• glutamate;
  • horizontal cells;
  • photoreceptor cells;
  • ribbon synapses;
  • synaptogenesis


The expression of synapse-associated proteins (SAPs) was monitored throughout postnatal development of the rat retina using specific antibodies and immunocytochemistry. The distribution of chapsin-110/postsynaptic density protein (PSD)-93, SAP90/PSD-95, SAP97 and SAP102 immunoreactivity was characterized. All SAPs were found to be expressed in the inner plexiform layer (IPL) 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 week. 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. All SAPs showed a differential cellular and temporal distribution being either exclusively pre- or postsynaptically localized. Except for SAP90/PSD-95, immunoreactivity was also detected in the nerve fibre layer throughout postnatal development. Possible functions of the early expression of SAPs well before differentiation and maturation of glutamatergic ribbon synapses are discussed.