Functional reorganization of sensory pathways in the rat spinal dorsal horn following peripheral nerve injury

1. Functional reorganization of sensory pathways in the rat spinal dorsal horn following sciatic nerve transection was examined using spinal cord slices with an attached dorsal root. Slices were obtained from animals whose sciatic nerve had been transected 2-4 weeks previously and compared to sham-operated controls. 2. Whole-cell recordings from substantia gelatinosa neurones in sham-operated rats, to which nociceptive information was preferentially transmitted, revealed that dorsal root stimulation sufficient to activate A delta afferent fibres evoked a mono- and/or polysynaptic EPSC in 111 of 131 (similar to 85%) neurones. This is in contrast to the response following A beta fibre stimulation? where monosynaptic EPSCs were observed in 2 of 131 (similar to2%) neurones and polysynaptic EPSCs were observed in 18 of 131 (similar to 14%) neurones. 3. In sciatic nerve-transected rats, however, a polysynaptic EPSC following stimulation of A beta afferents was elicited in 30 of 37 (81%) neurones and a monosynaptic EPSC evoked by A beta afferent stimulation was detected in a subset of neurones (4 of 37, similar to 11%). 4. These observations suggest that, following sciatic nerve transection, large myelinated A beta afferent fibres establish synaptic contact with interneurones and transmit innocuous information to substantia gelatinosa. This functional reorganization of the sensory circuitry may constitute an underlying mechanism, at least in part, for sensory abnormalities following peripheral nerve injuries.