Light and electron microscopy of S-antigen- and opsin-immunoreactive photoreceptors in the retina of turtle, chicken, and hedgehog.

S-antigen and opsin-immunoreactive sites were studied in the retina of turtle (Pseudemys scripta elegans), chicken (Gallus domesticus), and hedgehog, (Erinaceus roumanicus) by light-microscopic avidin-biotin-peroxidase and electron-microscopic protein A-gold and immunoglobulin-gold (immunogold) techniques. In general, S-antigen and opsin immunoreactions were exclusively localized to certain photoreceptors of the retinae studied. In turtle and chicken, strong S-antigen immunoreactivity was found in the outer and inner segments, perikarya and synaptic bases of rod photoreceptors. Some--apparently green--single cones also exhibited immunoreactive outer and inner segments. In hedgehog, the inner segments, perikarya and pedicles of rods displayed immunoreaction of varying intensities. In all three species there was an accumulation of immunogold particles on the distal portion of the inner segment, the connecting piece and the proximal portion of the outer segment. Opsin immunoreactivity was found in the outer segments of rod photoreceptors, and in those of--apparently green--single cones of turtle and chicken. The localization and significance of the S-antigen immunoreaction is discussed in connection with the occurrence of different photopigments in the retinae studied. The correlation of the presence of S-antigen and of either rhodopsin or porphyropsin in rod and--apparently green--single cone photoreceptors was emphasized.