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Postnatal refinement of interareal feedforward projections in ferret visual cortex
Reem Khalil1,2,3, Violeta Contreras-Ramirez2, Jonathan B Levitt4,5
1Biology, Chemistry, and Environmental Sciences Department, American University of Sharjah, Sharjah, UAE.
Brain Structure & Function
|February 25, 2018
Summary
Feedforward (FF) brain circuits refine around eye opening, mirroring feedback (FB) circuit development. Postnatal visual experience is crucial for refining both FF and FB cortical circuits in ferrets.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Visual System Development
Background:
- Feedforward (FF) and feedback (FB) cortical circuits are crucial for visual processing.
- Understanding the developmental refinement of these circuits is key to understanding brain development.
Purpose of the Study:
- To investigate the postnatal refinement of FF projections from ferret primary visual cortex (V1) to extrastriate targets.
- To compare the developmental timeline of FF circuit refinement with that of FB circuits.
- To determine if FF pathways to different visual areas refine at similar rates.
Main Methods:
- Injected cholera toxin subunit beta (CTb) tracer into V1 of juvenile ferrets.
- Visualized and quantified labeled axon terminals in extrastriate target areas (18, 19, 21, Ssy).
- Analyzed bouton density, interbouton intervals, and axon density over a postnatal period (4-8 weeks).
Main Results:
- Bouton density of FF projections to areas 18, 19, and 21 decreased steadily from 4 to 8 weeks postnatal.
- Refinement in area Ssy was delayed, occurring after 6 weeks.
- Increased interbouton intervals and decreased axon density were observed in multiple target areas.
Conclusions:
- FF circuits from V1 to extrastriate targets remodel largely synchronously post-eye opening.
- FF and FB cortical circuits exhibit broadly similar developmental timecourses.
- Postnatal visual experience is critical for the refinement of both FF and FB cortical circuits.
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