Neurobiological studies on cephalopods III. Histochemistry of 24 enzymes in the optic system

Abstract

1. 1. In four species of cephalopods an investigation was made of the presence of several histochemically localizable enzymes. 2. 2. Among the enzymes studied were the cholinesterases, β-glucuronidase, various dehydrogenases, NADH 2- and NADPH 2-tetrazolium reductases, cytochrome c-oxidase, and several phosphatases. 3. 3. The main sites of hydrolysis of acetylcholine were the retinal plexus, some of the inner layers of the plexiform zone of the deep retina and the fibers of the optic ganglion. In decapods butyrylcholine was split at the same places, but in octopods the outer granular layer of the deep retina and the outer layers of the plexiform zone were the sole sites of hydrolysis in the optic lobe. 4. 4. β-glucoronidase was found in the distal segment of the retina and in the proximal segment in a zone just distal to the nuclei of the recepter cells. No other sites of activity could be demonstrated. 5. 5. NADH 2-terazolium reductase occurred in all parts of the retina, in the optic nerves and in the optic lobe, the highest concentration being found in the plexiform zone. The same is true for the NAD-linked dehydrogenases, of which isocitrate dehydrogenase and α-cerophosphate dehydrogenase are the only enzymes to be found in high amounts. NADPH 2-tetrazolium reductase occurred in the proximal segment of the retina, in the optic nerves and in the optic lobe, again in highest concentration in the plexiform zone. Succinate dehydrogenase shows the same localization as NADH 2-tetrazolium reductase but occurs in essentially smaller amounts. Cytochrome c-oxidase is present in the same localization as NADH 2-tetrazolium reductase. 6. 6. Alkaline and acid phosphatases were found in the retina and in all cells of the optic lobe. No activity could be detected in the nerve fibers or in the capillaries. A phosphatase splitting creatine phosphate at low pH, essentially different from acid phosphatase, has been demonstrated. Adenosine-monophosphatase and adenosinetriphosphatase occur in cells as well as axons of the optic system. The former enzyme is found in the highest concentration in the second radial layer of the plexiform zone, the latter is the only specific phosphatase found in the capillary walls. 7. 7. The main difference between the mammalian nervous system and the cephalopod optic ganglion were: the divergent behavior of true and aspecific cholinesterase towards specific inhibitors, the uniform moede of distribution of the reductases, dehydrogenases and cytochrome oxidase and the occurrence of alkaline phosphatase in the perikarya.