Photochemically induced transient spinal ischemia induces behavioral hypersensitivity to mechanical and cold stimuli, but not to noxious-heat stimuli, in the rat.

Pain-like sensory disorders lasting several days were observed in rats after transient ischemia in the lumbar region of the spinal cord. The ischemia was induced with a recently developed photochemical technique. Rats exhibited strong allodynia, a pain-like reaction to innocuous stimuli, to mechanical stimulation of the caudal trunk, hind limbs, and hind paws, which were areas innervated by the ischemic spinal segments. The rats also expressed hypersensitivity to cold stimuli. However, no changes in sensitivity to noxious heat could be detected with the hot-plate test. Furthermore, no morphological damage could be observed in the spinal cord at the light microscopic level in the majority of rats after transient spinal cord ischemia. The present results indicate that allodynia-like symptoms to mechanical stimuli after spinal ischemia may be mediated by myelinated afferents and could be associated with dysfunction of inhibitory transmission in the spinal cord. We suggest that this pain-related syndrome after spinal ischemia could be considered as an animal model of painful states of spinal origin.