Retrograde Migration of Transmitter-Related Molecules. In: Weiss DG, Gorio A, editors. Axoplasmic Transport in Physiology and Pathology. Berlin: Springer Berlin Heidelberg; 1982. pp. 160-6. [DOI: 10.1007/978-3-642-85714-0_22]

Rapid axoplasmic transport of free leucine

Axoplasmic transport of free 3H-leucine has been studied in vivo in the pike olfactory nerve following application of labeled leucine to the olfactory mucosa. A considerable amount of free 3H-leucine is transported at constant velocity along the axon in the form of a distinct peak. The maximum transport velocity for free 3H-leucine is the same as for rapidly transported 3H-protein (130 and 135 mm/day, respectively, at 19 degrees C). Microtubule inhibitors block or significantly reduce the amount of free 3H-leucine transported, but do not influence the transport velocity. Disruption of the oxygen supply abolishes free 3H-leucine transport, so that this phenomenon cannot be explained by diffusion. The amount of free leucine in the rapidly moving peak decreases with time and distance along the axon and is not detectable after 5 h or more. The transported 3H-leucine is not derived from the circulation or from proteolysis of rapidly transported proteins. This study may help to resolve the controversy over the axoplasmic transport of free amino acids since it shows that free 3H-leucine is transported rapidly but does not travel by rapid axoplasmic transport to the end of axons longer than about 30 mm.

3-O-methyl-D-glucose and beta-alanine: rapid axoplasmic transport of metabolically inert low molecular weight substances

The dynamics of the axoplasmic transport of free beta-alanine and 3-O-methyl-D-glucose were quantitatively characterized in vivo in the pike olfactory nerve following intranasal application of the tritiated substances. Both compounds were found to be taken up by the epithelium but not metabolized to a significant extent. Axoplasmic transport showed the same dynamics as rapid transport of protein and free leucine in this nerve. No synthesis or transport of carnosine was detectable. The results are in agreement with the view that rapid axoplasmic transport is capable of conveying free, low molecular weight molecules in a non-specific manner.