I came across this report on ScienceDaily.com this evening. Here's the link:

http://www.sciencedaily.com/releases...0122152447.htm

The upshot: A small molecule, dimethylsphingosine (DMS), appears not only to be overabundant in rats with induced nerve damage, it also appears to cause pain in healthy rats when it is injected.

DMS is "...an apparent byproduct of cellular reactions involving sphingomyelin, a major building block for the insulating sheaths of nerve fibers."

It may induce pain "...by stimulating the release of pro-inflammatory molecules from neuron-supporting cells called astrocytes."