Selectivity of antibody-mediated destruction of axons in the cat's optic nerve

The purpose of this study was to determine the selectivity with which polyspecific antibodies directed against large retinal ganglion cells destroy axons in the cat's optic nerve. Immune serum prepared against large ganglion cells isolated from ox retinas was injected into 1 eye of each of 2 cats. After more than 1 month, the cats were perfused with mixed aldehydes and the optic nerves were prepared for transmission electron microscopy. On the basis of a large sample of micrographs of transverse thin sections, we estimated that each of the nerves that issued from treated eyes contained approximately 62,500 necrotic fibers, amounting to 42–46% of the total fiber population in 1 case and 39–42% in the other. The diameters of 2900–5000 intact axons from each of 4 nerves (2 from immune-treated eyes and 2 from untreated eyes) were measured. Comparisons of histograms of axon diameter for nerves from treated and untreated eyes revealed that 90–100% of large axons with diameters above 3.5–4.0 μm were eliminated by the antibodies. Between 65 and 70% of medium-sized fibers were also eliminated. The number of small axons—those with diameters less than 1.2–1.6 μm — did not differ appreciably from normal. These results suggest that the immune serum destroyed virtually all α cell axons and a substantial fraction of β cell axons but did not reduce the number of small fibers that largely stem from the γ class of retinal ganglion cells.     

Retinal projections and functional architecture of cortical areas 17 and 18 in the tyrosinase-negative albino cat

The visual field representation and functional architecture of cortical areas 17 and 18 in albino cats were studied. In the same animals the distributions of ipsilaterally and contralaterally projecting retinal ganglion cells were determined by injecting horseradish peroxidase into the dorsal lateral geniculate nucleus or optic tract. All cats were tyrosinase-negative albinos (cc), not deaf white cats (W). The proportion of ipsilaterally projecting ganglion cells in the temporal retina of the albino cat was found to be much smaller than in the normal cat or in the Siamese cat. In the albino cat less than 5% of ganglion cells in temporal retina project ipsilaterally. Recordings from areas 17 and 18 provided evidence of a substantial representation of the ipsilateral hemifield in albino visual cortex; cells representing the contralateral and ipsilateral hemifields were often segregated into alternating zones in area 17 and were always segregated in area 18. Cells recorded at the borders of zones representing the ipsilateral and contralateral hemifields often had abnormal properties. Some border cells had two receptive fields separated by as much as 60 degrees of azimuth; one field subserved the contralateral hemifield (contralateral nasal retina) and the other subserved the mirror-symmetric part of ipsilateral hemifield (contralateral temporal retina). Receptive fields of cells subserving the two hemifields did not differ in size. The preferred orientations, preferred velocities, and other characteristics of the two fields were approximately the same; preferred orientation changed gradually and systematically across the borders of zones representing the two hemifields. Our results indicate that afferents representing nasal and temporal regions of retina of the same eye can segregate and form "hemiretina" domains in albino visual cortex. These afferents can also converge upon individual cortical cells in a fashion reminiscent of convergence of afferents from the two eyes upon binocular cells in the normal cortex. The organization of albino visual cortex is therefore different from the organization of Siamese visual cortex. This may be because, in the albino cat but not the Siamese cat, nearly all cells in temporal retina project contralaterally; afferents representing contralateral temporal retina are not at a significant competitive disadvantage in the albino.     

Gradients between nasal and temporal areas of the cat retina in the properties of retinal ganglion cells

Evidence is presented of gradients between nasal and temporal areas of the cat's retina in the properties of their ganglion cell populations. Mean ganglion cell size is greater in temporal retina than in nasal retina, partly because the α- and β-cells of temporal retina are distinctly bigger than their counterparts in nasal retina, and partly because more medium-sized cells, and fewer small cells, are to be found in temporal retina. This high proportion of medium-sized ganglion cells may reflect a high proportion of β-cells or of the medium sized γ-cells described by Stone and Clarke ('80). Several of these differences can be related to prior morphological, electrophysiological, and behavioural observations in the cat, and similar differnces have been reported in several other mammalian species. Evidence is presented that, in the cat, at least some of these differences are less marked near the vertical meridian of the retina than more temporally or nasally. The present results may therefore, be evidence of a nasal-temporal gradient in retinal structure and function common to many mammals, and distinct from previously recognised gradients in ganglion cell properties related to the area centralis and visual streak specialisations.     

Effects of antibodies to large retinal ganglion cells on developing retinogeniculate pathways in the cat

We investigated the effects of polyclonal antibodies, produced against ox large retinal ganglion cells, on the developing retinogeniculate pathways of cats. Four-week-old kittens were given an intraocular injection of either a low or a high concentration of the antibodies and effects were assessed 35-69 weeks later. After a low concentration (110 micrograms/33 microliter volume) injection, the density of retinal alpha-cells (the morphological counterpart of Y-cells) was reduced 44% in area centralis and 37% in peripheral retina. After a high concentration (333 micrograms/33 microliter volume) injection, alpha-cell density was reduced 76% in area centralis and 91% in peripheral retina. The same concentration of antibodies had no consistent effect on the numbers of medium- or small-size retinal ganglion cells. Electrophysiological recordings from single neurons in layers A and A1 of the lateral geniculate nucleus (LGN) revealed a 53% decrease in the percentage of Y-cells after a low-concentration injection and an 82% decrease after a high-concentration injection. There was a concomitant increase in the percentage of LGN cells that were non-responsive to light or that responded too poorly to be classified. No change was observed in the percentages of LGN X-cells or cells with mixed response properties. The reduced encounter rate of LGN Y-cells was not accompanied by significant changes in LGN cell-body size. Together, the results indicate that the immunoablation technique produces a large and apparently selective reduction of the Y-cell retinogeniculate pathway in developing kittens.     

Beta-like ganglion cells in the retina of the North American opossum

Injection of horseradish peroxidase into the severed optic tract or nerve of the opossum retrogradely filled retinal ganglion cells. An abundance of well-labeled ganglion cells had dendritic morphology closely resembling that of β-type ganglion cells in the cat retina. This finding suggests that an X-like functional class of ganglion cells is prominent in the retina of the opossum.     

Noradrenaline action on cat retinal ganglion cells is mediated by dopamine (D2) receptors

Effects of iontopheretically applied noradrenaline, dopamine and their receptor antagonists on the retinal ganglion cells, were studied in optically intact eyes of barbiturate-anaesthetized cats. Noradrenaline inhibited visually evoked and spontaneous firing of all classes of retinal ganglion cells: the effect being greater on ON-than on OFF-cells and slightly more potent than dopamine on a given cell. All α- and β-adrenoceptor blockers tested tended to change spikes but were generally ineffective in blocking the noradrenaline-induced inhibition, when not affecting spikes. The noradrenaline-induced inhibition was, however, effectively blocked by dopamine D₂-receptor antagonists. The α- and β-adrenoreceptor antagonists applied alone had no effect, suggesting the absence of endogenous noradrenergic antagonism, although α-type adrenergic antagonism was suggestive on a very small number of cells. These results suggest that: (1) noradrenaline action on cat retinal ganglion cells is mediated via dopamine D₂-receptors; (2) noradrenaline is not generally released on them, except there may be physiologically active α-receptors on a few cells; and (3) many of the adrenoreceptor blockers affect membrane properties of the retinal ganglion cells, in a similar manner to local anaesthetics.     

Class-specific cell death shapes the distribution and pattern of central projection of cat retinal ganglion cells

The development of the nasotemporal division in cat retina was studied. We find that in the normally pigmented neonatal cat significant numbers of ganglion cells of all types in temporal retina project to the contralateral dorsal lateral geniculate nucleus (LGNd); far fewer cells in temporal retina project contralaterally to the LGNd in the normal adult. Thus, most of these cells must be eliminated during development. Experimental interruption of one optic tract in the neonate results in the retrograde degeneration of the ipsilaterally projecting ganglion cells in the temporal retina ipsilateral to the lesion. Consequent to the loss of the ipsilaterally projecting cells in this hemiretina, many of the ganglion cells projecting to the intact contralateral LGNd, which are normally eliminated, survive. Also, unlike in the normal cat, in which very few of the small ganglion cells in temporal retina project contralaterally to the thalamus, in optic tract sectioned (OTX) cats, significant numbers of the smallest ganglion cells in the temporal retina ipsilateral to the lesion project contralaterally to the intact thalamus. In order to make a quantitative comparison of the distributions of ipsilaterally and contralaterally projecting cells in the temporal retinae of normal cats, OTX cats, and neonatal kittens, it was necessary to determine the position of the vertical meridian in all animals. We defined the vertical meridian as the median edge (Stone, 1966). The median edge was determined from the distribution of the most nasally located, ipsilaterally projecting cells in temporal retina. The results indicate that the angle of the vertical meridian (median edge) with respect to the area centralis and optic disc is specified before birth and does not differ in normal cats, OTX cats, or neonatal kittens. Since the location of the vertical meridian does not change with age in postnatal life and is not affected by optic tract section, corresponding regions of retina in the different groups could be compared. A quantitative analysis of ganglion cell density in the temporal retina contralateral to the section, ipsilateral to the intact hemisphere, indicated that there was a reduction in the population of ipsilaterally projecting ganglion cells that was complementary to the abnormally large number of contralaterally projecting cells surviving in the temporal retina ipsilateral to the lesion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Retinal ganglion cell layer of the Caspian seal Pusa caspica: topography and localization of the high-resolution area

Retinal topography, cell density and sizes of ganglion cells in the Caspian seal (Pusa caspica) were analyzed in retinal whole mounts stained with cresyl-violet. The topographic distribution of ganglion cells displayed an area of high cell density located in the temporal quadrant of the retina and was similar to the area centralis of terrestrial carnivores. It extended nasally, above the optic disk, as a streak of increased cell density. In different whole mounts, the peak cell density in the high-density area ranged from 1,684 to 1,844 cells/mm2 (mean 1,773 cells/mm2). The cell density data predict a retinal resolution of around 8.5 cycles/degree in water. A distinctive feature of the Caspian seal's retina is the large size of ganglion cells and the low cell density compared to terrestrial mammals. The ganglion cell diameter ranged from 10 to 58 μm. Cell size histograms featured bimodal patterns with groups of small and large ganglion cells. The large cells appeared similar to α-cells of terrestrial mammals and constituted 7% of the total ganglion cell population.     

Abnormal ipsilateral visual field representation in areas 17 and 18 of hypopigmented cats

We compared the central projections of retinal ganglion cells in temporal retina and the cortical representation of visual fields in areas 17 and 18 in cats with various hypopigmentation phenotypes (albino, heterozygous albino, Siamese, and heterozygous Siamese). In all cats studied, we found that the extent of abnormal ipsilateral visual field representation varied widely, and more of the ipsilateral visual field was represented in area 18 than in area 17. The greatest degree of ipsilateral visual field representation was found in albino cats, followed by Siamese, heterozygous albino and heterozygote Siamese cats, respectively. Additionally, in the different groups there was wide variation in the numbers of contralaterally projecting alpha and beta ganglion cells in temporal retina. In all cases, however, contralaterally projecting alpha cells were found to extend further into temporal retina than beta cells. We found that in each cat studied, the maximum extent of the abnormal ipsilateral visual field representation in areas 18 and 17 corresponded to the location of the 50% decussation line (i. e., the point where 50% of the ganglion cells in temporal retina project to the contralateral hemisphere) for alpha and beta cells, respectively, for that cat. Our results suggest that the extent of the abnormal visual field representations in visual cortex of hypopigmented cats reflects the extent of contralaterally projecting retinal ganglion cells in temporal retina. © 1995 Wiley-Liss, Inc.     

Critical flicker frequency in monocularly deprived cats

Critical flicker frequency (CFF) was determined for both eyes of long-term monocularly deprived (MD) cats over a wide luminance range. Although MD cats could discriminate flicker before and after lid opening, CFF of the deprived eye (30 Hz) was much lower than CFF of the non-deprived eye (40 Hz) and the CFF of the non-deprived eye was lower than a normal cat's monocular CFF (58 Hz). The CFF deficit of the deprived eye became less pronounced at low luminance levels. The observation (and magnitude) of a CFF deficit for the deprived eye is compatible with the reports of a Y-cell loss in LGNd. The CFF deficit of the non-deprived eye has no obvious explanation.     

Connexin α1 and Cell Proliferation in the Developing Chick Retina

During the formation of the eye, high levels of connexin α1 (connexin 43) are expressed within the tissues of the cornea, lens, and neural retina. In order to determine whether connexin α1 plays a role in the regulation of cell proliferation we have used a novel antisense technique to reduce its expression early in development (embryonic days 2–4). Application of Pluronic gel, containing antisense oligodeoxynucleotides (ODNs) to connexin α1, to one eye of early chick embryos results in a rapid and significant reduction of α1 protein which lasts for 24–48 h. Embryos grown for 48 h, after ODN application to one eye, showed a marked reduction in the diameter of the treated, compared to that of the contralateral untreated, eye. Sections cut from the treated eyes showed that the retina was also reduced in size. TUNEL labeling and staining with propidium iodide showed that apoptosis within the retinae of both treated and untreated eyes was rare and thus that the reduction in the area of the retina brought about by antisense ODNs directed at connexin α1 was unlikely to be the result of increased cell death. However, the number of mitotic figures in the ventricular zone of the antisense-treated retinae revealed by propidium iodide staining was significantly reduced (P < 0.0001) to 53 ± 3.5% (n = 5) of that in the contralateral untreated control eyes. Embryos in which one eye was sham operated, treated with pluronic gel, or treated with sense ODN showed no significant changes in eye size or in the number of mitotic figures within the neural retina. These results point to a role for connexin α1-mediated gap-junctional communication in controlling the early wave of neurogenesis in the chick retina.     

Origins of crossed and uncrossed retinal projections in pigmented and albino mice

The extent of the binocular cortical field in albino mice, as revealed by recording from single cells, was almost normal; although the input from the ipsilateral eye was weaker than normal, most cells were driven from both eyes. By backfilling retinal ganglion cells from one optic tract with horseradish peroxidase we examined the origins of the retinofugal projections. Filled cells ipsilateral to the injected tract were concentrated in a crescent-shaped area bordering the inferior temporal retina. In black mice this area constituted 20% of the total retinal area, in albinos 17%. In black mice we counted nearly 1,000 labeled cell in the ipsilateral retina, or 2.6% of all cells filled in both eyes. Albinos had about one-third fewer filled cells ipsilaterally than black mice. Four percent of all ipsilaterally filled cells in black mice and 8% in albinnos were scattered outside of the crescent region. The density of ipsilaterally projecting cells was uniform throughout the crescent region in black mice, but decreased toward the central retina in albinos. In retinas contralateral to the injection up to 39,000 cells were filled—about two-thirds of the cells in the ganglion-cell layer whose cytoplasm contained conspicuous Nissl substance. Depending on classification of unfilled cells as ganglion cells or interneurons, we estimated a total 48,000 to 65,000 ganglion cells to exist in the retina. The size distribution of ipsilateraly projecting ganglion cells was similar in albinos and normals. Ipsilaterally projecting ganglion cells were on average 1.8–3 times larger in volume than contralaterally projecting ones in both types of mice. Displaced ganglion cells were relatively more common in ipsilateral retinofugal projections: 21% of all ipsilateral ganglion cells were displaced versus less than 1% of all the contralateral ganglion cells in black mice. In albinos only 13% of the ganglion cells in the ipsilateral retina were displaced. The overall reduction in ipsilaterally projecting cells in albinos was reflected twice as much in displaced ganglion cells as in normally placed ones.     

Distribution of ganglion cells in the retina of adult pigmented ferret

The retinal ganglion cell distribution in adult pigmented ferret was mapped in Nissl-stained retinas and in retinas back-filled with HRP after large bilateral injections of the enzyme into the brain. In common with other carnivores the ferret has an area of peak cell density equivalent to the area centralis and a prominent visual streak of high cell density extending horizontally across the retina. The maximum ganglion cell densities for the retinas were estimated to be 3500-5200 cells/mm2 in Nissl-stained, dehydrated retinas and 3300-4300 cells/mm2 in HRP-labelled, undehydrated retinas. Three cell types were distinguished in the HRP-labelled retinas and they appear to correspond to alpha-, beta- and gamma-cell types of cat retina. However, unlike in cat, the retinal ganglion cells of the ferret do not consistently fall into 3 distinct groups with respect to cell size, nor is there a tendency for the cells in the area centralis to be smaller than those in the peripheral retina. Estimates for the total number of ganglion cells of 82,000 and 88,000 were obtained from Nissl-stained retinas, and of 74,000, 75,000 and 78,000 from HRP-labelled retinas.     

Selective damage to large cells in the cat retinogeniculate pathway by 2,5-hexanedione

The neurotoxic hexacarbon 2,5-hexanedione (2,5-HD), which produces transport abnormalities and swellings in the large diameter fibers of the peripheral nervous system, was administered to cats in an attempt to produce similar selective effects in the optic tract. Anatomical findings indicate damage to one type of retinal ganglion cell, the large (alpha) or Y-cell class, both during dosing and after a long recovery period. This selective involvement of the large ganglion cells during dosing was shown by decreased retrograde transport of HRP in these cells relative to smaller cells. Such selectivity was not apparent in axonal swellings and neurofilament accumulations which were present in fibers of all diameters in the distal optic tract. Visual threshold studies during dosing showed a loss of flicker resolution with preservation of visual acuity, a result consistent with the different physiological properties of alpha and beta ganglion cells. In one cat, which survived dosing for a period of 8 months, there was a dramatic reduction in the number of large cells and a pronounced shrinkage of those that remained, but no observed changes in other cell types. Thus, this intoxication caused (1) axonal swellings which were not selective for fiber size; (2) a selective defect in axonal transport with later neuronal degeneration and shrinkage that were limited to large cells; and (3) a loss of flicker resolution that may reflect dysfunction of large ganglion cells.     

Retinal specializations and visual ecology in an animal with an extremely elaborate pupil shape: the little skate Leucoraja (Raja) erinacea Mitchell, 1825

Investigating retinal specializations offers insights into eye functionality. Using retinal wholemount techniques, we investigated the distribution of retinal ganglion cells in the Little skate Leucoraja erinacea by (a) dye‐backfilling into the optic nerve prior to retinal wholemounting; (b) Nissl‐staining of retinal wholemounts. Retinas were examined for regional specializations (higher numbers) of ganglion cells that would indicate higher visual acuity in those areas. Total ganglion cell number were low compared to other elasmobranchs (backfilled: average 49,713 total ganglion cells, average peak cell density 1,315 ganglion cells mm^?2; Nissl‐stained: average 47,791 total ganglion cells, average peak cell density 1,319 ganglion cells mm^?2). Ganglion cells fit into three size categories: small (5–20 µm); medium (20–30 µm); large: (≥ 30 µm), and they were not homogeneously distributed across the retina. There was a dorsally located horizontal visual streak with increased ganglion cell density; additionally, there were approximately three local maxima in ganglion cell distribution (potential areae centrales) within this streak in which densities were highest. Using computerized tomography (CT) and micro‐CT, geometrical dimensions of the eye were obtained. Combined with ganglion cell distributions, spatial resolving power was determined to be between 1.21 and 1.37 cycles per degree. Additionally, photoreceptor sizes across different retinal areas varied; photoreceptors were longest within the horizontal visual streak. Variations in the locations of retinal specializations appear to be related to the animal's anatomy: shape of the head and eyes, position of eyes, location of tapetum, and shape of pupil, as well as the visual demands associated with lifestyle and habitat type.     

The retinal projection to the superior colliculus in the cat: A quantitative study with HRP

The projections of cat retinal ganglion cells to the superior colliculus (SC) were examined using the method of retrograde axonal transport of horseradish peroxidase (HRP). Several injections of HRP were made in a single SC after the visual projection to the injection sites had been established physiologically. The HRP injections resulted in a homogeneous distribution of labelled ganglion cells in whole mount preparations of the retinae of both eyes. In the eye contralateral to the injected colliculus, ganglion cells with a crossed projection were labelled in both nasal and temporal retina; in the ipsilateral eye, ganglion cells with uncrossed projection were labelled only in the temporal retina. Analysis of the counterstained retinal whole mounts indicated that at least 50% of all ganglion cells in the nasal retina and 26% in the temporal retina have a crossed projection to SC, and that 24% of all ganglion cells of the temporal retina have an uncrossed projection to the SC. The morphological classes of retinal ganglion cells have different patterns of crossed/uncrossed decussation and they participate in varying proportions in the retino-tectal projection. Almost all Alpha cells in the retina send axon collaterals to the SC. Probably only about 10% of the Beta cells project to the SC and at least 80% of all Gamma cells send axons to the SC.     

Experimental induction of an abnormal ipsilateral visual field representation in the geniculocortical pathway of normally pigmented cats

In the normally pigmented neonatal cat, many ganglion cells in temporal retina project to the contralateral dorsal lateral geniculate nucleus (LGNd) and medial interlaminar nucleus (MIN). Most of these cells are eliminated during postnatal development. If one optic tract is sectioned at birth, much of this exuberant projection from the contralateral temporal retina is stabilized (Leventhal et al., 1988b). To determine how the abnormal projection from the contralateral temporal retina is accommodated in the central visual pathways, neuronal activity was recorded in the visual thalamus and cortex of adult cats whose optic tracts were sectioned as neonates. The recordings showed that up to 20 degrees of the ipsilateral hemifield is represented in the LGNd and MIN. Recordings from areas 17 and 18 of the intact visual cortex showed that up to 20 degrees of the ipsilateral visual field is also represented and that the ipsilateral representation is organized as in a Boston Siamese cat (Hubel and Wiesel, 1971; Shatz, 1977; Cooper and Blasdel, 1980) or a heterozygous albino cat (Leventhal et al., 1985b). The extent of the ipsilateral visual field representation was greater in area 18 than in area 17; the extent of the ipsilateral hemifield representation in areas 17 and 18 varied with elevation, increasing with distance from the horizontal meridian. The receptive fields of cells in the LGNd and visual cortex subserving contralateral temporal retina were abnormally large. Otherwise, their receptive field properties seemed normal. In the same animals studied physiologically, HRP was injected into the ipsilateral hemifield representation in the LGNd and MIN of the intact hemisphere. The topographic distribution of the alpha and beta cells, respectively, labeled by these injections correlated with the elevation-related changes in the ipsilateral visual field representation in areas 18 and 17. Our results indicate that the retinotopic organization of the mature geniculocortical pathway reflects the abnormal pattern of central projections of ganglion cells in neonatally optic tract sectioned cats. Thus, if they do not die, retinal ganglion cells normally eliminated during development are capable of making seemingly normal, functional connections. The finding that an albino-like representation of the ipsilateral hemifield can be induced in the visual cortex of normally pigmented cats suggests that the well-documented defects in the geniculocortical pathways of albinos are secondary to the initial misrouting of ganglion cells at the optic chiasm (Kliot and Shatz, 1985) and not a result of albinism per se.     

Single retinal ganglion cells projecting in bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals in the cat

In most mammals with frontalized eyes, retinal ganglion cells in the nasal or temporal retina send their axons to the contralateral or ipsilateral half, respectively, of the brain. Previous studies in the cat, however, have indicated a retinal region of “nasotemporal overlap” from which arise the retinal projections to both the contralateral and ipsilateral halves of the brain. The present study thus examined in the cat whether any retinal ganglion cells give rise to bifurcating axons that innervate both halves of the brain. By employing fluorescent retrograde double labeling, we investigated whether or not single retinal ganglion cells project bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals. After Fast Blue was injected into the lateral geniculate nucleus on one side and Diamidino Yellow was injected contralaterally into the lateral geniculate nucleus, 100–200 ganglion cells in each retina were double labeled with both tracers. These double-labeled cells were distributed primarily in the temporal retina, including the region around the vertical meridian and, additionally, in the nasal retina. About 60–80% of the double-labeled cells had large cell bodies (more than 25 μm in diameter), and the others had medium-sized ones (15–25 μm in diameter). The pattern of distribution of double-labeled cells, which was observed after the combined injection into both superior colliculi, was similar to that seen after the combined injection into both lateral geniculate nuclei; more than 9% of double-labeled cells, however, were large. The results indicate that a certain population of ganglion cells in the cat retina send their axons bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals. The bilaterally projecting ganglion cells are mostly large, corresponding probably to α cells (the morphological counterparts of Y cells). In comparison with the patterns of bilateral projections of single retinal ganglion cells in the rat and monkey, the pattern of the bilateral retinofugal projections in the cat could represent an intermediate between those in the rat and monkey. © 1994 Wiley-Liss, Inc.     

Retinal ganglion cell loss produced by intraocular kainic acid in cats: variation with somal size and eccentricity

Eight eyes of adult cats were injected with different doses of kainic acid (KA) and examined following survival times of either 5 or 12 days. At a survival time of 12 days, a dose of 76 nmol produced an 18% lossof ganglion cells in the center of the area centralis (AC), 70% loss at a location 2 mm from the AC, and 95% loss at a location 6 mm from the AC. Larger doses (240, 760 and 2400 nmol) produced losses comparable to that observed for 76 nmol. For example, 2400 nmol produced a 35% loss in the AC, 81% at 2 mm, and 88% at 6 mm. At a survival time of 5 days, doses of 240 and 760 nmol produced a loss of ganglion cells comparable to that seen at 12 days. In one eye, a large dose of KA (7600 nmol) produced total loss of ganglion cells at a survival time of 5 days. By comparing loss of cells in restricted somal diameter ranges at different retinal eccentricities, it was possible to distinguish two significant correlations that were largely independent of survival time and dose: (1) at 2 mm, loss of cells with somal diameters larger than 21 μm significantly exceeded loss of cells with smaller somata. In particular, alpha cells were totally eliminated in 6 of the 8 KA-treated eyes. (2) The mean loss of ganglion cells with somal diameters less than 21 μm was significantly greater at 2 mm and 6 mm than in the AC. Together, these results show that loss of ganglion cells produced by KA varies somal size and retinal eccentricity.     

Structure/function relationships of retinal ganglion cells in the cat

Intracellular recording and horseradish peroxidase (HRP) iontophoresis was used to define structure/function relationships for single retinal ganglion cells in the intact cat eye. Fifteen physiologically characterized cells were labeled as follows. Five W-cells had gamma morphology, 6 X-cells had beta morphology, and 1 Y-cell had alpha morphology, and these relationships support earlier conclusions. However, one cell could not be physiologically classified despite beta morphology, one X-cell was not a beta cell, and one Y-cell was not an alpha cell. Whether these unusual structure/function relationships represent an artifact of methodology or complications to be added to prevailing notions requires further study.