Transplanted Sympathetic Neurons From Old Rats Survive in the Anterior Eye Chamber: A Histochemical and Electron Microscopic Study

摘要

The purpose of this study was to investigatethe viability and ultrastructural characteristicsof intraocular superior cervical ganglion (SCG)grafts from young (3 months), aged (24 months)and very old (36 months) rats after short-term(1 month) grafting. The formaldehyde-inducedfluorescence (FIF) technique for histochemicaldemonstration of catecholamines was used toindicate the functionality of transplantedneurons. Ultrastructural changes in grafts weredemonstrated by electron microscopy. Fourweeks after transplantation, catecholaminehistofluorescence in young transplants wasalmost as strong as in the intact ganglia, whileaged and very old grafts showed decreasedfluorescence and contained a markedaccumulation of autofluorescent lipopigmentbodies. Catecholamine histofluorescence showeda decrease in neuronal density of 47%, 59% and68% in young, aged and very old graftedganglia, respectively. The shape of most of thetransplanted neurons did not differ from that inthe intact ganglia, but the average diameter ofneurons was decreased after grafting. Inelectron microscopy, both neurons with normal in vivo fine structure and neurons showing someabnormal cytological alterations were seen ineach age group of the transplants. The mostprominent feature after grafting was the accumulation of different types of lipopigmentbodies in the perikarya of neurons. Theorganization of the rough endoplasmicreticulum was more irregular in transplantedneurons than in intact neurons. In addition, theamount of neurofilament aggregates increasedand some mitochondria were swollen in neuronsafter transplantation. These results suggest thatyoung sympathetic ganglion tissue survivesrather well after transplantation into theanterior eye chamber, while in the agedsympathetic ganglion implants the survival rateis poorer. However, aged and very old SCGgrafts were shown to contain and continue toproduce noradrenaline, indicating thatsympathetic neurons maintain their plasticityand regenerative ability in advanced age.Catecholamine histofluorescence and finestructural changes in the cell structure ofgrafted sympathetic neurons may indicate anaccelerated aging process induced by thetransplantation procedure.