Study on changes in the projection manner of myelinated fibers following transection of the trigeminal nerve.

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The projection manner of myelinated primary affferents, the rat infraorbital nerve and lingual nerve, into the trigeminal nuclear complex was investigated histochemically at 1998. These myelinated fibers terminated in the main sensory nucleus, nucleus oralis, nucleus interporalis and the lamina I and laminae III-V of the nucleus caudalis. After the infraorbital nerve was transected, the projection fashion of myelinated fibers was changed in the trigeminal nucleus caudalis one week after this treatment. Although myelinated fibers do not terminate basically in lamina II of naive rats, a new projection of this myelinated fiber was observed in lamina II, suggesting that transection of primary afferents produces changes in neural plasticity in the central nervous system.To clarify the mechanisms involved in neural plasticity after nerve transection, the expression of transcription factors, c-Fos and Zif/268, was investigated by transection of primary afferents during 1999-2000. The expressi … More on of these transcription factors was induced by both transection and exposure of the infraorbital nerve in the trigeminal nucleus caudalis, but the region expressing these proteins following the two treatments was closely similar to each other in this nucleus, indicating that it is difficult to distinguish neurons expressing these proteins according to transection or exposure of the infraorbital nerve. On the other hand, transection of the sciatic nerve produced the expression of these proteins throughout laminae I/II of the dorsal horn at the 4 and 5th levels of the lumbar spinal cord, while the induction of these proteins by exposure of this nerve was restricted in the lateral one third of this lamina. The number of neurons expressed in this lateral one third of this lamina after nerve transection was closely similar to that derived from exposure of this nerve, indicating that the expression of these proteins induced in this region following transection of the sciatic nerve is derived from exposure of this nerve, while the expression of these proteins at the medial two third of this lamina is derived from nerve transection. This result suggested that it is able to investigate the mechanisms involved in the expression of these proteins induced by nerve transection. First, the effects of pretreatment with glutamate receptor antagonists on the expression of these proteins following transection of the sciatic nerve were investigated. The expression of these proteins in this lamina following nerve transection was reduced by this preteatment, but the effects were restricted in the lateral one third of this lamima whereas no effect was found in the medial two third of this region, suggesting that there may be considerable differences in the involvement of glutamate receptors between tissue injury following nerve exposure and nerve transection. Less