Responses of spinal neurones to cutaneous and dorsal root stimuli in rats with mechanical allodynia after contusive spinal cord injury

The firing of neurones in spinal segments adjacent to a contusive T13 spina l cord injury was characterised in anaesthetised rats. Three groups of rats were examined: (1) allodynic spinally injured, (2) non-allodynic spinally injured and (3) normal, uninjured. Spinal cord field potentials evoked by e lectrical dorsal root stimulation and the responses of 207 dorsal horn neur ones to mechanical stimuli applied to the skin were studied. Within the les ioned spinal segment few active neurones were encountered and field potenti als were absent. Depolarising field potentials recorded rostral to the lesi on were reduced in both allodynic and non-allodynic animals compared to uni njured controls, while those recorded in caudal segments were enhanced in a llodynic animals. Neuronal recordings revealed that allodynia was associate d with exaggerated responses, including afterdischarges, to innocuous and n oxious mechanical stimuli in a proportion of wide dynamic range, but not lo w threshold, neurones. These changes were observed both rostral and caudal to the site of injury. The results suggest that an increased responsiveness of some dorsal horn neurones in segments neighbouring a contusive spinal c ord injury may contribute to the expression of mechanical allodynia. It is proposed that a relative lack of inhibition underlies altered cell response s. (C) 2001 Elsevier Science B.V. All rights reserved.