Distribution pattern of c-Fos expression induced by sciatic nerve sectioning in the rat central nervous system

c-Fos expression in the rat central nervous system following sciatic nerve section was compared using an immunohistochemical procedure with control skin-incisions. c-Fos-immunoreactive (IR) materials were localized in the nuclei of nerve cells, and these positive cells were most abundantly observed 120 min after the operation. In the spinal cord, c-Fos-IR cells were seen in the posterior horn on the operated, but not in the contralateral side. The anterior horn and the dorsal root ganglia did not contain c-Fos-IR cells. The experimental animals had the largest number of c-Fos-IR cells in the lumbosacral segments, especially in laminae I and II of L4 and L5 segments. The difference in the number of c-Fos-IR cells and IR intensity between the experimental and control animals was conspicuous in the lumbosacral segments, but there was no significant difference between them in the cervical and thoracic segments. In the brain, an apparent difference in positive cell distribution was not recognized between the experimental and control animals. c-Fos-IR cells were observed in various regions of the brain. A high concentration of positive cells was seen in the temporal cortex, the clastrum, the lateral septal nucleus (ventral part), the hypothalamic nuclei such as periventricular, suprachiasmatic, paraventricular, arcuate, dorsomedial and supramammillary nuclei, the paraventricular thalamic nucleus, the ventral lateral geniculate nucleus (magnocellular part), the pontine nuclei, the dorsal and dorsolateral tegmental nuclei, the parabrachial nucleus (Kölliker-Fuse nucleus), the locus coeruleus, and the nucleus of the solitary tract. Among them, the paraventricular and suprachiasmatic hypothalamic nuclei exhibited the most dense concentration of c-Fos-IR cells and intensity. These results indicate that the c-Fos expression in the brain is induced by transsynaptic stimulation. The findings that there was a clear difference in the distribution of c-Fos-IR cells and in intensity between the experimental and control animals in the lumbosacral segment of the spinal cord but not in the upper portion and the brain, suggested that there is poor discrimination of nociceptive information in the brain between stimulation by nerve section and skin-incision.