仙髄副交感神経核と会陰横紋筋支配核の関連性にっいて—逆行性軸索流を利用した実験的研究

ORGANIZATION OF THE SACRAL SPINAL CORD IN RELATION TO THE PARASYMPATHETIC PREGANGLIONIC NEURONS AND THOSE INNERVATING THE PERINEAL SPHINCTERIC STRIATED MUSCLES : EXPERIMENTAL STUDY IN THE CAT WITH THE USE OF RETROGRADE AXOPLASMIC TRANSPORT OF HORSERADISH PEROXIDASE

I．はじめに

　仙髄は膀胱，直腸，性機能などに関係する平滑筋および横紋筋の支配神経核を含んでいる^3,10,17）。これらの平滑筋は，主に壁在神経節に終止する副交感神経節前線維の支配を受けているが，その起始核の局在については，逆行性chromatolysisによる同定は困難であるとされ^30），細胞構築学的研究^{14,15,18,21,23,24,26,27）}と，電気生理学的研究^5,6,30）によるものが大部分である。形態学的に仙髄副交感神経核と考えられてきたものは，1）仙髄中間外側核および内側核^14,15,18,21），2）内側平滑筋核^{14,15,16,21）}，3） Onuf核^18,27）などである。しかし，電気生理学的方法によつて副交感神経核と同定されたものは，中間外側核のみであり^5,6,30），内側平滑筋核とOnuf核については，生理学的文献はもとより，最近の神経解剖学教科書にも，二，三の例外を除いて，言及されていない。

　副交感神経の支配を受ける諸臓器の中で，特に直腸と膀胱の平滑筋は，その正常の機能のために，横紋筋である外肛門括約筋や尿道周囲筋群との密接な協同運動を必要とする^{1,2,3,7,11,17）}。本研究は膀胱，直腸の平滑筋を支配する神経核と，会陰の横紋筋を支配する神経核が，仙髄内でどのような相互関係にあるかということをhorse—radish peroxidase （HRP）の逆行性軸索内輸送法^{8,29,32,33）}を利用して検討したものである。その結果，中間外側核，内側平滑筋核およびOnuf核の相互関係について興味ある所見を得たので報告する。

Attempts were made to investigate the central organization of efferent neurons to the rectal and vesical smooth muscles and the external anal sphincter and bulbospongiosus muscles by meansof the retrograde axoplasmic transport of horse-radish peroxidase (HRP). HRP was injected into each of these muscles in fifteen cats and retro-gradely labeled neurons were identified in the sacral spinal cord.

1. HRP injections into the rectal, internal anal and vesical smooth muscles.

Labeled neurons were found in the intermedio-lateral and intermediomedial cell columns in S2-Cxl. The cell group X of Onuf, identifiable be-tween the lower S1 and S2 cord level, contained retrogradely labeled neurons also. Yet, another group of labeled neurons were found in the ventro-medial aspect of the ventral horn between S2-Cx1, location of which corresponds to the nucleus myo-leioticus medialis (Massazza).

2. HRP injections into the external anal sphincter and bulbospongiosus muscles.

Labeled neurons were found in the cell group X of Onuf, whereas they were not found in the inter-mediate gray. A small number of labeled neurons were also found in the nucleus myoleioticus medialis in cases of external anal sphincter injections but not in bulbospongiosus cases.

The above results indicate that the sacral para-sympathetic preganglionic neurons are certainly located in the intermediolateral and intermedio-medial cell columns. In addition, the nucleus myoleioticus medialis of the ventral horn appears to participate in innervation of the rectal and vesical smooth muscles and also the external anal sphincter muscle to some extent. The cell group X of Onuf is unique in that it appears to innervate both smooth and striated muscles, although the exact mode of termination to these structures are not known. Thus, the sacral spinal cord as to the innervation of the striated and smooth muscle structures appears to be organized in a special way, which is not like the cranial parasympathetic innervations. This may be due to the particular situation of the rectum and the urinary bladder, functions of which require close coordinations of the smooth and striated muscles so that retention and evacuation of their contents would be efficiently maintained on voluntary and involuntary bases.