cone pedicles, but that synaptic relation is not reciprocated. These synapses between the cones have important bearing upon interpretation of the bipolar cell connectivity patterns. In their light, the interaction between colour channels which the convergence of different cones onto the mixed cone bipolar dendrites mediates, seems to re-iterate a process already undertaken more peripherally. Likewise, whereas the anatomy of the selective cone bipolars appears designed to convey activity from the individual cone populations, the responses of the receptors they sample must already be influenced by activity in other colour channels.

EFFECTS OF LIGHT AND DARK ON PHOSPHORYLASE ACTIVITY IN THE PARABOLOID OF THE ACCESSORY CONE OF THE CHICK RETINA

Glycolytic aspect in dark and light adapted retinas of the chicks was studied by the use of histochemical techniques for phosphorylase activity.In the dark adapted retina, the paraboloid of the accessory cone contained synthesized polyglucose particles which were approximately 300 A in diameter. These particles were less stainable with lead citrate and located in the cytoplasmic matrices. In the retina incubated in the medium for phosphorylase activity under exposure to light, synthesized polyglucose particles in the paraboloid varied from 95 to 380 A in diameter and were less stainable with lead citrate. Synthesized polyglucose particles in the accessory cone were so many that the tubular structure was flattened and the cytoplasm was expanded. Therefore, phosphorylase activity in the accessory cone of the chick retina is higher in light adaptation than in dark adaptation.

Electron microscopic and cytochemical study on paraboloid glycogen of the accessory cone of the chick retina.

Glycogen synthetase and phosphorylase activities in the paraboloid glycogen of the accessory cone of the chick retina were studied electron histochemically, while the paraboloid glycogen was observed by electron microscopy. Some of the paraboloid of the accessory cone of the chick retina contained abundant glycogen granules, but some showed no glycogen granules. Some inner segments of the accessory cones were occupied by deposition of glycogen granules. Polyglucose particles synthesized by glycogen synthetase activity in the chick paraboloid were demonstrated in fine granular form with diameter from 70 to 130 A. These particles were less stainable with lead citrate than native glycogen granules. Synthesized polyglucose particles were located in the cytoplasmic matrices and expanded them. Lamellar and membrane structures were not related to synthesized polyglucose. Polyglucose particles synthesized by phosphorylase activity in the chick paraboloid were located in the cytoplasmic matrices and expanded them widely. Tubular structure appeared to be flattened by deposition of synthesized polyglucose particles. These features showed the resemblance to the inner segment of the accessory cone filled with a great amount of glycogen granules. Synthesized polyglucose was demonstrated in macromolecular form with diameter from 200 to 500 A. There were no relationships between lamellar or membrane structures and polyglucose. The present study suggests that the chick paraboloid not only is a field for active glycogen metabolism, but also becomes a storage of glycogen.

The topographical distribution of rods and cones in the adult chicken retina

The relative proportion of rods and cones (single and double) in the chicken retina was determined by counting these elements in each of nine pre-determined segments prepared as periodic acid-Schiff serial sections for rod (hyperboloid glycogen) and double cone (accessory cone paraboloid glycogen) identifications and as unfixed, flat preparations for cone determinations (colored oil droplets). Periodic acid-Schiff preparations revealed that rods and accessory cones were equal in number in all retinal segments except those located directly posterior to the posterior extremity of the pecten where the double cones out-numbered the rods in a ratio of 14 : 10. On the basis of oil-droplet pigmentation, double cones housing a golden-yellow droplet in their chief component and a small yellowish-green droplet in their accessory members were constantly observed to be twice as numerous as single cones (red droplet) in all retinal segments. These data reveal that the proportion of rods to double and single cones is 2 : 2 : 1, respectively, in all areas of the chicken retina except a posterior (lateral) segment where the ratio is 10 : 14 : 7. This area of greater cone concentration corresponds to the site of the temporal fovea of some birds and may represent the area of most acute vision in the fovea-free chicken retina.

Time differences in the formation of the receptor types in the developing chick retina.

AbstractThe times at which the receptor types completed their final S phase was measured by injecting 3H‐thymidine at a series of incubation times and then rearing the embryos to hatching. Incorporation of 3H‐thymidine by the developing receptors was examined, subsequently, in EM autoradiographs of differentiated receptors whose type could be identified. The time at which each receptor type completed final S was estimated from the proportions unlabelled at each of the times at which 3H‐thymidine was injected. The incubation time at which 50% of the receptor type had completed final S was 134.2 hours for principal cones, 139.5 hours for rods, 145.6 hours for single cones and 153.5 hours for accessory cones. It is unlikely, from these estimates, that a principal cone, rod, single cone and an accessory cone, which constitute the repeating group in the retinal mosaic pattern in the periphery, are formed from one stem cell. Each receptor type in a repeating group is probably formed, in the final cell cycle, from a different precursor cell.

The isolated receptor potential of the frog isolated retina: Action spectra before and after extensive bleaching

We have used sodium aspartate Ringer's to enable us to record gross potentials from the receptors of the frog's isolated retina. After bleaching 92 per cent of the rhodopsin, at least two receptors recover their sensitivity, although no rhodopsin is regenerated. Selective chromatic adaptation was used to demonstrate that the receptors involved have λ max around 500 and 580 nm. One receptor must be the 580 cone. The other receptor has an action spectrum fitted by a 502 nomogram pigment and must be the red rod or accessory cone. The implications of these recoveries in sensitivity are discussed.

The fine structure of the retina in the newt, Triturus viridescens.

AbstractThe normal adult retina of the North American Urodele, Triturus viridescens, has been studied with the electron microscope. Three basic types of photoreceptors are observed: rods, possibly distinguishable as either red or green rods, single cones, and double cones. The photoreceptors differ from those reported in other amphibia in that: (1) none of photoreceptors contain an oil droplet; (2) all photoreceptors possess an enlarged paraboloid, and, (3) the double cones consist of two complete photoreceptors, a principal cone member and an accessory cone member. The two members are closely related to one another along the length of the inner segment through a clasping of the principal member within cytoplasmic expansions of the accessory member. The principal member inner segment bears strong resemblance to the single cone while the accessory member inner segment is rod‐like in nature.The sustentacular elements of this avascular retina display a diversity of scleral processes. The presence of specific collar‐like glial ensheathments of the photoreceptors at the external limiting membrane contrasts with the extensive interreceptor contacts between all photoreceptor elements throughout the outer nuclear layer. The synaptic bases are characterized by the presence of three types of specific contact sites: (1) interreceptor contacts among all receptor bases; (2) clusters of fine horizontal cell dendrites penetrate the receptor base and terminate in a superficial spray of typical axodendritic synapses; (3) prominent bipolar dendrites enter within the horizontal cell processes terminating in the typical retinal ribbon synapse.The significance of these observations are discussed with respect to the origin of the amphibian double cone, the metabolic support of the retinal, and the potential integration among the receptor cells.

Visual pigments of frog and tadpole ( Rana pipiens)

Photoreceptor cell outer segments of five different morphologies from frog and tadpole retinas have been examined by microspectrophotometry. Photosensitive pigments were found with the following λ max : Frog: red rod 502, green rod 432, principal cone 575, accessory cone 502, single cone 575; Tadpole: red rod 527, green rod 438, principal cone 620, accessory cone 527, and single cone 620. Axial densities of pigments are computed from their measured transverse densities. A 2 derived pigments have wider bandwidths on a wavenumber plot than A 1 based pigments. Red rod wavenumber plots match published nomograms but other pigments do not. All pigments are dichroic and have comparable photosensitivities. Molar concentration of visual pigments is nearly the same in all cells. However, the small size and number of cones in frog retinas probably makes the total relative contribution of cone pigment molecules too small for successful spectroscopic studies in extracts. Animals in the visual pigment phase of metamorphosis have identical pigment mixtures in all red rods.

An electron microscope study of types of receptor in the chick retina.

AbstractRods, double cones which comprise a principal and an accessory cone, and two types of single cones occur in the chick retina. The rod is narrow and contains a paraboloid, a basal nucleus and a small synaptic body with long synaptic lamellae. The principal cone has a pale‐staining oil droplet and is aligned against an accessory cone, which has a paraboloid, no oil droplet, but a small granular vesicle instead. The synaptic body of the principal cone is large and partly surrounds that of its associated accessory cone. The synaptic body of the accessory cone has a long process extending into the outer plexiform layer. Single cone type I has a dark oil droplet and the mitochondria in the ellipsoid are dense with cristae. Single cone type II has a lighter‐staining oil droplet and fewer cristae. The synaptic bodies of both types of single cone lie vitreal to those of rods and double cones. Fibres connect the synaptic body to the nuclear region in single cones and accessory cones, but not in rods and principal cones. Another type of synaptic body, which is not that of a receptor, occurs in the outer plexiform layer. Groups of small vesicles, like those in the synaptic body, occur near the base of the inner segments; synaptic vesicles may originate here. Muller cells separate each receptor, except the members of a double cone, at the outer limiting membrane and may position the receptors in relation to the pigment epithelium to allow a radial orientation of the inner and outer segments.