Abstract: To explore the response to nociceptive stimuli in spinal cord of immature rat and observe the electrical stimulation of the sciatic nerve on synaptic plasticity of the spinal dorsal horn and spinal c-fos expression in rats of different ages, MK-801 was added to the spinal cord of rats, and the resulting changes in field potential as well as c-fos expression were recorded. LTP in neonatal rats was mainly evoked by A-type nerve fibers, whereas LTP in juvenile and adult rats was mainly evoked by C-type nerve fibers. C-fos expression was significantly increased in the superficial and deep layers of the spinal dorsal horn and in the ventral horn in neonatal rats indicating that the pain signal changed with age. [Copyright &y& Elsevier]