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LEECH HEART INTERNEURON 8-CELL MODEL PARAMETER EDITOR
Andrew Hill, Steve Van Hooser, Ron Calabrese
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The model editor allows one to edit the conductances of ionic
channels in the individual cells of the model and to edit the
strength of the synaptic connections between the cells. One
can save these settings to a file, restore settings from a
previously saved file, or restore the original settings used
by Andrew Hill in his paper.
Note: This help describes how to edit the parameters of the
model. For a general introduction to the leech heart
interneuron circuit or a technical description of the model,
please see the "Introduction". For help running the model
or displaying graphs, see "Help" in the "Windows:" section of
the window titled "Leech Heart Interneuron 8-Cell Model".
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TABLE OF CONTENTS:
(1). Understanding the network schematic
(2). Editing the ionic conductances of a cell
(3). Editing the strengths of the synaptic connections
(4). Saving and restoring parameters
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(1). UNDERSTANDING THE NETWORK SCHEMATIC
The model simulates four bilateral pairs of inhibitory
neurons in the first four ganglia (G1-G4) in the medicinal
leech. The heart interneuron cells are labeled according
to the ganglion and the side of the animal in which it
resides. Thus, HN4L is the cell on the left in ganglion 4.
The cell pairs in ganglia 3 and 4 oscillate out of phase,
while the cells in ganglia 1 and 2 fire out of phase with
the G3 and G4 cells on the same lateral side.
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| ___________________________________ |
| G1: | HN1L(+) HN1R(-) | |
| -----------------|----------------- |
| | |
| _________________|_________________ |
| G2: | HN2L(+) HN2R(-) | |
| -----------------|----------------- |
| | |
| _________________|_________________ |
| G3: | HN3L(-) HN3R(+) | |
| -----------------|----------------- |
| | |
| _________________|_________________ |
| G4: | HN4L(-) HN4R(+) | |
| ----------------------------------- |
| |
| The HN cells in the first four ganglia in |
| the leech. +/- indicate phase relationships. |
| (Synaptic connections not shown.) |
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The bilateral pairs in G3 and G4 are reciprocally
inhibitory. The connections between the cell pairs in the
animal and in the model include both spike-mediated
synapses and graded synapses. In the model editor
schematic, each line between the pairs represents both the
spike-mediated _and_ graded connections between the cells,
with a dot indicating the post-synaptic cell. The cells
themselves are represented by a filled circle.
The cell pairs in G1 and G2 are not reciprocally inhibitory.
Each HN neuron in G1 and G2 makes reciprocally inhibitory
connections with the G3 and G4 neuron on the same side of
the animal. For example, HN1L has reciprocally inhibitory
connections with HN3L and HN4L. (In the animal, these
connections probably include both spike-mediated and graded
synapses, but only the spike-mediated contribution is
modeled.) These synapses are not made close to the cell
bodies of the cells in G1 or G2, but rather on distal
processes of these cells located in G3 and G4. As is typical
in the literature, a square is drawn between G3 and G4 to
represent these processes. Since the HN1's and HN2's on
identical sides fire in phase, and since they both make
reciprocal connections between the same cells in G3 and G4
on the same side, we do not draw one square for each cell
but instead draw one square for each side. Thus, we draw
one square to represent HN1L and HN2L, and another to
represent HN1R and HN2R. In addition, we draw one line
to represent the connection from both HN1 and HN2 cells
to the post-synaptic G3 or G4 cell.
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(2). EDITING THE IONIC CONDUCTANCES OF A CELL
To edit the ionic conductances of an HN3 or HN4 cell,
simply click on the circle representing the cell. To
edit the ionic conductances of an HN1 or HN2 cell, click
on the square representing its processes--clicking on a
square will bring up a window for each of the two cells
the square represents.
In the cell window, the original values for the
conductances used in Andrew Hill's paper are given in
parentheses for reference. Note: One needs to hit return
or click the field label to register the entry of a new
value.
Example:
To change the value of the h current in HN3R to 1e-9,
click on the filled circle labeled HN3R to bring up the
window of conductances, click on the text field labeled
"h", and change the value to 1e-9. Click the "h" label
or hit return to register the changes.
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(3). EDITING THE STRENGTHS OF THE SYNAPTIC CONNECTIONS
To edit the strengths of the synaptic connections
between cells, click on the "Show Weights" button in
the editor window. An editable text field containing
the current value of the weight for each connection
will appear. Recall that in the schematic, each line
represents two synaptic connections-- a spike-mediated
synapse and a graded synapse in the case of the G3 and
G4 reciprocal connections or an HN1 and HN2 to HN3 or
HN4 connection in the case of the G1,2 to G3 or G4
reciprocal connections. Thus, two text fields will
appear for each line drawn on the schematic. To make
it easier to see which line is associated with a
particular text field, each text field is drawn in
the same color as its corresponding line. In the case
of G3 or G4 bilateral connections, one text field is
labeled with an "s" for the spike-mediated connection,
and one is labeled with a "g" for the graded synapse.
In the case of the G1,2 to G3 or G4 connections, one
text field is labeled with a "1" for the G1 to G3 or
G4 connection, and the other is labeled with a "2" for
the G2 to G3 or G4 connection. For all connections,
the strength used in Andrew Hill's paper is given in
parentheses for reference.
Examples:
To set the graded synapse connection from HN4L to HN4R
to zero, click on "Show Weights" in the model editor
window, and locate the text field beginning with a "g"
nearest the line from HN4L to HN4R. Notice that the
line from HN4L to HN4R is in red, and that the two text
field nearest the line are also drawn in red. Change
the value of the "g" field from its present value
(the default is 3e-8) to 0 and click the label or hit
return to register the change.
To set the (spike-mediated) connection from HN2L to HN3L
to 0, find the line running from the square labeled
"HN1,2L" to HN3L. Notice that the line itself is red,
and that the two text fields nearest the line are red
as well. Find the text field beginning "2", and set
the value to 0. Again, click the label or hit return
to register the change.
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(4). SAVING AND RESTORING PARAMETERS
To save a set of parameters to a file, enter the file
name in the "Save" text field and click the "Save"
label. To restore a set of parameters from an existing
file, enter the file name in the "Restore" text field
and click on the label "Restore". To restore the
original parameters used in Andrew Hill's paper,
click on "Use Defaults".
Note: For technical reasons, one needs to have write
permission for the tutorial directory in order to load
files. If this is not possible, look at the file
"README" in the tutorial directory for a work-around.
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