Ultracytochemistry of enzymes in cell biology of the retina.

In matured chick retina, alkaline phosphatase activity is specifically localized in the outer plexiform layer and in the horizontal and Müller cells. In developing chick retina, the activity is recognized in growing neurites from horizontal cells, when synaptogenesis begins in the outer plexiform layer. Using levamisole, a potent inhibitor of alkaline phosphatase, on chick retina in vivo and in vitro, the enzyme was shown to play a significant role in retinal cell differentiation. 5'-Nucleotidase is used as a marker for the rod photoreceptors. It became apparent that the 'displaced' rod cells are localized in the inner nuclear layer of postnatal retina. High activity of glucose-6-phosphatase is confirmed in the cisternae of the smooth and rough endoplasmic reticulum, together with the space of the perinuclear envelope in the pigment epithelium of rat. The process of disc membrane recycling in the rod outer segment was investigated cytochemically to reveal sequential changes in lysosomal digestion both by conventional enzyme cytochemistry and by high voltage electron microscopy. With conventional enzyme histochemistry as well as with rapid freeze substitution enzyme cytochemistry, all enzyme for cGMP metabolism were observed to be on the cytoplasmic side of the disc membranes.