Axonal transport in the electromotor nerves of Torpedo marmorata

Abstract

Studies on the axonal transport of cholinergic cell components were made on the electromotor nerves of Torpedo marmorata. Choline acetyltransferase was rapidly accumulated at ligatures on Torpedo nerves, both in vivo and in segments incubated in vitro. In vivo accumulation was maximal approximately one month after nerve interruption. Orthograde transport (both in vitro and in vivo) is calculated to have a velocity of 50--140 mm/day, if, as double-ligature experiments suggest, only about 15% of the axoplasmic enzyme is mobile. A small retrograde accumulation of the transferase was demonstrated. Lactate dehydrogenase did not accumulate but a slight reduction of its activity at ligatures was observed. In contrast to mammalian cholinergic nerves, no accumulation of esterase was observed. ACh accumulation proximal to a cut was apparent and may result in part from local synthesis in the presence of elevated levels of its synthesizing enzyme. Measurements have been made on the activity of choline acetyltransferase in the brain and all parts of the "electric system". In view of these results it is difficult to see how the measured rate of axonal translocation is sufficient to supply the levels of the enzyme found within the electric organ. Within the electromotor cells, choline acetyltransferase is highly concentrated in the axon terminals.