Synaptic inputs compete during rapid formation of the calyx of Held: a new model system for neural development.
Hallmark features of neural circuit development include early exuberant innervation followed by competition and pruning to mature innervation topography. Several neural systems, including the neuromuscular junction and climbing fiber innervation of Purkinje cells, are models to study neural development in part because they establish a recognizable endpoint of monoinnervation of their targets and because the presynaptic terminals are large and easily monitored. We demonstrate here that calyx of Held (CH) innervation of its target, which forms a key element of auditory brainstem binaural circuitry, exhibits all of these characteristics. To investigate CH development, we made the first application of serial block-face scanning electron microscopy to neural development with fine temporal resolution and thereby accomplished the first time series for 3D ultrastructural analysis of neural circuit formation. This approach revealed a growth spurt of added apposed surface area (ASA)>200 μm2/d centered on a single age at postnatal day 3 in mice and an initial rapid phase of growth and competition that resolved to monoinnervation in two-thirds of cells within 3 d. This rapid growth occurred in parallel with an increase in action potential threshold, which may mediate selection of the strongest input as the winning competitor. ASAs of competing inputs were segregated on the cell body surface. These data suggest mechanisms to select "winning" inputs by regional reinforcement of postsynaptic membrane to mediate size and strength of competing synaptic inputs.
Center for Neuroscience, West Virginia University School of Medicine, Morgantown, West Virginia 26506-9303, USA.
Paul S
PS
Holcomb
Brian K
BK
Hoffpauir
Mitchell C
MC
Hoyson
Dakota R
DR
Jackson
Thomas J
TJ
Deerinck
Glenn S
GS
Marrs
Marlin
M
Dehoff
Jonathan
J
Wu
Mark H
MH
Ellisman
George A
GA
Spirou
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000648:ultrastructure; D001933:Brain Stem / Q000166:cytology* / Q000254:growth & development; D002118:Calcium / Q000378:metabolism; D003198:Computer Simulation; D004622:Embryo, Mammalian; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D021621:Imaging, Three-Dimensional; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008855:Microscopy, Electron, Scanning; D008959:Models, Neurological; D009415:Nerve Net / Q000648:ultrastructure; D009474:Neurons / Q000502:physiology* / Q000648:ultrastructure; D017711:Nonlinear Dynamics; D011247:Pregnancy; D017729:Presynaptic Terminals / Q000648:ultrastructure; D018709:Statistics, Nonparametric; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013572:Synaptic Vesicles / Q000648:ultrastructure
D002118:Calcium