That again illustrates the great difference between nurologic pain and "normal" pain. Normal pain is mediated at the pain receptor, as interpreted by the brain. Nerve pain is the brain's response to inappropriate nerve activity over many days, months, and years, 24 hours a day. The brain doen't know what these inappropriate signals mean, and so interprets them as various types of pain: burning, shock, achyness, tightness. Substance "P" at the nerve receptors has little or nothing to do with neuropathic pain.

As time goes on, the brain becomes hypersensitive to the activity in the feet, hands, wherever the PN is occuring. That's the acute phase of PN, when pain increases rapidly. That's also why tranquilizers and anticonvulsants help somewhat...they reduce the brain's hypersensitivity. And, that's why Capsicum is so godawful painful for neuropathy; it increases nerve activity in the peripheral location, without calming the secondary source of the problem, the hypersensitive sensory receptor areas in the brain.