Development of glycine-accumulating neurons in retinal transplants

Previous studies have shown that the fetal retina not only survives transpl antation but also continues to develop and differentiate in the host eye. S everal structural and functional proteins have been demonstrated in the tra nsplanted retinas, and the presence of such proteins has been taken as evid ence for the capability of retinal transplants to function. Glycine is an i mportant inhibitory neurotransmitter and is found in a large number of the retinal neurons. Uptake of glycine rather than de novo synthesis is the mai n source of glycine in glycinergic neurons. The present study examined whet her glycine-accumulating neurons develop normally in rabbit retina transpla nts. Embryonic day (E) 15 rabbit retinas were transplanted into the eyes of adult rabbits of the same strain. Transplants were allowed to survive for various times so that the grafts attained the equivalent ages of (donor age + survival time) E 19, 22 and 29 and postnatal days (PN) 2, 5, 9, 12, 19 a nd 58. On formaldehyde-fixed cryostat sections of these transplants, glycin e-accumulating neurons were demonstrated by immunohistochemistry by using a n antibody against one of the glycine transporters: GLYT1. Immunoreactivity was first detected 2 days before birth and increased with age until it rea ched its mature level at PN 19. The immunoreactivity was found in cells bel onging to the inner retinal layers, and in plexiform layers of the transpla nt equivalent to the normal inner and the outer plexiform layers. in places these cells integrated well with similar cells in the host. In the host re tina, the immunoreactivity was found in proximal cell layers of the inner n uclear layer, in certain bipolar cells, and in the inner and the outer plex iform layers. The immunoreactivity was preserved even in the degenerated re tina overlying the retinal graft. In conclusion, the present study demonstr ates that glycine-accumulating neurons develop, integrate and survive in re tinal transplants. Copyright (C) 2000 S. Karger AG, Basel.