I was wondering if someone could either help enlighten me or provide me an answer for a particular issue/phenomenon I am having.
I am attempting to recreate the Octopus Cell neuron (i.e. found in the cochlear nucleus) in NEURON based on the data and publications of D. Oertel and M. Spencer. I recreated the morphology of the cell (i.e. Soma, Axon Hillock, Axon Initial Segment and 4 Dendrites) as described by M. Spencer in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3486622/ and the specific ionic channels used are .mod files found in ModelDB from D. Oertel's work and P.B. Manis. I have not adjusted or changed these .mod files.
Currently, I am attempting to apply an Exp2Syn input to Dendrite 1 at a specific location on the length of the dendrite with the parameters setup in the code below, I assume I have managed to set this up correctly in code based on the suggestions in this Forum. The dendrite consists of 21 segments/ nseg = 21, again this was done based on the suggestion from Neuron examples that nseg should be odd not even. Furthermore, I have setup the code so that I can record and plot the Vm potential of each section (i.e. dendrites, soma, axon) to visualize what is happening.
Code: Select all
#============================================================================================ #Stimulation of Dendrite 1 @ 0.25, i.e. the most distal part of the dendrite from the soma. #============================================================================================ stim = h.NetStim() #Create a netstim() syn_ = h.Exp2Syn(cell.d["dend0"](0.25)) #Apply Exp2Syn on dend0 @ 0.25 stim.number = 1 #Number of Stimulations stim.start = 5 #Start time in ms ncstim = h.NetCon(stim, syn_) #Create a Netcon() ncstim.delay = 1 #Delay of stimulus in ms ncstim.weight = 2 #NetCon weight in nS. syn_.tau1 = 0.07 #The psp rise time in ms - 70 us syn_.tau2 = 0.34 #The psp decay time in ms - 340 us syn_.e = 0.0 #Synaptic reversal potential - 0 mV
When I stimulate Dendrite 1, in this case at location 0.25 with Exp2Syn with parameters as stated above, on my resulting Vm graphs I notice that the Vm potential rises on Dendrites 2, 3 and 4. Although, this change in Vm potential is rather small in comparison to the dendrite being stimulated, it is still noticeable and worrisome. So my question here is, is this normal? My logic says that something is wrong, as if a SPECIFIC dendrite is stimulated the Vm potential on the corresponding dendrites should not change/at least simply remain at steady state. So is there an underlying mechanism at work in the NEURON environment I am unaware of? Could it be that I'm incorrectly pointing to a section? Ps I have also attempted this with an IClamp and the same thing occurs, I have also attempted going through the NEURON GUI in search for answers by setting up a basic cell in Cell Builder (i.e. soma, axon and 2 dendrites) and stimulating one of those dendrites with an IClamp and plotting the Vm on both dendrites. Again the same problem/phenomenon occurs.
The other question I have is relating to the propagation of the stimulation along the different sections. I do not view a propagational delay (i.e. the onset of stimulation of the dendrite is the exact same onset of stimulation at the soma and the axon wrt to time). Again is this normal? Or is there a way to view this propagational delay?
Any insight into these issues will help. Ps I have not attached the .mod files and my entire code as I didnt want to make my query extremely lengthy, but I am willing to share it upon request.