I have rarely observed that high frequency stimulus protocol did not induce LTP despite correct electrode placement in anesthezed rats. On the contrary, field potential disappeared immediately after HFS and then gradually reemerged. Has anyone given a scientific explanation for my observation?
It all depends on your HFS protocol. It sounds like you are getting a local seizure from the HFS. This might be due to an interaction of the length of the stimulus train and the frequency used, or having tissue that is hyperexitable for some reason. Repeated brief bursts of HFS might work better than long trains.
There is always a failure rate for any LTP experiment regardless of what region of the brain. Have you tested any other regions and if so does the failure rate seem higher in the dentate?
My experience is not every protocol induce LTP in the dentate. I've tried 100Hz(1s) 2x and it did not produce LTP . Theta burst produce a nice LTP of 30-40% after 60min...
If you record from MPP-DG synapses, TBS protocol works better than HFS (100 Hz/s) as Fabrice mentioned.
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