HISTOCHEMICAL CHARACTERIZATION OF THE INTERPHOTORECEPTOR MATRIX IN THE RETINA OF OCTOPUS BIMACULOIDES

Proteoglycans, located in the interphotoreceptor matrix (IPM) of verte brate retinas, mediate interactions between the photoreceptors and ret inal pigment epithelium Molluscan retinas also have an IPM located bet ween apposing rhabdomeres. Like the cone matrix sheath of the vertebra te IPM, the octopus IPM is labeled by peanut agglutinin (PNA) and cont ains retinoid-binding-like proteins. In this study we demonstrate furt her similarities of the vertebrate/invertebrate IPM and identify speci fic molecular components in this extracellular compartment of the octo pus retina. For light microscopy, paraffin-embedded sections of octopu s retinas were stained with dyes specific for acid mucopolysaccharides including Alcian blue and colloidal iron. In addition, sections were digested with enzymes specific for hyaluronan, chondroitin sulfate, an d sialoglycoconjugates. Digestion of sections with these enzymes and s ubsequent staining with Alcian blue or colloidal iron demonstrated the presence of chondroitin sulfate and sialoglycoconjugates in the octop us IPM as well as other retinal layers and cells. At the electron-micr oscope level we treated retinal tissue with Cuprolinic Blue and observ ed the distribution of sulfated glycosaminoglycans along the rhabdomer e edges facing the IPM and in a more central area of the IPM where mic rovillous processes of supportive cells are located. The octopus IPM m ay have importance in retinal structure and may be a scaffolding on wh ich molecular components of the IPM are located.