In vivo patch-clamp recording from rat SI neurons. A: Typical example of spontaneous discharges of SI neurons. The excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) are shown by fluctuations above and below the resting membrane potential. Arrow head shows resting membrane potential. B: Location of each type of SI neurons successfully identified by biocytin injection. LTM: low-threshold mechanoreceptive, WDR: wide-dynamic range, NS: nociceptive specific. Values in parentheses are the number of neurons. C: Typical example of a biocytin-injected noxious specific SI neuron in layer IV with spontaneous discharges. Right panel, higher-power photomicrograph of left.