Dendritic morphologies of retinal ganglion cells projecting to the lateral geniculate nucleus in the rabbit.

Small injections of fluorescent Rhodamine-latex microspheres and Fast Blue were made into the dorsal lateral geniculate nucleus (dLGN) of fifteen rabbits. After 8-15 day survival times, the somas of projecting ganglion cells were found to be labelled in the contralateral retinas by retrograde transport. The dendritic morphologies of the labelled ganglion cells were revealed by intracellular injection of Lucifer Yellow or horseradish peroxidase while superfusing the retinas. At least ten distinct dendritic morphologies were observed among 161 injected ganglion cells. The three most commonly recovered dendritic morphologies were those of: (1) alpha-like cells; (2) large, complex dendritic field cells; and (3) cells with small, dense dendritic fields that resemble intracellularly identified brisk sustained cells (Amthor et al., J. Comp. Neurol. 1989; 280:72-96). Smaller percentages of cells whose dendritic morphologies resembled those of several physiologically identified sluggish and complex receptive field ganglion cell classes (Amthor et al., J. Comp. Neurol. 1989; 280:72-96, 97-21) were also recovered. Several morphological types were also found that were previously unknown or could not be confidently related to those of previously known classes. Most dLGN injections labelled many different types of ganglion cells, but restricted injections in some dLGN loci labelled only a limited number of ganglion cell classes.     

Retinal ganglion cells projecting to the dorsal raphe and lateral geniculate complex in Mongolian gerbils

Injections of rhodamine-B into the dorsal raphe nucleus (DRN) and Fluoro-Gold into the lateral geniculate nucleus (LGN) revealed double-labeled retinal ganglion cells (DL RGCs) projecting to both nuclei. The soma-size distribution of DL RGCs was compared with three other distributions: DRN-projecting RGCs, LGN-projecting RGCs, and a large sample of RGCs labeled via the optic nerve with DiI. DL RGC soma diameters fell primarily within the mid-to-upper size range of all three distributions. DL RGCs may provide information to both nuclei concerning comparable aspects of light and visual stimulation via collateralized axons.     

Development of the dorsal lateral geniculate nucleus in normal and visually deprived cats

Although much is known about the cell size changes that take place in the cat dorsal lateral geniculate nucleus as a result of visual deprivation, very little is known about the time course of either of these changes or the changes that occur during normal development. In addition, all previous studies of lateral geniculate nucleus cell size have been confined to the dorsal laminae A and A1 since the more ventral “C” laminae are impossible to identify in normal Nissl stained material. However, it is possible to extend the cell measurement data to laminae C, C1, and C2 by using autoradiographic techniques. Cross-sectional area measurements of dorsal lateral geniculate nucleus cells were made in 47 normally reared kittens and 45 monocularly deprived kittens. All of the normal kittens and 39 of the 45 deprived kittens were studied during the first 70 days of postnatal life. Six deprived cats used to study the deprivatin induced changes in cell size in the “C” laminae were allowed to survive for longer periods. In normal kittens, lateral geniculate nucleus cells grow rapidly during the first four weeks of life. Cells in the deprived layers also grow rapidly during this time, however, at the end of the first month their growth stops and a slow shrinkage takes place over the next several weeks. In the ‘C’ laminae of deprived cats significant changes in cell size are confined to layer C. Although many of the deprived cats show greater deprivation induced changes in cell size in the binocular segment of the lateral geniculate nucleus than in the monocular segment, other cats show approximately equal changes in cell size in the two regions. In addition, some cats exhibit little, if any, deprivation induced change in lamina A cell size but do show quite severe cell shrinkage in lamina A1.     

Visual pretectal neurons projecting to the dorsal lateral geniculate nucleus and pulvinar nucleus in the cat

We observed morphological subtypes of visual pretectal neurons ascending to the dorsal thalamus, following injections of wheat germ agglutinin conjugated to horseradish peroxidase into the dorsal lateral geniculate nucleus (LGNd) or the pulvinar nucleus. These neurons are composed of fusiform cells and small-sized multipolar cells in the olivary pretectal nucleus, superficial horizontal cells, fusiform cells, small-, medium- and large-sized multipolar cells in the optic tract nucleus, and small- and medium-sized multipolar cells in the posterior pretectal nucleus. When somal size of the neurons projecting to the LGNd was compared to the size of neurons projecting to the pulvinar, the neuronal groups were not identical.     

Cholecystokinin-like immunoreactive retinal ganglion cells project to the ventral lateral geniculate nucleus in pigeons

A subpopulation of retinal ganglion cells projecting to the pigeon ventral lateral geniculate nucleus was shown to contain cholecystokinin-like immunoreactivity. These ganglion cells were mainly distributed in the peripheral retina, and their somata sizes were medium to large (14-23 microns). Taken together with previous findings, these results indicate that the retinal input to the ventral geniculate is chemically heterogeneous.     

Cortical projections from the dorsal lateral geniculate nucleus of cats

Lesions were placed in the dorsal lateral geniculate nucleus of cats (LGN) and cortical degeneration studied with a modified Nauta method. Besides local degeneration attributable to the electrode track, dense projections to Areas 17 and 18 ipsilateral to the lesion were found. Medium or dense degeneration was found on both banks of the suprasylvian fissure ipsilaterally and light degeneration widely distributed in Area 19 and on the suprasylvian and posterior ectosylvian gyri. In addition to commissural degeneration homotopic to the electrode track, degenerating fibers were found in the visual areas of the opposite hemisphere, suggesting the presence of a crossed geniculo-cortical pathway.     

Retinal ganglion cell size groups projecting to the superior colliculus and the dorsal lateral geniculate nucleus in the North American opossum

The retinal ganglion cells projecting to the superior colliculus (SC) and dorsal lateral geniculate nucleus (LGNd) of the North American opossum (Didelphis virginiana) were studied by using the retrograde transport of horseradish peroxidase (HRP). The four ganglion cell size groups recognized previously were found to project in systematically different ways. After injections of HRP into the superior colliculus, labeled cells were seen in nasal retina contralateral to the injection and in temporal retina both ipsilateral and contralateral to the injection. In contralateral nasal retina cells of all size classes were labeled, while in contralateral temporal retina small (8-14 micrometers diameter), small-medium (15-19 micrometers diameter), and large (greater than 24 micrometers diameter) cells were labeled but few, if any, large-medium (20-24 micrometers diameter) cells were labeled. In ipsilateral temporal retina, soma size groups labeled included small-medium, large-medium, and large cells, but very few small cells. A nasal-temporal difference in the soma size of ganglion cells projecting to the SC was found: Labeled cells in temporal retina were 1.7-4.2 micrometers larger than their counterparts in nasal retina. Following injection of HRP into the LGNd, label was seen in contralateral nasal and ipsilateral temporal retina with no label seen in contralateral temporal retina. The labeled cells were small-medium, large-medium, and large. No small ganglion cells were labeled from the LGNd. A small nasal-temporal soma size difference in retinal ganglion cells projecting to the LGNd was seen: labeled cells in temporal retina were 1.0-2.1 micrometers larger than in nasal. It is concluded that all four ganglion cell size groups in the opossum project to the SC, but that only the three largest project to the LGNd.     

Ventral lateral geniculate nucleus projects to the dorsal lateral geniculate nucleus in the cat

The lamina C3 of the dorsal lateral geniculate nucleus of the cat does not receive retinal projections but instead receives visual information from the small subpopulation of W-type ganglion cells via the upper substratum of the stratum griseum superficiale of the superior colliculus. We herein report a projection from the lateral division of the ventral lateral geniculate nucleus into the lamina C3 of the dorsal lateral geniculate nucleus. As the lateral division receives projections from the contralateral retina and the ipsilateral upper stratum griseum superficiale of the superior colliculus, we suggest that these regions make up a small cell type W-cell neuronal network that provides visual information to layer I of the striate cortex via the lamina C3.     

Distribution of morphologically different retinal axon terminals in the hamster dorsal lateral geniculate nucleus

Afferent terminal arbors in the hamster LGBd were labelled with horseradish peroxidase (HRP) implanted into the optic tract. Three morphologically distinct terminal types, each with a different regional distribution, were observed. Type R1 terminals are large, ovoid swellings and are predominantly distributed medially within the nucleus. Type R2 terminals are very small, clustered varicosities and are distributed laterally and ventrally. Type R3 terminals are medium in size and their distribution overlaps with that of Type R1 and R2 terminals.     

Morphology of ganglion cells which project to the dorsal lateral geniculate and superior colliculus in the ground squirrel

We wished to determine whether retinal ganglion cells that have axons terminating in the dorsal lateral geniculate and/or the superior colliculus have specific sizes of somata, comprising only part of the entire size range of ganglion cell somata. If so, then perhaps the specific functional types described by Michael might be associated with morphological types based on soma size. HRP was injected into either the superior colliculus (SC) or dorsal lateral geniculate nucleus (LGd) of thirteen-lined ground squirrels. Soma diameter of labeled ganglion cells was measured and the relation between cell size and frequency determined. After SC injections HRP-filled cells were mostly small and medium-sized. They ranged in diameter from 3 to 14 microns and the mean diameter of labeled neurons was 7.35 microns. Cells labeled after SC injections were often distributed as doublets or triplets in the retina. After LGD injections the majority of labeled cells were medium and large-sized. They ranged from 4 to 18 microns in diameter with a mean of 9.1 microns and were more regularly spaced within the retinal region of labeled cells. Thus, the present results provide reason to believe that functional classes of ganglion cells in ground squirrels may be correlated with particular morphological types.     

Properties of X- and Y-type retinal ganglion cells in Siamese cats

There is ample evidence that the visual system of the Siamese cat is different from common cats. These abnormalities suggest possible retinal origins, although no documentation exists. In the present study, single unit recordings were made from 91 misrouted and 209 normally-routed optic tract fibers in Siamese cats. Electrophysiological responses of the misrouted fibers did not differ from those found in the normally-routed fibers of the Siamese cat with the exception of depressed responses to contrast reversal stimuli. X/Y classification of units and experiments on receptive field center sizes, intensity-response functions, and responses to flicker failed to demonstrate significant differences between the misrouted and normally-routed fibers in Siamese cats. These results were not affected by different degrees of interocular misalignment exhibited by the Siamese cat studied. Response properties of retinal ganglion cells in Siamese cats, however, were found to be quite abnormal when compared with common cats. Only 14% (42/300) of all units studied were Y-cells in Siamese cats in comparison to 35% (60/170) in common cats. The percentage of Y-units also was correlated with the severity of interocular misalignment in Siamese cats, i.e. the greater the misalignment of the eyes, the lower the percentage of Y-cells. Experiments on response to contrast reversal stimuli, intensity-response functions and responses to flicker revealed that the ganglion cells in Siamese cats are not as responsive as those in common cats.     

Morphology of rabbit retinal ganglion cells projecting to the medial terminal nucleus of the accessory optic system

Rabbit retinal ganglion cells were retrogradely labeled following injection of rhodamine-labeled microspheres into the medial terminal nucleus. The small fraction of rhodamine-labeled neurons reached their peak concentration within the visual streak and then decreased with increasing eccentricity until none were encountered in the far periphery. The same rabbits also received injections of the fluorescent tracer Fast Blue into the superior colliculus. No double-labeled neurons were observed, i.e., ganglion cells projecting to the medial terminal nucleus (MTN) had no axon collaterals to the superior colliculus. In fixed retinae rhodamine-labeled ganglion cells were intracellularly injected with the fluorescent dye Lucifer Yellow to reveal their full dendritic arborization. MTN-projecting cells had medium-sized to large somata with thin and frequently branched dendrites. The large dendritic trees had a distinct morphology and were predominantly unistratified in a narrow band that presumably corresponded to the electrophysiologically determined on-sublamina of the inner plexiform layer. Dendritic field sizes were inversely related to ganglion cell density, thus providing an eccentricity-independent, constant dendritic coverage factor. Approximately five to six dendritic fields from neighboring cells cover every point of the retina. Published reports claim that the physiological class of on-direction-selective ganglion cells provides the sole retinal input to the MTN in the rabbit. In this context morphological features of MTN-projecting cells and their presumed functional correlation with on-direction-selective ganglion cells are discussed.     

The influence of retinal afferents upon the development of layers in the dorsal lateral geniculate nucleus of mustelids

The extent to which the development of a normal laminated lateral geniculate nucleus depends upon retinal afferents has been studied in normal and albino ferrets and in mink. Removal of all retinal afferents before they invade the nucleus (28 days in utero) or before they establish distinct monocular terminal fields (newborn, approximately 41 days post-conception) produces a nucleus that is smaller than normal and poorly separated from the adjacent perigeniculate and medial interlaminar nuclei. However, the nucleus is wedge-shaped, resembling a normal adult nucleus, in which a broad medial binocular segment is distinguishable from a narrower lateral monocular segment. There is a normal mediolateral gradient of cell sizes and some signs of a laminar differentiation, cells next to the optic tract being morphologically distinguishable from cells near the optic radiation, but no cell-free interlaminar zones are formed. The development of a monocularly innervated nucleus depends on the size of the surviving retinal input. In normally pigmented ferrets or mink the crossed retinofugal component is larger than the uncrossed component. In the monocular animals one sees essentially a monocular set of geniculate layers on each side, with an appropriate asymmetry. Each nucleus can be regarded as representing the survival of those layers which would have been innervated by the good eye, together with some additional geniculate territory that appears to be added to the surviving layers as retinogeniculate axons occupy territory normally innervated by the other eye. The crossed component of an albino ferret is abnormally large and the monocularly innervated contralateral nucleus is almost like that of a normal albino. There is a full complement of geniculate layers and interlaminar zones, which appears to develop without any binocular interactions. The ipsilateral retinogeniculate component of albinos is extremely small. In the monocular albino animals it forms discontinuous terminal patches, leaving sectors of the poorly differentiated nucleus uninnervated. These results show that in geniculate development there is a limited interaction between the two sets of retinal afferents. Each set plays a well defined and distinctive role, and one can replace the other to a limited extent only.     

Subdivisions of the dorsal raphe nucleus projecting to the lateral geniculate nucleus and primary visual cortex in the Mongolian gerbil

The mammalian dorsal raphe nucleus (DRN) is composed of sub-divisions with different anatomical and functional properties. Using cholera toxin subunit B as a retrograde tracer, DRN subdivisions projecting to the lateral geniculate nucleus and to the primary visual cortex were examined in the Mongolian gerbil. DRN neurons projecting to the lateral geniculate nucleus were observed in the lateral DRN (rostrally) and in the ventromedial DRN (caudally), while DRN cells projecting to the primary visual cortex were observed at all rostral-caudal levels in the ventromedial DRN. These results demonstrate a significant overlap between the DRN projections to the lateral geniculate and superior colliculus, and show that only the caudal ventromedial DRN projects to all three major visual targets: the lateral geniculate nucleus, primary visual cortex, and superior colliculus. Since the DRN is involved in depression and other neuropsychiatric disorders, as well as is affected by many psychotropic substances, these data may help to develop new treatments and therapies targeting specific DRN subdivisions.     

Y retinal terminals contact interneurons in the cat dorsal lateral geniculate nucleus

One of the largest influences on dorsal lateral geniculate nucleus (dLGN) activity comes from interneurons, which use the neurotransmitter gamma-aminobutyric acid (GABA). It is well established that X retinogeniculate terminals contact interneurons and thalamocortical cells in complex synaptic arrangements known as glomeruli. However, there is little anatomical evidence for the involvement of dLGN interneurons in the Y pathway. To determine whether Y retinogeniculate axons contact interneurons, we injected the superior colliculus (SC) with biotinylated dextran amine (BDA) to backfill retinal axons, which also project to the SC. Within the A lamina of the dLGN, this BDA labeling allowed us to distinguish Y retinogeniculate axons from X retinogeniculate axons, which do not project to the SC. In BDA-labeled tissue prepared for electron microscopic analysis, we subsequently used postembedding immunocytochemical staining for GABA to distinguish interneurons from thalamocortical cells. We found that the majority of profiles postsynaptic to Y retinal axons were GABA-negative dendrites of thalamocortical cells (117/200 or 58.5%). The remainder (83/200 or 41.5%) were GABA-positive dendrites, many of which contained vesicles (59/200 or 29.5%). Thus, Y retinogeniculate axons do contact interneurons. However, these contacts differed from X retinogeniculate axons, in that triadic arrangements were rare. This indicates that the X and Y pathways participate in unique circuitries but that interneurons are involved in the modulation of both pathways.     

Synaptology of retinal terminals in the dorsal lateral geniculate nucleus of the cat

We have made a fine structural investigation of the synaptic patterns made by axon terminals of retinal ganglion cells in the dorsal lateral geniculate nucleus of the cat. We compared the retinal input to dendritic processes that bear clusters of large appendages with the retinal input to relatively smooth dendritic segments that have only a few isolated spines. The study was restricted to the portion of laminae A and A1 that receive central visual field input. We were able to completely reconstruct 33 individual terminal boutons from long series of consecutive thin sections. Retinal terminals that were presynaptic to dendritic appendages tended to occupy the central position in the complex synaptic zones of geniculate fine structure called glomeruli. These terminals were surrounded by significantly more profiles than retinal terminals that were presynaptic to dendritic stems and averaged twice as many synaptic contacts per terminal bouton. The retinal input to dentritic appendages was heavily involved in a specific synaptic pattern called the triadic arrangement while retinal input to dendritic stems was only lightly involved in triads. Dendritic appendages in triads received greater synaptic input from profiles with flattened vesicles than did the dendritic stems that were found in triads.     

Prenatal development of retinal ganglion cell axons: segregation into eye-specific layers within the cat's lateral geniculate nucleus

The morphological changes in individual retinal ganglion cell axons associated with the formation of the eye-specific layers in the dorsal lateral geniculate nucleus (LGN) were studied during the prenatal development of the cat's visual system. Previous work has shown that the pattern of segregated eye inputs found in the adult arises from an immature state in which inputs from the two eyes are intermixed within the nucleus (Shatz, 1983). Here, this developmental process is examined at its fundamental unit of connectivity--the individual retinal ganglion cell axon. To do so, an in vitro method was used to label fetal cat optic tract axons with HRP at various times during development between embryonic day 38 (E38) and postnatal day 2 (P2) (gestation = 65 d). The results presented here are based on reconstructions of 172 axons. During the initial period of intermixing (E38-43), axons are relatively simple in morphology. Many axons studied at the earliest ages (E38) end in growth cones and have very few branches along the main axon trunk as they traverse the nucleus. By E43, the number of side branches given off along the main axon trunk has increased and most axons also have a simple terminal arbor. Over the next 2 weeks (E43-55), the majority of axons are studded with side branches and the terminal arbor is well defined. Then, between E55 and birth, axons lose their side branches and the eye-specific layers appear. By birth, nearly all axons have a smooth trunk and an elaborate terminal arbor restricted to the LGN layer appropriate to the eye of axon origin. When the number of side branches per axon was quantified, the time course of appearance and subsequent loss of side branches was found to parallel the time course of the initial intermixing of inputs and subsequent reduction in territory shared by the two eyes as determined from previous intraocular injection experiments. Our results also showed that the side branches along each axon were located primarily within LGN territory destined to be occupied by the other eye. Thus, the side branches are likely to represent a morphological substrate for the intermixing of inputs from the two eyes. These observations suggest that the segregation of eye input to the LGN involves two fundamental and simultaneous events. One event is the remodeling of the branching pattern along the length of the main axon trunk so that the side branches present early on are eliminated and the main axon trunk becomes smooth.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dendritic morphology of cat retinal ganglion cells projecting to suprachiasmatic nucleus.

The morphological properties of cat retinal ganglion cells projecting to the suprachiasmatic nucleus (SCN) of the hypothalamus were studied by using retrograde labeling, in vitro intracellular injection, confocal optical section, and computer three-dimensional reconstruction techniques. A total of 218 stained cells were studied. Neither the dendritic fields nor soma diameters of SCN-projecting cells varied with eccentricity. Approximately 50% of cells were concentrated not in the area centralis, but rather in the visual streak. SCN-projecting cells showed large and symmetrical dendritic fields (596 +/- 159 microm) and medium to small sized somas (17.2 +/- 3.3 microm). The ramification patterns of SCN-projecting cells were similar. Most cells primarily ramify in either sublamina A or B. Evidence from quantitatively analyzed cells (n = 39) suggests that these cells ramified more frequently in sublamina A (n = 17) than in sublamina B (n = 8). A large number of cells, on the other hand, showed diffuse ramification (n = 14) throughout the inner plexiform layer (IPL). The functional roles of these cells and the corresponding retinal neurocircuitry in circadian entrainment remain to be studied.