Lamination Speeds the Functional Development of Visual Circuits

 

New research from the Department of Developmental Neurobiology at the Institute of Psychiatry, Psychology & Neuroscience, King’s College London, sheds light into the role of layers in the brain. The study, published in Neuron, shows that the formation of layers speeds the development of neuronal circuits although, surprisingly, it is not crucial for the establishment of functional and cell-type specific connections.

  • Robo2 directs lamination of direction-selective retinal axons and tectal dendrites
  • Tectal lamination is required for rapid assembly of direction-selective circuits
  • Functional direction-selective circuits eventually form when lamination is lost
  • Structural plasticity compensates for the loss of tectal lamination

Summary

A common feature of the brain is the arrangement of synapses in layers. To examine the significance of this organizational feature, we studied the functional development of direction-selective (DS) circuits in the tectum of astray mutant zebrafish in which lamination of retinal ganglion cell (RGC) axons is lost. We show that although never laminar, the tuning of DS-RGC axons targeting the mutant tectum is normal. Analysis of mutant tectal neurons at late developmental stages reveals that directional tuning is indistinguishable from wild-type larvae. Furthermore, we show that structural plasticity of tectal dendrites and RGC axons compensates for the loss of lamination, establishing connectivity between DS-RGCs and their normal tectal targets. However, tectal direction selectivity is severely perturbed at earlier developmental stages. Thus, the formation of synaptic laminae is ultimately dispensable for the correct wiring of direction-selective tectal circuits, but it is crucial for the rapid assembly of these networks.

Full article: http://www.cell.com/neuron/abstract/S0896-6273(15)00886-7

Nikolas Nikolaou and Martin P. Meyer

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