> I'm trying to selectively stimulate a nucleus but there are axons that
> pass through the nucleus. I used minimal stimulation on the assumption
> that cell bodies have a lower threshold for extracellular stimulation
> than axons, but this did not satisfy the reviewers.
It is generally accepted that the Na+ channel density is higher in the
axons than in the soma (see for example Schmidt-Hieber et al., 2008), so
in principle it is easier that if you stimulate extracellularly, the
axons would be stimulated easier than the soma.
So I want to try
> on-cell stimulation. My question is, how much current do you think I
> will need to pass through the on-cell electrode (so I can figure out
> what piece of equipment I can use),
I would suggest you to use intracellular methods. To do stimulation with
extracellular electrodes is rather unspecific. I read some papers that
claimed that the track stimulation can lead to a single fiber
stimulation (see for example Jonas et al., 1993 for mossy fiber
In any case, I would recommend you to perform whole-cell patch-clamp
recording form the soma, or even better, to do paired recordings from
synaptically interconnected neurons. If you are sure that this soma is
connected to the target you are studying, a whole-cell recording for the
presynaptic neuron is the way to go.
If you want to test which presynaptic neuron is connected to your target
cell, you can use cell attached or loose-attached configurations. The
stimulation intensities for these configurations varies between 4 to 9
nA, depending on the cell type.
and how will I know if I am
> succeeding in generating an action potential? I should be able to see
> an on-cell spike?
With intracellular methods, in C-clamp you can easily distinguish the spike.
Hope it helps a bit.