title: Functional elimination of excitatory feedforward inputs underlies developmental refinement of visual receptive fields in zebrafish.
abstract: In many sensory systems, receptive fields (RFs) measured by spike responses undergo progressive refinement during development. It has been proposed that elimination of excitatory synaptic inputs underlies such functional refinement. However, despite many extracellular recording and anatomical studies, direct in vivo intracellular evidence has remained limited. In this study, by cell-attached recordings in the developing optic tectum of zebrafish, we found that during a short period after the initial formation of retinotectal synapses, spike visual RFs of tectal neurons underwent a two-stage developmental modulation: from an initial expansion to a later refinement. Whole-cell voltage-clamp recordings revealed that the underlying excitatory synaptic RF exhibited a similar developmental progression, with its spatial extent first increased and then reduced, and its spatial tuning profile gradually sharpened. The inhibitory RF was initially larger than the excitatory RF but became matched with the excitatory RF at later stages. Simulation with the integrate-and-fire neuron model suggested that the developmental changes of excitatory RFs primarily accounted for the initial enlargement and later refinement of spike RFs, whereas inhibitory inputs generally reduced the size of the spike RF without affecting its developmental progression. In addition, spike RF of individual retinal ganglion cells did not significantly change in size during the same period, and the spatial extent and tuning profile of the tectal excitatory RF barely changed after intratectal excitatory connections were silenced. Together, our results demonstrate that the functional refinement of tectal visual RFs results primarily from a selective elimination of feedforward retinotectal inputs.
authors.affiliation: Zilkha Neurogenetic Institute, Graduate Program, Keck School of Medicine, University of Southern California, Los Angeles, California 90089, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Sheng-zhi
authors.initials: SZ
authors.lastname: Wang
authors.forename: Wen
authors.initials: W
authors.lastname: Zhong
authors.forename: Bao-hua
authors.initials: BH
authors.lastname: Liu
authors.forename: Huizhong Whit
authors.initials: HW
authors.lastname: Tao
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D001703:Biophysics / Q000379:methods; D001931:Brain Mapping; D003198:Computer Simulation; D004558:Electric Stimulation / Q000379:methods; D007839:Functional Laterality; D018756:GABA Antagonists / Q000494:pharmacology; D008959:Models, Neurological; D009025:Morpholines / Q000494:pharmacology; D009415:Nerve Net / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D010775:Photic Stimulation / Q000379:methods; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000502:physiology; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology; D013477:Superior Colliculi / Q000166:cytology* / Q000254:growth & development*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014794:Visual Fields / Q000502:physiology*; D015027:Zebrafish
chemical_list: C095804:(+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid; D018756:GABA Antagonists; D009025:Morpholines