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R D Lund

Publications and source records attributed to R D Lund.

At least 37 records · Page 2Linked to original sources
PubMed2001

Graft location affects functional rescue following RPE cell transplantation in the RCS rat.

Photoreceptor (PRC) rescue in the dystrophic Royal College of Surgeons (RCS) rat has been well documented following a variety of interventions. Although the dystrophic process is asymmetric with respect to the horizontal meridian, little attention has been paid to the effect of topographic position on treatment outcome. In this study, RPE cells from adult congenic nondystrophic animals were injected into the subretinal space of 1-month-old dystrophic RCS rats in either the dorsal or the ventral equatorial region. Animals were followed longitudinally during the degenerative process using the pupillary light reflex (PLR). The parameter of the PLR most sensitive to PRC rescue is latency at low light levels. At 3 months of age this parameter showed statistically better performance (ANOVA, P = 0.016) for eyes with grafts placed dorsally compared to those placed ventrally or untreated controls. There was no treatment effect on amplitude. By 6 months of age the dorsal/ventral disparity in latency was less apparent and amplitude remained equivalent across groups. Late analysis of retinal whole-mounts using RT-97 fluorescent labeling showed extensive irregularities in ventral axonal morphology in all treatment groups. These results indicate that functional rescue of the RCS retina is significantly influenced by the local degenerative timetable. The role of initial local conditions on treatment outcome is worthy of consideration in other models of neuroprotection.

Analysis of Variance↗
PubMed2001

Progressive visual sensitivity loss in the Royal College of Surgeons rat: perimetric study in the superior colliculus.

The Royal College of Surgeons rat has a retinal pigment epithelial cell defect which causes a progressive loss of rods occurring primarily over the first few months of life. We have studied the consequences of this degenerative process on visual sensitivity across the visual field. Sensitivities were determined in the superior colliculus for unit responses recorded from 22 days up to one year of age from sites encompassing the whole visual field representation. Following visual sensitivity assessment, retinae were examined anatomically at the light and electron microscopic level. At 22 days of age, sensitivities in dystrophic rats were comparable to those of non-dystrophics at any age (40+/-1 and 41+/-1dB, respectively), despite the fact that signs of degenerative events were clear at the electron microscopic level, including presence of pyknotic photoreceptor nuclei, disorganised outer segments and accumulation of debris. However, loss in sensitivity was first detected only at 28-36 days of age (27+/-4dB). From then on, sensitivities progressively decreased to reach a plateau by 180-240 days (4+/-2dB). Starting around 90 days and onward, there was a positive gradient of sensitivities from temporal to nasal field. Drops in visual sensitivity were parallelled by several changes in visual response properties, including prolonged latency, inconsistent responsiveness, appearance of bursting spontaneous activity and activation of units by stimuli presented outside their classical receptive fields. The measure of visual sensitivities by recording visual responses at specific sites in the superior colliculus provides a reliable point-to-point assessment of retinal function comparable to visual perimetry testing in humans. This experimental approach provides the background for answering questions arising during the development of potential experimental therapies for retinal degeneration using animal models like the Royal College of Surgeons rat.

Animals↗
PubMed2001

Basal increase in c-Fos-like expression in superior colliculus of Royal College of Surgeons dystrophic rats can be abolished by intraocular injection of tetrodotoxin.

In normal rats maintained in the dark, very few cells in the primary visual centers, including the superior colliculus, show Fos-like immunoreactivity. By contrast, in rats presented with flashing lights many Fos-like immunoreactivity cells are observed distributed throughout the visual centers. In the dystrophic Royal College of Surgeons rat, in which there is major loss of photoreceptors over the first 3 months of life, similar numbers of Fos-like immunoreactivity cells are seen on light presentation, but in marked contrast, cell densities in the rats maintained in the dark are many times higher than in non-dystrophic rats maintained under similar conditions. Here we show that this elevated dark response can be abolished by intravitreal injection of the sodium channel blocker tetrodotoxin, indicating that this effect results from changed retinal activity, rather than being centrally generated. We suggest that since Fos-like immunoreactivity is not usually elicited by steady state conditions, the elevated levels in the superior colliculus in these animals reflect the return of waves of activity, first seen in development coursing across the retina, but lost with photoreceptor maturation.

Action Potentials↗
PubMed2001

Cell transplantation as a treatment for retinal disease.

It has been shown that photoreceptor degeneration can be limited in experimental animals by transplantation of fresh RPE to the subretinal space. There is also evidence that retinal cell transplants can be used to reconstruct retinal circuitry in dystrophic animals. Here we describe and review recent developments that highlight the necessary steps that should be taken prior to embarking on clinical trials in humans.

Animals↗
PubMed2000

Selective innervation of retinorecipient brainstem nuclei by retinal ganglion cell axons regenerating through peripheral nerve grafts in adult rats.

The pattern of axonal regeneration, specificity of reinnervation, and terminal arborization in the brainstem by axotomized retinal ganglion cell axons was studied in rats with peripheral nerve grafts linking the retina with ipsilateral regions of the brainstem, including dorsal and lateral aspects of the diencephalon and lateral aspect of the superior colliculus. Four to 13 months later, regenerated retinal projections were traced using intraocular injection of cholera toxin B subunit. In approximately one-third of the animals, regenerated retinal axons extended into the brainstem for distances of up to 6 mm. Although axons followed different patterns of ingrowth depending on their site of entry to the brainstem, within the pretectum, they innervated preferentially the nucleus of the optic tract and the olivary pretectal nucleus in which they formed two types of terminal arbors. Within the superior colliculus, axons extended laterally and formed a different terminal arbor type within the stratum griseum superficiale. In the remaining two-thirds of the animals, retinal fibers formed a neuroma-like structure at the site of entry into the brainstem, or a few fibers extended for very short distances within the neighboring neuropil. These experiments suggest that regenerated retinal axons are capable of a highly selective reinnervation pattern within adult denervated retinorecipient nuclei in which they form well defined terminal arbors that may persist for long periods of time. In addition, these studies provide the anatomical correlate for our previous functional study on the re-establishment of the pupillary light reflex in this experimental paradigm.

Age Factors↗
PubMed2000

Schwann cell grafting into the retina of the dystrophic RCS rat limits functional deterioration. Royal College of Surgeons.

PURPOSE: To examine whether congenic Schwann cells grafted into the subretinal space of dystrophic Royal College of Surgeons (RCS) rats can prevent photoreceptor loss and maintain visual function. METHODS: Purified neonatal Schwann cells derived from congenic rats were grafted into the subretinal space of 3- to 4-week-old dystrophic RCS rats. Graft placement was confirmed using Schwann cells labeled in vitro with the fluorescent dye Hoechst 33342 or in grafted eyes processed for electron microscopy (48-hour to 1-month survival). At longer intervals, up to 9 months after surgery, animals were examined for photoreceptor survival; preservation of a visual reflex, head-tracking to moving stripes; and preservation of visual receptive fields associated with the region of graft placement. RESULTS: One week after the graft was performed, Schwann cells had integrated into the subretinal space with little evidence of a reactive response. When screened for head-tracking to moving stripes, Schwann cell-grafted animals performed better than sham-treated or control dystrophic animals. Threshold sensitivity measurements and visual field assessment made by recording from the superior colliculus also showed a significant level of preserved function compared with control animals. Functional rescue was correlated with photoreceptor survival and could be observed for at least 9 months after grafting. CONCLUSIONS: Schwann cells injected into the subretinal space limit functional deterioration and prolong photoreceptor survival. It is suggested that they act by local release of growth factors that either support photoreceptors directly and/or stimulate phagocytosis in RPE cells.

Animals↗
PubMed2000

Progressive optic axon dystrophy and vacuslar changes in rd mice.

PURPOSE: To examine how the vascular plexuses in the rd mouse retina are affected by the loss of photoreceptors and how this compares with the Royal College of Surgeons (RCS) rat. To examine whether the profound effects of vascular pathology on retinal ganglion cells (RGCs) and their axons seen in RCS rats are also found in rd mice. METHODS: Vascular patterns were studied in flatmounted and sectioned retinas using either nicotinamide adenine dinucleotide phosphate(NADPH)-diaphorase histochemistry or vessel filling with horseradish peroxidase. Optic axons were visualized using RT97 (an antibody against the 200-kDa neurofilament subunit), and RGCs were labeled by retrograde transport of fluorescence label, the Fluorogold, applied to the superior colliculus. RESULTS: The present study showed that in the rd mouse, similar to the RCS rat, vascular complexes developed in association with retinal pigment epithelial cells at the outer border of the retina. The number and distribution of complexes were very different from the rat, but as in the rat, progressive axonal dystrophy was seen in the optic fiber layer. RGC loss, rather than being local was more broadly distributed, but some, at least, appeared to be secondary to axonal dystrophy caused by vessels supplying vascular formation. CONCLUSIONS: Photoreceptor loss in the rd mouse leads to RGC axonal dystrophy and loss. The lesser degree and different distribution of RGC loss caused by abnormal vasculature associated with vascular formations in the outer retina in the rd mouse may be due to the early atrophy of the deep vascular plexus in this animal.

Animals↗
PubMed2000

Sensory capacity of the royal college of surgeons rat.

PURPOSE: To apply noninvasive tests for examining visual and other sensory functions of pigmented Royal College of Surgeons (RCS) rats compared with pigmented and albino control animals. METHODS: Rats aged 3 and 7 months were tested with a general neurologic examination that assessed visual, auditory, tactile, and whisker displacement responses. Photophobic responses and visual discrimination were also measured. RESULTS: Dystrophic RCS rats failed the visual presentation tests, even at 3 months of age, and showed diminished performance on tactile tests. Auditory and whisker displacement performances were normal. Albino rats also showed diminished performance on the visual test, particularly to stimuli presented in the upper visual field. Photophobic responses were diminished in the dystrophic RCS rats compared with the pigmented control animals. Albino animals showed heightened photophobia. The dystrophic rats failed to reach criterion levels of performance on the visual discrimination test even with gratings of 0.045 cyc/deg. CONCLUSIONS: The tests used discriminate deteriorated complex visual functions in RCS rats at ages when some simple reflexes can still be demonstrated. As such, they provide easily executed tests for screening for the effects of reparative treatments such as transplantation, administration of growth factors, and gene transfer technology. The integrity of whisker and auditory function are important when using tests requiring polysensory inputs. The somatosensory defect is surprising but may be useful in searching for the gene locus of the retinal disorder. The aberrations seen in the albino rats may be attributable to the effects of light damage and unfiltered light.

Animals↗
PubMed1999

Effects of neurotrophins on embryonic retinal outgrowth.

The neurotrophins brain derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3) and neurotrophin 4 (NT-4), as well as their receptors, are expressed in both the developing and adult visual system. In vitro and in vivo studies suggest that BDNF in particular can enhance the survival of developing and injured retinal ganglion cells. We have previously shown that BDNF secreted by transgenic fibroblasts promotes outgrowth from embryonic retinae when cotransplanted into the cerebral cortex. The roles of NT-3 and NT-4 were investigated in this system along with BDNF, on retinal neuronal outgrowth, both on in vivo retinal transplants and on in vitro retinal explant cultures. Our results confirm that BDNF promotes retinal outgrowth of embryonic retinae both in vivo, and in vitro. NT4 was shown only to promote retinal outgrowth in vitro in the presence of proliferating glia. NT-3 was shown to have no effect on embryonic retinal outgrowth in vivo or in vitro. While other molecules have been proposed to play a role, the present results, together with evidence for BDNF in the developing superior colliculus and receptors on retinal cells, argue for an important role for BDNF in normal retinal neuronal outgrowth, with NT-4 playing a secondary role.

3T3 Cells↗
PubMed1999

Photoreceptor layer reconstruction in a rodent model of retinal degeneration.

We have examined the potential of retinal cell transplantation to dystrophic retinal degeneration mice as a way of replacing photoreceptors lost because of an intrinsic genetic defect. Early postnatal retinae which had been gently dissociated survived for at least 6 weeks after transplantation to the subretinal space. Over a significant area of distribution, transplanted cells formed outer segments which lay in close apposition to the host retinal pigment epithelial cell layer. The grafts integrated with the remaining host retina, sufficient at least to mediate a simple light-dark preference. A new synaptic layer was seen at the graft-host interface, which contained substantial numbers of photoreceptor synapses. This and the fact that the behavior could be elicited at low luminance levels argue for functional circuit reconstruction between grafted cells and host retina.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1999

Receptive field properties of single neurons in rat primary visual cortex.

The rat is used widely to study various aspects of vision including developmental events and numerous pathologies, but surprisingly little is known about the functional properties of single neurons in the rat primary visual cortex (V1). These were investigated in the anesthetized (Hypnorm-Hypnovel), paralyzed animal by presenting gratings of different orientations, spatial and temporal frequencies, dimensions, and contrasts. Stimulus presentation and data collection were automated. Most neurons (190/205) showed sharply tuned (</=30 degrees bandwidth at half height) orientation selectivity with a bias for horizontal stimuli (31%). Analysis of response modulation of oriented cells showed a bimodal distribution consistent with the distinction between simple and complex cell types. Orientation specific interactions occurred between the center and the periphery of receptive fields, usually resulting in strong inhibition to center stimulation when both stimuli had the same orientation. There was no evidence for orientation columns nor for orderly change in optimal orientation with tangential tracks through V1. Responses were elicited by spatial frequencies ranging from zero (no grating) to 1.2 cycle/degree (c/ degrees ), peaking at 0.1 c/ degrees, and with a modal cutoff of 0.6 c/ degrees. Half of the neurons responded optimally to drifting gratings rather than flashing uniform field stimuli. Directional preference was seen for 59% of oriented units at all depths in the cortex. Optimal stimuli velocities varied from 10 to 250 degrees /s. Some units, mainly confined to layer 4, responded to velocities as high as 700 degrees /s. Response versus contrast curves (best fit with Naka-Rushton) varied from nearly linear to extremely steep (mean contrast semisaturation 50% and threshold 6%). There was a trend for cells from superficial layers to be more selective to different stimulus parameters than deeper layers cells. We conclude that neurons in rat V1 have complex and diverse visual properties, necessary for precise visual form perception with low spatial resolution.

Animals↗
PubMed1998

Anatomical comparison of the macaque and marsupial visual cortex: common features that may reflect retention of essential cortical elements.

This study identifies fundamental anatomical features of primary visual cortex, area V1 of macaque monkey cerebral cortex, i.e., features that are present in area V1 of phylogenetically distant mammals of quite different lifestyle and features that are common to other regions of cortex. We compared anatomical constituents of macaque V1 with V1 of members of the two principal marsupial lines, the dunnart and the quokka, that diverged from the eutherian mammalian line over 135 million years ago. Features of V1 common to both macaque and marsupials were then compared with anatomical features we have previously described for macaque prefrontal cortex. Despite large differences in overall area and thickness of V1 cortex between these animals, the absolute size of pyramidal neurons is remarkably similar, as are their specific dendritic branch patterns and patterns of distribution of intrinsic axons. Pyramidal neuron patchy connections exist in the supragranular V1 in both the marsupial quokka and macaque as well as in macaque prefrontal cortex. Several specific types of aspinous interneurons are common to area V1 in both marsupial and macaque and are also present in macaque prefrontal cortex. Spiny stellate cells are a common feature of the thalamic-recipient, mid-depth lamina 4 of V1 in all three species. Because these similarities exist despite the very different lifestyles and evolutionary histories of the animals compared, this finding argues for a highly conserved framework of cellular detail in macaque primary visual cortex rather than convergent evolution of these features.

Anatomy, Artistic↗
PubMed1998

The retinal ganglion cells that drive the pupilloconstrictor response in rats.

It is well established that the pupillary light reflex (PLR) in rats is mediated by a direct retinal projection to the olivary pretectal nucleus (OPN). Although several authors have commented on the specific subpopulation of retinal ganglion cells (RGC) that project to the rat pretectum, much of this evidence is circumstantial, and depends mostly upon electrophysiological data (e.g., conduction velocity). Here, we have used microinjections of Fluoro-Gold into the OPN (pretectum and superior colliculus as controls) to retrogradely label RGCs projecting to this region. The retinae were whole-mounted, viewed under fluorescence, and the regional distribution pattern, laterality of projection, and cell soma sizes determined. The results show OPN injections label a small subpopulation of RGCs. In the contralateral retinae, labeled RGCs were most numerous and widespread, with 97% projecting to the contralateral pretectum. The highest density of cells in the contralateral retinae was found in the inferior and nasal retinal quadrants. In the ipsilateral retinae, the small number of labeled cells were concentrated in the periphery of the inferior and nasal retinal quadrants. A striking feature of both ipsilateral and contralateral retinae was the paucity of labeled cells found in the dorsal hemiretina (lower visual field). Cell size measurements indicate 90-95% of labeled RGCs had diameters of 9-13 microm, while most of the remaining cells had diameters of 20-25 microm. This would suggest class III cells may be the predominant RGC type mediating pupilloconstriction, although a smaller population of larger cells (e.g., class I and/or II) may also contribute to this pathway. The recent reports utilizing the PLR as an assay for the efficacy of intraretinal grafts has highlighted the significance of the regional distribution results. The extremely low number of labeled cells in the dorsal hemiretina would argue for the placement of such grafts in the ventral hemiretina.

Animals↗
PubMed1998

Ganglion cell loss in RCS rat retina: a result of compression of axons by contracting intraretinal vessels linked to the pigment epithelium.

In the dystrophic Royal College of Surgeons (RCS) rat retina, there is a progressive loss of photoreceptors. As a result, the retinal circulation becomes apposed to the retinal pigment epithelium (RPE) and neovascular formations develop. RPE and inner nuclear layer cells migrate along these vessels towards the retinal ganglion cell (RGC) layer. The retinal layers gradually become disrupted, and some of the RGC axon bundles involute into the retina. These bundles are always associated with blood vessels, and there is evidence of axon damage where they juxtapose. In wholemount preparations of dystrophic retinae (> or =6 months of age), abrupt changes are observed in the trajectory of RGC axon bundles, where they are crossed by circumferential vessels. Degenerative profiles can be seen at these locations. Visualisation of RGCs with Fluoro-gold shows wedge-shaped sectors in the dystrophic retina devoid of labelling, initially in the ventral retina but later spreading dorsally. It is hypothesised that the vessels supplying the neovascular formations contract and pull surface vessels into the retina, thus displacing any axon bundles that lie beneath them into the inner plexiform layer. The contractility may be an intrinsic property of the vessels or it may be conferred by the cells migrating along them. Axonal transport becomes blocked at the points of tension, thereby causing retrograde degeneration of the parent RGCs. Because RGC loss is also a feature of human retinitis pigmentosa, the RCS rat may provide a model to test interventions devised to prevent such loss following photoreceptor degeneration. This model also may be useful for testing methods designed to control blood vessel and matrix formation.

Animals↗
PubMed1998

Changes in the pupillary light reflex of pigmented royal college of surgeons rats with Age.

We studied the latency and amplitude of the pupillary light reflex response of the Royal College of Surgeons rat from 10 to 52 weeks of age. The responses of these dystrophic rats were diminished compared to those of normal, non-dystrophic rats at all ages examined. This was most marked at the dimmest light intensity studied here and for the latency of dystrophic animals' responses. The latency deteriorated over the course of 52 weeks, although there was some evidence of improvement beyond 36 weeks of age. The amplitude of the dystrophic animals' responses also suggested some deterioration occurring up to 36 weeks of age, but with a substantial improvement beyond this time. In addition to these parameters, we also observed a break in the constriction phase of the pupillary light reflex that was unique to the dystrophic animals' responses. The frequency with which the anomaly occurred decreased in a light-dependent manner with age. The improvement of the pupillary light reflex at older ages, even when very few photoreceptors remain, may reflect compensatory events occurring in the inner retinal layers and/or in the central connections of the pupillary light reflex pathway. We suggest that the break in the constriction phase is a reflection of dual inputs driving the response, one of which is affected more by the degenerative events. This study provides baseline data on the effect of degeneration on function over time which can be used to evaluate the efficacy of repair strategies such as transplantation.

Aging↗
PubMed1998

Visual field loss in RCS rats and the effect of RPE cell transplantation.

The consequences of progressive retinal degeneration on central visual function were studied by recording single and multiunit receptive fields (RFs) across the surface of the superior colliculus (SC) of pigmented dystrophic RCS rats. Retinal morphology was used to provide a correlation between function and histological appearance. In addition, the potential protective effect of retinal pigment epithelium (RPE) transplantation was studied in a similar manner in dystrophic animals in which RPE cells were injected into the subretinal space, or the vitreous humor, at between 21 and 28 days of age. The visual responsiveness of SC units in dystrophic rats differed markedly from those in nondystrophics. Dystrophic rats developed a relative scotoma beginning in the central visual field by 42-45 days of age and expanding to include 50% of the visual field by 97-107 days. In contrast, following subretinal RPE transplantation, there was photoreceptor rescue correlated with a partial to complete preservation of RF representation when examined at 85 to 108 days of age. The majority of photoreceptor rescue occurred in the region of graft placement with possible low level rescue across the central retina. Dystrophic animals that had received intravitreal RPE transplants showed poor photoreceptor survival as well as minimal functional preservation. Our results indicate that there is a progressive central to peripheral loss of visual responsiveness in the SC of dystrophic RCS rats which can be limited by subretinal injections of healthy RPE cells.

Animals↗
PubMed1998

Extent and duration of recovered pupillary light reflex following retinal ganglion cell axon regeneration through peripheral nerve grafts directed to the pretectum in adult rats.

The functional reinnervation of the olivary pretectal nucleus (OPN) was studied in adult rats with peripheral nerve (PN) grafts bridging the interrupted retinopretectal pathway. Functional recovery was assessed quantitatively using established pupillometry techniques. The effect of intravitreal tuftsin fragment 1-3 (tuftsin 1-3) injections during the grafting procedure was also studied. A total of 53 adult rats received autologous PN grafts connecting the ocular stump of the transected optic nerve to the ipsilateral OPN. The contralateral eye was enucleated to remove the input from that eye to the OPN. A pupillary light reflex was elicited from 35 of the 53 PN-grafted animals and in the best cases, a response was obtained which compared closely to that recorded from control animals. Tuftsin 1-3 was found to increase the rate of recovery of the response. The response amplitude of PN-grafted rats was generally found to diminish with repeated stimulus presentation and also appeared to deteriorate with age. This was in contrast to control animals' responses. However, a PLR could still be elicited in 3 of the 6 animals studied 15 months after PN-grafting. These findings indicate that a near-normal PLR function can be restored using a peripheral nerve graft, but there are a number of factors that are likely to compromise optimal outcome.

Age Factors↗