Dynamic Range Of Vertebrate Retina Ganglion Cells

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Published Paper Analysis
40 pts.

ASSIGNMENT: Find an original research (not review) article published within the last ten years and answer the questions below. You must approve the article with your instructor in order to ensure that it is appropriate and that nobody else is using the same one.

You must attach a photocopy of the paper to this form to receive credit.

1. 3 pts. Please provide the citation the article you are analyzing.

Publio, R., Ceballos, C., & Roque, A. C. (2012). Dynamic Range of Vertebrate Retina Ganglion Cells: Importance of Active Dendrites and Coupling by Electrical Synapses. Plos ONE, 7(10), 1-9. doi:10.1371/journal.pone.0048517

2. 10 pts. What was the main purpose, goal, and/or hypothesis of the research? (There may have been more than one.)

Morphologically reconstructed multi-compartmental ganglion cell models were used to perform two studies. In the first study, they investigated the relationship between single ganglion cell dynamic range and number of dendritic branches/total dendritic area for both active and passive dendrites. In the second study they investigated the dynamic range of a square array of ganglion cells with passive or active dendritic trees coupled with each other via dendrodendritic gap junctions. A single neuron characteristic, which is claimed to be fundamental for enhancing the neuronal dynamic range, in general is the size and complexity of the neuronal dendritic tree with active conductance. The idea behind this is that dendritic trees with many bifurcations and active ionic conductance’s act as spatially extended excitable systems whose nonlinear input-output transfer function give the neuron a large dynamic range. If this hypothesis is proven to be correct, most cells of the retina in vertebrates do not benefit from this because they have simple dendritic structures.

3. 3 pts. Use a flowchart diagram to outline the main steps of the experiment and briefly describe the purpose of each step. (The goal is not to report procedural details but rather to show understanding of the rationale behind the experimental design).

Single Cell Models
They worked with a sample of 20 morphologically reconstructed, three-dimensional ganglion cell models from the tiger salamander (Ambystoma tigrinum) retina.
The reconstructed neurons were classified into four groups: medium-complex (MC), medium-simple (MS), small-complex (SC), and small-simple (SS).
Five different neurons were taken from each group totalizing 20 neurons with distinct morphologies.
In addition to the reconstructed dendritic tree, each model includes an axon with an initial and a narrow segment.
The same set of active ion channels were placed in all ganglion cell models. Each model has four voltage-dependent channels (Na, Ca, K, and KA), one calcium-dependent channel (KCa).
The dynamics and parameters of the calcium current were able to fit the high-voltage activated component of the calcium current (L-type) described in a previous experimental work.
The K channel simulates the classical delayed rectifier potassium current and was modeled with no inactivation kinetics while the Na and KA channels have inactivation kinetics.
To obtain the F-I curve of an isolated ganglion cell they submitted it to steps of somatic current clamp of fixed amplitudes.
The duration of each step was 300 ms and the current amplitudes varied from 10 pA to 1000 pA.
For all stimulations, the dynamics range was calculated as ∆ = log (Imax/Imin).
The single compartment model of a lateral geniculate nucleus pyramidal neuron was taken without changes from a previous work. It contains a slow voltage-dependent K current, the Ina and IK currents and the T-type calcium current.

Synaptic Connections and Network Topology
They used experimental evidence of dendrodendritic bidirectional gap junctions connecting ganglion cells to simulate the electrical coupling between two neighboring cells as a single
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