Immunohistochemical Study of the Effect on Motor Cortex Stimulation for Deafferentation Pain; Comparison of c-Fos Expression Sites

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The effect of motor cortex stimulation therapy (MCS) for deafferentation pain evaluated on the basis of c-fos gene, a known pain marker. [Materials] Fifteen mature cats, weighing 1.5-3.5 kilograms were used. [Methods] The cats were divided into three groups: a deafferentation pain group in which the trigeminal ganglion was destroyed, an MCS group in which MCS was used after destruction of the trigeminal ganglion, and a control group. Sites and levels of c-fos expression were examined immunohistochemically. [Result] The percentage of c-Fos-positive cells in the spinal nucleus of the trigeminus increased in both the deafferentation pain and MCS groups, however, the increase was smaller in the left side of the brain in the MCS group. In the cingulate gyrus, the percentage of c-Fos-positive cells increased bilaterally in the deafferentation pain group, but the increase was greater in the MCS group. Although the percentage of c-Fos-positive cells in the insula and the parietal operculum increased bilaterally in the deafferentation pain and MCS groups, there were no statistically significant differences between these groups. In the pontine gray and periaqueductal gray matter, the percentage of c-Fos-positive cells in the deafferentation pain group increased bilaterally. There was no significant difference between the MCS group and the control group. [Conclusion] The cingulate gyrus, insula, and pariental operculum are activated after deafferentation. This activation is related to the development of deafferentation pain. Pain relief due to MCS is not dependent on the descending analgesic mechanism of the brain stem. Activation of the cingulate gyrus appears to be a factor in the analgesic mechanism of MCS.