Fractionation of human brain by differential and isopycnic equilibration techniques

Fractionation of brain tissue by either differential or isopycnic centrifugation is a useful cytological and biochemical tool to study the intracellular localization of neuronal elements involved in neurotransmission. Several neuroreceptors and uptake sites were found to display a subcellular bimodal distribution in rat brain. However, in the human brain, little is known about the subcellular distribution of neurotransmitter receptors and amine uptake sites. Despite the inevitable post-mortem delay which seems to induce many more morphological changes than modifications of enzymatic or receptor distribution profile from the subcellular fractions, fractionation of human brain areas remains a valid procedure to explore the subcellular localization of neuronal constituents. This paper describes the methods used to separate human brain tissue. As we have previously demonstrated in rat and dog brains, our results indicate that differential and isopycnic fractionation techniques, used with a large number of markers such as enzymes, receptors and uptake sites, make it possible to separate tissue fractions enriched in nerve endings, dendrites, dendritic spines, plasma membranes or vesicles.