Dendritic processing of excitatory synaptic input in GnRH neurons (Roberts et al. 2006)

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"... we used electrophysiological recordings and neuronal reconstructions to generate computer models of (Gonadotopin-Releasing Hormone) GnRH neurons to examine the effects of synaptic inputs at varying distances from the soma along dendrites. ... analysis of reduced morphology models indicated that this population of cells is unlikely to exhibit low-frequency tonic spiking in the absence of synaptic input. ... applying realistic patterns of synaptic input to modeled GnRH neurons indicates that synapses located more than about 30% of the average dendrite length from the soma cannot drive firing at frequencies consistent with neuropeptide release. Thus, processing of synaptic input to dendrites of GnRH neurons is probably more complex than simple summation."
1 . Roberts CB, Best JA, Suter KJ (2006) Dendritic processing of excitatory synaptic input in hypothalamic gonadotropin releasing-hormone neurons. Endocrinology 147:1545-55 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell;
Brain Region(s)/Organism:
Cell Type(s): GnRH neuron;
Channel(s): I Na,t; I L high threshold; I K;
Gap Junctions:
Simulation Environment: GENESIS;
Model Concept(s): Synaptic Integration;
Implementer(s): Roberts, Carson [carson.b.roberts at];
Search NeuronDB for information about:  I Na,t; I L high threshold; I K;
Genesis Simulation of GnRH cells

Author: Carson B. Roberts
Emory University
University of Texas at San Antonio


This archive consists of a number of files that work together to generate simulated voltage
responses from model Gonadotropin-Releasing Hormone cells.  There is a single-compartment 
version of the model, and a multi-compartment model, based on actual reconstructed
cell morphology.

As written, the simulations require Genesis to be installed on the host computer.

Genesis can be obtained and simply installed from:

                 Single and Multi-Compartment Models
As delivered, this package contains both single-comaprtment and multi-compartment 
Genesis models. 
 To look at a 448 compartment model with realistic morphology, an active
soma and axon and passive dendrites, invoke GENESIS at the command line with:
>  genesis gnrh_runcell_GABA

To run a single-compartment version of the same model, invoke GENESIS with:
>  genesis gnrh_runcell_GABA_singlecomp

                 Current Injections and Phase Plane Analysis

As delivered, the scripts are set up to perform a series of current injections, first to 
generate a single spike, and then to do a gradual increase in injected current, to generate 
a sort of phase-plane diagram.  The current injections are all set up in the script:
This script can be edited to change the types of current injections being performed. 
Existing lines can be uncommented (remove the "//" from the beginning of each line).  Many
lines have comments indicating the type of behavior expected from the injections.

The two loops at the end can be modified to change the rates of increase of current, or just
eliminated by changing the "<" in the "while" loops to ">".

                 Simulated Synaptic Inputs
The main Genesis script that runs the simulation is:
                     gnrh_runcell_GABA.g   (for the full-morphology model)      

Near the end of that script (~ line 354), after everything is set up, there are two blocks of code,
with comments and a single executable line.  To do the current injections, (as delivered)
leave uncommented the line:
To look at effects of synaptic inputs, comment this line out, (add a "//" at the start of 
the line) and uncomment the preceeding executable line:
                       // step {run_time} -time
(remove the "//")

This will then cause the simulation to run for a time (run_time) set in the script:
                        gnrh_const.g (for the full-morphology model)
It is in this script that the densities of the various channels, and the strength, number 
and frequency of AMPA and GABA synapses can be varied.  Look around line 126 for parameters
for GABA synapses, and around line 139 for parameters for GABA synapses.  

Once values for numbers of AMPA and GABA synapses have been set, set the "run_time" variable 
(around line 117) to an appropriate value in seconds (the default is 0.5 sec.)

                  Voltage-gated  Channel Dynamics
The equations describing the Hodgkin-Huxley models of the various voltage-gated channels are
in the script:
These should not need to be changed, but if new information (such as from Voltage-clamp
experiments) become available, this is where the model will need to be changed.

			Running Without MATLAB
It is not necessary to use the MATLAB shell to run the simulations.  What the Genesis 
scripts do is to output simulation results into ASCII files, stored in the "output"
subdirectory.  The data files are:

                    Vm_traces.asc -------- First column seconds, second column Volts
                    Current_traces.asc------First column seconds, second column Amperes
                    gsyn_AMPA_traces.asc  ------ First column seconds, Following columns
                                                 (one for each AMPA synapse) Siemens
                    gsyn_GABA_traces.asc  ------ First column seconds, Following columns
                                                 (one for each GABA synapse) Siemens
The simulations can be run from a shell command line with the syntax:
                   genesis gnrh_runcell_GABA_singlecomp
                   genesis gnrh_runcell_GABA
The files in the output subdirectory can then be analyzed with any plotting program.

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