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 ultrast ructural characteristics of intraocular superior cervical ganglion (SC G) grafts from young (3 months), aged (24 months) and very old (36 mon ths) rats after short-term (1 month) grafting. The formaldehyde-induce d fluorescence (FIF) technique for histochemical demonstration of cate cholamines was used to indicate the functionality of transplanted neur ons. Ultrastructural changes in grafts were demonstrated by electron m icroscopy. Four weeks after transplantation, catecholamine histofluore scence in young transplants was almost as strong as in the intact gang lia, 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, resp ectively. 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 wit h normal in vivo fine structure and neurons showing some abnormal cyto logical alterations were seen in each age group of the transplants. Th e most prominent feature after grafting was the accumulation of differ ent types of lipopigment bodies in the perikarya of neurons. The organ ization of the rough endoplasmic reticulum was more irregular in trans planted neurons than in intact neurons. In addition, the amount of neu rofilament aggregates increased and some mitochondria were swollen in neurons after transplantation. These results suggest that young sympat hetic ganglion tissue survives rather well after transplantation into the anterior eye chamber, while in the aged sympathetic ganglion impla nts the survival rate is poorer. However, aged and very old SCG grafts were shown to contain and continue to produce noradrenaline, indicati ng that sympathetic neurons maintain their plasticity and regenerative ability in advanced age. Catecholamine histofluorescence and fine str uctural changes in the cell structure of grafted sympathetic neurons m ay indicate an accelerated aging process induced by the transplantatio n procedure.