Neuronal integration in an abutting-retinas culture system.

PURPOSE Limited integration is consistently observed between subretinal transplants and host retinas. In the current study, an in vitro model system for studying connections forming between two abutting retinas was developed. METHODS Neuroretinas were dissected from normal wild-type (WT) mice and green fluorescent protein (GFP) transgenic mice (obtained at postnatal days [P]0, P5, or P60), as well as from adult rd mice. Pieces from two different retinas (WT-WT, GFP-WT, GFP-rd) were placed side-by-side (contacting each other at the margins) or overlapping each other in organ cultures for 7 or 12 days. The abutting retinal pieces derived from animals of the same age (P5-P5; P60-P60) or of different ages (P0-P60; P5-P60). Retinal cells and fibers were visualized in wholemount preparations and in cross sections by immunocytochemistry using antibodies against neurofilament (NF+), neuronal nitric oxide synthase (NOS+), and protein kinase C (PKC+) and by GFP fluorescence (GFP+). RESULTS In side-by-side pairs (WT-WT, GFP-WT), numerous horizontal cell fibers (NF+) and amacrine cell fibers (NOS+) crossed the interface between the two pieces, forming continuous plexiform layers. In overlapping pairs, NF+, NOS+, and PKC+ fibers displayed parallel plexiform layers, and no crossover of fibers was observed in any of the pair combinations examined (WT-WT, GFP-WT, GFP-rd). Some integration was seen only in small areas where the structure of both retinal pieces was disrupted at the interface. CONCLUSIONS The results demonstrate the ability of neurites to extend between abutting retinas and to make appropriate target choices when they are placed side-by-side. However, this ability is limited when they overlap each other, similar to that observed in subretinal transplantation.