Transferrin receptors in rat brain: neuropeptide-like pattern and relationship to iron distribution.

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Abstract
The binding of 125I-labeled transferrin to sections of rat brain was characterized and visualized. This saturable, reversible, high-affinity (Kd = 1 .times. 10-9 M) binding site appears indistinguishable from transferrin receptors previously characterized in other tissues. A monoclonal antibody raised to rat lymphocyte transferrin receptors could immunoprecipitate recovered intact transferrin solubilized from labeled brain slices, indicating that labeling was to the same molecular entity previously characterized as the transferrin receptor. The pattern of transferrin receptor distribution visualized in brain with both 125I-labeled transferrin and an anti-transferrin receptor monoclonal antibody are almost indistinguishable but differ from the pattern of Fe distribution. Fe-rich brain areas generally receive neuronal projections from areas with abundant transferrin receptors, suggesting that Fe may be transported neuronally. Many brain areas with a high density of transferrin receptors appear unrelated to Fe uptake and neuronal transport and form a receptor distribution pattern similar to that of other known neuropeptides. This neuropeptide-like distribution pattern suggests that transferrin may have neuromodulatory, perhaps behavioral, function in brain.