The postnatal refinement of interareal circuits in ferret visual cortex
Item
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Title
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The postnatal refinement of interareal circuits in ferret visual cortex
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Identifier
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d_2009_2013:7f827738fef5:12019
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identifier
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12712
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Creator
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Khalil, Reem,
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Contributor
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Jonathan B. Levitt
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Date
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2013
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Language
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English
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Publisher
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City University of New York.
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Subject
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Neurosciences | Biology | circuits | cortex | feedback | feedforward | ferret | visual
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Abstract
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Visual cortical areas are presumed to subserve different perceptual functions as a result of their rich network of interareal anatomical circuits. Interareal circuits have been shown to undergo extensive remodeling in the postnatal period. Revealing the timing of when brain circuits mature may help us assign particular neural substrates to particular visual functions. To illuminate perceptual development, we assessed the postnatal anatomical refinement of interareal feedforward and feedback projections in ferret visual cortex. We also described the developmental trajectory of zinc levels in ferret visual cortex, reflecting a subset of glutamatergic interareal feedforward and feedback processes. We find that the period of major reorganization in feedback circuits, feedforward circuits, as well as the dramatic decline in zinc levels in ferret visual cortex occurs in the month following eye opening. In chapter 1, we demonstrated that zinc histochemistry can be reliably used to distinguish visual cortical areas in juvenile visual cortex and further reveals circuit refinement. We show that the postnatal decline in levels of synaptic zinc follows a broadly similar timecourse in multiple areas of ferret visual cortex. In chapter 2, we assessed the developmental refinement of feedback projections between primary visual cortex and extrastriate areas in the juvenile ferret brain. We reveal substantial refinement in the spatial organization of feedback projections arising from multiple visual areas to primary visual cortex of the ferret during the period after eye opening. We find that while certain aspects of feedback circuitry refine with a similar timecourse in all areas, other aspects refine asynchronously. In chapter 3, we investigated the postnatal development of feedforward projections from V1 to different target areas. Before eye opening, at 4 weeks postnatal, synaptic bouton density is very high, and interbouton interval along individual axons is quite short. In all areas examined, both bouton density decreased, and interbouton interval increased substantially from 6 weeks to 8 weeks postnatal. Therefore, feedback and feedforward cortical circuits appear to share a broadly similar developmental trajectory. Our findings are consistent with the notion that visual experience is necessary and crucial in the refinement of these cortical circuits. Furthermore, our findings suggest that at least some aspects of cortical maturation occur largely synchronously in multiple visual areas.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Biology
