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

Nerve injury can result in neuropathic pain, which persists after the injury and may occur after healing is completed. The long-term central reorganization associated with neuropathic pain has been previously studied in animal models. The immediate effects of nerve injury on central representation, however, are poorly understood. We examined the population response properties of closely neighboring neurons located in the hindlimb representation area of the somatosensory thalamus. Changes in the neuronal population properties 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, receptive fields observed before ligation disappeared temporarily after ligation, and changes in number of spikes evoked by the same stimulus. The rates of these changes in central representation were essentially zero before ligation, maximal within minutes after ligation, and decreased to a steady sustained rate of change within 1 to 2 hours. The incidence of functional connectivity, as measured by cross-correlations, remained unchanged. However, the strength of functional connectivity increased after ligation. The results show immediate reorganization of lateral thalamic networks with peripheral nerve damage. When the population response is considered as the underlying code, this reorganization does not reflect the behavioral manifestations of hyperalgesia and allodynia, even though some of the individual neuronal responses do reflect properties consistent with the hyperalgesia and allodynia reported within the same time frame after nerve injury in the rat.