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Lab Meeting: the Highlights of Audrey’s Amacrine Paper (Submitted, J. Neurophys). Audrey Royer January 12, 2007. Amacrine Cell Modeling. Began as a rotation project Objective: reproduce previously published electrophysiological data with a computer model - PowerPoint PPT Presentation
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Lab Meeting: the Highlights ofAudrey’s Amacrine Paper (Submitted, J. Neurophys)
Audrey RoyerJanuary 12, 2007
Amacrine Cell Modeling
Began as a rotation project Objective: reproduce previously published
electrophysiological data with a computer model
Objective achieved, written up, and submitted as a paper
Paper was firmly and rightfully rejected What contribution did the paper make to the
scientific community?
Amacrine Cell Modeling – Round 2
Used reviewers’ feedback to expand modeling Why did these new results not agree with
previous results? Investigation into discrepancy led to novel
discovery Could only have been found through modeling Explains electrophysiological data
New paper written and submitted on 11/29/06
Dendritic impulse collisions and shifting sites of action potential initiation contract and extend the receptive field of an amacrine cell
Problem Amacrine cells only retinal neurons with
observable dendritic action potentials (AP) APs needed to laterally spread inhibition over
more than 250 um (Cook et al. 1998) Receptive field size (Bloomfield 1992, 1996)
Approximates dendritic tree Significantly reduced in the presence of TTX (Na
channel blocker) Evaluate influence of dendritic APs on receptive
field properties of amacrine cells
Why Modeling?
Electrophysiological data obtained from soma Sometimes from proximal dendrites
Very limited view of the electrical activity of the cell
Methods NEURON
computer program
I Na
I K I K, A
I K, Ca I Ca
I Leak
Annular Data Voltage recording in
soma Somatic and dendritic
APs Active dendrites: all
annuli capable of influencing soma
Dendritic spikes same amplitude in A and D
Passive dendrites: annuli 300 um no effect on soma
Cumulative Annular Injected Charge
Points of interest: Shapes of graphs Where each model reaches 100%
Used to predict receptive field size in area summation simulations
Area Summation Data
Somatic response increases until it saturates
Active dendrites saturate later than passive dendrites Larger receptive
field
Area Summation Receptive Fields
Saturation of the Soma with Passive Dendrites
Active Dendrites Prevent Saturation –Shifting Sites of Impulse Initiation
Impulse Collisions Reduce Influence of Distal Dendrites in Area Summation Sims As increased peak synaptic
conductance, increased number of APs
APs started to overlap in time course and interact Collisions Refractory
Interactions reduced influence of distal dendritic APs
References Bloomfield SA. Relationship between receptive and dendritic
field size of amacrine cells in the rabbit retina. J Neurophysiol 68: 711-725, 1992.
Bloomfield SA. Effect of spike blockade on the receptive-field size of amacrine and ganglion cells in the rabbit retina. J Neurophysiol 75: 1878-1893, 1996.
Cook PB, Lukasiewicz PD and McReynolds JS. Action potentials are required for the lateral transmission of glycinergic transient inhibition in the amphibian retina. J Neurosci 18: 2301-2308, 1998.
After Accounting for Collisions, Annular Data Predicts Area Summation Receptive Fields