Immunoreactivity to synaptosomal-associated protein-25 in developing rat retinas: effects of a glutamate agonist and retinal transplantation to a host brain.

In the postnatal rat retina immunoreactivity to synaptosomal-associated protein-25 (SNAP-25) was expressed primarily in the photoreceptors, inner and outer plexiform layers, and optic nerve fibres in a highly specific and age related manner. Of special interest are observations of characteristic changes of intracellular immunostaining in photoreceptors and distinct immunoreactive sublaminae in the inner plexiform layer during early postnatal stages. The overall pattern of immunoreactivity in the photoreceptor and plexiform layers remained unchanged after neonatal intravitreal injection of the glutamate agonist 2-amino-4-phosphonobutyric acid or optic tract lesion, and after adult intraorbital optic nerve section. However, a significant reduction in immunostaining in the inner plexiform and optic nerve fibre layers was observed several weeks after transplantation of the retina to a neonatal host brain. These results provide new insights into the role of SNAP-25 in membrane remodelling in relation to specific cell types and functions, and into intraretinal regulatory mechanisms that seem to be independent of the levels of glutamate and the influence of retinal ganglion cells.