I record synaptic responses in thalamic neurons in brain slices using whole cell patch clamp. The stimulating electrode is a bipolar parallel stimulating electrode (separation ~ 1 mm) and this generally works well in evoking synaptic responses. Off-late, there has been a huge antidromic spike in every cell that is visible just prior to the PSP. Its not clear why the antodromic spike is being generated, even when the stimulating electrode is well separated from the recording electrode. Nothing in the set-up has changed except for replacing the stimulating electrode with an identical new one. Since then, we have tried several new electrodes and even replaced the GRASS stimulator to eliminate the antidromic spike but its always present.
This problem is not there with a bipolar concentric stimulating electrode, that generates a short duration stimulus artifact, but unfortunately that does not evoke synaptics in most cells even at the highest stimulating amplitude.
It would be very helpful to hear any suggestions for eliminating the antidromic spike.\