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Intrinsic determinants of retinal axon collateralization and arborization patterns
1Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02129, USA. bhide@helix.mgh.harvard.edu
The Journal of Comparative Neurology
|July 15, 1999
Summary
Surgically induced retinal projections in hamsters follow normal developmental stages. Only superficial optic tract axons form permanent connections in novel thalamic targets, suggesting intrinsic axon properties guide projection development.
Area of Science:
- Neuroscience
- Developmental Biology
- Axon Guidance
Background:
- Permanent, novel retinal projections to the somatosensory or auditory thalamus can be induced in adult hamsters.
- This requires early-life surgical manipulation, including superior colliculus ablation and lemniscal axon transection.
Purpose of the Study:
- To investigate the developmental processes underlying these surgically induced retinal projections.
- To determine the roles of intrinsic factors versus target interactions in specifying retinal axon connections.
Main Methods:
- Utilized a fluorescent tracer (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) to label retinal ganglion cell axons.
- Examined the morphology and development of retinal projections in surgically altered hamsters compared to normal hamsters.
Main Results:
- Retinal axons in operated hamsters exhibited three developmental stages: elongation, collateralization, and arborization, similar to normal visual pathway development.
- Initially, collateral branches formed in both superficial and internal optic tract components, but only superficial collaterals resulted in permanent projections.
- Retinofugal axon terminal arbors in novel thalamic nuclei resembled those in the normal dorsal lateral geniculate nucleus, though size differed.
Conclusions:
- Both superficial and internal optic tract axons can form thalamic collaterals during development.
- Only superficial optic tract axons possess the intrinsic properties to retain these thalamic collaterals permanently.
- The same morphological types of retinofugal axons contribute to both normal and surgically induced retinal projections, highlighting conserved developmental mechanisms.