Preparation of synaptosomes, neuromelanin granules and
Kiebler et al  was the first group to describe the use of a discontinuous iodixanol gradient in the isolation of dendritic spines from mouse hippocampus. The gradient comprised four layers of 9%, 12.5%, 15% and 25% (w/v) iodixanol (equivalent to densities of 1.076, 1.095, 1.105 and 1.152 g/ml); the densest solution contained the material pelleted from the hippocampal homogenate at 900 g for 10 min. The gradient was centrifuged at 18,000 g for 20 min and it was described as a velocity flotation separation.
The primary aim of the gradient was to isolate dendritic spines and the material that banded at the 9%/12.5% interface was further fractionated in a secondary Percoll-sucrose gradient. The basic methodology has subsequently been adapted to the isolation of synaptosomes. Bagni et al  were the first group to report this approach and they reversed the order of the Percoll and the iodixanol flotation gradients.
Material at the 15-23% Percoll interface has generally been used for
subsequent purification in the iodixanol gradient, which is generally modified to include a denser
layer of 35% (w/v) iodixanol and the centrifugation conditions changed to 10,000 g for 20 min.
Synaptosomes band at the 15%/25% iodixanol interface. Essentially the same methodology has been
used by other workers [3-10].