Hypersensitivity of dorsal horn wide dynamic range neurons to cutaneous mechanical stimuli after transient spinal cord ischemia in the rat.

The responsiveness of dorsal horn wide dynamic range (WDR) neurons to cutaneous mechanical stimuli was studied in decerebrate, spinalized, unanesthetized rats before and after transient photochemically induced spinal cord ischemia. In normal rats, the discharges of dorsal horn WDR neurons to the graded mechanical stimuli applied with calibrated von Frey hairs increase linearly. One to four days after spinal ischemia, when the rats exhibit a strong allodynia-like behavioral reaction to cutaneous stimuli, the sensitivity of dorsal horn WDR neurons to mechanical pressure is greatly increased. There is a significant decrease in the threshold pressure to evoke neuronal discharges and the exponential stimulus-response curve is shifted to the left. Thus, transient ischemia of the spinal cord results in hyperexcitability of dorsal horn WDR neurons, which may underly the allodynia-like sensory abnormalities observed in behaving animals. The present results may contribute to understanding the mechanism of the development of chronic central pain in patients after central nervous system injury involving ischemia.