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PubMed1999

The nondiscriminating zone of directionally selective retinal ganglion cells: comparison with dendritic structure and implications for mechanism.

We have studied, at high resolution, the sizes and pattern of dendrites of directionally selective retinal ganglion cells in the rabbit. The dendrites had a distinctive pattern of branching. The major dendritic trunks were relatively thick, beginning at approximately 1 micrometer and tapering to approximately 0.5 micrometer in diameter. Higher order dendrites exiting from them generally stepped abruptly to a diameter of 0.4-0.6 micrometer, which they maintained throughout their length. Recording confirmed the existence of a zone within the receptive field, usually occupying 20-25% of its area, where direction of movement was only weakly discriminated. The dendritic arbors of cells, injected with Lucifer yellow after recording, revealed no difference in dendritic structure between the discriminating and nondiscriminating zones. The nondiscriminating zone was located on the preferred side of the receptive field (the side from which movement in the preferred direction originates). This is consistent with a mechanism of direction selectivity based on inhibition generated by movement in the null direction but not with feedforward excitation, as occurs in flies and is postulated in some models of mammalian direction selectivity.

Animals↗
PubMed1990

Morphological recovery of axotomized goldfish retinal ganglion cells in an environment known to prevent retinotopic refinement of their regenerated tectal arbors.

Axonal injury provokes well-characterized morphological changes in goldfish retinal ganglion cells. These reach a peak as the regenerating axons restore a grossly retinotopic projection map to the tectum, and then regress as the map is refined by a mechanism involving locally-correlated activity. The aim of this study was to look for any interdependence between morphological recovery and retinotopic refinement. Stroboscopic light was used to keep regenerated optic arbors in non-retinotopic locations for 70 days after optic nerve cut and lens ablation. Controls were kept in constant or diurnal light, both of which allow refinement of the retinotectal map. Nucleolar frequency, perikaryal area and nuclear area were used as indices of neuronal recovery, and ganglion cell counts were performed. After 35 days in diurnal light, the nucleoli of axotomized cells had increased in size, prominence and number, and both nucleus and cytoplasm had roughly doubled in area. After 70 days, these features had almost returned to normal not only in diurnal and constant light but in stroboscopic light as well. A small but significant cell loss, averaging 13.4-14.7%, was seen after optic nerve cut and lens ablation regardless of stage in regeneration (35 or 70 days) or lighting. Evidently, morphological recovery is independent of retinotopic refinement, which is known to be no further advanced after 70 days in stroboscopic light than after 35 days in diurnal light.

Animals↗
PubMed1995

Development and regulation of dendritic stratification in retinal ganglion cells by glutamate-mediated afferent activity.

In the mature retina, the dendrites of retinal ganglion cells (RGCs) are segregated into either ON or OFF sublaminae of the inner plexiform layer (IPL), but early in development the dendritic processes of these cells are multistratified, ramifying throughout the IPL. We examined the time course of dendritic stratification in developing beta cells, the largest class of ganglion cells in the cat retina, by retrograde labeling of fixed tissue with Dil. Dendritic stratification begins in the central and peripheral retina by embryonic day 50, about 2 weeks before birth and is not fully completed until 5 months postnatally. A clear central-to-peripheral gradient in the incidence of stratified beta cells first becomes evident shortly after birth. This stratification process was effectively halted by short-term intraocular injections (4-11 d) of the glutamate analog 2-amino-4-phosphonobutyrate (APB), which hyperpolarizes rod bipolar cells and ON cone bipolar cells, thereby preventing the release of glutamate by these interneurons. APB treatment did not alter the somal sizes or the tangential extent of the dendrites of developing beta cells, nor did it cause abnormal loss of these neurons. The organization of the inner nuclear layer, containing the APB-sensitive bipolar cells, was also not compromised by such injections. When APB treatment was discontinued there was a rapid resumption of dendritic stratification resulting in a normal incidence of stratified RGCs. Thus, short-term APB treatment causes a delay rather than a permanent arrest of the stratification process.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1990

Target dependence of chick retinal ganglion cells during embryogenesis: cell survival and dendritic development.

The survival of retinal ganglion cells and the dendritic development were investigated a) in normal chick embryos, b) in embryos whose primordial optic lobes and adjacent areas were removed (target reduced embryos), and c) in embryos whose optic nerves were transected (target deprived embryos) in order to study the influences of central targets on developing ganglion cells. The ganglion cells were stained postmortem with the carbocyanine dye DiI. Cell body and dendritic field diameters were measured in whole-mounted retinae before and after the period of cell death at embryonic day 10 (E10) and E16. The cell densities within the ganglion cell layer were counted in cresyl violet/thionine stained retinae. The central retinal projection in target reduced embryos was studied with the anterogradely transported fluorescent marker rhodamine-B-isothiocyanate (RITC). In normal embryos, the earliest dendritic processes were observed at E6 in the central retina, whereas at E10 elaborate dendritic branching was found across the retina. Different morphological types of ganglion cells could be identified at E16. In both, target reduced embryos and target deprived embryos, the initial dendritic growth and pattern of ramification were indistinguishable from those of normal embryos up to E10. Cell body diameters, dendritic tree diameters, and cell densities were not significantly different. At the end of the naturally occurring cell death period (E16), the ganglion cell density was strongly reduced in both experimental groups compared to controls. In particular, when the optic nerve was transected, it resulted in the almost complete degeneration of ganglion cells. In target reduced embryos, a small population (about 5% of the normal number) of ganglion cells survived. The proportion of large cells was increased within the total population compared to normal retinae. Displaced ganglion cells were not affected by partial target removal but strongly affected by transection of the optic nerve. Anterograde labelling from the retina revealed that in target reduced embryos the remaining ganglion cells innervated non-tectal primary visual nuclei. The present results suggest the following: a) Before the onset of the cell death period, the growth and ramification of ganglion cell dendrites occur independently of central visual targets. b) In target reduced embryos, a small population of ganglion cells survives, namely, those cells that project to remaining central areas. Complete disconnection from central targets by transecting the optic nerve leads to the degeneration of almost all ganglion cells. c) The surviving ganglion cell population consists mainly of large ganglion cells.

Animals↗
PubMed1985

Formation of retinotopic connections: selective stabilization by an activity-dependent mechanism.

During regeneration of the optic nerve in goldfish, the ingrowing retinal fibers successfully seek out their correct places in the overall retinotopic projection on the tectum. Chemospecific cell-surface interactions appear to be sufficient to organize only a crude retinotopic map on the tectum during regeneration. Precise retinotopic ordering appears to be achieved via an activity-dependent stabilization of appropriate synapses and is based upon the correlated activity of neighboring ganglion cells of the same receptive-field type in the retina. Four treatments have been found to block the sharpening process: (a) blocking the activity of the ganglion cells with intraocular tetrodotoxin (TTX), (b) rearing in total darkness, (c) correlating the activation of all ganglion cells via stroboscopic illumination and (d) blocking retinotectal synaptic transmission with alpha-bungarotoxin (alphaBTX). These experiments support a role for correlated visually driven activity in sharpening the diffuse projection and suggest that this correlated activity interacts within the postsynaptic cells, probably through the summation of excitatory postsynaptic potentials (EPSPs). Other experiments support the concept that effective synapses are stabilized: a local postsynaptic block of transmission causes a local disruption in the retinotectal map. The changes that occur during this disruption suggest that each arbor can move to maximize its synaptic efficacy. In development, initial retinotectal projections are often diffuse and may undergo a similar activity-dependent sharpening. Indirect retinotectal maps, as well as auditory maps, appear to be brought into register with the direct retinotopic projections by promoting the convergence of contacts with correlated activity. A similar mechanism may drive both the formation of ocular dominance patches in fish tectum and kitten visual cortex and the segregation of different receptive-field types in the lateral geniculate nucleus. Activity-dependent synaptic stabilization may therefore be a general mechanism whereby the diffuse projections of early development are brought to the precise, mature level of organization.

Animals↗
PubMed1988

Dendritic growth and remodeling of cat retinal ganglion cells during fetal and postnatal development.

We have studied the development of retinal ganglion cell morphology in the cat's visual system from early fetal to postnatal times. In particular, we have examined the contribution of growth and remodeling to the establishment of mature retinal ganglion cell form. Ganglion cells were identified by retrograde labeling with rhodamine latex microspheres deposited in the superior colliculus and lateral geniculate nucleus between embryonic day 34 (E34; birth = E65) and adulthood. To reveal the fine morphological details of retrogradely labeled ganglion cells, 48 hr later Lucifer yellow was injected intracellularly in living retinae that had been dissected and maintained in vitro. Our results show that at E35-37 the majority of ganglion cells are very simple in morphology, with a few dendritic processes that are generally aligned in a radial direction towards or away from the optic disc. During the ensuing 2 week period, there is a progressive growth and elaboration of dendrites. By E50, some ganglion cells resembling the adult alpha, beta, and gamma classes can be identified based on comparisons of the appearance and dimensions of their dendritic trees and somata with neighboring filled cells. However, ganglion cell dendrites and axons at this age express several transient morphological features. The axons of ganglion cells give rise to delicate processes originating from the intraretinal portion of the axon, including side branches, present in about half of the cells, and occasionally bifurcations that give rise to axon collaterals. These transient axonal features are present throughout development, including the neonatal period; no axon collaterals were observed after postnatal day 15, while axonal side branches persisted even at P31 but were gone by adulthood. Ganglion cell dendrites exhibit excessive branches and exuberant somatic and dendritic spines. Quantitative analysis of these processes shows that after E45 dendritic trees increase dramatically in complexity, reaching the peak number of spines and branch points by the first week of postnatal life. The number of dendritic processes then falls abruptly to reach near-adult levels by the end of the first postnatal month. Even though dendritic morphology closely resembles that seen in the adult at this age, ganglion cell bodies and dendrites must continue to grow to reach their adult size.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Competitive interactions between retinal ganglion cells during prenatal development.

In the mammalian visual system, retinal ganglion cell axons terminate within the LGN in a series of alternating eye-specific layers. These layers are not present initially during development. In the cat they emerge secondarily following a prenatal period in which originally intermixed inputs from the two eyes gradually segregate from each other to give rise to the characteristic set of layers by birth. Many lines of evidence suggest that activity-dependent competitive interactions between ganglion cell axons from the two eyes for LGN neurons play an important role in the final patterning of retinogeniculate connections. Studies of the branching patterns of individual ganglion cell axons suggest that during the period when inputs from the two eyes are intermixed, axons from one eye send side branches into territory later occupied exclusively by axons from the other eye. Ultrastructural studies indicate that these branches in fact are sites of synaptic contacts, which are later eliminated since the side branches disappear as axons form their mature terminal arbors in appropriate territory. In vitro microelectrode recordings from LGN neurons indicate that they can receive convergent synaptic excitation from electrical stimulation of the optic nerves before but not after the eye-specific layers form, suggesting that at least some of the synaptic contacts seen at the ultrastructural level are functional. Finally, experiments in which tetrodotoxin was infused intracranially during the two week period during which the eye-specific layers normally form demonstrate that it is possible to prevent, or at least delay, the formation of the layers. Accordingly, individual axons fail to develop their restricted terminal arbor branching pattern and instead branch widely throughout the LGN. These results indicate that all of the machinery necessary for synaptic function and competition is present during fetal life. Moreover, it is highly likely that neuronal activity is required for the formation of the eye-specific layers. If so, then activity would have to be present in the form of spontaneously generated action potentials, since vision is not possible at these early ages. Thus, the functioning of the retinogeniculate system many weeks before it is put to the use for which it is ultimately designed may contribute to the final patterning of connections present in the adult.

Animals↗
PubMed1988

Retinotopically inappropriate synapses of subnormal density formed by surgically misdirected optic fibers in goldfish tectum.

Selected optic fibers were surgically deflected from one tectum onto the opposite host tectum which was denervated by eye enucleation. At 6-8 months, deflected fibers were labeled with horseradish peroxidase and the retinotopically inappropriate part of tectum was examined using electron microscopy. Numerous (labeled) optic synapses were found in the primary optic innervation layer of the 'wrong' part of tectum but they were about half the normal density. The number and density of non-optic synapses was not found to be affected. These findings indicate optic fibers compete with each other but not with non-optic fibers for synaptic sites in tectum.

Animals↗
PubMed1988

Afferent input for target survival in marsupial visual development.

The influence of afferent input on the survival of target neurons in mammals has been examined by the removal of one eye of pouch young of the marsupial native cat (Dasyurus hallucatus). The ages at eye removal spanned the period of neurogenesis of the ascending visual pathway, and were earlier than the time of maximal axon number in the optic nerve. Autoradiography following the injection of tritiated proline into the intact eye of adult animals shows that the lateral geniculate nucleus contralateral to the injected eye of the earliest enucleates retains its laminated structure, despite the total absence of binocular competition throughout development. However, we find a dramatic, age-related reduction in the volume of those parts of the lateral geniculate nucleus and superior colliculus which would normally receive a contralateral-only projection from the enucleated eye. The effects of the enucleation are not restricted to the primary termination sites of the optic axons but ramify throughout a large part of the neo- and archicortex.

Age Factors↗
PubMed1996

Quantitative analysis of triphasic (H3) horizontal cell-cone connectivity in the cyprinid fish (roach) retina.

Although horizontal cells encode chromatic information by means of a variety of spectrally opponent light-evoked response patterns, their synaptic connections with the different spectral classes of cone are not completely understood. In the cyprinid fish retina, where a hierarchical set of interactions between horizontal cells and cone types has been proposed, a particular type of horizontal cell generates light-evoked triphasic (red-hyperpolarizing/green depolarizing/blue-hyperpolarizing) responses. In the present study, we have studied the cone connectivity of these cells by intracellular recording and staining in the roach retina. The horizontal cells were first identified electrophysiologically using spectral stimuli, and then stained intracellularly with horseradish peroxidase. Light microscopy revealed that the cells had consistent H3-like morphologies. At an ultrastructural level, these horizontal cells were deduced to contact selectively blue-sensitive cones. Within the cone pedicles, the majority (approximately 80%) of the contacts were "central" to synaptic ribbons. Some 50% of the "lateral" processes were large and engulfed cone cytoplasm. Spinules were present within the contacted pedicles but not upon the dendrites of the stained horizontal cells, although previous work had suggested that horseradish peroxidase would not interfere with spinule dynamics. The results are discussed in terms of existing modes of horizontal cell-cone connectivity in cyprinid fish retinae.

Animals↗
PubMedDate not supplied

Rearing in different photic and chromatic environments modifies spectral responses of cone horizontal cells in adult fish retina.

We investigated chromatic processing in the outer retina of the cichlid fish Aequidens pulcher. Intracellular recordings from cone-specific horizontal cells (CHCs) revealed that the two morphologically identified types (H1 and H2) also have different spectral responses. H1-L cells hyperpolarize to all wavelengths ("luminosity"). H2-Cb cells depolarize to long wavelengths and hyperpolarize to short wavelengths ("chromaticity", biphasic). Furthermore, we verified by immunocytochemistry that H2-Cb cells of A. pulcher predominantly contact the middle-wavelength-sensitive (MWS) members of double cones. Developmental plasticity in the cone-CHC networks was induced by rearing fish under conditions of spectral deprivation and different levels of white light. H1-L spectral responses were unaffected by the rearing conditions. Different intensity levels of white light and deprivation of long wavelengths during rearing both induced changes in the spectral responses of H2-Cb. Deprivation of short and middle wavelengths had no effect. Our results indicate that spectral processing in the outer retina of fishes can be modulated in response to different visual experiences and suggest that developmental fine tuning of the color-vision system occurs at early levels of visual processing.

Adaptation, Physiological↗
PubMedDate not supplied

Effect of impulse blockage on cytochrome oxidase activity in monkey visual system.

Cytochrome oxidase (cytochrome c oxidase; ferrocytochrome c: oxygen oxidoreductase, EC 1.9.2.1) has been introduced as an oxidative metabolic marker for neurones in the central nervous system. Previous studies have shown that mature neurones remained sensitive to altered functional demands, and that both developing and adult neurones responded to sensory deprivation or deafferentation by reducing their cytochrome oxidase (Cyt. Ox.) activity. More recently, we showed that the blockage of retinal impulse transmission with tetrodotoxin led to a reversible reduction in Cyt. Ox. staining of affected lateral geniculate (LGN) and striate neurones in adult cats. The present study sought to extend these findings to adult monkeys, where Cyt. Ox. 'puffs' or 'blobs' are uniquely present in the visual cortex. We found that, while the retina remained histologically intact, with only moderate decreases in Cyt. Ox. staining of large ganglion cells and the two plexiform layers, subtle changes occurred in the LGN as early as 1 day post-tetrodotoxin injection, and clear reduction in enzyme levels was evident in both the LGN and the visual cortex by 3 days. Changes became progressively more severe up to 4 weeks post-injection. Within area 17, alternating bands of high and low Cyt. Ox. staining occurred in lamina IV, with alternating rows of dark and lightly reactive puffs superimposed in exact register. Thus, the mature visual neurones in the primate remain extremely sensitive to the cessation of retinal impulse transmission, and plastic metabolic changes occur through several synapses along the sensory pathway.

Animals↗
PubMed1978

An improved electrode for electroretinography: design and standardization.

An electrode for electroretinography was developed that fits over the patient's lower lid. The electrode incorporates a platinum strip embedded in a piece of shaped plexiglass. The electrode was standardized for clinical use by comparing ERG recordings from this platinum lid electrode with those recorded from a Burian-Allen electrode. The a- and b-wave implicit times and amplitudes were measured in four subjects, using both electrodes under varying luminance conditions, to provide a measure of the validity of the platinum lid electrode. The same experimental procedure was repeated five times on two individuals to provide a measure of the reliability of both electrodes. Results indicate amplitudes approximately 65% of those recorded with a Burian-Allen electrode but which are otherwise in good agreement.

Electrodes↗
PubMed1994

Cones contribute to light-evoked, dopamine-mediated uncoupling of horizontal cells in the mudpuppy retina.

1. The relative effectiveness of adapting lights of different wave-lengths on uncoupling of horizontal cells was measured in dark-adapted mudpuppy retinas. Diffuse blue (470 nm) or red (620 nm) adapting stimuli were adjusted in intensity to be equally effective for rods or for cones. Uncoupling of horizontal cells was measured by intracellular recording of changes in their responses to spot and annulus stimuli. The intensities of the adapting light pairs were varied over 3 log units. The responses of the horizontal cells indicated that both rods and cones were stimulated by the adapting lights. 2. Relatively dim adapting lights did not produce detectable changes in horizontal cell coupling. Brighter adapting lights caused uncoupling of horizontal cells. When the brighter adapting lights were rod matched, the uncoupling effect of the 620-nm light was significantly greater than that of the 470 nm light, indicating that cones contribute to the uncoupling effect. 3. When the adapting lights were cone matched, the effects of the two wavelengths were not significantly different, but this did not rule out a rod contribution because the effective adapting lights probably produced maximal or nearly maximal, and hence equal or nearly equal, responses in rods. 4. The results indicate that cones contribute to the light-evoked uncoupling of horizontal cells in mudpuppy, although a contribution from rods could not be ruled out. Because it was shown previously that light-evoked uncoupling of horizontal cells in mudpuppy is mediated by dopamine, the results also suggest that cones contribute to the light-evoked release of dopamine.

Adaptation, Ocular↗
PubMed2005

Multiple receptors coupled to phospholipase C gate long-term depression in visual cortex.

Long-term depression (LTD) in sensory cortices depends on the activation of NMDA receptors. Here, we report that in visual cortical slices, the induction of LTD (but not long-term potentiation) also requires the activation of receptors coupled to the phospholipase C (PLC) pathway. Using immunolesions in combination with agonists and antagonists, we selectively manipulated the activation of alpha1 adrenergic, M1 muscarinic, and mGluR5 glutamatergic receptors. Inactivation of these PLC-coupled receptors prevents the induction of LTD, but only when the three receptors were inactivated together. LTD is fully restored by activating any one of them or by supplying intracellular D-myo-inositol-1,4,5-triphosphate (IP3). LTD was also impaired by intracellular application of PLC or IP3 receptor blockers, and it was absent in mice lacking PLCbeta1, the predominant PLC isoform in the forebrain. We propose that visual cortical LTD requires a minimum of PLC activity that can be supplied independently by at least three neurotransmitter systems. This essential requirement places PLC-linked receptors in a unique position to control the induction of LTD and provides a mechanism for gating visual cortical plasticity via extra-retinal inputs in the intact organism.

Animals↗
PubMed2003

Retarded outer segment development in TrkB knockout mouse retina organ culture.

PURPOSE: To determine the effects of trkB deficiency in the mouse retina on photoreceptor development and retinal organization, in the absence of confounding systemic effects. METHODS: Newborn mice that carried two null trkB alleles (trkB-/-) and their wild type (WT) littermates were used for retinal organ cultures. On Day 21, rod development was assessed histologically in plastic sections (outer segment length) and retinal organization was analyzed using retinal cell-type specific antibodies. Anatomical data obtained from the organ cultures were compared to previously published histological results from in vivo data. RESULTS: (1) Rod outer segment length was significantly shorter in retinas from trkB-/- mice in the presence of normal numbers of rods. (2) No dopaminergic amacrine cells were observed in the knockout retina. (3) Unlike in the in vivo condition, recoverin-positive OFF-cone bipolar cells were present in trkB-/- retinas grown in culture. CONCLUSIONS: (1) These results demonstrate that rod outer segment development is compromised in the absence of trkB in the retina. (2) This study further supports our previous conclusion that the elimination of trkB expression alters rod development, because the presence of trkB receptors within the retina is essential for normal rod maturation and not because of confounding systemic effects. (3) More generally, this study stresses the importance of investigating complex phenotypes in gene knockout mice under conditions that isolate the organ under investigation from unrelated systemic variations.

Animals↗