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1
Activity-Dependent Neural Circuit Formation
Nobuhiko YamamotoCellular and Molecular Neurobiology
Graduate School of Frontier BiosciencesOsaka University
1. Cellular and Molecular mechanisms of activity-dependent neuronal circuit formation
2. Evolutional mechanism of neuronal circuit formation
2
Principle of neural circuit formation
1. Genetically defined program (inheritance)
2. Activity-dependent process (environment)
Nature vs Nurture
Ffrom Daily Sports
Axon guidance by attractive and repulsive factors
Guidance by attractive factors
By repulsive factors
3
After reaching the target, axons form branching and make synaptic contacts with target neurons.
Axon branching is an essential process for determining the neuronal connectivity
target cells
4
Visual system
Neocortex
I
II/III
IV
V
VI
Lamina-specific thalamocortical axon branching
Thalamocortical axons
Cat (Humphrey et al., 1985)
0.1 mm
5
Hubel et al, 1977
Ocular dominance column in the visual cortex
Antonini and Stryker, 1993
Methods
6
Organotypic slice cultureSemi-permeable membrane method
0.5 mm
III/IIIIV
VVI
Semi-permeablemembrane
Culturemedium
Neural tissue
Thalamocortical axons form branches in layer 4, the target layer, of the cortex even in culture
Yamamoto et al. Science, 1989Yamamoto et al. Neuron 1992
7
Thalamocortical axons form functional synapses in layer 4
Yamamoto et al, JNS 1997
8
Neocortex
I
II/III
IV
V
VI
Branch-promoting molecule
Thalamocortical axons
Branch-promoting activity in the target layer
How does neuronal activity influence thalamic axon branching?
Naoyuki Uesaka
9
Axon morphology and firing activity can be studied continuously in cocultures where the thalamocortical projection is recapitulated.
300 μ
Thalamocortical axon branching in culture
CX
TH
YFP-labeled axon 14 days in vitro
After 2 weeks in vitro After 1 week in vitro
Uesaka et al.,JNS, 2007
10
Spontaneous firing activity in thalamic and cortical cells
CTX
TH
Drug application
Uesaka et al.,JNS, 2007
Reduction of neural activity suppresses axonal branching
Uesaka et al.,JNS, 2007
11
Role of pre- and post-synaptic cell activity?
Akito Yamada
Which activity, pre or postsynaptic, is required for thalamocortical axon branching?
Corticalneurons
Thalamicneurons
Normal TTXKIR2.1
KIR2.1
? ?
12
Kir2.1-overexpressing thalamic neurons in the coculture
Yamada et al., PNAS, 2010
Kir2.1EYFP
Spontaneous firing is considerably reduced in thalamic neurons which overexpress Kir2.1
Patch recording
Extracellular recording (MED)
Kir + EYFP
Yamada et al., PNAS, 2010
13
CTX (KIR2.1)
Thalamus
-
+
Spontaneous firing is reduced in cortical explants where Kir2.1 was overexpressed by in utero electroporation
TC axon branching by introducing Kir2.1 to thalamic or cortical cells
control
+
+
-
+
-
+
KIR2.1 in CTX
KIR2.1 in TH
Yamada et al., PNAS, 2010
14
Both pre- and post-synaptic activity is required for thalamocortical axon branching
Thalamic neurons
Cortical neurons
Yamada et al., PNAS, 2010
Is Netrin-4 only the factor for TC axon branching?
Akiko Fukunishi
15
Sema7A is expressed specifically in layer 4 of the developing sensory cortex
Fukunishi et al. J Neurochem, 2011
Sema7A promotes TC axon branching in dissociated cell culture
Fukunishi et al. J Neurochem, 2011
16
TC presynaptic particles are decreased in Sema7A KO
Fukunishi et al. J Neurochem, 2011
Activity-dependent transcription regulation
17
Activity-dependent HDAC9 translocation contributes to gene expression and cellular development
OFF ON
Neuronal activity
HDAC9
Sugo et al. EJNS, 2010
Activity-dependent nuclearcytoplasmic translocation of HDAC9
Low High neuronal activity
Gene regulation(c-fos, Ark)
Dendritic growth
Sugo et al. EJNS, 2010