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Retinal ganglion cells were studied in pigmented ferrets that received small electrophoretic injections of horseradish peroxidase (HRP) into the dorsal lateral geniculate nucleus (LGNd) or optic tract. Ferret retina contains a number of types of retinal ganglion cells of which the relative cell body sizes, dendritic field structures, and central projections correspond closely to those of retinal ganglion cell types in the cat. Ferret retina contains about the same proportion of alphalike cells, a lower proportion of betalike cells, and thus a high proportion of other types of ganglion cells than cat retina. Ferret retina has a visual streak and somewhat weaker area centralis than cat retina. Changes in ganglion cell morphology associated with eccentricity are less pronounced in the ferret than in the cat. The adult ferret retina is about 12.5 mm in diameter, and the nasotemporal division is about 2.7 mm from the temporal margin. Interestingly, virtually all alpha cells in the pigmented ferrets studied projected contralaterally. Studies of infant ferrets indicate that 4 days after birth (P4) the area of ferret retina is 25% that of the adult. The neonatal ferret retina contains numerous small, densely packed cells in the presumptive ganglion cell layer. At P4 these cells appear to be uniformly distributed across the retina. The area centralis and visual streak are not obvious as late as 8 days after birth.

The morphology of ganglion cell dendritic trees varies across the cat retina. Evidence is presented that the variation in two attributes of ganglion cell dendritic structure can be accounted for by specific aspects of the topography of the adult and developing retina. The first attribute considered was the displacement of the center of the dendritic field from the cell body in the plane of the retina. The results of this study provide evidence that most ganglion cell dendritic fields are displaced away from neighboring cells, i.e., down the retinal ganglion cell density gradient. Because of the systematic dendritic displacement locally, the centers of the dendritic fields are arranged in a more precise mosaic than are their cell bodies. The second attribute considered was the elongation and orientation of the dendritic fields. From approximately embryonic day 50 to postnatal day 10 the cat retina undergoes a process of maturation (reviewed by Rapaport and Stone: Neuroscience 11:289–301, '84) that begins at the area centralis and spreads over the retina in a horizontally elongated wave. We found that the elongation and orientation of retinal ganglion cell dendritic fields is significantly correlated with the shape of the wave of maturation. The orientation of a dendritic field is not predicted by the direction of its displacement nor is it directly related to the distribution of neighboring retinal ganglion cells. These results indicate that the displacement of a ganglion cell's dendritic field from its cell body results from mechanisms different from those responsible for the orientation of the dendritic field. Factors that may be responsible for these two attributes of ganglion cell dendritic morphology are discussed.

The dendritic field size, the distribution of the dendrites relative to the cell body, and the overall shape of the dendritic field of type I ganglion cells in the rat retina were analyzed. These features of neuronal structure were related to the topography of the rat retina. As in the cat, the cell bodies of type I ganglion cells are arranged in a nonrandom mosaic. Previous work has demonstrated that the density of type I cells in the rat retina does not covary with the density of all ganglion cells. Type I dendritic field size varies over the retina; the increase in dendritic field size is accounted for better by the decrease in type I density than by the decrease in overall ganglion cell density. The center of the dendritic field of most type I cells is displaced in the plane of the retina from the cell body. Unlike in carnivore retina (Schall and Leventhal: J. Comp. Neurol. 257:149-159, '87), the dendritic fields in the rat are not displaced down the ganglion cell density gradient. Rather, there is a tendency for the dendritic trees, especially in temporal retina, to be displaced toward dorsal retina. Most of the dendritic fields are elongated, but the degree of elongation is less than that observed in carnivore or primate retina. Unlike in carnivore and primate retina (Leventhal and Schall: J. Comp. Neurol. 220:465-475, '83; Schall et al.: Brain Res. 368:18-23, '86), there is no relationship between dendritic tree orientation and position relative to any point on the retina in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Orientation sensitivity is a characteristic of most retinal ganglion cells (Levick and Thibos, '82), most relay cells in the dorsal lateral geniculate nucleus (Vidyasagar and Urbas, '82), and most neurons in the visual cortex (Hubel and Wiesel, '62) in the cat. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis most retinal ganglion cells respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick and Thibos, '82). This relationship is strongest along the horizontal meridian (the visual streak) and appears to reflect the innate, radial orientation of retinal ganglion cell dendritic fields (Leventhal and Schall, '83). A relationship between preferred orientation and polar angle also exists in cat striate cortex; outside of the area centralis representation most cells respond best to lines oriented radially. This relationship is strongest for S type cells, the most orientation-selective cells, and cells in regions representing the horizontal meridian (Leventhal, '83). To determine if similar relationships exist in cat extrastriate cortex, the preferred orientations and receptive field positions of 226 neurons in area 19 were studied. We find that, as in area 17, most area 19 cells outside of the representation of the area centralis respond best to lines oriented radially; this relationship is strongest for the cells having the narrowest receptive fields and in regions subserving the horizontal meridian. Unlike in striate cortex, in area 19 the relationship between preferred orientation and polar angle is not dependent upon cell type (S or C) or to the degree of orientation sensitivity exhibited. Also, in area 19, but not in area 17, the relationship between preferred orientation and polar angle fails for the cells having the widest receptive fields. The results of this study show that the systematic relationship between preferred orientation and receptive field position which begins in the retina is largely preserved through extrastriate cortex. The functional architecture of orientation sensitive cells throughout the visual pathways may depend ultimately upon the innate, radial orientation of the dendritic fields of retinal ganglion cells.

We investigated the structural basis of the physiological orientation sensitivity of retinal ganglion cells (Levick and Thibos, '82). The dendritic fields of 840 retinal ganglion cells labeled by injections of horseradish peroxidase into the dorsal lateral geniculate nucleus (LGNd) or optic tracts of normal cats, Siamese cats, and cat deprived of patterned visual experience from birth by monocular lid-suture (MD) were studied. Mathematical techniques designed to analyze direction were used to find the dendritic field orientation of each cell. Statistical techniques designed for angular data were used to determine the relationship between dendritic field orientation and angular position on the retina (polar angle). Our results indicate that 88% of retinal ganglion cells have oriented dendritic fields and that dendritic field orientation is related systematically to retinal position. In all regions of retina more than 0.5 mm from the area centralis the dendritic fields of retinal ganglion cells are oriented radially, i.e., like the spokes of a wheel having the area centralis at its hub. This relationship was present in all animals and cell types studied and was strongest for cells located close to the horizontal meridian (visual streak) of the retina. Retinal ganglion cells appear to be sensitive to stimulus orientation because they have oriented dendritic fields.