Ultrastructure of retinal rod synapses of the guinea pig eye as revealed by three-dimensional reconstructions from serial sections

Abstract

The structure of the synaptic bodies of the retinal receptors of the guinea pig eye and the synaptic connections of these receptors have been studied on three-dimensional reconstructions from serial sections. Series with up to forty ultrathin sections (average thickness 250 Å) were examined. Two types of synaptic bodies belonging to the α- and the β-cells respectively can be distinguished. Both types contain the same basic structural components: the synaptic granules or vesicles, the synaptic vacuoles and the synaptic ribbon. The α-cells are in synaptic contact with dendrites presumably belonging to two different bipolars. The dendrites end inside an invagination of the plasma membrane of the synaptic body at its vitreal pole and make contact with two synaptic vacuoles forming a pair of vacuoles which are in mutual contact. Extensions from three to four synaptic bodies belonging to the β-cell type enter into contact relation to each α-cell and the dendrites which are synaptically connected to the α-cell. These contacts are interpreted as synaptic contacts. It is proposed that this extensive system of interreceptor contacts might exert inhibitory effects on the transmission between α-cells and bipolars. © 1958 Academic Press.