Yoav LivnehYoav Livneh

yoav.livneh@mail.huji.ac.ilyoav.livneh@mail.huji.ac.il

02-658516302-6585163

neurogenesis and

migration

Refinement of synaptic

connections

outgrowth of axons and dendrites, and synaptogenesis

Neuronal development Neuronal development (generally)(generally)

Adult neurogenesis Adult neurogenesis (hippocampus)(hippocampus)

* also occurs in the adult olfactory bulb

Neuronal development Neuronal development (in the adult (in the adult hippocampus)hippocampus)

Ge et al., J Physiol, 2008

GABA in neuronal developmentGABA in neuronal development

Ben-Ari, Nature Reviews: Neuroscience, 2002

1. Genesis of neurons (and migration).2. Outgrowth of axons and dendrites, and synaptogenesis.3. Refinement of synaptic connections.

Development of GABA Development of GABA (and glutamate)(and glutamate) currents in adult-born hippocampal currents in adult-born hippocampal

neuronsneurons

tonic

GA

BA

cu

rrents

evoke

d G

AB

A

curr

ents

evoke

d G

lu.

curr

ents

3 dpi 7 dpi 14 dpi 28 dpi

DCX (doublecortin) - a marker for immature neurons

Bicuculine – GABAa-R antagonist

CNQX – AMPA-R antagonist

The big question – The big question –

What is the role of these What is the role of these tonic excitatory GABA tonic excitatory GABA

currents? currents?

Exploration and manipulation of GABA Exploration and manipulation of GABA currents in adult-born hippocampal currents in adult-born hippocampal

neuronsneuronsexc. inh.- GABA is excitatory from 3 to ~14 dpi.

- Afterwards GABA currents mature to become inhibitory.

- shRNA-mediated knockdown of NKCC1 (chloride transporter) eliminated the excitatory nature of GABA (high [Cl]in is not maintained).

~inh.

Perforated patch – initially keeps the original intracellular content.

Whole-cell patch – content is very rapidly replaced with the electrode’s content.

How will this manipulation How will this manipulation affect adult-born neuron affect adult-born neuron

development?development?

Effects of eliminating excitatory GABA Effects of eliminating excitatory GABA currents – part I currents – part I

(dendritic development)(dendritic development)

Excitatory GABA currents are essential (necessary) for proper dendritic development

- Shorter total dendritic length.

- Less branches.

- Occupy a smaller volume of space.

Effects of Effects of enhancingenhancing excitatory excitatory GABA currentsGABA currents

The opposite, complementary, trends were observed with administration of a GABA agonist (suggesting it might also be

sufficient).

)should be positively correlated (

Pentobarbital – GABA agonist

Effects of eliminating excitatory GABA Effects of eliminating excitatory GABA currents – part II currents – part II

((inhibitoryinhibitory synaptic integration) synaptic integration)

Excitatory GABA currents are essential for proper inhibitory synaptic integration

evoked

spontaneous

- Less neurons with evoked inhibitory responses.

- Lower evoked response amplitudes.

- Lower spontaneous response frequencies (but similar amplitudes).

Effects of eliminating excitatory GABA Effects of eliminating excitatory GABA currents – part II currents – part II

((excitatoryexcitatory synaptic integration) synaptic integration)

Excitatory GABA currents are essential for proper excitatory synaptic integration

evoked

spontaneous

- Dramatically less neurons with evoked excitatory responses.

- Lower evoked response amplitudes.

- Lower spontaneous response frequencies (but similar amplitudes).

Effects of eliminating excitatory GABA Effects of eliminating excitatory GABA currents currents from birthfrom birth (KO mice) (KO mice)

The same trends were observed with NKCC1 KO

mice.

Conclusions and interpretationsConclusions and interpretations

Conclusions:

-At the initial stages of the development of adult-born neurons, GABA is excitatory due to high intracellular Cl concentration (mediated by the transporter NKCC1).

- This excitatory action of GABA is essential (necessary and perhaps sufficient) for proper development of dendrites and synaptic connections.

Interpretations:

- New neurons initially “listen” to network activity, before they “talk” (what they “hear” might affect their integration).

- Tonic excitatory GABA might act through low-threshold (-57 mV) T-type calcium channels (expressed in these neurons). Calcium then initiates changes in gene expression, cytoskeletal rearrangement, etc.

Questions?Questions?