Stimulation of apical dendrites (stratum radiatum) in CA1 region in hippocampal slices using MEA device induces a negative extracellular response due to Ca2+ and Na+ inward flow by activated-NMDAR and AMPAR at the synapsis. It also induces extracellular positive response in soma and basal dendrites due to passive return current.
I would like to know the ionic basis of this passive return current. Could It be due to Ca2+ waves and activation of BK and SK channels at the soma?
Think simpler. Any inward current in the dendrites must be associated with an outward current in the rest of the cell. What is available to pass that current? Firstly there is the current due to the capacitance of the membrane (which I believe is negligible, but don't quote me on that), and secondly there are the ion channels that are open at rest. Most notably leak potassium currents, and the h-current.
Thanks for your answer Mr. Connelly. I supposed it was due to potasium transition and probably BK and SK channels have a slow action in comparing with that response obtained in the soma. However, I have seen nothing in the literature discribing the reason of this possitive polarity, at the ionic level. So thank you so much.
Please read this nice Cohen and Miles 2000 paper
www.ncbi.nlm.nih.gov/pmc/articles/PMC2269886/
Also the wave shape of LFP depends on recording electrode position