脊髄前根知覚性線維の起始細胞と終止部位について—逆行性軸索流を利用した実験的研究

ORIGINS AND TERMINATIONS OF PRIMARY AFFERENT FIBERS IN THE SPINAL VENTRAL ROOTS IN THE CAT AS DEMONSTRATED BY THE RETROGRADE AXOPLASMIC TRANSPORT OF HORESERADISH PEROXIDASE

I．はじめに

　脊髄前根が運動性遠心性線維からなり，後根が知覚性求心性線維からなることは，Bell-Magendieの法則として知られ，脊椎動物の神経系を構成する基本原理の1つと信じられている。

　しかし臨床的には疼痛を有する患者に行なわれる脊髄後根切断術が時に疼痛を完全に除去し得なかつた症例も報告され^11,19），知覚が後根以外の何らかの経路によって中枢に伝達される可能性も古くから議論されている^4,6,11,19）。Sherrington （1894）^15）はサルとネコの脊髄前根を切断した後，断端から脊髄側に数本の変性した神経線維を見出し，前根中に求心性線維が存在することを示唆したが，それ以来，脊髄前根中に求心性線維が含まれることを確認した報告が散見され^{7,8,13,14,20）}，その存在が後根切断後も疼痛を残す理由であると主張するものもある^4）。

Origins of primary afferent fibers in the ventralroots of the lumbosacral and cervical spinal cord inthe cat were investigated by the horseradish per-oxidase method.

The first group of animals (5 cats) underwentinjection of horseradish peroxidase (HRP) into theL7-S3 areas of the spinal cord bilaterally followinga unilateral dorsal rhizotomy. In the second groupof animals (4 cats) HRP was injected into thenucleus gracilis of both sides following a unilateraldorsal rhizotomy of L7-S3. The third group ofanimals (3 cats) underwent a unilateral dorsal rhi-zotomy of several cervical segments following HRPinjection into the cervical spinal cord gray of thesame side. The fourth group of animals (3 cats)similarly underwent a unilateral dorsal rhizotomyof several cervical segments following HRP injec-tion into the ipsilateral nucleus cuneatus. Theanimals were allowed to survive for two or threedays and were sacrificed by intracardiac perfusionof aldehyde solution. The ventral roots, spinalganglia and portions of mixed nerves distal to theganglia were prepared for benzidine reaction todemonstrate peroxidase activity.

The spinal ganglia of the rhizotomized side ofthe first two groups showed no labelled ganglioncells while many labelled cells were found in theganglia of the non-rhizotomized side. However,the ventral roots of both sides in the first groupof animals contained a number of aberrant nervecell bodies particularly in the S2 and S3 segments, many of which possessed HRP reaction productsin their perikarya. They were scattered throughoutthe length of the ventral roots and some werefound in the mixed nerve portions distal to theganglia. No labelled aberrant cell bodies werefound in cases of HRP injection to the nucleusgracilis. The last two groups of animals whichunderwent a cervical dorsal rhizotomy showed nolabelled cells in the spinal ganglia of the rhizoto-mized side. No aberrant nerve cell bodies werefound in the ventral roots of the cervical segments.

This study proves that aberrant nerve cell bodiesare the major source of afferent fibers in the lum-bosacral ventral roots and the majority of themappear to terminate in the spinal cord gray whichis territorial for the individual ventral roots.There was no evidence which would support the presenceof afferent fibers in the ventral roots of thecervicalsegments.