Search

Satisfactory regeneration of axons after crush injury of periferal nerve is supported by proliferating Schwann cells (SC) in the distal stump and their basal laminae (BL). SC secrete diffusable growth-promoting substances, whereasbasal laminae provide a good growth substratum within the neurilemmal tubes. The results of previous studies of the relative importance of diffusable growth-promoting substances and growth substratum are partly contradictory. A recent study showed that sensory axons regenerating through the acellular distal nerve segment elongated fairly rapidly during the first week after axonotmesis, but then ceased to grow. The leading axons retracted towards the site of axonotmesis. Subsequent elongation was possible only with concurrent migration of SC from the proximal stump. Previous experiments indicated that degeneration of growth substratum in the absence of Schwann cells could be responsible for the cessation of axonal growth. The objective of the study was to examine the following hypotheses: that cessation of axonalgrowth and retraction of sensory axons during the second week of regeneration in the absence of cell support is a consequence of an unfavourable microenviroment of the regenerating axons and is not due to permanent "exhaustion" of the neuron cell body; that, if an adequate growth substratum is maintained, axons continue to grow during the second week even in the absence of SC; and that elongation of axons can be maintained during prolonged regeneration through the acellular distal nerve segment by providingdiffusable growth promoting substances of SC, even though the growth substratum is partly degenerated. In this study, a rat sural nerve was crushed. In the first group of animals, cells in the distal stump were killed by freezing the entire distal segment at once. (Abstract truncated at 2000 characters.) Dobro regeneracijo aksonov po poškodbi perifernega živca omogočajo razmnožene Schwannove celice (SC) v distalnem krnu, ki izločajo topne spodbujevalne dejavnike, in bazalne lamine SC. Le-te tvorijo nevrilemske cevke, ki predstavljajo ugodno rastno podlago za aksone. Rezultati raziskav o relativnempomenu topnih dejavnikov in rastne podlage so delno protislovni. Novejša študija je pokazala, da se senzorični aksoni med regeneracijo skozi brezcelični distalni krn po relativno hitri rasti v prvem tednu po poškodbi ustavijo. Vodeči aksoni se nato retrahirajo proti mestu poškodbe. Do nove rasti pride samo, če je možna migracija SC iz proksimalnega krna. Dosedanji rezultati kažejo, da bi za zaustavitev rasti aksonov lahko bila odgovorna degeneracija rastne podlage v odsotnosti SC. Preverili bomo hipotezo, da je zazaustavitev rasti aksonov po prvem tednu regeneracije krivo mikrookolje aksonov, ne pa morebitna izčrpanost perikariona, hipotezo, da je z ohranjanjemprimerne rastne podlage mogoče vzdrževati rast v drugem tednu tudi brez podpore SC, ter hipotezo, da je z zagotavljanjem topnih rastnih dejavnikov v drugem tednu kljub odsotnosti SC in delno degenerirani rastni podlagi moč preprečiti retrakcijo aksonov. V raziskavi smo suralni živec podgane poškodovali z aksonotmezo. V prvi skupini živali smo celice v distalnem odseku živca z enkratnim zmrzovanjem uničili vse do konca odseka, kontinuiteta cevk BL pa ni bila prekinjena. V drugi skupini živali smo zmrzovali le 10 oz. 15 mm dolg odsek živca za mestom aksonotmeze in pustili celice distalno ohranjene. V tretji skupini živali smo distalni odsek dvakrat zapored zmrzovali v razmaku štirih dni. Drugo zmrzovanje je zajelo odsek distalno od prvega. V četrti skupini smo v celoti zmrzovani distalni odsek n. suralisa ovili v degeneriran odsek n. peroneusa. Hitrost regeneracije najhitrejših aksonov smo testirali s testom uščipa živca. (Izvleček prekinjen pri 2000 znakih.)