Serum protein leakage in aged human brain and inhibition of ligand binding at alpha₂‐ adrenergic and cholinergic binding sites

Serum proteins are known to extravasate into the brain parenchyma in senile and presenile dementia (Glenner: Hum. Pathol. 16:433–435, 1986; Wisniewski and Kozlowski: Ann. NY Acad. Sci. 396:119–129, 1982). We have recently demonstrated that human serum Cohn fraction IV (alpha‐globulin enriched) inhibits ligand binding at putative dopamine and serotonin₂ receptors labeled by [³H]spiroperidol in human brain (Andorn, Pappolla, Fox, Klemens, and Martello: Proc. Natl. Acad. Sci. USA 83:4572–4575, 1986). We now demonstrate that serum proteins can be identified in the neuropil and in neuronal cell bodies in normal aged brain, that alpha‐globulin‐enriched fractions inhibit ligand binding at alpha₂‐adrenergic and muscarinic binding sites in human brain as well, and that serum proteins can be identified within neuronal cytoplasm and axons.