Neuron. 1991 Mar;6(3):333-44.

Control of postsynaptic Ca2+ influx in developing neocortex by excitatory and inhibitory neurotransmitters.

Yuste R, Katz LC.

Laboratory of Neurobiology, Rockefeller University, New York, New York 10021.

We assessed the pathways by which excitatory and inhibitory neurotransmitters elicit postsynaptic changes in [Ca2+]i in brain slices of developing rat and cat neocortex, using fura 2. Glutamate, NMDA, and quisqualate transiently elevated [Ca2%]i in all neurons. While the quisqualate response relied exclusively on voltage-gated Ca2+ channels, almost all of the NMDA-induced Ca2+ influx was via the NMDA ionophore itself, rather than through voltage-gated Ca2+ channels. Glutamate itself altered [Ca2+]i almost exclusively via the NMDA receptor. Furthermore, synaptically induced Ca2+ entry relied almost completely on NMDA receptor activation, even with low-frequency stimulation. The inhibitory neurotransmitter GABA also increased [Ca2+]i, probably via voltage-sensitive Ca2+ channels, whereas the neuromodulator acetylcholine caused Ca2+ release from intracellular stores via a muscarinic receptor. Low concentrations of these agonists produced nonperiodic [Ca2+]i oscillations, which were temporally correlated in neighbouring cells. Optical recording with Ca2(+)-sensitive indicators may thus permit the visualization of functional networks in developing cortical circuits.

Calcium imaging of cortical microcircuits

Single-cell resolution imaging of Ca2+

influx due to action potentials

• L5 pyramid loaded with 50µM fura• imaged by photodiode array at 1.6 kHz (0.6ms/frame)

Whole-cell filled

AM filled

Trains of action potentials

50 Hz 40 Hz

Cortical circuits in vitro are spontaneously active:spontaneous activity as a tool, let the circuit speak

QuickTime™ and aCinepak decompressor

are needed to see this picture.

V

IV

II/III

Automatic identification of cells

Detection of calcium transients

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Spontaneous synchronizations of a small % of neuronsLow temporal resolution- 1sec/frame

Spontaneous coactivations have specific spatial patterns

9 mV5 s

-70 mV, 0 pA

500 ms9 mV

1.3 s9 mV9 mV

500 ms

1 2 3 4

1 2 3 4

Synchronizations correspond to UP states

UP states can last several seconds

Stereotyped dynamics of circuit coactivations

Cortical motifs and songs: repeated sequences of activityIntermediate temporal resolution- 50 msec/frame

Shuffling tests

Photodiode array: 0.6 msec/frame

Local synchronizations

Sequential activations of cells

Pacemakers

Pacemakers are more regular

Repeated network activity measured in a single cell10 KHz resolution

i iii iv

10 pA

200 ms

Repeated motifs of spontaneous activity in slices

Millisecond precision

Correlation between intracellular and optical repetitions

Repetitions in vivo

Ilan Lampl/David Ferster

What is role of thalamic stimulation on cortical dynamics?

L4

L2/3

L5

Adapted from Brecht et al 2003

Thalamic Stimulation

4-8 stimuli40 Hz200 s50 – 100 A

ThalamusThalamus

““Barrel” CortexBarrel” Cortex

Stimulation ElectrodeStimulation Electrode

Imaging Layer 4 response to thalamic stimulation

20 mV

1 s

Thalamic stimulation generates cortical UP states

UP states• Prolonged depolarizations • ~ 10 mV depolarized from rest• Preferential state for action potential

generation• Coincident with multiple nearby neurons

Vm -70 mV

500 ms

20 mV

Spontaneous

Spontaneous activity also generates cortical UP states

Triggered

Triggered Core

SpontaneousX 5 X 4

Spontaneous Core

Overlap

Overlap Core

Spontaneous activity and thalamic stimulation engage the same neurons !!!

Triggered Spontaneous Overlap

5mV

20mV

500 ms1 s

Amplitude Duration No. APs

Similar Spontaneous and Evoked Intracellular UP states

# of APs

Amplitude

DurationCorrelation of UPstates within cells

Triggered Spontaneous Core

1

2

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Fra

me

Nu

mb

erIdentical Network Dynamics during Spontaneous

and Evoked Network Events- 100 msec/frame

Tim

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10 mV

500 ms

5 mV

100 ms

Millisecond Precision in the Repetition of Synaptic inputs during spontaneous and thalamic UP states

Novel types of spontaneous network dynamicsData:

• Reverberating activity is prevalent at all temporal scales• Spatiotemporal patterns are real: statistics, two techniques, spatial profile, UP states, they can be triggered• Sparse dynamics: small number of cells • Single neurons can participate in many patterns• Repetitions never exact• Thalamic stimulation triggers internal states

Speculation:

• Spatially organized ensembles: related to circuit features?• Preferred states: attractors or metastable states?• Precisely repeated dynamics: Abeles’ synfire chains?• Cortex as a giant CPG?

Spinal Central Pattern Generator Cortical Microcircuit

Cortex as a giant CPG

Buqing Mao-postdoc

Rosa Cossart-postdoc

Dimitry Aronov-undergraduate student

Yuji Ikegaya-visiting professor

Gloster Aaron-postdoc

Jason McLean-postdoc

Brendon Watson-MD PhD student

National Eye Institute- HHMI

Synfire chains hypothesis- Moshe Abeles

Synchronous firing

Nonlinear gain paradoxically reduces jitter

Faithful propagation

Faithful repetition

Precise Firing Sequences

Two theories of brain function:

Feed forward: SherringtonHubel &WieselReceptive fieldsSpeed of processing

Feedback: Brown

Lorente/HebbLlinásRecurrent connectivitySpontaneous activity

Pyramidal neurons in layer 5

1

2

3

Fra

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TriggeredNaive Core

An Already Existing Network Mediates the Observed Dynamics

Tim

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10 mV

500 ms

An Already Existing Network Mediates the Observed Dynamics

40 %

30 %

<10 %Thalamus

Even in L4, the vast majority of excitatory synapses arise

locally within cortex

(20 % long corticocortical excitatory connections)

Circuit attractors

Attractors

Input

Inputs

Adapted from Wilson, 1999

Memories

Example of an emergent computation

Synfire chains

Evidence for synfire chainsAbeles PFSSpatial navigation in hippocampusBirdsong sequencesCPGs

Arguments against Statistics Nonlinear null hypotheses Mechanism unknown

-52 mV

-72 mV

-72 mV

-72 mV

-52 mV

UP states promote precise firing patterns in response to thalamic input

50 mV

25 ms

Train of StimuliDuring DOWN state

Single Thalamic StimulationDuring DOWN state

Train of StimuliDuring UP state

1st Spike<2 ms jitter

2nd Spike<5 ms jitter

1st Spike40 ms jitter

Searching for repeats of activity in

a single neuronal recording

Examine the covariance, h(), between segments: (AxB), (AxC),...(BxC), (BxD),......

Two competing world views:How is perception shaped?

Feed Forward Feedback

Empiricism Nativism

Synchronizations correspond to maximum organization