Biomedical subjects

D M Dacey

Publications and source records attributed to D M Dacey.

35 records · Page 2Linked to original sources

PubMed1986

Optic tectum of the eastern garter snake, Thamnophis sirtalis. V. Morphology of brainstem afferents and general discussion.

Brainstem neurons that project to the optic tectum of the eastern garter snake were identified by retrograde transport of horseradish peroxidase. The distribution and morphology of tectal afferent axons from the thalamus, pretectum, nucleus isthmi, and midbrain reticular formation were then studied by anterograde transport of horseradish peroxidase. Diencephalic projections to the tectum arise from the ventral lateral geniculate complex ipsilaterally and the ventrolateral nucleus, suprapeduncular nucleus, and nucleus of the ventral supraoptic decussation bilaterally. Three pretectal groups (the lentiform thalamic nucleus, the lentiform mesencephalic-pretectal complex and the geniculate pretectal nucleus) give rise to heavy, bilateral tectal projections. Small neurons in nucleus isthmi and large reticular neurons in nucleus lateralis profundus mesencephali also give rise to bilateral projections. Caudal to the tectum, projections arise bilaterally from the pontine and medullary tegmentum, nuclei of the lateral lemniscus, the posterior colliculus, and the sensory trigeminal nucleus. A small contralateral projection arises from the medial vestibular complex. Tectal afferents from the thalamus, pretectum, nucleus isthmi, and midbrain reticular formation had characteristic morphologies and laminar distributions within the tectum. However, these afferents fall into two groups based on their spatial organization. Afferents from the thalamus and nucleus isthmi arise from small neurons with spatially restricted, highly branched dendritic trees. Their axons terminate in single, highly branched and bouton-rich arbors about 100 micron in diameter. By contrast, afferents from the midbrain reticular formation and the pretectum arise from large neurons with long, radiate, and sparsely branched dendritic trees. Their axons course parallel to the tectal surface and emit numerous collateral branches that are distributed widely through the mediolateral and rostrocaudal extent of either the central or superficial gray layers. Each collateral bears several small, spatially disjunct clusters of boutons.

Animals↗

PubMed1986

Optic tectum of the eastern garter snake, Thamnophis sirtalis. III. Morphology of intrinsic neurons.

Extracellular iontophoretic injections of horseradish peroxidase and Golgi preparations were used to study the distribution and morphology of intrinsic neurons of the garter snake optic tectum. Four morphologically distinct classes of neurons were identified. The type A neuron is found throughout the retinorecipient tectal layers. It has a large, fusiform soma and infrequently branching dendrites that radiate in the horizontal plane and are studded with varicose appendages. An axon arises from the soma or proximal dendrite and gives rise to widely spreading branches that overlap the cell's dendritic field. The type B neuron has a small, spherical soma in sublayer b of the stratum fibrosum et griseum superficiale. Thick, varicose dendrites ascend from the soma and form a bushy arbor in the overlying sublayer a. A thin axon descends vertically from the soma and arborizes in vertical alignment with the cell's dendritic field in sublayer c of the stratum fibrosum et griseum superficiale and the upper third of the stratum griseum centrale. The type C neuron is a bipolar cell with a small, vertically fusiform soma situated at the upper border of the stratum griseum centrale. Thin, sparsely branching dendrites extend vertically into the superficial and central gray layers. An axon arises from the soma and courses ventrally into the stratum griseum centrale where it gives rise to a plexus of widely spreading branches that extend medially from the cell's dendritic field. The type D neuron is a small, stellate cell with a spherical soma and fine, appendage-laden dendrites that are restricted to the stratum griseum centrale. The axon of the type D cell courses in the central gray where it gives rise to widely spreading branches that extend laterally from the cell's dendritic field.

Animals↗

PubMed1986

Optic tectum of the eastern garter snake, Thamnophis sirtalis. IV. Morphology of afferents from the retina.

The morphology of single retinal terminals in the optic tectum of the eastern garter snake was demonstrated by orthograde filling from extracellular injections of horseradish peroxidase (HRP) into the optic tract. HRP-filled terminals share a characteristic shape and structure. Their parent axons course caudally in the stratum opticum within fascicles of 200-300 fibers of varying diameters. Single axons exit a fascicle and course into either the stratum fibrosum et griseum superficiale, ventrally, or the stratum zonale, dorsally, where they bifurcate successively two or three times into preterminal branches. Each preterminal branch gives rise to many thin, terminal branchlets laden with boutons. The arbors are ellipsoidal with their long axes oriented mediolaterally and their short axes oriented rostrocaudally. Arbors vary in their overall size (from 45 to 150 micron), in the diameters of their parent axons (from less than 0.5 to 3.0 micron), and in the size of their terminal boutons (from 0.5 to 3.5 micron). Bouton size increased with increasing diameter of the parent axon. The great majority of arbors are confined to one of three retinorecipient sublayers in the superficial tectum. However, the full range of arbor sizes and axon diameters is present in each sublayer.

Afferent Pathways↗

PubMed1986

Optic tectum of the eastern garter snake, Thamnophis sirtalis. II. Morphology of efferent cells.

Tectal efferent neurons were retrogradely filled from extracellular injections of horseradish peroxidase (HRP) into pathways efferent from the tectum. Tectorotundal neurons have cylindrical dendritic trees, 80-100 microns in diameter, that extend vertically across the central and superficial tectal layers. Apical and basal dendrites are laden with complex appendages. The axon gives rise to an intratectal, collateral arbor that extends horizontally into the stratum griseum centrale beyond the cell's dendritic tree. The parent axon exits the tectum laterally in the tectothalamic tract. Tectogeniculate neurons also have narrow, radially oriented, and highly branched apical dendrites, but their basal dendrites are infrequently branched and lack appendages. An intratectal axon collateral forms a small, spherical arbor overlapping the apical dendrites in sublayer c of the stratum fibrosum et griseum superficiale. The parent axon ascends vertically and just below the stratum opticum turns rostrad to follow the optic fibers to the diencephalon. Tectoisthmi neurons have small somata and thin, radial dendrites that arborize below the pial surface in the stratum zonale. An intratectal axon collateral forms a spatially restricted arbor ventral to the soma in register with the dendritic tree. Tectoisthmobulbar neurons have dendrites that arborize extensively in sublayer a of the stratum fibrosum et griseum superficiale. The axon exits the tectum without collateralizing and joins a small-caliber component of the ventral tectobulbar tract. Ipsilateral tectobulbar neurons have stellate dendritic fields, 150-250 microns in diameter, that are restricted to the deep layers of the tectum. Sparsely branched dendrites are appendage-free but bear many short, fine spicules. The axon initially ascends from the soma and recurves into the stratum album centrale without collateralizing before joining a medium-caliber component of the ventral tectobulbar tract. Crossed tectobulbar neurons have large, stellate dendritic trees with diameters ranging from 200 to 500 microns. Like ipsilateral tectobulbar neurons, their dendrites are appendage-free but bear spicules. Their thick-caliber axons exit the tectum without collateralizing and course deep in the stratum album centrale to reach the dorsal tectobulbar tract.

Animals↗

PubMed1986

Optic tectum of the eastern garter snake, Thamnophis sirtalis. I. Efferent pathways.

Extracellular, iontophoretic injections of horseradish peroxidase were used to anterogradely fill axons efferent from the optic tectum in garter snakes. The tectal efferent pathways consist of six axon types with distinct projections and terminal morphologies. Tectogeniculate axons pass into the diencephalon via the optic tract, bearing collaterals that form spatially restricted, rodlike arbors in the pretectum, the ventral lateral geniculate nucleus, and the ventrolateral nucleus. Tectoisthmi axons exit the tectum as a thin-caliber component of the ventral tectobulbar tract. They form spatially restricted, spherical arbors within nucleus isthmi. Tectoisthmobulbar axons also give rise to small, spherical arbors within nucleus isthmi, but the parent axons continue caudally into the pontine and medullary reticular formation issuing many short collateral branches. Tectorotundal axons reach the diencephalon via the tectothalamic tract and give rise to fine terminal collaterals in the nucleus of the tectothalamic tract ipsilaterally and in nucleus rotundus bilaterally. Single axons form sheetlike terminal fields that span the rostrocaudal extent of nucleus rotundus. Ipsilateral tectobulbar axons descend into the midbrain tegmentum where they issue several thick collaterals that terminate widely throughout the nucleus lateralis profundus mesencephali. The parent axon continues caudally giving off several widely spreading collaterals within the pontine and medullary reticular formation. Crossed tectobulbar axons enter the dorsal tectobulbar tract and cross the midline to form the predorsal bundle. Single axons give rise to terminal collaterals in the nucleus lateralis profundus mesencephali bilaterally, the contralateral pontine and medullary reticular formation, and the intermediate gray of the cervical spinal cord.

Animals↗

PubMed1985

Wide-spreading terminal axons in the inner plexiform layer of the cat's retina: evidence for intrinsic axon collaterals of ganglion cells.

Extracellular, iontophoretic injections of horseradish peroxidase (HRP) were made directly into the cat's retina. The retinas were processed with the cobalt-enhanced diaminobenzidine method and prepared as whole-mounts. These retinas reveal HRP-filled axons that extend widely and terminate within the inner plexiform layer. The axons are morphologically distinct from ganglion and amacrine cell dendritic trees that were retrogradely labelled from the same injection sites. The axons are long and straight, approximately 1 micron in diameter, and in some cases can be traced for several millimeters in the inner plexiform layer. Each axon gives rise to many short, terminal branches that extend, on average, 100 microns from the parent axon and bear clusters of boutons. The terminal branches are widely spaced so that the bouton clusters are distributed in small, isolated patches along the length of the axon. Bouton clusters vary in size and contain from two to over 100 loosely arranged boutons. Single boutons are frequently large, up to 3 microns in diameter. In one case a terminal axon was traced to its origin from the parent axon of an HRP-filled ganglion cell. It is suggested, therefore, that these axons are intrinsic to the retina and originate as primary collaterals of ganglion cells.

Animals↗

PubMed1983

Nucleus rotundus in a snake, Thamnophis sirtalis: an analysis of a nonretinotopic projection.

Nucleus rotundus, a tectorecipient thalamic nucleus in reptiles and birds, is described for the first time in a snake. The morphology of rotundal neurons and tectorotundal axons was studied at the light microscopic level by using anterograde and retrograde filling with the horseradish peroxidase (HRP). Injections of HRP in the dorsal ventricular ridge retrogradely fill neurons in rotundus. Rotundus is situated centrally in the caudal diencephalon medial to the cell plate of the retinorecipient geniculate complex and ventrolateral to the lentiform thalamic nucleus. The dendrites of rotundal neurons are long and radiate, but are confined within the cytoarchitectonically defined borders of the nucleus. Injections of HRP into the optic tectum anterogradely fill axons that project to rotundus bilaterally via the tectothalamic tract. Small injections show that axons arising from a single tectal locus distribute to all sectors of rotundus. Thus, this projection may not be retinotopically organized. However, single axons reconstructed through serial sections form spatially restricted, sheetlike terminal fields that pass caudorostrally through the entire extent of rotundus. Several hypotheses on the functional significance of such organized but nonretinotopic visual projections are discussed.

Animals↗

PubMed1982

Axon morphology of mesencephalic trigeminal neurons in a snake, Thamnophis sirtalis.

The morphology of single axons of mesencephalic trigeminal neurons (Mes V) was studied in the eastern garter snake (Thamnophis sirtalis) by solid filling them with an extracellular horseradish peroxidase technique. Each Mes V axon can be divided into central, peripheral, and descending branches. The central branch descends from its soma of origin in the mid-brain to the dorsal aspect of the motor nucleus of the trigeminal (Motor V) and the motor root, where it splits into peripheral and descending branches. The descending branch travels caudally from Motor V to the brainstem-spinal cord junction. The peripheral branch passes dorsal to motor V and joins the motor root of V to exit the brainstem. All three branches issue a massive collateral system that distributes terminal swelling within the nuclear boundaries of Motor V. Single Mes V axons diverge to sparsely contact a large number of motoneurons throughout the nucleus, suggesting that single motoneurons receive a convergent input from many Mes V neurons. Since Motor V contains multiple, highly overlapping motor pools, single afferents are positioned to contact different motor pools. The descending branch is situated medial and adjacent to the spinal sensory nucleus of the trigeminal (Sensory V). It issues a collateral field to the entire length of Sensory V. The terminal swellings of these collaterals form rostrocaudally aligned sheets, flattened in the horizontal plane. Single terminal sheets have a divergent projection to a large field of sensory cells and single, fusiform sensory cells are positioned to receive a convergent projection from many terminal sheets. The results provide the first detailed description of Mes V axon morphology. The overall pattern of these axons closely resembles that recently described for spinal Ia afferent fibers in cat. There is evidence in both cases for divergence of single afferent terminal fields to set of spatially overlapping motor pools and a convergence of input to single motoneurons from a large population of afferents. This anatomical pattern is consistent with the recently proposed role of sensory feedback in the activity of single motoneurons.

Animals↗

PubMed1977

Aphagia, adipsia, and sensory-motor deficits produced by amygdala lesions: a function of extra-amygdaloid damage.

Small bilateral electrolytic lesions confined to the region of the central nuclei of the amygdala failed to affect food and water consumption in male rats. More medially-placed lesions which damaged portions of the internal capsule, entopeduncular nucleus and globus pallidus adjacent to the central nucleus produced transient aphagia and adipsia accompanied by sensory-motor impairments that interfered with the act of feeding, as evidenced by a large postoperative increase in the amount of food spilled. In some cases lesions restricted to the internal capsule and entopeduncular nucleus produced these sensory-motor deficits but no aphagia or adipsia. Small lesions damaging primarily ventral portions of the posteromedial pallidi resulted in aphagia and adipsia but no apparent sensory-motor impairment. The results indicate that at least two, possibly independent, deficits in food intake may be produced by lesions in the immediate area of the dorsomedial amygdala. It is suggested that the effects on ingestive behavior which several investigators have observed in rats with dorsomedial amygdaloid damage may in fact be due to incidental destruction of adjacent tissues.

Amygdala↗

PubMedDate not supplied

Recoverin immunoreactivity in mammalian cone bipolar cells.

Human, macaque monkey, and rat retinas were immunostained with a polyclonal antibody preparation against purified recoverin, a 23-kD calcium-binding protein isolated from bovine retina that localizes to rods and cones (Dizhoor et al., 1991). In addition to immunoreactive photoreceptors, we have identified subpopulations of recoverin-positive bipolar cells in all three species. Results from immunostaining with progressive dilutions of anti-recoverin and preadsorption of the antibody with a dilution series of purified recoverin showed that photoreceptors and bipolar cells had similar affinities for the antibody and suggested that the molecule recognized by the antibody in both cell types is recoverin. Immunoreactivity for recoverin and protein kinase C, a selective marker for all rod bipolar cells, was found in separate bipolar cell populations. Recoverin immunoreactivity is therefore a characteristic of certain cone bipolar cell types. In rat retina, anti-recoverin labeled two morphologically distinct subpopulations of cone bipolar cells whose axonal arbors stratified at different depths in the inner plexiform layer (IPL). The bipolar cells labeled with anti-recoverin did not correspond to those that were reactive for calbindin, another cone bipolar cell marker. Human and monkey retinas also had two populations of cone bipolar cells that were recoverin-positive. One population showed a distinct pattern of narrow bistratification at the outer border of the IPL and a regular mosaic arrangement of its axonal arbors, suggesting that the entire population of a single cone bipolar type was labeled. Cell density, dendritic morphology, and axonal-field size and stratification indicate that anti-recoverin selectively strains the flat midget (presumed OFF-center) cone bipolar cell type observed previously in Golgi preparations. By contrast the second bipolar cell population had axonal stratification in the inner half of the IPL and showed an unusual but consistent morphology and spatial distribution. Individual cells were intensely stained but were present at an extremely low density (approximately 2-5 cells/mm2). These cells had multibranched dendritic trees characteristic of the diffuse bipolar cell class, but very small axonal fields in the size range of the midget bipolar class. Neither of the two recoverin-positive bipolar cell types in monkey was labeled with anti-calbindin or anti-cholecystokinin. An antibody preparation against bovine pineal hydroxyindole-O-methyltransferase (HIOMT) labeled photoreceptors and bipolar cells that closely resembled the recoverin-positive bipolar cells in human and rat retinas.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMedDate not supplied

Morphology of a small-field bistratified ganglion cell type in the macaque and human retina.

In in-vitro preparations of both macaque and human retina, intracellular injections of Neurobiotin and horseradish peroxidase were used to characterize the morphology, depth of stratification, and mosaic organization of a type of bistratified ganglion cell. This cell type, here called the small bistratified cell, has been shown to project to the parvocellular layers of the dorsal lateral geniculate nucleus (Rodieck, 1991) and is therefore likely to show color-opponent response properties. In both human and macaque, the two dendritic tiers of the bistratified cell are narrowly stratified close to the inner and outer borders of the inner plexiform layer. The inner tier is larger in diameter and more densely branched than the outer tier and gives rise to distinct spine-like branchlets bearing large, often lobulated heads. By contrast the smaller, outer tier is sparsely branched and relatively spine-free. In human retina, the small bistratified cells range in dendritic field diameter from approximately 50 microns in central retina to approximately 400 microns in the far periphery. The human small bistratified cells are about 20% larger in dendritic-field diameter than their counterparts in the macaque. However, when the difference in retinal magnification between human and macaque is taken into account, the small bistratified cells are similar in size in both species. In macaque, the small bistratified cell has a dendritic-field size that is approximately 10% larger than that of the magnocellular-projecting parasol ganglion cell. Human small bistratified ganglion cells tend to have smaller dendritic-field diameters than parasol cells. This is because parasol ganglion cells are larger in human than in macaque retina (Dacey & Petersen, 1992). In macaque retina, intracellular injections of Neurobiotin revealed heterotypic tracer coupling to a distinct mosaic of amacrine cells and probable homotypic coupling to an array of neighboring ganglion cells around the perimeter of the injected cell's dendritic tree. The amacrine cell mosaic had a density of 1700 cells/mm2 in peripheral retina. Individual amacrines had small, densely branched and bistratified dendritic fields. From the homotypic coupling, it was possible to estimate for the small bistratified cell a coverage factor of approximately 1.8, and a density of approximately 1% of the total ganglion cells in central retina, increasing to approximately 6-10% in the retinal periphery. The estimated density, dendritic-field size, and depth of stratification all suggest that the small bistratified ganglion cell type is the morphological counterpart of the common short-wavelength sensitive or 'blue-ON' physiological type.

Adolescent↗

PubMedDate not supplied

A coupled network for parasol but not midget ganglion cells in the primate retina.

Intracellular injections of Neurobiotin were used to determine whether the major ganglion cell classes of the macaque monkey retina, the magnocellular-projecting parasol, and the parvocellular-projecting midget cells showed evidence of cellular coupling similar to that recently described for cat retinal ganglion cells. Ganglion cells were labeled with the fluorescent dye acridine orange in an in vitro, isolated retina preparation and were selectively targeted for intracellular injection under direct microscopic control. The macaque midget cells, like the beta cells of the cat's retina, showed no evidence of tracer coupling when injected with Neurobiotin. By contrast, Neurobiotin-filled parasol cells, like cat alpha cells, showed a distinct pattern of tracer coupling to each other (homotypic coupling) and to amacrine cells (heterotypic coupling). In instances of homotypic coupling, the injected parasol cell was surrounded by a regular array of 3-6 neighboring parasol cells. The somata and proximal dendrites of these tracer-coupled cells were lightly labeled and appeared to costratify with the injected cell. Analysis of the nearest-neighbor distances for the parasol cell clusters showed that dendritic-field overlap remained constant as dendritic-field size increased from 100-400 microns in diameter. At least two amacrine cell types showed tracer coupling to parasol cells. One amacrine type had a small soma and thin, sparsely branching dendrites that extended for 1-2 mm in the inner plexiform layer. A second amacrine type had a relatively large soma, thick main dendrites, and distinct, axon-like processes that extended for at least 2-3 mm in the inner plexiform layer. The main dendrites of the large amacrine cells were closely apposed to the dendrites of parasol cells and may be the site of Neurobiotin transfer between the two cell types. We suggest that the tracer coupling between neighboring parasol cells takes place indirectly via the dendrites of the large amacrine cells and provides a mechanism, absent in midget cells, for increasing parasol cell receptive-field size and luminance contrast sensitivity.

Acridine Orange↗

PubMedDate not supplied

Physiology of the A1 amacrine: a spiking, axon-bearing interneuron of the macaque monkey retina.

We characterized the light response, morphology, and receptive-field structure of a distinctive amacrine cell type (Dacey, 1989), termed here the A1 amacrine, by applying intracellular recording and staining methods to the macaque monkey retina in vitro. A1 cells show two morphologically distinct components: a highly branched and spiny dendritic tree, and a more sparsely branched axon-like tree that arises from one or more hillock-like structures near the soma and extends for several millimeters beyond the dendritic tree. Intracellular injection of Neurobiotin reveals an extensive and complex pattern of tracer coupling to neighboring A1 amacrine cells, to two other amacrine cell types, and to a single ganglion cell type. The A1 amacrine is an ON-OFF cell, showing a large (10-20 mV) transient depolarization at both onset and offset of a photopic, luminance modulated stimulus. A burst of fast, large-amplitude (approximately 60 mV) action potentials is associated with the depolarizations at both the ON and OFF phase of the response. No evidence was found for an inhibitory receptive-field surround. The spatial extent of the ON-OFF response was mapped by measuring the strength of the spike discharge and/or the amplitude of the depolarizing slow potential as a function of the position of a bar or spot of light within the receptive field. Receptive fields derived from the slow potential and associated spike discharge corresponded in size and shape. Thus, the amplitude of the slow potential above spike threshold was well encoded as spike frequency. The diameter of the receptive field determined from the spike discharge was approximately 10% larger than the spiny dendritic field. The correspondence in size between the spiking receptive field and the spiny dendritic tree suggests that light driven signals are conducted to the soma from the dendritic tree but not from the axon-like arbor. The function of the axon-like component is unknown but we speculate that it serves a classical output function, transmitting spikes distally from initiation sites near the soma.

Action Potentials↗

PubMedDate not supplied

Morphology of wide-field bistratified and diffuse human retinal ganglion cells.

To study the detailed morphology of human retinal ganglion cells, we used intracellular injection of horseradish peroxidase and Neurobiotin to label over 1,000 cells in an in vitro, wholemount preparation of the human retina. This study reports on the morphology of 119 wide-field bistratified and 42 diffuse ganglion cells. Cells were analyzed quantitatively on the basis of dendritic-field size, soma size, and the extent of dendritic branching. Bistratified cells were similar in dendritic-field diameter (mean +/- S.D. = 682 +/- 130 microm) and soma diameter (mean +/- S.D. = 18 +/- 3.3 microm) but showed a broad distribution in the extent of dendritic branching (mean +/- S.D. branch point number = 67 +/- 32; range = 15-167). Differences in the extent of branching and in dendritic morphology and the pattern of branching suggest that the human retina may contain at least three types of wide-field bistratified cells. Diffuse ganglion cells comprised a largely homogeneous group whose dendrites ramified throughout the inner plexiform layer. The diffuse cells had similar dendritic-field diameters (mean +/- S.D. = 486 +/- 113 microm), soma diameters (mean +/- S.D. = 16 +/- 2.3 microm), and branch points numbers (mean +/- s.D. = 92 +/- 32). The majority had densely branched dendritic trees and thin, very spiny dendrites with many short, fine, twig-like thorny processes. Five of the diffuse cells had much more sparsely branched dendritic trees (<50 branch points) and less spiny dendrites, suggesting that there are possibly two types of diffuse ganglion cells in human retina. Although the presence of a diversity of large bistratified and diffuse ganglion cells has been observed in a variety of mammalian retinas, little is known about the number of cell types, their physiological properties, or their central projections. Some of the human wide-field bistratified cells in the present study, however, show morphological similarities to monkey large bistratified cells that are known to project to the superior colliculus.

Adolescent↗

PubMedDate not supplied

The mosaic of horizontal cells in the macaque monkey retina: with a comment on biplexiform ganglion cells.

To further characterize the H1 and H2 horizontal cell populations in macaque monkey retinae, cells were injected with the tracer Neurobiotin following intracellular recordings. Tracer coupling between cells of the same type revealed all H1 or H2 cells in small patches around the injected cell. The mosaics of their cell bodies and the tiling of the retina with their dendrites were analyzed. Morphological differences between the H1 and H2 cells observable in Neurobiotin-labeled patches made it possible to recognize H1 and H2 cells in retinae immunolabeled for the calcium-binding proteins parvalbumin and calbindin, and thus to study their relative spatial densities across the retina. These data, together with the intracellularly stained patches, show that H1 cells outnumber H2 cells at all eccentricities. There is, however, a change in the relative proportions of H1 and H2 cells with eccentricity: close to the fovea the ratio of H1 to H2 cells is approximately 4 to 1, in midperipheral retina approximately 3 to 1, and in peripheral retina approximately 2 to 1. In both the Neurobiotin-stained and the immunostained retinae, about 3-5% of the H2 cells were obviously misplaced into the ganglion cell layer. Several features of the morphology of the misplaced H2 cells suggest that they represent the so-called "biplexiform ganglion cells" previously described in Golgi studies of primate retina.

Animals↗

PubMedDate not supplied

Morphology of human retinal ganglion cells with intraretinal axon collaterals.

Ganglion cells with intraretinal axon collaterals have been described in monkey (Usai et al., 1991), cat (Dacey, 1985), and turtle (Gardiner & Dacey, 1988) retina. Using intracellular injection of horseradish peroxidase and Neurobiotin in in vitro whole-mount preparations of human retina, we filled over 1000 ganglion cells, 19 of which had intraretinal axon collaterals and wide-field, spiny dendritic trees stratifying in the inner half of the inner plexiform layer. The axons were smooth and thin (approximately 2 microm) and gave off thin (<1 microm), bouton-studded terminal collaterals that extended vertically to terminate in the outer half of the inner plexiform layer. Terminal collaterals were typically 3-300 microm in length, though sometimes as long as 700 microm, and were present in clusters, or as single branched or unbranched varicose processes with round or somewhat flattened lobular terminal boutons 1-2 microm in diameter. Some cells had a single axon whereas other cells had a primary axon that gave rise to 2-4 axon branches. Axons were located either in the optic fiber layer or just beneath it in the ganglion cell layer, or near the border of the ganglion cell layer and the inner plexiform layer. This study shows that in the human retina, intraretinal axon collaterals are associated with a morphologically distinct ganglion cell type. The synaptic connections and functional role of these cells are not yet known. Since distinct ganglion cell types with intraretinal axon collaterals have also been found in monkey, cat, and turtle, this cell type may be common to all vertebrate retinas.

Axons↗

PubMedDate not supplied

Morphology of wide-field, monostratified ganglion cells of the human retina.

To determine the number of wide-field, monostratified ganglion cell classes present in the human retina, we analyzed a large sample of ganglion cells by intracellular staining in an in vitro, whole-mount preparation of the retina. Over 1000 cells were labeled by horseradish peroxidase or Neurobiotin; some 200 cells had wide dendritic trees narrowly or broadly stratified within either the inner (ON) or outer (OFF) portion of the inner plexiform layer. Based on dendritic-field size and the pattern and extent of dendritic branching, we have distinguished six wide-field cell groups. The giant very sparse ganglion cells included both inner and outer stratifying cells and were unique both for their extremely large dendritic field (mean diameter = 1077 microm) and extremely sparsely branched dendrites. Four of the cell groups had similarly large dendritic fields, ranging in mean diameter from 737 to 791 microm, but differed in the pattern and extent of dendritic branching, with the number of dendritic branch points ranging from a mean of 33 to 129. Of these four groups, the large very sparse group and the large dense group included both inner and outer stratifying cells, while the large sparse and large moderate groups consisted of inner stratifying cells only. The thorny monostratified ganglion cells were distinct from the other cells in having medium size dendritic fields (mean diameter = 517 microm) and moderately branched, inner stratifying dendritic trees with many thin, spiny, twig-like branchlets. All six groups had medium-size cell bodies, with mean soma diameters ranging from 17 to 21 microm. Though the physiological properties and central projections of human wide-field, monostratified ganglion cells are not known, some of the cells resemble macaque ganglion cells known to project to the lateral geniculate nucleus, the pretectum, or the superior colliculus.

Adolescent↗