Kaushik Majumdar Center for Complex Systems and Brain Sciences

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Presentation transcript:

Astrocyte Dynamics: Towards a More Complete Picture of Computation in the Brain Kaushik Majumdar Center for Complex Systems and Brain Sciences Florida Atlantic University

Some Compelling Facts Schummers-Yu-Sur paper in Science reports astrocytes, like neurons, respond to visual stimuli including orientation and spatial frequency. Astrocytes secrete thrombospondin that triggers synapse formation (structural aspect of neuronal networks).

Compelling Facts (cont.) Astrocytes can secrete transmitters like glutamate and ATP and can have excitatory or inhibitory effects on neurons (functional aspect of neuronal networks).

Tri-Partite Synapse Synapse Presynaptic Neuron Postsynaptic Neuron Gliotransmitter release Gliotransmitter release Astrocyte Ca2+ increase

Neuronal-Glial Phase Relationship

Neuron to Astrocyte Communication: Example

Astrocyte to Neuron Communication: Example

Astrocyte to Astrocyte Communication: Example

Mechanism

Computation by Neurons, Synapses and Astrocytes Synaptic plasticity can convey different messages to the postsynaptic neuron of the same spike train generated by the presynaptic cell. Synaptic plasticity is mediated by neuronal firing. Astrocytes control synaptic transmissions and new synapse formation.

Computational Paradigm Ionic Diffusion Potentiation Chemical Synapse Neuron Ca2+ increase Ca2+ increase Astrocyte Transmitter Diffusion Action

Prevailing Scenario Currently computation in the brain amounts to neural computation alone that is, only ionic diffusion potentiation (the Hodgkin-Huxley model or various derivatives of that).

Future Scenario In view of the synaptic computation (Abbott and Regehr in Nature of 14 Oct, 2004) and astrocytic computation (PhD thesis of Suhita Nadkarni, Ohio State University, 2005) in order to get a more complete picture of brain computation neurotransmitter diffusion actions will have to be incorporated alongside the ionic diffusion potentiation.

Transmitter Actions on Astrocytes Glutamate release mGluR Ca2+ IP3 Ca2+ waves

Astrocyte Dynamics: IP3

Astrocyte Dynamics: IP3R

Astrocyte Dynamics: Ca2+ Flux

Ca2+ Conservancy in Cell