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Early dendritic outgrowth of primate retinal ganglion cells
1Department of Pediatrics, School of Medicine, Loma Linda University, CA 92350.
Abstract:
The pattern of dendritic stratification of retinal ganglion cells in the fetal monkey (Macaca mulatta) was examined using horseradish peroxidase and retinal explants. Ganglion cells in the rhesus monkey are born between embryonic day (E) 30-70 (LaVail et al., 1983). At E60, E67, and E68, approximately 50% of all ganglion cells within the central 3.0 mm of the retina had dendritic arbors that were unistratified within the inner plexiform layer (IPL), while the remaining 50% had bistratified arbors. Unistratified cells had relatively flat arbors that ramified within a restricted portion of the IPL. In contrast, bistratified cells had one portion of the arbor that branched in the inner half of the IPL and a second portion that branched in the outer half of the IPL. Relatively few bistratified cells were encountered in the central 1.0 mm of the retina but were more numerous with increasing eccentricity. At E81, E90, and E110, the dendritic arbors of ganglion cells increased in both area and complexity, but occupied a relatively small percentage of the total depth of the IPL. The bistratified cells encountered at these fetal ages were typically located in the far retinal periphery. Between E125-E140, the dendritic arbors of individual ganglion cells increased in area and depth to occupy a greater proportion of the total IPL than at earlier fetal ages. These observations suggest that ganglion cells in the macaque undergo at least three stages of dendritic stratification: (1) an initial period of dendritic growth during which the cells have either unistratified or bistratified dendritic arbors; (2) a loss of the majority of bistratified cells through cell death or remodeling of the arbor; and (3) growth or expansion of the arbor to occupy a greater percentage of the total depth of the IPL. The first two stages are similar to recent observations in the fetal cat (Maslim & Stone, 1988) with the exception that dendritic development in the primate lacks an initial diffuse ingrowth to the IPL. Additionally, primate ganglion cells undergo a third stage of dendritic growth in late fetal development during which the arbor occupies a greater proportion of the depth of the IPL.
Insights
Rhesus monkey retinal ganglion cells show distinct dendritic stratification patterns during fetal development. Early stages feature unistratified and bistratified arbors, followed by cell loss and later arbor expansion within the inner plexiform layer.
Area of Science:
- Neuroscience
- Developmental Biology
- Ophthalmology
Background:
- Retinal ganglion cells (RGCs) are crucial for visual processing.
- Understanding RGC dendritic development provides insights into neural circuit formation.
- Primate RGC development patterns are essential for comparative neuroscience.
Purpose of the Study:
- To investigate the temporal and spatial patterns of dendritic stratification in fetal rhesus monkey RGCs.
- To characterize the developmental stages of RGC dendritic arbors within the inner plexiform layer (IPL).
Main Methods:
- Utilized horseradish peroxidase (HRP) and retinal explants for tracing dendritic arbors.
- Examined RGCs at various embryonic days (E) from E60 to E140.
- Analyzed dendritic stratification patterns, arbor complexity, and IPL occupancy.
Main Results:
- At early fetal stages (E60-E68), RGCs exhibited approximately 50% unistratified and 50% bistratified dendritic arbors.
- Bistratified cells were less common centrally and increased with retinal eccentricity.
- By late fetal stages (E125-E140), dendritic arbors expanded in area and depth, occupying a larger IPL proportion.
Conclusions:
- Macaque RGCs undergo at least three dendritic stratification stages: initial growth, bistratified cell reduction, and late-stage arbor expansion.
- Primate RGC development differs from feline RGCs, notably lacking an initial diffuse IPL ingrowth.
- Late fetal development involves significant arbor expansion, increasing IPL depth occupancy.