I'm trying to perform extracellular recordings in visual cortical slices during kainate/carbachol bath application to track induction of oscillation and/or spiking activity, but despite zeroing out the signal, the voltage recording incessantly wanders about, tarnishing the quality of my data.
I'm using pipettes pulled from borosilicate glass (1-2 MOhms), incubating in a submerged slice chamber with constant perfusion of aCSF, amplifying my signal 100x with an Axopatch 700B amplifier combined with further amplification by a DAM50 amplifier from WPI, bandpass filtering between 0.1 Hz and 10kHz and digitizing with an Axon Digidata 1440A digitizer.
Waving my hand in front of the DAM50 causes similar voltage deflections, but the random wandering persists despite wrapping the DAM50 in tin foil and repositioning it away from the rig. The voltage changes also show up on the signal that is not amplified further by the DAM50.
I'm currently trying to adapt this rig that I historically have only used for whole-cell experiments for these extracellular recordings, and this is an issue I've never experienced with the whole-cell prep.
If anyone has seen noise like this before, I'm open to any and all suggestions!
Thanks,
Max
The record appears to have a very slow time base, if I am reading it correctly (5 secs per horizontal box). The fluctuations are not likely to be biological in origin, so we should consider artifacts. If you've successfully performed whole-cell patch clamp on this rig, that suggests that overall the system is probably adequately grounded. Do you have a faraday cage?
The electrode resistance is very low. What is the solution in the pipette? If you're still using your internal solution from whole cell recording, my guess is that you're looking at junction potential fluctuations due to bath solution and pipette solution intermixing at the solution interface at the pipette tip. Depending on what you aim to record, you might consider changing electrode types and amplifier. Also, consider AC coupling, if you're looking for spiking activity. AC coupling should eliminate the slow drift in voltage baseline.
I agree with previous comments. Additionally you should review the quality of yor indiferent electrode, it is very critical it is clean. Are you using an Ag/AgCl pellet or a salt bridge ?
Best regards
Enrique
Hi all,
Thanks for your advice. I narrowed down the possible sources of noise to bath level, ground electrode quality/positioning and the AC vs DC amplification setting on my multiclamp 700b amplifier (I'm using aCSF as my internal, a faraday cage and a peristaltic pump that feeds into a handmade 'bubble catcher'). I removed the bubble catcher as I suspected it may be contributing to fluctuating bath level, and despite stabilizing the water bath level, this did not eliminate the drifting issue. Next, I installed a new AgCl pellet as my ground electrode and ensured that it is always submerged, but this did not eliminate the noise either. Finally, I switched my multiclamp 700b amplifier from the DC setting to low frequency AC (1 Hz or 3 Hz), and this successfully stabilized the recording. I've recorded action potentials and am hoping to extract theta and/or gamma oscillations generated in the kainate/carbachol conditions.
Thanks again,
Max
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