Deafferentation painの発現機—脊髄根切除モデルを用いた実験的研究

MECHANISM OF DEAFFERENTATION PAIN:EXPERIMENTAL RESEARCH USING SPINAL ROOT RESECTION MODEL

　抄録　求心路遮断痛の発現機序解明のため，ラットを用い，脊髄根切除モデルを作製し，その後の自傷行為の観察および検討を行った。雄のSD系ラットを用い，椎弓切除および椎間孔開放にて，C5-Th1の後根のみを切除した群および前根後根を同時に切除した群を用いた。コントロールおよびホルマリンを根切除前あるいは後に肢背に投与して7群に分け，3か月以上観察した。後根切除のコントロールでは，3か月の観察では自傷行為はみられなかった。ホルマリン患側肢前投与および両側肢後投与群では半数が7日以内に肘関節までの激しい自傷行為を開始し，1か月以内に100％に達した。一側のみ後投与群では，3週間以上たって指先に限局した自傷行為が始まり，50％に発現したのみであった。前根後根切除群では，患側肢前投与では25％に自傷行為を認めたが，それ以外では，3か月の観察にて自傷行為は全くみられなかった。これらの自傷行為の結果より，痛みの経験の記憶および前根の存在が自傷行為の発現に何らかの形で関与している可能性が示唆された。

In rats, autotomy of the digits following dorsal root resection has been observed by many resear-chers and is considered as an animal model of deaf-ferentation pain. Using C 5-Th 1 root resection model of rats, we investigated the role of the ventral roots and pain experience given before deafferentation in the development of autotomy. Male Spraque-Dawley rats of eight weeks old, weighing about 200 g, were used. Animals were devided into two major groups ; dorsal root resec-tion group and total (both ventral and dorsal) root resection group. Each group was further divided into several sub-groups, according to the use of formalin injection, before or after surgery, and to the side of formalin injection, the forearm of the affected (root resection) side or unaffected side or of both sides. In pre-injection groups, O.1 ml of 5% formalin was given subcutaneously on the forearm one hour before surgery. In the post-injection groups, formalin was given within one hour after surgery. Dorsal root resection groupwithout formalin injection was used as control. Under anesthesia with intraperitoneal injection of nembuthal, left C 5-Th 1 dorsal root resection was performed by C 4-Th 1 laminectomy and left C5- Th 1 total root resection by opening of the cor-responding vertebral foramens. After surgery, we checked neurological findings, systemic condition and local changes of all the extremities everyday during the first week and once a week thereafter for at least three months. In control group, auto-tomy was not observed at all during the observa-tion period of three months. In dorsal root re-section groups of formalin pre-injection on the affected forearm and of formalin post-injection on both forearms, severe autotomy up to the elbow joint occurred in about half of the animals within a week and in 100% in four weeks. In groups of formalin post-injection on one side only, mild autotomy limited to the digits on the affected side started to occur after three weeks and by the end of three months it occurred in about 50%. In total root resection group of formalin pre-injection on the affected forearm, autotomy occurred in about 25%. In total root resection group of for-malin post-injection on both forearms, autotomy did not occurred at all during the observation period. This showed a distinct contrast to severe autotomy observed in all the animals in the dorsal root resection group of formalin post-injection on both forearms. These results might suggest rather active participation of the ventral roots and some contribution of pain experience in the development of autotomy following dorsal root resection.