Enlargement of the receptive field size to low intensity mechanical stimulation in the rat spinal nerve ligation model of neuropathy

One characteristic of plasticity after peripheral tissue or nerve damage is receptive field reorganization, and enlargement of receptive held size has been suggested to occur in certain models of neuropathic pain. The aim of the present study was to explore whether enlargement of neuronal receptive fields could contribute to the mechanical allodynia found on the ipsilatera l pam in the spinal nerve ligation model of neuropathy. After ligation of L -5-L-6 spinal nerves, all rats developed behavioral signs of mechanical all odynia, while the sham-operated control group displayed no such changes. Th e characteristics of the evoked responses of the neurones recorded in the d orsal horn of the rats were similar between the spinal nerve ligation, the sham operated control group, and the nonoperated control group, except for spontaneous activity, which was significantly increased in the spinal nerve ligation group. The mean size of the receptive field on the ipsilateral hi ndpaw, mapped using low-intensity stimulation with 9-g von Frey hair, was s ignificantly increased in the spinal nerve ligation group, as compared to t he sham-operated group. No significant difference was seen with 15- or 75-g von Frey hairs. The distribution of the receptive fields over the plantar surface of the paw was similar between the study groups. The enlargement of receptive field for nonnoxious touch could be an indication of central sen sitization in this model. (C) 2000 Academic Press.