Slow axoplasmic transport: a fiction?

Abstract

Ribosomes have not been observed in axoplasm. This had led to the notions that the perikaryon is the only source of neuronal proteins and that the axoplasm is supplied by a (slow) transport mechanism. However, we question these two notions because they are unable to give an account of real neurones in accordance with the body of biological knowledge. We point out, for example, that the synthetic rate of perikarya or the life span of axoplasmic proteins should be beyond known ranges for animal cells and that a uniform axon is unlikely to result if it is fed from one end. We propose an alternative view for the maintenance of the axon which accepts the controversial idea of axoplasmic synthesis of proteins; as a result, the slow transport becomes unnecessary. Our view gives a qualitative account of the observations dealing with the maintenance of the axoplasm. To account for the phenomenology in a more quantitative fashion, a computer simulation was carried out where the equations of the program provided only for axoplasmic synthesis of proteins; the set of curves retrieved were in good agreement with experimental findings believed so far to support the notion of slow transport. In conclusion, we think that the notion of "slow axoplasmic transport" has been a misinterpretation of good observations because the frame of reference was incomplete in not providing for axoplasmic synthesis of proteins.