Müller cells in long-term full-thickness retinal transplants.

Müller cells are essential in creating and maintaining intricate neuroretinal architecture. The functions of this important glial cell are not limited to mere support of the retinal neurons, but also include interaction in synaptic transmission and activation in response to retinal insult. In this study, we have examined Müller cell morphology and degree of activation in embryonic full-thickness rabbit neuroretinal grafts, which were positioned under the host retina using vitrectomy technique. After surviving 3-10 months, retinal specimens were examined with hematoxylin and eosin staining and immunohistochemical analysis of vimentin and glial fibrillary acidic protein (GFAP) expression. In the host retina covering the graft, outer layers were degenerated, and vimentin-labeled Müller cells in this area appeared short, disorganized, and displayed strong GFAP labeling. In the graft, vimentin-labeled Müller cells spanning the retinal layers in the normal manner were found. Müller cells in 3-month grafts were well labeled by GFAP, whereas in older grafts, GFAP labeling was very weak or absent. Our results suggest that Müller cells in well-laminated full-thickness retinal grafts display many of the normal morphological features and retain a normal organization even after prolonged survival times. The loss of the initial degree of Müller cell activation indicates a long-term stability of the graft. The degeneration and gliosis of the host retina covering the graft is best explained by the merangiotic nature of the rabbit retina and may limit the usefulness of the rabbit in retinal transplantation experiments.