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Yoav Livneh
[email protected]
02-6585163
Neuronal development
(generally)
neurogenesis
and migration
outgrowth of axons and dendrites,
and synaptogenesis
Refinement of
synaptic connections
Adult neurogenesis
(hippocampus)
* also occurs in the adult olfactory bulb
Neuronal development
(in the adult hippocampus)
Ge et al., J Physiol, 2008
GABA 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 (and glutamate)
currents in adult-born hippocampal neurons
7 dpi
14 dpi
28 dpi
evoked Glu.
currents
evoked GABA
currents
tonic GABA
currents
3 dpi
DCX (doublecortin) - a marker
for immature neurons
Bicuculine – GABAa-R
antagonist
CNQX – AMPA-R antagonist
The big question –
What is the role of these tonic
excitatory GABA currents?
Exploration and manipulation of GABA
currents in adult-born hippocampal neurons
exc.
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
affect adult-born neuron
development?
Effects of eliminating excitatory GABA
currents – part I
(dendritic development)
- Shorter total dendritic length.
- Less branches.
- Occupy a smaller volume of space.
Excitatory GABA currents are essential (necessary)
for proper dendritic development
Effects of enhancing excitatory
GABA currents
(should be positively correlated)
Pentobarbital –
GABA agonist
The opposite, complementary, trends were observed with administration
of a GABA agonist (suggesting it might also be sufficient).
Effects of eliminating excitatory GABA
currents – part II
(inhibitory synaptic integration)
evoked
spontaneous
- Less neurons with evoked inhibitory responses.
- Lower evoked response amplitudes.
- Lower spontaneous response frequencies (but similar amplitudes).
Excitatory GABA currents are essential for proper
inhibitory synaptic integration
Effects of eliminating excitatory GABA
currents – part II
(excitatory synaptic integration)
evoked
spontaneous
- Dramatically less neurons with evoked excitatory responses.
- Lower evoked response amplitudes.
- Lower spontaneous response frequencies (but similar amplitudes).
Excitatory GABA currents are essential for proper
excitatory synaptic integration
Effects of eliminating excitatory GABA
currents from birth (KO mice)
The same trends were observed
with NKCC1 KO mice.
Conclusions 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) Ttype calcium channels (expressed in these neurons). Calcium then
initiates changes in gene expression, cytoskeletal rearrangement, etc.
Questions?