Developmental expression of a synaptic vesicle-specific protein in the rat retina

In order to examine the appearance of synaptic vesicles and to correlate it with the formation of the synaptic layers, we have determined the staining pattern of a murine monoclonal antibody (SV 48) to a synaptic vesicle-associated protein in developing rat retina. The antigen was detected by the indirect immunofluorescence technique using cryostat sections of paraformaldehyde-fixed retinas. In the adult retina, the antibody stained both the outer plexiform (OPL) and the inner plexiform layers (IPL). The nuclear layers and the nerve fiber layer (NFL) were devoid of any staining. In prenatal and early postnatal (P) retinas, the antibody stained two bands which corresponded to the respective locations of the NFL and IPL. Staining in the NFL increased until P-4 and began to decline subsequently, and by P-8 little staining was left in this layer. In contrast, in the IPL, the intensity of staining increased gradually and leveled off by P-10. In the outer retina, a band of fluorescence corresponding to the OPL was first observed at P-5 and increased in intensity up to P-10. Immunoblotting studies showed that the major immunoreactive material from adult and embryonic retinas had a M_r ∼ 65,000-67,000. As expected from its developmental pattern, all bands appeared initially in the central retina and subsequently in the peripheral retina. Our results show that the synaptic vesicle-protein is present in the nerve fiber layer before synaptogenesis in the central nervous system. Subsequently, the protein is lost from the NFL, possibly as a consequence of synapse formation.