Remodeling of inhibitory synaptic connections in developing ferret visual cortex.
BACKGROUND
In the visual cortex, as in many other regions of the developing brain, excitatory synaptic connections undergo substantial remodeling during development. While evidence suggests that local inhibitory synapses may behave similarly, the extent and mechanisms that mediate remodeling of inhibitory connections are not well understood.


RESULTS
Using scanning laser photostimulation in slices of developing ferret visual cortex, we assessed the overall patterns of developing inhibitory and excitatory synaptic connections converging onto individual neurons. Inhibitory synaptic inputs onto pyramidal neurons in cortical layers 2 and 3 were already present as early as postnatal day 20, well before eye opening, and originated from regions close to the recorded neurons. During the ensuing 2 weeks, the numbers of synaptic inputs increased, with the numbers of inhibitory (and excitatory) synaptic inputs peaking near the time of eye opening. The pattern of inhibitory inputs refined rapidly prior to the refinement of excitatory inputs. By uncaging the neurotransmitter GABA in brain slices from animals of different ages, we find that this rapid refinement correlated with a loss of excitatory activity by GABA.


CONCLUSIONS
Inhibitory synapses, like excitatory synapses, undergo significant postnatal remodeling. The time course of the remodeling of inhibitory connections correlates with the emergence of orientation tuning in the visual cortex, implicating these rearrangements in the genesis of adult cortical response properties.
Dalva
Matthew B
MB
Department of Neuroscience, BRB II/III rm 1114, University of Pennsylvania Medical School, 421 Curie Blvd, Philadelphia, PA 19104, USA. dalva@mail.med.upenn.edu
D000818:Animals; D000831:Animals, Newborn; D001931:Brain Mapping; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005289:Ferrets; D053444:Inhibitory Postsynaptic Potentials / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009434:Neural Pathways / Q000254:growth & development / Q000502:physiology; D017966:Pyramidal Cells / Q000254:growth & development / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D013997:Time Factors; D014793:Visual Cortex / Q000254:growth & development* / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000032:analysis
D005680:gamma-Aminobutyric Acid