Neuronal uptake of iron: somatopetal axonal transport and fate of cationized and native ferritin, and iron-dextran after intramuscular injections.

Mice were injected into the muscles of the vibrissae with native ferritin (NF), cationized ferritin (CF) and iron-dextran. CF adsorbed on to the surface of the axon terminal at the neuromuscular junction, while NF did not. Both CF and NF were incorporated into vesicles and vacuoles at the synapse, but CF uptake was detected after injections at much lower concentrations than NF. In contrast to NF, CF was also found histochemically in cell bodies of facial neurones after a single i.m. injection, showing that the electrical charge of a molecule is one factor of importance for its potential to be incorporated in axons and transported somatopetally. Repeated i.m. injection of iron-dextran into suckling mice resulted in a marked iron load of Schwann cells and nerve cell bodies. This produced no signs of toxicity and the nerve fibre developed normally. Iron had disappeared from the nerve cell bodies after 25 days, while in Schwann cells it still persisted after 223 days.