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

The purpose of this study was to investigate the viability and ultrastructural characteristics of 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-induced fluorescence (FIF) technique for histochemical demonstration of catecholamines was used to indicate the functionality of transplanted neurons. Ultrastructural changes in grafts were demonstrated by electron microscopy. Four weeks after transplantation, catecholamine histofluorescence in young transplants was almost as strong as in the intact ganglia, while aged and very old grafts showed decreased fluorescence and contained a marked accumulation of autofluorescent lipopigment bodies. Catecholamine histofluorescence showed a decrease in neuronal density of 47%, 59% and 68% in young, aged and very old grafted ganglia, respectively. The shape of most of the transplanted neurons did not differ from that in the intact ganglia, but the average diameter of neurons was decreased after grafting. In electron microscopy, both neurons with normal in vivo fine structure and neurons showing some abnormal cytological alterations were seen in each age group of the transplants. The most prominent feature after grafting was the accumulation of different types of lipopigment bodies in the perikarya of neurons. The organization of the rough endoplasmic reticulum was more irregular in transplanted neurons than in intact neurons. In addition, the amount of neurofilament aggregates increased and some mitochondria were swollen in neurons after transplantation. These results suggest that young sympathetic ganglion tissue survives rather well after transplantation into the anterior eye chamber, while in the aged sympathetic ganglion implants the survival rate is poorer. However, aged and very old SCG grafts were shown to contain and continue to produce noradrenaline, indicating that sympathetic neurons maintain their plasticity and regenerative ability in advanced age. Catecholamine histofluorescence and fine structural changes in the cell structure of grafted sympathetic neurons may indicate an accelerated aging process induced by the transplantation procedure.