Immediate reorganization of the rat somatosensory thalamus after partial ligation of sciatic nerve

Nerve injury can result in neuropathic pain, which persists after the injur y and may occur after healing is completed. The long-term central reorganiz ation associated with neuropathic pain has been previously studied in anima l models. The immediate effects of nerve injury on central representation, however, are poorly understood. We examined the population response propert ies of closely neighboring neurons located in the hindlimb representation a rea of the somatosensory thalamus. Changes in the neuronal population prope rties were characterized before, during, and after (up to 6 hours) partial ligation of the sciatic nerve in the rat. Changes in these properties were observed within minutes after nerve injury. There were changes in neuronal class and receptive field size, emergence of new receptive fields, receptiv e fields observed before ligation disappeared temporarily after ligation, a nd changes in number of spikes evoked by the same stimulus. The rates of th ese changes in central representation were essentially zero before ligation , maximal within minutes after ligation, and decreased to a steady sustaine d rate of change within 1 to 2 hours. The incidence of functional connectiv ity, as measured by cross-correlations, remained unchanged. However, the st rength of functional connectivity increased after ligation. The results sho w immediate reorganization of lateral thalamic networks with peripheral ner ve damage. When the population response is considered as the underlying cod e, this reorganization does not reflect the behavioral manifestations of hy peralgesia and allodynia, even though some of the individual neuronal respo nses do reflect properties consistent with the hyperalgesia and allodynia r eported within the same time frame after nerve injury in the rat. (C) 2001 by the American Pain Society.