I'm using 400um coronally sectioned slices to perform a 40Hz LTP protocol in the visual cortex of 4 week old mice. I'm relatively new to ephys, and am struggling to troubleshoot the fact that I can't seem to get LTP in my slices. I've tried 2x100Hz instead to see if that's any more successful, but it still doesn't potentiate. Are there some obvious pitfalls that I can avoid to try and have a little more success?
I'm using a high sucrose cutting aCSF for slicing, and then storing them in a standard recording aCSF. I place my stim electrode in layer IV and my recording in layer 2/3. Any and all field troubleshooting is welcome.
Cortical LTP is a nightmare.
1) Are you recording at > 30 degrees? Room temperature LTP probably wont be a thing
2) Are your EPSPs large and brief? e.g. at least half a mV in amplitude, and 5ms wide?
3) Are you certain you're recording an EPSP? Does it go away when you apply CNQX? (This may seem a bit insulting, but without some waveforms, we can't tell, and plenty other biginners have thought the stimulus artefact was an fEPSP)
You may try by applying either a single 1-sec train (100 Hz, at test strength) or four 1-sec trains (100 Hz, test strength) spaced 5 min apart.
Good luck