The transport of proteins in Mauthner axon in fish as studied by autoradiography and interference microscopy

Abstract

Using ¹ C‐Leucine the rate of transport of proteins in single nerve fiber was investigated by quantitative autoradiography using the desheathed, hand‐free isolated Mauthner axons of fish.After different times of incubation of living fish in the radioactive medium a non‐uniform labelling of the isolated axons along their length was observed, which showed a characteristic pattern. The distribution of the label indicates: (a) a continuous supply of labelled proteins from the cell body to the axon, (b) accumulation of labelled proteins near the terminal end of the axon, (c) two different rates of the somato‐axonal transport of proteins (30–40 mm 24hr; 3.5 mm/24 hr).After the transection of the spinal cord no incorporation into the segments of the axon below the lesion was detectable.No changes of the dry mass between the proximal and distal parts of the Mauthner axon were detectable in interference microscope.The alternative explanations for the observed pattern of axonal labelling, i.e. local protein synthesis in axons and somato‐axonal flow of proteins, are discussed.