Retention and redistribution of proteins in mammalian nerve fibres by axoplasmic transport.

Fast axoplasmic transport is characterized by a crest of labelled activity moving down nerve fibres after injection of the L7 dorsal root ganglion with the amino acid precursor (3H) leucine, the crest followed by a plateau which represents in part a later egress of labelled components from compartments in the cell bodies and in part materials left behind the advancing crest. 2. after making ligations just below the ganglia at different times after injection of the precursor, a small downward slope of locally retained activity of incorporated materials is seen in the plateau remaining in the nerves. The slope becomes changed to a horizontal level when in addition a distal ligation is made as a result of the redistribution of labelled materials within the doubly ligated nerve segments. 3. the outlfow pattern at later times, at a day and longer after injection, shows an additional spread of activity from the cell body region. The pattern of outflow gradually levels off at later times as additions of activity are made to the more distal part of the nerves. The activity retained in the nerves becomes less free to become redistributed in the course of several days. 4. The temporal changes in the outflow patterns can be accounted for by the local retention and redistribution of the labelled materials within the fibres. Later additions of labelled materials compartmented in the cell bodies also contribute to the later pattern of outflow. A "unitary" view for fast and slow transport is presented based on the transport filament hypothesis earlier proposed to account for fast axoplasmic transport.