synaptosomes

Synaptosomes are resealed nerve terminals prepared from brain tissue by homogenization and differential or density-gradient centrifugation. They are pinched-off presynaptic endings that preserve key elements of the synapse, including synaptic vesicles, portions of the presynaptic membrane, and surrounding cytosol, and they often contain fragments of the postsynaptic membrane as well. The resulting particles are small, membrane-bound compartments that behave like miniature, self-contained synapses in vitro.

Preparation and variants: The standard method uses brain homogenate, low-speed spins to remove nuclei, followed by higher-speed centrifugation to enrich the terminal fraction, frequently with sucrose, Percoll, or Ficoll gradients. Some preparations are referred to as synaptoneurosomes when a more intact postsynaptic element is retained.

Function and applications: Synaptosomes maintain Ca2+-dependent neurotransmitter release in response to depolarization, enabling study of exocytosis, vesicle recycling, and uptake by transporters. They are also used to study transmitter storage, metabolism, receptor and transporter pharmacology, and binding kinetics. Because they preserve presynaptic machinery in a relatively intact environment, they are widely used in neurochemistry and pharmacology to model presynaptic function and to screen compounds that affect release, uptake, or vesicle dynamics.

Limitations: They lack the full in vivo neural circuitry and glial interactions, may vary by brain region and preparation, and can reflect damaged or altered terminals. Some postsynaptic signals may be reduced or altered compared with intact synapses.

History: Synaptosomes were developed in the 1960s as a tool to study presynaptic processes and have since become a standard experimental model in neuroscience.