The Nature of Light Response after Retinal Transplantation

Background: In a study supported by a "Schrödinger Stipendium" we transplanted retinaldegenerate (blind) rd- mice at postnatal day 13 and 8 weeks with neural retinal tissue from newborn C57 mice. 5 weeks after transplantation we repeatedly recorded bursts of single ganglion cell action potentials in the young animal group over the transplanted area in response to light stimulation. Light response could not be found in one of the 3 control groups or in animals transplanted at the age of 8 weeks. Two explanations are possible for this phenomenon (a) functional integration of the transplant or (b) a rescue effect on remaining host cone photoreceptor cells. Purpose: The aim of the proposed study is to clarify the origin of this RGC response to light in this experimental model. Methods: The approach to find an explanation for this phenomenon (i.e. light response in rd-mice after retinal transplantation at postnatal days 10 to 13) is to (a) electrophysiologically confirm this finding by reproducing these results, (b) clarify the origin of the light responses using conventional histology and immunohistochemistry, and (c) to investigate the natural time course of retinal ganglion cell activity in the rd-mouse. C3H/ HeJ (rd/rd) retinal degenerate mice will be transplanted (one eye only) at either postnatal day P10 to P14 or at age 8 weeks, with neural retinal tissue isolated from newborn normal C57/ BL6J mice or the green fluorescent mouse strain. Five to 6 weeks after transplantation the eyes will be hemisected (removed) to allow the measurement of electrical RGC responses directly from the retinal surface with a surface electrode from transplants. Similar electrical recordings were performed in age-matched sham-operated and control eyes. Measurements will also be performed in groups of rd-mice aged 1 week, 2 weeks, 3 week,... up to 8 weeks. Animals will euthanized after the recordings and the eyes were processed for light- (LM) and transmission electron microscopy, and immunohistochemistry. Expected Accomplishments: We expect to demonstrate host-transplant synapses if functional integration is responsible for the light response. If on the other hand light response is due to a rescue effect on remaining host cone photoreceptors we should find functional outer photoreceptor segments or increased photoreceptor cell counts. For better interpretation of the electrophysiological results the natural time course of the ganglion cell activity will be investigated.