Can you help me with extracellular recording of wide dynamic range neurons in the mouse spinal dorsal horn? I am trying to induce windup in the WDR neuron to eventually compare if a knockout mouse has different windup properties, but for now I am using wild type mice. I search for WDR neurons around vertebral segments T13, L1, and L2 with receptive field at the plantar surface of the hindpaw. Then, I insert needle electrodes around the receptive field to deliver constant current stimulation. The aim is to stimulate at the hindpaw and record spikes at the dorsal horn.
My results are that sometimes I deliver currents and there are no spikes at the dorsal horn...it doesn't work. I can mechanically stimulate with light brushing and pinching the skin and get evoked responses, but electrical stimulation does not work sometimes. I don't know why. Anybody have suggestions? I checked and found that stimulating electrodes are good, current stimulator is good, current output is good--these are obvious things to check. And then I increased the current to 5mA and nothing. Usually a current of 0.3mA is enough to get evoked spikes...when I can get it to work.
Also, does anyone know how to reduce or eliminate stimulus artifact in this preparation? I cover the hindpaw and stimulating electrodes with foil and connect to ground; this seems to reduce it a bit, but not by much. I wonder if the gigantic stimulus artifact spike is masking some short-latency spikes.
Thanks so much!