The morphology, number, and distribution of a large population of confirmed displaced amacrine cells in the adult cat retina

Morphological and Immunohistochemical Differentiation of Neuronal and Glial Cells of the Vascular and Avascular Regions of the Donkey's Paurangiotic Retina

INTRODUCTION

Ocular diseases pose a significant health concern for donkeys. However, studies examining the microanatomy and cell populations of the donkey retina are scarce. The current study aimed to describe the vascular pattern of the donkey retina and document its cellular components.

METHODS

The donkey retina specimens were obtained from different retinal regions and prepared for semithin sectioning and immunohistochemistry.

RESULTS

The donkey has a paurangiotic retina in which retinal vessels are confined to a narrow area around the optic disc. Glial cells coexist with the blood vessels being very numerous in the vascular region and become scanty in the avascular ones. S-100-positive astrocytes could be observed in these avascular areas. Ganglion cells are organized in a single layer with the least population existing in the peripheral retina. Acidic fibroblast growth factor (AFGF) is immunoreactive in amacrine and ganglion cells. A subpopulation of amacrine cells reacted strongly to tyrosine hydroxylase (TH), and others reacted positively to S-100 protein. Ganglion cell nuclei exhibited a strong immunoreactivity to S-100 protein as well. Furthermore, glial fibrillary acidic protein (GFAP) is used to identify Müller cells that extend their processes across the retina from the inner to the outer limiting membrane.

CONCLUSIONS

In conclusion, our findings provide novel insights into the normal retinal organization. The donkey retina shows the characteristic expression of immunohistochemical markers for the major cell types. In addition, the distribution of glial cells is comparable between the vascular and avascular regions.

Retinal morphology in Astyanax mexicanus during eye degeneration

The teleost Astyanax mexicanus is one species extant in two readily available forms. One that lives in Mexican rivers and various convergent forms that live in nearby caves. These fish are born with eyes but in the cavefish, they degenerate during development. It is known that the lens of cavefish undergoes apoptosis and that some cells in the neuroretina also die. It has not been described, however, if glia and various components of the neuroretina form before complete eye degeneration. Here we examined the development of the retina of the closest living ancestor that lives in the rivers and two independently adapted of cavefish. We report that although the neuroretina is smaller and more compact, it has all cell types and layers including amacrine cells and Müller glia. While various makers for photoreceptors are present in the cavefish inner segments, the outer segments of the photoreceptors in cavefish are missing from the earliest stages examined. This shows that the machinery for visual transducing discs might still be present but not organized in one part of the cell. It is interesting to note that the deficiencies in Astyanax cavefish resemble retinal diseases, such as retinitis pigmentosa.

The Best-Vision Zones and Visual Resolution of the Retina of Neonatal Bottlenose Dolphins Tursiops truncatus

The topography of ganglion cells in the retina of three neonatal bottlenose dolphins Tursiops truncatus has been studied in retinal wholemounts. Two areas of high ganglion cell density have been identified in the form of local spots in the temporal and nasal quadrants of the retina, near a horizontal diameter at a distance of 10-15 mm from the optical disk. The maximum density of ganglion cells in these areas on average for five preparations is 657 and 636 cells/mm² in the temporal and nasal quadrants, respectively. The retinal resolution, estimated by the maximum density of ganglion cells and a posterior nodal distance of 13 mm, was 0.17° for the temporal quadrant and 0.18° for the nasal one. These data are comparable with the results for the previously studied adult dolphin and whale species.

Cell type-specific expression of FoxP2 in the ferret and mouse retina

Although the anatomical and physiological properties of subtypes of retinal ganglion cells (RGCs) have been extensively investigated, their molecular properties are still unclear. Here, we examined the expression patterns of FoxP2 in the retina of ferrets and mice. We found that FoxP2 was expressed in small subsets of neurons in the adult ferret retina. FoxP2-positive neurons in the ganglion cell layer were divided into two groups. Large FoxP2-positive neurons expressed Brn3a and were retrogradely labeled with cholera toxin subunit B injected into the optic nerve, indicating that they are RGCs. The soma size and the projection pattern of FoxP2-positive RGCs were consistent with those of X cells. Because we previously reported that FoxP2 was selectively expressed in X cells in the ferret lateral geniculate nucleus (LGN), our findings indicate that FoxP2 is specifically expressed in the parvocellular pathway from the retina to the LGN. Small FoxP2-positive neurons were positive for GAD65/67, suggesting that they are GABAergic amacrine cells. Most Foxp2-positive cells were RGCs in the adult mouse retina. Dendritic morphological analyses suggested that Foxp2-positive RGCs included direction-selective RGCs in mice. Thus, our findings suggest that FoxP2 is expressed in specific subtypes of RGCs in the retina of ferrets and mice.

Retinal Ganglion Cell Topography and Retinal Resolution in the Baikal Seal (Pusa sibirica)

The total number, size, topographic distribution, and cell density of ganglion cells were studied in retinal wholemounts of Baikal seals (Pusa sibirica). The ganglion cell size varied from 10 to 38 μm. A distinct cell group consisted of large ganglion cells of more than 30 μm in diameter. The topographic distribution of ganglion cells showed a definite area of high cell density similar to the area centralis of terrestrial carnivores. This area was located approximately 6-7 mm dorsotemporally of the geometric center of the wholemount. In this area, the peak cell densities in two wholemounts were 3,800 and 3,400 cells/mm2 (mean 3,600 cells/mm2). With a posterior nodal distance of 24 mm (underwater), this density corresponds to 631 cells/square degree. These values predict a retinal resolution of 2.4' in water and 3.0' in air. The topographic distribution of large cells featured the highest density in the same location as the total ganglion cell population.

BDNF treatment and extended recovery from optic nerve trauma in the cat

PURPOSE

We examined the treatment period necessary to restore retinal and visual stability following trauma to the optic nerve.

METHODS

Cats received unilateral optic nerve crush and no treatment (NT), treatment of the injured eye with brain-derived neurotrophic factor (BDNF), or treatment of the injured eye combined with treatment of visual cortex for 2 or 4 weeks. After 1-, 2-, 4-, or 6-week survival periods, pattern electroretinograms (PERGs) were obtained and retinal ganglion cell (RGC) survival determined.

RESULTS

In the peripheral retina, RGC survival for NT, eye only, and eye + cortex animals was 55%, 78%, and 92%, respectively, at 1 week, and 31%, 60%, and 93%, respectively, at 2 weeks. PERGs showed a similar pattern of improvement. After 4 weeks, RGC survival was 7%, 29%, and 53% in each group, with PERGs in the dual-treated animals similar to the 1- to 2-week animals. For area centralis (AC), the NT, eye only, and eye + cortex animals showed 47%, 78%, and 82% survival, respectively, at 2 weeks, and 13%, 54%, and 81% survival, respectively, at 4 weeks. Removing the pumps at 2 weeks resulted in ganglion cell survival levels of 76% and 74% in the AC at 4 and 6 weeks postcrush, respectively. The PERGs from 2-week treated, but 4- and 6-week survival animals were comparable to those of the 2-week animals.

CONCLUSIONS

Treating the entire central visual pathway is important following optic nerve trauma. Long-term preservation of central vision may be achieved with as little as 2 weeks of treatment using this approach.

Morphology of retinal ganglion cells in the ferret (Mustela putorius furo)

The ferret is the premiere mammalian model of retinal and visual system development, but the spectrum and properties of its retinal ganglion cells are less well understood than in another member of the Carnivora, the domestic cat. Here, we have extensively surveyed the dendritic architecture of ferret ganglion cells and report that the classification scheme previously developed for cat ganglion cells can be applied with few modifications to the ferret retina. We confirm the presence of alpha and beta cells in ferret retina, which are very similar to those in cat retina. Both cell types exhibited an increase in dendritic field size with distance from the area centralis (eccentricity) and with distance from the visual streak. Both alpha and beta cell populations existed as two subtypes whose dendrites stratified mainly in sublamina a or b of the inner plexiform layer. Six additional morphological types of ganglion cells were identified: four monostratified cell types (delta, epsilon, zeta, and eta) and two bistratified types (theta and iota). These types closely resembled their counterparts in the cat in terms of form, relative field size, and stratification. Our data indicate that, among carnivore species, the retinal ganglion cells resemble one another closely and that the ferret is a useful model for studies of the ontogenetic differentiation of ganglion cell types.

Combined application of BDNF to the eye and brain enhances ganglion cell survival and function in the cat after optic nerve injury

PURPOSE

To determine whether application of BDNF to the eye and brain provides a greater level of neuroprotection after optic nerve injury than treatment of the eye alone.

METHODS

Retinal ganglion cell survival and pattern electroretinographic responses were compared in normal cat eyes and in eyes that received (1) a mild nerve crush and no treatment, (2) a single intravitreal injection of BDNF at the time of the nerve injury, or (3) intravitreal treatment combined with 1 to 2 weeks of continuous delivery of BDNF to the visual cortex, bilaterally.

RESULTS

Relative to no treatment, administration of BDNF to the eye alone resulted in a significant increase in ganglion cell survival at both 1 and 2 weeks after nerve crush (1 week, 79% vs. 55%; 2 weeks, 60% vs. 31%). Combined treatment of the eye and visual cortex resulted in a modest additional increase (17%) in ganglion cell survival in the 1-week eyes, a further significant increase (55%) in the 2-week eyes, and ganglion cell survival levels for both that were comparable to normal (92%-93% survival). Pattern ERG responses for all the treated eyes were comparable to normal at 1 week after injury; however, at 2 weeks, only the responses of eyes receiving the combined BDNF treatment remained so.

CONCLUSIONS

Although treatment of the eye alone with BDNF has a significant impact on ganglion cell survival after optic nerve injury, combined treatment of the eye and brain may represent an even more effective approach and should be considered in the development of future optic neuropathy-related neuroprotection strategies.

Comparative anatomy of the optic nerve head and inner retina in non-primate animal models used for glaucoma research

To judge the information of experimental settings in relation to the human situation, it is crucial to be aware of morphological differences and peculiarities in the species studied. Related to glaucoma, the most important structures of the posterior eye segment are the optic nerve head including the lamina cribrosa, and the inner retinal layers. The review highlights the differences of the lamina cribrosa and its vascular supply, the prelaminar optic nerve head, and the retinal ganglion cell layer in the most widely used animal models for glaucoma research, including mouse, rat, rabbit, pig, dog, cat, chicken, and quail. Although all species show some differences to the human situation, the rabbit seems to be the most problematic animal for glaucoma research.

Adaptive features of aquatic mammals' eye

The eye of aquatic mammals demonstrates several adaptations to both underwater and aerial vision. This study offers a review of eye anatomy in four groups of aquatic animals: cetaceans (toothed and baleen whales), pinnipeds (seals, sea lions, and walruses), sirenians (manatees and dugongs), and sea otters. Eye anatomy and optics, retinal laminar morphology, and topography of ganglion cell distribution are discussed with particular reference to aquatic specializations for underwater versus aerial vision. Aquatic mammals display emmetropia (i.e., refraction of light to focus on the retina) while submerged, and most have mechanisms to achieve emmetropia above water to counter the resulting aerial myopia. As underwater vision necessitates adjusting to wide variations in luminosity, iris muscle contractions create species-specific pupil shapes that regulate the amount of light entering the pupil and, in pinnipeds, work in conjunction with a reflective optic tapetum. The retina of aquatic mammals is similar to that of nocturnal terrestrial mammals in containing mainly rod photoreceptors and a minor number of cones (however, residual color vision may take place). A characteristic feature of the cetacean and pinniped retina is the large size of ganglion cells separated by wide intercellular spaces. Studies of topographic distribution of ganglion cells in the retina of cetaceans revealed two areas of ganglion cell concentration (the best-vision areas) located in the temporal and nasal quadrants; pinnipeds, sirenians, and sea otters have only one such area. In general, the visual system of marine mammals demonstrates a high degree of development and several specific features associated with adaptation for vision in both the aquatic and aerial environments.

The number, morphology, and distribution of retinal ganglion cells and optic axons in the Australian lungfishNeoceratodus forsteri(Krefft 1870)

Australian lungfishNeoceratodus forsterimay be the closest living relative to the first tetrapods and yet little is known about their retinal ganglion cells. This study reveals that lungfish possess a heterogeneous population of ganglion cells distributed in a horizontal streak across the retinal meridian, which is formed early in development and maintained through to adult stages. The number and complement of both ganglion cells and a population of putative amacrine cells within the ganglion cell layer are examined using retrograde labelling from the optic nerve and transmission electron-microscopic analysis of axons within the optic nerve. At least four types of retinal ganglion cells are present and lie predominantly within a thin ganglion cell layer, although two subpopulations are identified, one within the inner plexiform and the other within the inner nuclear layer. A subpopulation of retinal ganglion cells comprising up to 7% of the total population are significantly larger (>400 μm2) and are characterized as giant or alpha-like cells. Up to 44% of cells within the retinal ganglion cell layer represent a population of presumed amacrine cells. The optic nerve is heavily fasciculated and the proportion of myelinated axons increases with body length from 17% in subadults to 74% in adults. Spatial resolving power, based on ganglion cell spacing, is low (1.6–1.9 cycles deg−1,n= 2) and does not significantly increase with growth. This represents the first detailed study of retinal ganglion cells in sarcopterygian fish, and reveals that, despite variation amongst animal groups, trends in ganglion cell density distribution and characteristics of cell types were defined early in vertebrate evolution.

Physiological response properties of displaced amacrine cells of the adult ferret retina

The ganglion cell layer (GCL) of the mammalian retina contains a large number of neurons called displaced amacrine cells (DACs) that do not project to the optic nerve. However, with the exception of the rabbit starburst amacrine cell little is known regarding the function of this large population due to the difficulty experienced in making physiological recordings from these neurons. We have overcome these difficulties and have used whole-cell patch-clamp techniques to examine the intrinsic membrane properties of DACs in the ferret retina. Our results indicate a large degree of diversity in their intrinsic membrane properties. In response to maintained depolarizing current injection, DACs responded with graded depolarization or by eliciting either transient or sustained bursts of spiking activity. At the resting membrane potential, 10% of the DACs generated spontaneous spikes in either an apparently random manner or at the peak of intrinsic waves of depolarization. The resting membrane activity of the remaining DACs recorded could be classified into three groups that were quiescent (28%), had robust uncorrelated synaptic activity (30%), or underwent slow waves of depolarization (42%). Diversity was also revealed in the membrane currents recorded in voltage-clamp where some DACs were quiescent (19%), or exhibited robust nonrhythmic synaptic events (42%). The remaining DACs exhibited waves of oscillatory activity (39%), characterized by either rhythmic bursts of synaptic events (17%) or slow inward currents (22%). Bath application of 50 μM biccuculine or 150 μM picrotoxin had no effect on the waves of activity, however, the gap junction blocker, carbenoxolone (100 μm), blocked both oscillatory patterns. By including Lucifer yellow and biocytin in the recording pipette, it was possible to determine the morphology of recorded neurons and group them based on dendritic extent as small-, medium-, or large-field DACs. There were few relationships between these morphologically defined groups and their intrinsic membrane properties. The present study provides the first in-depth examination of the intrinsic membrane properties of DACs in the ferret retina and provides new insights into the potential roles these neurons play in the processing of visual information in the mammalian retina.

Apoptotic death of beta cells after optic nerve transection in adult cats

We have revealed previously that the survival rate of beta cells of cat retinal ganglion cells (RGCs) rapidly decreased to 29% on day 7 after optic nerve transection, whereas that of alpha cells slowly decreased to 64% on day 14 (Watanabe et al., 2001). The reason that beta cells die more rapidly than alpha cells was not clear. In the present study, we tested the possibility that the rapid death of beta cells is attributable to apoptosis, as shown for some axotomized RGCs in rats. The following results were obtained. First, the proportion of pyknotic cells in Nissl-stained cat retinas started to increase sharply starting on day 4 and reached a peak on day 6 after optic nerve transection. The time course of occurrence of pyknotic cells corresponded well with that of the rapid death of axotomized beta cells. Secondly, the proportion of pyknotic cells was the highest in the area centralis (AC), in which beta cells are densely distributed. The preferential death of axotomized RGCs in the AC was also confirmed by terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling staining in cross sections. Thirdly, after the intravitreal injection of caspase 3 inhibitor (z-DEVD-cmk) the survival of axotomized beta cells on day 7 was significantly enhanced, whereas no such survival-promoting effect was obtained in axotomized alpha cells. Taken together, these results suggest that the rapid death of axotomized beta cells is attributable mainly to apoptosis, which is mediated by caspase 3.

Theta ganglion cell type of cat retina

We define a new bistratified ganglion cell type of cat retina using intracellular staining in vitro. The theta cell has a small soma, slender axon, and delicate, highly branched dendritic arbor. Dendritic fields are intermediate in size among cat ganglion cells, with diameters typically two to three times those of beta cells. Fields increase in size with distance from the area centralis, ranging in diameter from 70 to 150 microns centrally to a maximum of 700 microns in the periphery. Theta cells have markedly smaller dendritic fields within the nasal visual streak than above or below it and smaller fields nasally than temporally. Dendritic arbors are narrowly bistratified. The outer arbor lies in the lower part of sublamina a (OFF sublayer) of the inner plexiform layer where it costratifies with the dendrites of OFF alpha cells. The inner arbor occupies the upper part of sublamina b (ON sublayer), where it costratifies with ON alpha dendrites. The outer and inner arbors are composed of many relatively short segments and are densely interconnected by branches that traverse the a/b sublaminar border. Experiments combining retrograde labeling with intracellular staining indicate that theta cells project to the superior colliculus and to two components of the dorsal lateral geniculate nucleus (the C laminae and medial interlaminar nucleus). Theta cells project contralaterally from the nasal retina and ipsilaterally from the temporal retina. They apparently correspond to a sluggish transient or phasic W-cell with an ON-OFF receptive field center.

Transneuronal degeneration of retinal ganglion cells in early hemispherectomized monkeys

Transneuronal retrograde cell changes in the retina of the primate have been well documented after lesions to striate cortex, but little is known about the effects of hemispherectomy, a surgical procedure used in humans for the treatment of intractable epilepsy. In order to follow the time course of this degenerative process, we examined the retinae of six monkeys who underwent a total hemispherectomy at various postnatal ages with a survival period of 4 years. We demonstrate that transneuronal retrograde degeneration in the retina following hemispherectomy is inversely correlated with age at the time of the lesion. This degeneration is maximal when the lesion is induced within the first 4-6 months of life and less pronounced from 8 months to adulthood.

The eyes of deep-sea fish. II. Functional morphology of the retina

Three different aspects of the morphological organisation of deep-sea fish retinae are reviewed: First, questions of general cell biological relevance are addressed with respect to the development and proliferation patterns of photoreceptors, and problems associated with the growth of multibank retinae, and with outer segment renewal are discussed in situations where there is no direct contact between the retinal pigment epithelium and the tips of rod outer segments. The second part deals with the neural portion of the deep-sea fish retina. Cell densities are greatly reduced, yet neurohistochemistry demonstrates that all major neurotransmitters and neuropeptides found in other vertebrate retinae are also present in deep-sea fish. Quantitatively, convergence rates in unspecialised parts of the retina are similar to those in nocturnal mammals. The differentiation of horizontal cells makes it unlikely that species with more than a single visual pigment are capable of colour vision. In the third part, the diversity of deep-sea fish retinae is highlighted. Based on the topography of ganglion cells, species are identified with areae or foveae located in various parts of the retina, giving them a greatly improved spatial resolving power in specific parts of their visual fields. The highest degree of specialisation is found in tubular eyes. This is demonstrated in a case study of the scopelarchid retina, where as many as seven regions with different degrees of differentiation can be distinguished, ranging from an area giganto cellularis, regions with grouped rods to retinal diverticulum.

The zeta cell: a new ganglion cell type in cat retina

We define a new morphological type of ganglion cell in cat retina by using intracellular staining in vitro. The zeta cell has a small soma, slender axon, and compact, tufted, unistratified dendritic arbor. Dendritic fields were intermediate in size among cat ganglion cells, typically twice the diameter of beta cell fields. They were smallest in the nasal visual streak (<280 microm diameter), especially near the area centralis (60-150 microm diameter), and largest in the nonstreak periphery (maximum diameter 570 microm). Fields sizes were symmetric about the nasotemporal raphe except near the visual streak, where nasal fields were smaller than temporal ones. Zeta-cell dendrites ramified near the boundary between sublaminae a and b (OFF and ON sublayers) of the inner plexiform layer, occupying the narrow gap separating the dendrites of ON and OFF alpha cells. There was no evidence for separate ON and OFF types of zeta cell. Retrograde labeling studies revealed that both nasally and temporally located zeta cells project to the contralateral superior colliculus, whereas few project to the ipsilateral colliculus or to any subdivision of the dorsal lateral geniculate nucleus. The zeta cell's morphology and projection patterns suggest that it corresponds to the ON-OFF phasic W-cell (also known as the local edge detector) of physiological studies. Zeta cells have particularly small dendritic fields in the visual streak, presumably because they are disproportionately represented in the streak in comparison with other ganglion cell types. These conditions are consistent with optimal spatial resolution along the retinal projection of the visual horizon rather than principally at the center of gaze. Strong commonalities with similar ganglion cell types in ferret, rabbit, and monkey suggest that "zeta-like" cells may be a universal feature of the mammalian retina.

Transneuronal retrograde degeneration of retinal ganglion cells following cerebral hemispherectomy in cats

We have assessed the extent of transneuronal retrograde degeneration of retinal ganglion cells (RGCs) following the removal of a whole cerebral hemisphere at postnatal age 16 and 25 days. In the P16 animal, the nasal retina contralateral to the lesion suffered a 41% cell loss, whereas cell loss in the temporal retina ipsilateral to the lesion was 33%. Cell loss was greater in nasal retina and mainly included medium sized cells (200-600 microns2). In the P25 animal overall there was no evidence for ganglion cell loss.

Size and distribution of retinal ganglion cells in the St. Kitts green monkey (Cercopithecus aethiops sabeus)

The topographical distribution of density and the soma size of retinal ganglion cells (RGCs) were studied in the St. Kitts green monkey (Cercopithecus aethiops sabeus). The total number of RGCs, estimated from light microscopic analysis of wholemounted and of transversely sectioned retinae, ranged between 1,183,721 and 1,273,715 (mean 1,228,646). These estimates are comparable to the number of optic nerve fibres (1,220,000) estimated from semithin sections. The topographic distribution of RGCs shows a strong centroperipheral gradient. The soma size distribution of RGCs in Nissl-stained flatmounts falls within a range of between 5.7 microm and 22.9 microm and is comparable to other primate species. Somata of RGCs were found to be generally smaller within the fovea than in peripheral regions. Ganglion cells, as reported for other diurnal primates, are nonuniformly distributed with a slight nasotemporal elongation of isodensity contours, and they exhibit nasotemporal asymmetry in the frequency distribution of soma size. The topography of the RGC distribution of this semiarboreal, ground-dwelling monkey is similar to what has been found in other diurnal Old World species.

Distribution and coverage of beta cells in the cat retina

We have reexamined the retinal distribution and dendritic field dimensions of beta cells in the cat retina. Beta cells were labeled by retrograde transport from the A-layers of the lateral geniculate nucleus and distinguished from alpha cells on the basis of soma size. Dendritic fields of beta cells were visualized by intracellular staining in vitro. The fraction of cat ganglion cells that were beta cells varied with retinal location. Except near the area centralis, beta cells represented about half of all ganglion cells in the nasal hemiretina. They contributed as heavily as the other major ganglion cell classes to the nasal visual streak. In and near the area centralis and in the temporal retina, beta cells represented about two-thirds of all ganglion cells. The areas of beta cell dendritic fields were reciprocally related to beta cell density. For example, they were 3-fold smaller within the visual streak than at matched eccentricities outside it. For many cells, we could estimate both local beta cell density and dendritic field area. Coverage factor (dendritic field area x local density) remained constant at about 4 despite 100-fold variations in beta cell density, and was independent of eccentricity, nasotemporal location, or position relative to the visual streak. Analysis in terms of sampling theory suggests that the beta cell array is matched to X-cell spatial resolution so as to optimize acuity. The beta cell distribution and its systematic reflection in dendritic architecture predict acuity levels that apparently correlate well with actual visual performance across the cat's visual field.

Role of transcription factors Brn-3.1 and Brn-3.2 in auditory and visual system development

The neurally expressed genes Brn-3.1 and Brn-3.2 (refs 1-6) are mammalian orthologues of the Caenorhabditis elegans unc-86 gene that constitute, with Brn-3.0 (refs 1-3,8,9), the class IV POU-domain transcription factors. Brn-3.1 and Brn-3.2 provide a means of exploring the potentially distinct biological functions of expanded gene families in neural development. The highly related members of the Brn-3 family have similar DNA-binding preferences and overlapping expression patterns in the sensory nervous system, midbrain and hindbrain, suggesting functional redundancy. Here we report that Brn-3.1 and Brn-3.2 critically modulate the terminal differentiation of distinct sensorineural cells in which they exhibit selective spatial and temporal expression patterns. Deletion of the Brn-3.2 gene causes the loss of most retinal ganglion cells, defining distinct ganglion cell populations. Mutation of Brn-3.1 results in complete deafness, owing to a failure of hair cells to appear in the inner ear, with subsequent loss of cochlear and vestibular ganglia.

Factors affecting the survival of cat retinal ganglion cells after optic nerve injury

After partial transection of one optic nerve in adult cats the majority of beta retinal ganglion cells degenerate and die 1 week after axotomy, whilst other cell classes degenerate slowly and survive for a long period after the lesion. We have investigated the effects of intravitreal and intraperitoneal injections of MK-801, a NMDA-glutamate receptor antagonist, on the early degeneration of retinal ganglion cells after partial optic nerve section. Control animals received saline intravitreal injections. Retinal flat mounts were retrogradely labelled with horseradish peroxidase and counterstained with Cresyl Violet. We evaluated the ganglion cell loss in the three experimental groups 1 week after lesion and compared them with normal uninjured controls and injured untreated retinae. In untreated retinae 49% of ganglion cells die 1 week after the lesion. Systemic MK-801 or saline prolonged survival of 41% of retinal ganglion cells that would die without treatment. Intravitreal MK-801 or saline prolonged survival of 71% of retinal ganglion cells that would die without treatment, but the results of saline administration had a larger range of variability. In untreated retinae many pyknotic cells were observed. They decreased in number after systemic MK-801 treatment and in some retinae treated with intravitreal injections of saline solution. There were no pyknotic cells after local, intravitreal MK-801 treatment. These results support the hypothesis that NMDA-receptor mediated neurotoxicity plays an important role in the early retinal ganglion cell death after retrobulbar axotomy. They also support the existence of an endogenous source of neurotrophins whose release is triggered by eyeball injury. We conclude that the early death of beta retinal ganglion cells after axotomy occurs by a mechanism that can be controlled by neurotrophins and antagonists to NMDA-glutamate receptors.

Retinal pathology in Alzheimer's disease. II. Regional neuron loss and glial changes in GCL

Detailed analyses of neuronal and astrocyte cell numbers in the ganglion cell layer (GCL) of whole-mounted peripheral retinas from 16 Alzheimer's disease (AD) and 11 control eyes (11 and 9 cases, respectively) demonstrate extensive neuronal loss throughout the entire retina in AD as compared to control eyes. The observed neuronal loss is most pronounced in the superior and inferior quadrants, ranging between 40 and 49% throughout the midperipheral regions, and reaching 50-59% in the far peripheral inferior retina, while the overall neuronal loss throughout the entire retina amounts to 36.4% (p < 0.004). Although the 16% increase in astrocyte numbers is not significant, the ratio of astrocytes to neurons is significantly higher (82%; p < 0.0008) in AD as compared to normal retina (0.238 +/- 0.070 vs. 0.131 +/- 0.042). These results are strengthened by the close agreement (within +/- 15% of respective means) found between fellow eyes. Analysis of glial fibrillary acidic protein immunoreactivity (GFAP-ir) in sections of retinas from an additional 12 AD and 19 control cases show increased GFAP-ir with more extensive labeling of astrocytes in the GCL as well as increased labeling of Müller cell end-feet and radial processes in AD as compared to control retinas. The extensive loss of neurons documented in these retinas, accompanied by an increased astrocyte/neuron ratio, provides further support for the substantial involvement of the retina in AD.

Monoclonal antibody C38 recognizes retinal ganglion cells in cats and rats

We developed monoclonal antibody C38 which specifically recognizes retinal ganglion cells (RGCs) in flatmount preparations of cat and rat retinas. We first induced immunological tolerance in Balb/c mice against axotomized rat retinas which lack most of the RGCs. Then the mice were immunized with intact rat retinas to produce antibodies against RGCs. Monoclonal antibody C38 appeared to be specific for cat RGCs based on immunoreactivities seen in flatmounts and vertical sections of the retina. In rats, we verified that over 90% of retrogradely labeled RGCs were immunoreactive for C38 antibody. In axotomized rat retinas, surviving RGCs were labeled with C38 without erroneous labeling of glial cells. The antigen that C38 recognized was 24 kDa in molecular weight and found in cerebrum, cerebellum, and spinal cord as well as retina. It is suggested that monoclonal antibody C38 is a useful label for RGCs.

Topography of ganglion cells and photoreceptors in the retina of a New World monkey: the marmoset Callithrix jacchus

We studied the anatomical substrates of spatial vision in a New World monkey, the marmoset Callithrix jacchus. This species has good visual acuity and a foveal specialization which is qualitatively similar to that of humans and other Old World primates. We measured the spatial density of retinal ganglion cells and photoreceptors, and calculated the relative numbers of these cell populations. We find that ganglion cells outnumber photoreceptors by between 2.4:1 and 4.2:1 in the fovea. The peak sampling density of ganglion cells is close to 550,000 cells/mm2. This value falls by almost 1000-fold between the fovea and peripheral retina; a value which approaches recent estimates of the centroperipheral ganglion cell gradient for human and macaque monkey retina and primary visual cortex. The marmoset shows a sex-linked polymorphism of color vision: all male and some female marmosets are dichromats. Six of the retinas used in the present study came from animals whose chromatic phenotype was identified in electrophysiological experiments and confirmed by polymerase chain reaction (PCR) amplification of cone opsin encoding genes. One animal was a trichromat and the others were dichromats. Antibodies against short wavelength-sensitive (SWS) cones labeled close to 8% of all cones near the fovea of one dichromat animal, consistent with electrophysiological evidence that the SWS system is present in all marmosets. The topography and spatial density of cone photoreceptors and ganglion cells was similar to that reported for macaque retina, and we found no obvious difference between dichromatic and trichromatic marmoset retinas. These results reinforce the view that the main determinate of primate foveal topography is the requirement for maximal spatial resolution.

Somatostatin-immunoreactive neurons in the adult rabbit retina

Somatostatin (SRIF) is a neuroactive peptide that is distributed throughout the nervous system, including the retina. This peptide has been localized to populations of amacrine cells in a variety of vertebrate species. In the rabbit retina, SRIF immunoreactivity is present in a sparse population of medium to large neurons (13.72 microns in diameter, or 147.84 mu 2) in the ganglion cell layer and in a small number of neurons in the inner nuclear layer. These cells display a preferential distribution to the inferior retina, with the highest density near the ventral and ventrolateral retinal margins (11.33 cells/mm2). SRIF-immunoreactive cells have two to five primary processes that arborize in the proximal inner plexiform layer (IPL). These give rise to a plexus of finer processes in the distal IPL. Occasional immunoreactive processes are also present in the outer plexiform layer. In the IPL, these laminar networks are present in all retinal regions. In addition, SRIF-immunoreactive cells often have a fine-caliber axonlike process that eminates from the soma or perisomal region. These processes travel for great distances across the retina in either the nerve fiber layer or in the distal IPL but are never seen to enter the optic nerve head. In addition, the number of SRIF-immunoreactive somata remains unchanged following transection of the optic nerve. Taken together, these data indicate that SRIF-immunoreactive neurons of the rabbit retina are displaced amacrine cells. Furthermore, the sparse distribution of SRIF-immunoreactive somata, the wide-ranging, asymmetric arborization of their cellular processes, and previous pharmacological studies suggest that these neurons mediate a broad modulatory role in retinal function.

Retinal neurons of the California ground squirrel, Spermophilus beecheyi: a Golgi study

Although the optic nerve fibers of the cone-dominant ground squirrel retina have been well studied physiologically, the morphological details of the retinal neurons have not. To that end, retinal neurons of the California ground squirrel have been studied in Golgi-impregnated wholemounts. Two types of horizontal cell have been identified: H1 has an axon and axon terminal, whereas H2 is axonless. The dendritic field of H1 cells enlarges in a nonuniform manner with increasing displacement from the central retina. The smallest examples lie centrally in the visual streak, and the largest occur in the superior periphery. Eight types of bipolar cell are distinguished by morphological differences in dendritic branching pattern and field size in the outer plexiform layer, cell body size, and layering within the inner nuclear layer and by the morphology and stratification of axon terminals in the inner plexiform layer. A large bistratified bipolar cell (B8) is introduced here; the other 7 types closely resemble those in the retinas of other sciurid species described by R.W. West (1976, J. Comp. Neurol. 168:355-378; 1978, Vision Res. 18:129-136). The B1 type is proposed as a blue cone bipolar cell. Amacrine cells are classified into 27 cell types. Six of these occur as mirror-image pairs across the inner plexiform layer, the soma of one of each pair being "displaced" to the ganglion cell layer. The best described of these pairs is the very elaborate starburst amacrine cell, A5, which stains regularly in these wholemounted retinas. Changes in dendritic field size of both A5 subtypes with retinal location are quantified. The morphology of three amacrine cell types identified in Spermophilus beecheyi suggests that their possible counterparts in S. mexicanus (West, 1976) were, as displaced amacrine cells, misidentified as ganglion cells. Amacrine cell types that may play roles in the rod pathway, the blue cone pathway, and ganglion cell directional selectivity are discussed. No type of interplexiform cell was observed. Ganglion cells are classified into 19 cell types, 9 of which probably correspond to the ganglion cells described by West (1976) in the Mexican ground squirrel. The bistratified G11 cell is proposed as an ON-OFF directionally selective type.

On the distribution of gamma cells in the cat retina

Ganglion cells of the cat retina that are neither alpha nor beta cells are often lumped for convenience into a single anatomical group--the gamma cells (Boycott & Wässle, 1974; Stone, 1983; Wässle & Boycott, 1991). Defined in this way, gamma cells are the morphological counterpart to the physiological W-cell class, which includes all ganglion cells that are neither Y (alpha) nor X (beta) cells. We have estimated the retinal distribution of gamma cells by using retrograde transport to label ganglion cells innervating the superior colliculus and by assuming that these included virtually all gamma cells and no beta cells. We excluded labeled alpha cells on the basis of soma size. Our data suggest that gamma cells represent just under half of the ganglion cells in most of the nasal retina, but only about a third of those in the area centralis and temporal retina. Gamma cells do not appear to be more highly concentrated in the nasal visual streak than are other ganglion cells. In the temporal retina, gamma cells with crossed projections to the brain are apparently at least twice as common as those with uncrossed projections.

Retinal ganglion cell axon diameter spectrum of the cat: mean axon diameter varies according to retinal position

Axon diameters of retinal ganglion cells were measured from electron micrographs of the nerve fiber layer of the cat. Three adult retinae were examined which had mean axonal diameters of 1.18 +/- 0.86 (n = 5553), 1.12 +/- 0.79 (n = 7265), and 1.47 +/- 1.11 microns (n = 10,867). Cumulative histograms from several locations adjacent to the optic disc were unimodal (modal peaks: 0.6-0.8 microns). This unimodal distribution, however, did not reflect the regional differences in axonal diameters found throughout the retina. In many locations, especially those related to axons of the temporal retina, axon diameter distributions were clearly bimodal or even trimodal (modal peaks: 0.6-0.8, 1.4-2.1, and 3.3 microns). Measurements from one retina indicated that the mean diameters of axons arising from the area centralis and visual streak (0.94 +/- 0.63 and 0.98 +/- 0.68, respectively) were not significantly different from each other; however, when compared to other areas around the optic disc, the percentage of fibers with diameters between 1.5-2.0 microns was highest in the sample adjacent to the area centralis. Axons temporal to the optic disc were found to be on average larger than those nasal to the optic disc; similarly superior axons were larger than inferior axons. Axonal distributions at the retinal periphery were found to be significantly different from those at the optic disc (P < or = 0.05) and contained a higher percentage of medium-sized axons and fewer small axons. In each of the three retinae the proportions small, medium, and large axons were respectively gamma: 46; 47; 48, beta: 50; 49; 48, and alpha: 4; 4; 4; regional differences in the proportions of each axonal class are compared to previously published ganglion cell density maps. Differences between axonal bundles within each sample location were not significantly different; however, in one retina axons in the scleral half of the fiber layer were significantly larger (P < or = 0.01) than axons in the vitreal half of the nerve fiber layer adjacent to the optic disc. When compared to the axonal diameter distributions found within the optic nerve (Cottee et al., 1991) and optic tract (Reese et al., 1991), our data indicates that the diameter of retinal axons may increase by up to 30% along the length of the visual pathway.

Birthdates of neurons in the retinal ganglion cell layer of the ferret

The present study determined the temporal and spatial patterns of genesis for neurons of different sizes in the retinal ganglion cell layer of the ferret. Fetal ferrets were exposed to tritiated thymidine on embryonic days E-22 through E-36. One to 3 months after birth, they were perfused and their retinae dissected, and autoradiographs were prepared from resin-embedded sections throughout the entire flattened retinal ganglion cell layer. Soma size differences in conjunction with separate retrograde labeling and calbindin immunocytochemical studies were used as criteria for identifying different retinal ganglion cell subtypes in juvenile and adult ferrets. Neurons of different sizes in the ganglion cell layer were generated at different stages during development. Medium sized cells were generated primarily between E-22 and E-26; the largest cells were generated between E-24 and E-29; small cells were generated between E-26 and E-32; and very small cells were generated between E-29 and E-36. The former three groups were interpreted to be three subtypes of retinal ganglion cells, while the latter group was interpreted to be displaced amacrine cells. This temporal order of the genesis of ganglion cell classes is consistent with the spatial ordering of their fibers in the mature optic chiasm and tract, and it is consistent with the developmental change in decussation pattern recently shown in the optic pathway of embryonic ferrets. The spatial pattern of genesis suggests that ganglion cells of a particular class are added to the ganglion cell layer in a centroperipheral fashion initiated in the dorsocentral retina nasal to the area centralis. No evidence was found for a wave of ganglion cell addition that proceeded in a spiralling pattern around the area centralis, as has been reported in the cat.

An immunocytochemical marker for hamster retinal ganglion cells

We examined the specificity and developmental time course of the labelling of retinal ganglion cells in Syrian hamsters by a monoclonal antibody AB5. In adult hamsters, AB5 selectively labelled somata in the ganglion cell layer, dendrites in the inner plexiform layer and axons in the nerve fibre layer. When retinal ganglion cells were retrogradely labelled with DiI prior to AB5 immunocytochemistry, all of the retrogradely labelled retinal ganglion cells in the ganglion cell layer were AB5 immunoreactive, indicating that AB5 labels all classes of ganglion cell in that layer. In retinae depleted of retinal ganglion cells by neonatal optic nerve transections, AB5 did not label any somata or processes, indicating that AB5 specifically labels retinal ganglion cells. During development, AB5 labelling first appeared as a weak staining of cell bodies in the ganglion cell layer on postnatal day 12 (P12; PO = first 24 h following birth) and acquired the staining pattern seen in the adult by postnatal day 14. From the onset of AB5 immunoreactivity, AB5-labelled somata of varying sizes were present across the entire retinal surface. Although AB5 labelled retinal ganglion cell axons in the nerve fibre layer of the retina it did not label the optic nerve or retinal ganglion cell axons in the brain at any age examined. AB5 labelling was also found to be compatible with bromodeoxyuridine immunocytochemistry and, therefore, useful for determining the time of generation of hamster retinal ganglion cells.

Morphometry and distribution of displaced dopaminergic cells in rat retina

The majority of dopaminergic (DA) cells, labeled by tyrosine hydroxylase (TH) immunohistochemistry, are located in the amacrine cell layer (i.e., the innermost sublayer of the inner nuclear layer) in the rat retina. We describe a small population of DA cells, observed in retinal wholemounts, that are displaced to either the inner plexiform layer (DAIcs) or the ganglion cell layer (DAGcs). Contrary to some other species, such cells are few in number in the rat retina. Their systematic study was made in young and adult retinas by retinal mapping, camera lucida drawing, and computer-aided three-dimensional reconstruction. Located predominantly in the superior temporal quadrant, they are observed as soon as the second postnatal day. Most of the morphometric parameters studied were not significantly different between the two types of displaced DA cells, despite the characteristic appearance of interstitial cells. Two hypotheses are proposed for the origin of their displacement: either it is accidental or programmed. Our results favor the former possibility.

Microglial invasion and activation in response to naturally occurring neuronal degeneration in the ganglion cell layer of the postnatal cat retina

Retinae of kittens between postnatal (P) days 2 and 10 were examined for the presence of degenerating neuronal profiles, normal nucleoli and microglia. Comparison of the numbers of degenerating profiles with numbers of axons lost from the optic nerve suggest that the majority of these profiles result from the degeneration of retinal ganglion cells. Analysis of local densities of the different profiles revealed different rates of cell loss, occurring at different times in central and peripheral retina. The period of rapid cell loss occurred between P2 and P3 in central retina compared to between P8 and P10 in peripheral retina. At both locations, these periods of rapid cell loss were accompanied by a decrease in the ratio of microglia to dying cells even though the absolute densities of microglia increased. However, calculation of the clearance times of cellular debris indicate that the speed of removal of degeneration products is greater during rapid cell loss, which suggests that cellular degeneration serves to activate the phagocytic process.

Neurotoxic effects of neonatal injections of monosodium L-glutamate (L-MSG) on the retinal ganglion cell layer of the golden hamster: anatomical and functional consequences on the circadian system

In rodents, daily injection of neurotoxic monosodium L-glutamate (MSG) during the postnatal period induces retinal lesions, optic nerve degeneration with an alteration of visual pathway and an absence of the b-wave in the electroretinogram. Despite this damage, electrophysiological responses subsist in the lateral geniculate bodies and synchronization of circadian rhythms to the light/dark cycle can still occur. Using two formal properties of the circadian system (entrainment and phase-shift by light), we assessed the functionality of retinal projections to the circadian clock in MSG-treated hamsters. Displaced amacrine and ganglion cell populations were quantified and retinal terminals in the suprachiasmatic nuclei were estimated. Animals received daily doses of glutamate during the first ten days after birth according to two protocols. The two treatments similarly destroyed 56% of the overall population of the ganglion cell layer: 30% of displaced amacrine and 89% of ganglion cells. Surviving ganglion neurons (7,500 cells) were evenly distributed across the entire retina except in one area of high cell density located in the temporoventral quadrant. Retinal projections of the "image-forming" pathway were drastically reduced in the dorsal lateral geniculate bodies, less in their ventral part. The "nonimage-forming" pathway was also affected since the volume of labeled terminals in the suprachiasmatic nuclei was reduced by one-half to one-third. Nevertheless, treated hamsters exhibited a free-running locomotor activity rhythm after several months in constant darkness, could be entrained by the light/dark cycle and phase-shifted by light pulses. These results suggest that a damaged retinohypothalamic tract can still assume the photic entrainment of the circadian clock.

Transient period of correlated bursting activity during development of the mammalian retina

The refinement of early connections in the visual pathway requires electrical activity in the retina before the onset of vision. Using a multielectrode array, we have shown that the spontaneous activity of cells in the neonatal ferret retina is correlated by patterns of periodically generated traveling waves. Here, we examine developmental changes in the characteristics of the waves and show that retinal ganglion cells participate in these patterns of activity, which are seen during the same period as synaptic modification in the lateral geniculate nucleus; that the waves subside gradually as the connectivity in the lateral geniculate nucleus stabilizes; and that their spatial structure allows for refinement of the retinotopic map, as well as for eye-specific segregation in the lateral geniculate nucleus.

The retinal ganglion cell distribution and the representation of the visual field in area 17 of the owl monkey, Aotus trivirgatus

The distribution of ganglion cells and displaced amacrine cells was determined in whole-mounted Aotus retinae. In contrast to diurnal simians, Aotus has only a rudimentary fovea. Ganglion cell density decreases towards the periphery at approximately the same rate along all meridians, but is 1.2-1.8 times higher in the nasal periphery when compared to temporal region at the same eccentricities. The total number of ganglion cells varied from 421,500 to 508,700. Ganglion cell density peaked at 15,000/mm2 at 0.25 mm dorsal to the fovea. The displaced amacrine cells have a shallow density gradient, their peak density in the central region is about 1500-2000/mm2 and their total number varied from 315,900 to 482,800. Comparison between ganglion cell density and areal cortical magnification factor for the primary visual cortex, area 17, shows that there is not a simple proportional representation of the ganglion cell distribution. There is an overrepresentation of the central 10 deg of the visual field in the visual cortex. The present results for Aotus and the results of a similar analysis of data from other primates indicate that the overrepresentation of the central visual field is a general feature of the visual system of primates.

Translaminar deficits in the retinae of albinos

The central retina in albino mammals is poorly developed. There is a general reduction in ganglion cell density compared with the normal animal, and there are irregularities in the center to periphery gradient in ganglion cell density. It is not known whether, and if so to what extent, this abnormality is associated with deficits in other retinal layers. In this study the distribution of cells in the ganglion cell layer has been determined in horizontally sectioned eyes from pigmented and albino ferrets. This was undertaken to define the location of the region of highest cell density and the relative cell gradients around it. Detailed counts and measurements were then undertaken to determine the cell density within, and thickness of, the inner and the outer nuclear layers in these animals. All the albino animals had an abnormal distribution of cells in the ganglion cell layer in the central retina when compared with pigmented animals. The extent of this abnormality was variable. No differences between pigmented and albino animals could be found in the packing density of cells within the inner or the outer nuclear layer. However, in the pigmented animals there was a clear increase in the thickness of these layers associated with the region of highest density in the ganglion cell layer. This feature was absent in the albino animals, where the gradient in layer thickness was less marked and frequently contained irregularities. These abnormalities were most obvious in the outer nuclear layer.

Gliosis and ganglion cell death in the developing cat retina during hydrocephalus and after decompression

Even after surgical decompression, infantile hydrocephalus often results in permanent neurological symptoms, including visual deficits. However, little is known about the cellular changes that may be responsible for these effects. The present study was designed to analyze the retinae of normal, mildly hydrocephalic, severely hydrocephalic and surgically decompressed kittens to determine if changes occur in the density and size of retinal ganglion cells. Hydrocephalus was induced in 10 day old kittens by intra-cisternal injection of kaolin. Kittens were allowed to survive from 7 to 28 days after injection. Animals that were decompressed received ventriculoperitoneal shunts 10-15 days after the induction of hydrocephalus and were sacrificed 10-14 days after shunt placement. The density and area of neuronal and glial cells were determined within a sample area in peripheral nasal retina. Total cell density was significantly increased in mildly and severely hydrocephalic animals but returned to normal following decompression. This change represents a significant increase in the glial population. In addition, there was a significant loss of ganglion cells in both the severely hydrocephalic and the shunted groups. Based on these findings, we conclude that gliosis occurs as a result of cell death in the retina following severe hydrocephalus, and decompression is unable to reverse these effects. Furthermore, gliosis occurs in mild cases of hydrocephalus, and may be an early indication that cellular degeneration will follow.

The superficial plexiform layer: a third retinal association area

Electron microscopy enables the identification of a new association area in the mammalian retina. It is a region whose processes and synaptic junctions form a diffuse and intermittent layer bridging the boundary between the optic nerve fibre layer and ganglion cell layer. It involves displaced amacrine cells, retinal ganglion cells and probably interplexiform cell processes. Because it is close to the vitreal surface of the retina and has several properties of a plexiform layer, it has been named the superficial plexiform layer. It is much more sparse than the outer or inner plexiform layers in the rabbit, but contains a significant and substantial density of 6,100 synapses/mm2 near the visual streak. Morphological criteria distinguish two classes of synapses in the new association area. One has features of Colonnier's symmetric type and is formed by amacrine-like processes or their terminals, onto other amacrine-like processes or the cell bodies, dendrites and axon hillocks of some large ganglion cells. It makes up 79% of the population at a density of 4,800 synapses/mm2 in the examined sample. The second class arises from large processes of the fibre layer, which resemble axons rather than amacrine cell branches, has Colonnier's asymmetric form, and synapses onto a variety of other neuronal processes and cells. At a local density of 1,300/mm2 this type forms 21% of the population. A series of experiments including Wallerian degeneration, retrograde degeneration, electron microscopy and horseradish peroxidase (HRP) transport was employed to determine the nature of the large synapse-forming processes of the fibre layer that were the most amenable to investigation. It is concluded that the processes project into the optic nerve because they can be filled with HRP by retrograde transport from the end of the transected optic nerve. Although this result is based on limited evidence, it is complemented by the observation that the majority of the fibres undergo retrograde degeneration within 25 days of optic nerve section. It is concluded that the processes are either centrifugal fibres or the axons of retinal ganglion cells. The persistence of a relatively normal density of synapse-forming large fibres for seven days after optic nerve section, without Wallerian degeneration, argues that they are not the terminals of centrifugal axons. This conclusion is complemented by a separate class of profiles that did degenerate in this short period and are concluded to represent the centrifugal fibres. The large synapsing processes of the fibre layer are concluded to be the axons of some large ganglion cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Retinal ganglion cell degeneration following loss of postsynaptic target neurons in the dorsal lateral geniculate nucleus of the adult cat

Kainic acid was used to produce selective degeneration of neurons in the dorsal lateral geniculate nucleus of the adult cat. This degeneration mimics the rapid loss of geniculate neurons seen after visual cortex ablation in the neonate. Following survivals of 2, 4, or 6 months, the geniculate was injected with horseradish peroxidase and the retinae were examined for the presence of retrogradely labeled cells. Analysis of ganglion cell density in peripheral nasal retina revealed a 58% loss of cells overall at 6 months. The proportion of cells labeled with horseradish peroxidase decreased more rapidly, until none were labeled at 6 months. Separate analysis of small, medium, and large ganglion cell populations revealed that only medium-sized cells were lost at 2 months whereas both medium and large cells were lost at 4 and 6 months. By 6 months, 92% of medium cells and 65% of large cells had degenerated. These results show that mature retinal ganglion cells in the cat maintain a dependence on target integrity for their continued survival. When the appropriate target is lost, the ganglion cells respond first by axon terminal retraction and then by cell death.

Visual factors in sound localization in mammals

The ability of mammals to localize sound varies widely among species. During the past decade, evidence has accumulated that this variation cannot be accounted for simply on the basis of the availability of the physical cues for locus. Evidence is presented that a major factor in sound localization is the need to direct the field of best vision to a sound source for further scrutiny. Thus, species with broad fields of best vision (such as visual streaks) require less accurate information regarding the location of a sound source than do species with very narrow fields of best vision (such as foveae). To support this suggestion, data are reported for the width of the field of best vision in the form of retinal ganglion cell isodensity contours for thirteen species of mammals. The possible contribution of other factors including binocular fields, visual acuity, and the degree to which a species is predatory in lifestyle, is also examined.