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