Localization of synapse-associated proteins during postnatal development of the rat retina

The expression of synapse-associated proteins (SAPs) was monitored througho ut postnatal development of the rat retina using specific antibodies and im munocytochemistry. The distribution of chapsin-110/postsynaptic density pro tein (PSD)-93, SAP90/PSD-95, SAP97 and SAP102 immunoreactivity was characte rized. All SAPs were found to be expressed in the inner plexiform layer (IP L) from birth on or soon after birth. With the exception of SAP97, the IPL labelling changed from a diffuse pattern staining the whole developing IPL to the typical adult punctate synaptic staining in the second postnatal wee k. Staining in the outer retina was first observed at postnatal day 5 (P5) for all proteins at the onset of outer plexiform layer (OPL) development. A ll SAPs showed a differential cellular and temporal distribution being eith er exclusively pre- or postsynaptically localized. Except for SAP90/PSD-95, immunoreactivity was also detected in the nerve fibre layer throughout pos tnatal development. Possible functions of the early expression of SAPs well before differentiation and maturation of glutamatergic ribbon synapses are discussed.