Abstract
It is well known that referred pain is provoked by noxious stimulation of skeletal muscle in human. In this study, we examined the plastic changes of rat dorsal horn neurons after myositis induced by carrageenan. The experiments were performed on 25 SD rats with urethane anesthesia. The spinal cord was exposed by laminectomy and the activity of single neuron at the L3-L5 level was extracellularly recorded. The neurons were searched by applying mechanical stimulation. The type of neurons and the area of receptive fields (RFs) were determined, 2% carageenan was injected into the skeletal muscle which was separated from the original RF by a major joint. Five low-threshold mechanosensitive (LTM), 15 wide dynamic range (WDR) and five noxious specific neuron (NS) were examined. All neurons had RFs both skin and deep tissues. After injection of carageenan into the muscle, none of the neurons changed the responsiveness and character in original RF. The new RFs appeared or expanded in five out of 15 WDR and two out of 5 NS neurons. In one WDR neuron, the RF area reduced slightly, and no change of RF in the LTM neuron. The expansion of RFs was continued during experiment and reversed after lidocaine injection into the myositic muscle in 2 (one WDR and 1 NS) out of three neurons tested. These results suggest that the myositis produced by intramuscular injection of carageenan might be activated the silent synaptic connection at the spinal dorsal horn. [Jpn J Physiol 54 Suppl:S156 (2004)]
