Spinal Cord Injuries Containing Asymmetrical Damage in the Ventrolateral Funiculus Is Associated With a Higher Incidence of At-Level Allodynia

Approximately 70% of male rats receiving severe T8 spinal contusions develop allodynia in T5-7 dermatomes (at-level) beginning two weeks post-injury. In contrast, rats having either complete transections or dorsal hemisections do not develop allodynia at-level following chronic spinal cord injury (SCI). In the present study, incomplete laceration and contusion injuries were made to test for neuroanatomical correlates between areas of white matter damage/sparing at the lesion epicenter and the presence/absence of allodynia. Following incomplete laceration lesions and six weeks of behavioral testing, histological reconstruction and analysis of the lesion epicenters revealed a significant difference (p<.001) in the amount of ventrolateral funiculus (VLF) asymmetry between rats showing pain-like responses evoked by touch (74.5% ± 8.4% side-to-side difference in VLF damage) versus those not responding to touch (11.3% ± 4.4% side-to-side difference in VLF damage). A five week mean allodynia score for each rat that incorporates a full range of forces that are all innocuous in intact controls revealed that the degree of hypersensitivity at level is related to the extent of VLF asymmetry post-SCI. No other damaged spinal white matter or gray matter area was correlated with sensitivity to touch. Similar findings were obtained for rats receiving T8 contusions, a more clinically relevant injury. These data suggest that different extents of damage/sparing between the two sides of VLF are likely a requisite for the development of allodynia after SCI.