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Retinal ganglion beta cells project transiently to the superior colliculus during development
A S Ramoa1, G Campbell, C J Shatz
1Department of Neurobiology, Stanford University, CA 94305.
Summary
During feline development, beta retinal ganglion cells initially project to the superior colliculus (SC) but later retract these connections. This axon collateral elimination refines visual system specificity.
Area of Science:
- Neuroscience
- Developmental Biology
- Visual System Research
Background:
- Adult cats exhibit specific retinal ganglion cell (RGC) projections, with beta cells targeting the lateral geniculate nucleus (LGN) over the superior colliculus (SC).
- Understanding the developmental basis of this target specificity is crucial for comprehending visual system organization.
Purpose of the Study:
- To investigate whether the adult-specific target projection of beta RGCs is established during early feline development.
- To determine the developmental timeline for the retraction of axon collaterals from the SC by beta RGCs.
Main Methods:
- Retrograde labeling using rhodamine-labeled microspheres injected into the SC at embryonic day (E) 38, E43, and postnatal day (P) 4.
- Intracellular injection of Lucifer yellow into retrogradely labeled RGCs in ex vivo retinal tissue slices (E56–P32) to determine morphological class.
Main Results:
- Beta RGCs were retrogradely labeled from SC injections at E38 and E43, indicating initial SC projection.
- These developing beta RGCs projecting to the SC were morphologically indistinguishable from those projecting to the LGN.
- No beta RGCs could be labeled from SC injections at P4, and collateral loss persisted beyond the major RGC cell death period.
Conclusions:
- Beta RGCs initially extend axon collaterals to the SC during development.
- A significant retraction of these SC axon collaterals occurs between E43 and P4.
- This collateral elimination process is essential for establishing the precise adult visual system circuitry.