Uptake of plasma IgG by CNS motoneurons: comparison of antineuronal and normal IgG.

We studied the uptake of antisynaptosomal and nonspecific IgG by ventral horn motoneurons in rats, using immunohistochemical and radionuclide techniques. Plasma antisynaptosomal IgG is taken up to a much greater extent than nonspecific IgG by motoneurons that project outside the blood-brain barrier, as is radiolabeled antisynaptosomal IgG injected intramuscularly. Competition with unlabeled antisynaptosomal IgG inhibits the uptake of radiolabeled antisynaptosomal IgG. By contrast, competition with unlabeled nonspecific IgG does not inhibit the uptake of radiolabeled nonspecific IgG. These results support the hypothesis that certain neurons in the CNS take up IgG from the systemic circulation, and that IgG which binds to elements of the synaptic plasma membrane is taken up in greater amounts than nonspecific IgG through a process of adsorptive endocytosis at the nerve terminus. An increase in intraneuronal IgG may serve as an index of the action of antineuronal IgG at the presynaptic membrane.