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PubMed2002

Extent of retinal ganglion cell death in the frog Litoria moorei after optic nerve regeneration induced by lesions of different sizes.

Some amphibian retinal ganglion cells die during optic nerve regeneration. Here we have investigated whether ganglion cell death in the frog Litoria moorei is associated with the lesion site. For one experimental series, the optic nerve lesion extended for 0.15 mm; in the other, it extended for 1.5 mm. The extent of ganglion cell death was estimated from cresyl violet-stained whole mounts at 24 weeks post lesion. In other animals, individual regenerating axons were visualised in the optic nerve by horseradish peroxidase (HRP) labelling from 1 day to 24 weeks post lesion; counterstaining with cresyl violet allowed examination of cells that repopulated the lesion site. Ganglion cell numbers fell significantly more after an extensive than after a localised lesion, long-term losses being 50% and 34%, respectively (P < 0.05). Regenerating axons were delayed in their passage across the cell-poor extensive lesion compared with the relatively cell-rich localised lesion. The differing rates of regeneration between series were matched by greater delay after extensive lesion in the return of visually guided behaviour as assessed by optokinetic horizontal head nystagmus. We suggest that delays in regeneration after an extensive lesion exacerbate ganglion cell death, indicating that conditions within the lesion are associated with the death of some ganglion cells.

Animals↗

PubMedDate not supplied

Tectal neurons that participate in centrifugal control of the quail retina: a morphological study by means of retrograde labeling with biocytin.

An avian retinopetal nucleus, the isthmo-optic nucleus (ION), is known to receive predominant inputs from the ipsilateral optic tectum. We injected biocytin into the ION in the Japanese quail, and retrogradely labeled tectal neurons projecting to the isthmo-optic (IO) neurons, or the tecto-IO neurons, with an extraordinary Golgi-like quality. Somata of the tecto-IO neurons were located in layer 9 of the tectum. The tecto-IO neurons did not have apical dendrites extending into superficial retino-recipient layers (layers 2-7), but had descending dendrites ramified in layers 9-12. They also possessed short ascending dendrites ramifying in the upper half of layer 9. This dendritic morphology suggests that main input to the tecto-IO neurons may not be of retinal origin. The tecto-IO neurons were spatially arranged in a regular pattern. Distances between neighboring tecto-IO neurons were 50-100 microns. The dendrites of each tecto-IO neuron were not widely dispersed in the horizontal plane, and were confined in a vertically oriented column of 100-200 microns diameter. They possessed axon collaterals extending horizontally in layers 12 and 13. The estimated total number of the tecto-IO neurons was approximately 7000-10,000, which is almost identical to the total cell number of the IO neurons. To label a small number of the tecto-IO terminals, biocytin was injected into a confined area of the optic tectum. The tecto-IO fibers densely arborized in a restricted space of the ION, which is comparable to the dimension of dendritic arborization of individual IO neurons. It is suggested that single tecto-IO neurons may make contact with single IO neurons. IO neurons are known to make synaptic contact with single target cells (association cells of Cajal) in the retina (Uchiyama & Ito, 1993; Uchiyama et al., 1995). The arborization pattern of the tecto-IO neurons' dendrites indicates that the tecto-IO neurons receive very local information in sensory and sensorimotor coordinate space. The morphology of the tecto-IO terminals suggests that the spatially confined information that drives the tecto-IO neurons is sent in parallel to single IO neurons, and then further to single retinal association cells of Cajal. Cellular-level restricted projection patterns of the tecto-isthmo-retinal system may reflect its function for centrifugal control of retinal function.

Animals↗

PubMed1993

Dopaminergic neurons in the cone-dominated ground squirrel retina: a light and electron microscopy study.

Tyrosine hydroxylase (TH), the rate limiting enzyme in the conversion of tyrosine to DOPA, is a reliable marker for catecholaminergic (dopaminergic) neurons. To investigate the distribution of dopamine in the cone-dominated retina of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), retinal sections and wholemounts were incubated with an antiserum directed against TH and then processed using immunofluorescence and the avidin-biotin immunohistochemical method. TH-like immunoreactivity was exhibited by amacrine and interplexiform-like cells in the innermost portion of the inner nuclear layer (INL) and by cells we presume to be displaced amacrines in the ganglion cell layer (GCL). Their somata were 12 to 28 microns in diameter, with the majority measuring approximately 18 microns. In transverse sections the processes of the three types of neurons were seen to extend into lamina 1 of the inner plexiform layer (IPL). In horizontal sections 2-3 primary dendrites were seen to ramify and the branches extended for considerable distances, with overlap between the dendritic fields of neighboring TH-cells. A distance to the nearest neighbor analysis suggested the TH-neurons in the INL are distributed in a non-random fashion. The mean overall density of labeled amacrines is 15 cells/mm2, low when compared to the mean density reported in other species. EM results indicate that TH-labeled amacrines make synaptic contacts with unlabeled amacrines, although the possibility that they may contact ganglion cells can not be ruled out.

Animals↗

PubMed1976

The retina and retinal projection on the lamina ganglionaris of the crayfish Pacifastacus leniusculus (Dana).

The retinular cell morphology and ommatidia arrangement in the crayfish retina are studied. Each ommatidium contains eight receptor cells (R1-R8). Seven of them (R1-R7) contribute to a large spindle-shaped rhabdom with orthogonal layers of microvilli. Distal to the rhabdom of R1-R7, the 8th receptor cell forms a separate rhabdom with horizontal microvilli. The cell is four-lobed, is devoid of screening pigments, and forms a thin axon projecting past the first optic neuropile (lamina ganglionaris) and has a terminal in the second (medulla externa), indicating a separate function of the receptor. The axons from the eight receptors of one ommatidium project to different synaptic compartments (cartridges) in the lamina. A pattern is described where eight axons from three adjacent ommatidia join in one cartridge; and conversely, the axons from one ommatidium split and join to three cartridges. The seven axons from R1-R7 terminate in two levels of the lamina plexiform layer (epl 1 and epl 2), four in the distal and three in the proximal part. Among the monopolar ganglion cells, two types are found with lateral branches restricted to either of the two receptor terminal layers (M3 in epl 1 and M4 in epl 2) and axons terminating in the second optic neuropile. A correlation between the two orthogonal channels for e-vector discrimination and the two levels of terminals within the lamina is suggested. The retina is divided into dorsal and a ventral part with a mirror symmetry axis horizontally in the eye.

Animals↗

PubMed2000

Mercury distribution in the squirrel monkey retina after in Utero exposure to mercury vapor.

Pregnant squirrel monkeys were exposed to mercury vapor during approximately 2/3 of a pregnancy, at a concentration of 0.5 or 1 mg Hg/m(3) air for 4 or 7 h a day, 5 days a week. The offspring were sacrificed at different ages (gestational week 16 to 5 years). The eyes were enucleated and horizontal sections of the retina, comprising the optic disc and the fovea, were processed for autometallographic (AMG) silver enhancement. The AMG mercury distribution was mapped using light and epipolarization microscopy. In young offspring (16-week-old fetus to 3 days old), mercury was detected mainly in the optic nerve, retinal pigment epithelium, inner plexiform layer, vessel walls, and ganglion cells. Three and a half months later, the amount of visualized mercury had decreased in all areas except for the retinal pigment epithelium. In adult monkeys that had survived for 2 to 5 years, only a faint AMG staining was seen in the retinal pigment epithelium, the optic nerve, and in some vessel walls. In conclusion, in offspring sacrificed in utero or shortly after birth, the structures accumulating mercury were the same as those which accumulate mercury following direct exposure through the lungs, as reported previously (K. Warfvinge and A. Bruun, 1996, Toxicology 107, 189-200), although the amount of AMG staining was less in transplacental animals. This demonstrates that inorganic mercury penetrates the blood-retina barrier. In monkeys that had survived 3 to 5 years, only tiny amounts of mercury were detected, which is in contrast to findings from direct exposure, in which large amounts were still found 3 years after exposure. This may suggest that the elimination process in the retina is more efficient in young animals, but a possible adverse effect of mercury on retinal development cannot be ruled out.

Animals↗

PubMed1984

Localization of L-glutamate and L-aspartate synaptic receptors in chick retinal neurons.

Kainic acid (KA) produces lesions in the chick retina when injected intravitreally. In order to ascribe L-glutamate and L-aspartate receptors to specific neuronal populations, we measured L-[3H]glutamate and L-[3H]aspartate specific binding to membranes from retinas treated with different doses of KA. A 20% reduction in glutamate and aspartate receptors was observed when amacrine cells were eliminated (50 nmol KA). When 120 nmol KA were injected, horizontal cells were highly decreased and so were glutamate (48%) and aspartate (22%) receptors. 200 nmol KA killed most of the bipolar cells in addition to the horizontal and amacrine cells; this lesion was associated with an additional 21% decrease in the specific binding of aspartate but not glutamate. Receptors for both compounds which remained after 200 nmol KA (30%) could be located in ganglion cells, which were spared by KA.

Animals↗

PubMed1981

Effect of body tilt on receptive field orientation of simple visual cortical neurons in unanesthetized cats.

The receptive field (RF) orientation of 53 simple visual cortical neurons was determined by recording the activity of single cells during presentation of stationary bars of light. An RF tuning curve was constructed for each cell by averaging the neural discharge resulting from the repeated presentation of a number of slit orientations. RF curves were then determined again, following a 45 degrees roll tilt of the entire head and body, and subsequently after the return of the animal to the original horizontal position. RF tuning curves were typical of what others have found to characterize simple cells, and were highly replicable on the return to the starting position. In 73% of the cells studied, the RF orientation after tilt remained unaltered relative to the head axis (+/- 15 degrees); in the remaining 27% of the cells RF orientations either under- or over-shot the retinal tilt by more than 15 degrees, and in some cases by as much as 45 degrees. These results support the hypothesis that the well documented vestibular inputs to visual cortex play a role in modifying the RF orientation selectively of visual cortical neurons, and suggest that such information may be an important neurophysiological substrate underlying visual spatial constancy mechanisms.

Animals↗

PubMedDate not supplied

The nob2 mouse, a null mutation in Cacna1f: anatomical and functional abnormalities in the outer retina and their consequences on ganglion cell visual responses.

Glutamate release from photoreceptor terminals is controlled by voltage-dependent calcium channels (VDCCs). In humans, mutations in the Cacna1f gene, encoding the alpha1F subunit of VDCCs, underlie the incomplete form of X-linked congenital stationary night blindness (CSNB2). These mutations impair synaptic transmission from rod and cone photoreceptors to bipolar cells. Here, we report anatomical and functional characterizations of the retina in the nob2 (no b-wave 2) mouse, a naturally occurring mutant caused by a null mutation in Cacna1f. Not surprisingly, the b-waves of both the light- and dark-adapted electroretinogram are abnormal in nob2 mice. The outer plexiform layer (OPL) is disorganized, with extension of ectopic neurites through the outer nuclear layer that originate from rod bipolar and horizontal cells, but not from hyperpolarizing bipolar cells. These ectopic neurites continue to express mGluR6, which is frequently associated with profiles that label with the presynaptic marker Ribeye, indicating potential points of ectopic synapse formation. However, the morphology of the presynaptic Ribeye-positive profiles is abnormal. While cone pedicles are present their morphology also appears compromised. Characterizations of visual responses in retinal ganglion cells in vivo, under photopic conditions, demonstrate that ON-center cells have a reduced dynamic range, although their basic center-surround organization is retained; no alteration in the responses of OFF-center cells was evident. These results indicate that nob2 mice are a valuable model in which to explore the pathophysiological mechanisms associated with Cacna1f mutations causing CSNB2, and the subsequent effects on visual information processing. Further, the nob2 mouse represents a model system in which to define the signals that guide synapse formation and/or maintenance in the OPL.

Action Potentials↗

PubMed1996

Fine structure of the retina and pigment epithelium in the creek chub, Semotilus atromaculatus (Cyprinidae, Teleostei).

The structure of the light- and dark-adapted retina, the pigment epithelium and the choroid of the creek chub, Semotilus atromaculatus (Cyprinidae, Teleostei) is examined by light and electron microscopy. An extensive network of vitreal blood vessels emanating from the hyaloid artery enters the eye with the optic nerve and overlies the inner limiting membrane. This membrane closely apposes the fine protrusions of the Müller cell processes which traverse the entire retina, dividing the inner retina into alternating fascicles of ganglion cells and optic axons. The inner nuclear layer consists of bipolar, amacrine, Müller cell soma and two layers of horizontal cells. The outer plexiform layer possesses both rod spherules and cone pedicles. Each rod spherule consists of a single synaptic ribbon in either a triad or quadrad junctional arrangement within the invaginating terminal endings of the bipolar and horizontal cell processes. In contrast, cone pedicles possess multiple synaptic ribbons within their junctional complexes and, in the light-adapted state, the horizontal cell processes show spinule formation. Four photoreceptor types are identified on morphological criteria; unequal double cones, large single cones, small single cones and rods. All but the small single cones are capable of retinomotor responses. The rod to cone ratio is approximately 5:1 and the rods form two ill-defined rows in the light-adapted condition. The retinal pigment epithelium possesses two types of osmiophilic granules. These are bound within slender microvilli and migrate vitread to surround the photoreceptors in response to light. Bruch's membrane is trilaminar and the vascularised choroid consists of up to three layers of melanocytes. The endothelial borders of the choroidal blood vessels abutting the outer lamina of Bruch's membrane are fenestrated.

Adaptation, Ocular↗

PubMed1992

Retinal topography in the koala (Phascolarctos cinereus).

Nissl-stained retinal wholemounts were used to investigate the topographical organization of the ganglion cell layer of the koala (Phascolarctos cinereus); the visual resolution limit of this animal was subsequently estimated from retinal ganglion cell density data. Two types of cells could be differentiated on the basis of their size and staining characteristics: a subpopulation of presumed ganglion cells, consisting of medium to large cells with Nissl substance in the cytoplasm and pale uniformly staining nuclei, and a further subpopulation of small, densely staining cells. The latter group were presumed to be neuroglia and displaced amacrine cells. Iso-density contour maps were prepared from total cell counts and also counts of presumed ganglion cells; in all cases, the density of cells was greatest in the inferior retina where there was an area of peak density occurring as a poorly developed, horizontal streak that extended across the inferior retina. The inferior position of the streak in the koala contrasts with reports of the superior position of streaks in other marsupials. Peak cell densities of 2370 cells/mm2 and 1480 cells/mm2 were recorded for the total cell population and the presumed ganglion cell subpopulation, respectively. The latter value is equivalent to a visual resolution of 2.4 cycles/degree, based on sampling theory and a square packing paradigm, placing the koala close in visual performance to two other marsupials, the Australian Northern native cat and the American Virginia opossum.

Animals↗

PubMed1994

Transduction of the light message: from the photon to the optic nerve.

Retinal transduction consists of the conversion of a physical stimulus, light, into an electrophysiological signal. This conversion takes place in several stages. First of all, at the photoreceptor level, via a sequence of molecular activations and deactivations, the detection of light results in an hyperpolarization of the cell membrane. This initial electrical signal is then relayed onto the functional cells of the retina. The bipolar cells are the first associated neurons, responding to the light stimulus by either hyperpolarization (OFF), or depolarization (ON). The second associated neurons are the ganglion cells where the ON-OFF duality also operates and whose fibers make up the optic nerve. In coloured photopic vision, the photoreceptor--bipolar cell--ganglion cell circuit is direct. For the cone-bipolar cell transmission, horizontal cells delimit excitatory (center) and inhibitory (surround) zones at the origin of the receptive field. In scotopic vision, however, i) there is only a single class of bipolar cells, that depolarize in response to light, and ii) the bipolar-ganglion cell connection is not direct. Here, the AII amacrine cells are responsible for the inhibition of the OFF ganglion cells directly connected to them or for the excitation of the ON ganglion cells via ON bipolar cells of the cone circuit. Finally, in mesopic vision, the sensory message originates in rods, and is subsequently relayed by the cone circuit via gap junctions between photoreceptors.

Animals↗

PubMed1979

Coding of visual information by units in the cat cerebellar vermis.

Extracellular records were made of the responses to precisely controlled stationary or moving visual stimuli of 174 units in the cerebellar vermis of cats anaesthetised with chloralose. Identified Purkinje cells and unidentified units responsed similarly. Responses to ON and to OFF steps of a stationary light bar had different characteristics. Some units showed changes in the form of their ON responses related to different positions of the stimulus in their large receptive fields. In some cases changes in response latency from different field positions were also noted. Some units responded only to binocular stimulation and others gave much larger responses to binocular than to monocular stimulation. In addition, some were sensitive to the relative retinal disparity of images and, of these, several were sensitive to vertical as well as to horizontal retinal disparity. Sinusoidally-moving light bars gave responses consisting of one or two bursts of impulses per cycle; the most effective frequency was about 3 Hz. These responses may represent detection of the instant of maximum velocity. The relatively precise coding of retinal disparity in spite of the large size of receptive fields and the coding of position within these large fields is discussed. A possible function for the disparity-sensitive units in the control of vergence is suggested and the relation of this control to visual depth detection and to the estimation of the absolute distance of objects from the animal is discussed.

Animals↗

PubMed2004

Characterization of retinoic acid neuromodulation in the carp retina.

Visual sensation in vertebrates starts with the isomerization of 11-cis retinaldehyde into all-trans retinaldehyde. Aldehyde dehydrogenases, present in the pigment epithelium and some retinal cells, convert all-trans retinaldehyde into all-trans retinoic acid (at-RA). Evidence in the retina and the hippocampus has accumulated, showing that at-RA, besides being a morphogenetic factor, also acts as a neuromodulator. In mature retina, at-RA affects visual processing by acting on gap junctional conductances and the synaptic transfer between photoreceptors and horizontal cells. We present evidence supporting a neuromodulatory role of at-RA in the carp retina. High performance liquid chromatography (HPLC) measurements and an RA bioassay indicate a light dependency of at-RA formation, which can explain the observed effects of at-RA on spinule formation at horizontal cell dendrites in this retina. Furthermore, inhibiting endogenous metabolism and catabolism of at-RA affects formation and persistence of spinules in a way, supporting a direct involvement of at-RA in this light-dependent mechanism of synaptic plasticity. The action of at-RA, however, seems independent of the dopaminergic system, known for its light-signaling role in the retina, because at-RA effects on spinule formation persisted in retina depleted of dopaminergic neurons or in the presence of haloperidol. Together, these data indicate that at-RA acts effectively as a direct neuromodulator in carp retina, transmitting information about ambient light conditions to the neuronal retina.

Animals↗

PubMed1980

Modelling and simulation of vertebrate retina: extended network.

In a recent work (Oğuztöreli, 1980) a mathematical model for studying the neutral activities in a vertebrate retina has been investigated, where the basic retinal network involves interconnected five neurons of different kind. This model is general enough to cover a great variety of neurons in the same retina as well as in the retinas of different species. In the present work we deal with an extension of the basic network considered in (Oğuztöreli, 1980). This extended model contains interconnected twelve neurons: three receptor cells, two horizontal cells, two bipolar cells, two amacrine cells and three ganglion cells. The performance of the model under different conditions, and, the experimental determination of the system parameters are discussed. The background of the modelling and simulations can be found in (Oğuztöreli, 1979, 1980).

Animals↗

PubMed1983

Dynamic properties of cat horizontal cell light responses.

The presented sinewave/squarewave light flicker responses of cat horizontal cells confirm the classification into Hn and Hm-units described by Foerster et al. (1977a,b) Expl Brain Res. 29, 347-385. However, we find somewhat higher order filter properties and develop a refinement of the model proposed by Foerster et al. to explain our new results. Using this model further analysis of Hm-unit responses suggests that cat retinal receptors have a smaller temporal bandwidth the smaller the spatial extent of the stimulus. Finally results from Gaussian white noise (GWN) stimulation are compared with those from classical flicker stimuli and Bode-plots. There are strong similarities in the results of these two types of analysis but some interesting differences are also found and discussed.

Action Potentials↗

PubMed1991

A horizontal stripe of displacement sensitivity in the human visual field.

Displacement thresholds of peripheral sites in monocular human vision were obtained. The average of 12 directional thresholds at different visual field sites was used to define isometric lines of average displacement threshold about central vision. Isometric lines extended further into the temporal visual fields along the horizontal meridian than along other meridians. At any single site in the peripheral visual field the thresholds were not the same in all directions; they were larger toward and away from central vision. These two psychophysical findings vary in a qualitatively similar manner across the retinal field, as does the average size and the collected orientation bias of dendritic fields of retinal ganglion cells.

Fixation, Ocular↗

PubMed2000

Expression of AMPA receptors in rat superior colliculus and effect of orbital enucleation.

We analyzed the distribution and the morphological characteristics of neurons expressing AMPA-type glutamate receptor subunits (GluR1 and GluR2) in the superficial partition (stratum zonale (SZ), stratum griseum superficiale (SGS) and stratum opticum (SO)) of the rat superior colliculus. GluR1-expressing neurons had round or ovoid somata in SGS and round or fusiform somata and primary dendrites extending tangential or horizontal side in SO. On the other hand, GluR2-expressing neurons mainly corresponded to vertical fusiform cells with vertically oriented dendrites in SGS and medium-sized stellate or ovoid cells with many primary dendrites in SO. The results suggest that the expressions of GluR1 and GluR2 are differentially regulated in individual neurons of the superficial partition. To analyze the effect of retinal deafferentation on the expression of the GluRs, we performed unilateral orbital enucleations in rats within a week after birth. Thirty days after retinal lesioning, lower expression of GluR2 mRNA was observed in the neurons of the contralateral side as compared with that of the ipsilateral side in SO, but not in SGS. These results indicate that GluR2 expression in the SO neurons is regulated by the correct afferentation from the retina.

Animals↗

PubMed1999

GABAergic system in the developing mammalian retina: dual sources of GABA at early stages of postnatal development.

In the present work, we have characterized the maturation of the GABAergic system in mammalian retina. Immunoreactivity for GABA, GAD (glutamic acid decarboxylase, EC 4.1.1.15) -65 and -67 in the adult rat retina was localized in cells in the inner nuclear and ganglion cell layers. This pattern was established around postnatal day 8 and included transient GABA and GAD-67 expression in horizontal cells. GAD activity was very low at P1 and P4, increasing after P8, reaching maximal activity by P21 and decreasing to attain adult values by P30. GABA content was approximately constant from P1 to P13, increasing thereafter to reach adult levels. GAD protein content increased progressively with postnatal development and the two isoforms could be distinguished at P8. The disparity between retinal GABA content vs. presence and activity of the synthesizing enzyme, led us to investigate the alternative pathway for GABA synthesis that utilizes putrescine as a substrate. Highest levels of ornithine decarboxylase activity (the limiting step for putrescine synthesis) were found between P1 and P4, decreasing to very low levels after P13. The same pattern was observed for putrescine content in the retina. Highest amounts were found at P1, that decreased and remained constant after P13. Additionally, approximately 40% of tritiated putrescine incorporated by P1, P4 and adult retinas was converted into GABA. Our results suggest the existence of two different sources of GABA in mammalian retina, one that uses glutamate as a precursor and predominates in the mature nervous system and another that utilizes putrescine and is present transiently at early developmental stages.

Animals↗