Cold exposure enhances tactile allodynia transiently in mononeuropathic rats.

A laser and erythrosin-B-induced sciatic nerve injury decreases thresholds of a mechanically induced paw withdrawal reflex and enhances cold-induced withdrawal behavior of the affected limb. Exposure of the affected paw to a normally innocuous cold stimulus results in a transient decrease in the threshold of the mechanically evoked paw withdrawal reflex in neuropathic but not in intact rats. The present data suggest that in an experimental neuropathic state a normally innocuous cold stimulus may further sensitize spinally mediated withdrawal reflexes to stimuli of another stimulus modality, in this case, to innocuous tactile stimuli. Therefore, testing mechanical allodynia in neuropathic rats immediately after testing cold allodynia may produce artifactual results.