I'm recording evoked EPSCs from CA1 in whole cell and I happen to see a slow, but marked increase in my eEPSCs for the first 10-20 minutes, even in plain csf. My stimulus is 5 V (on average), one every 20 sec. I see this happening all the time no matter the intensity of the stimulus.
Therefore, I have a very hard time obtaining a stable baseline, with pretty obvious consequences.
eEPSC amplitude drift